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Table of Contents

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American Society of Plumbing Engineers

Data Book

A Plumbing Engineer's Guide to System Design and Specifications

Volume 2 Plumbing Systems

American Society of Plumbing Engineers 3617 E. Thousand Oaks Blvd., Suite 210 Westlake Village, CA 91362

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ASPE Data Book — Volume 1

The ASPE Data Book is designed to provide accurate and authoritative information for the design and specification of plumbing systems. The publisher makes no guarantees or warranties, expressed or implied, regarding the data and information contained in this publication. All data and information are provided with the understanding that the publisher is not engaged in rendering legal, consulting, engineering, or other professional services. If legal, consulting, or engineering advice or other expert assistance is required, the services of a competent professional should be engaged.

American Society of Plumbing Engineers 3617 E. Thousand Oaks Blvd., Suite 210 Westlake Village, CA 91362 (805) 495-7120 • Fax: (805) 495-4861 E-mail: [email protected] • Internet: www.aspe.org

Copyright © 2000 by American Society of Plumbing Engineers All rights reserved, including rights of reproduction and use in any form or by any means, including the making of copies by any photographic process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction, or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the publisher.

ISBN 1–891255–12–6 Printed in the United States of America 10

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Data Book Volume 2 Plumbing Systems Data Book Chairperson: ASPE Vice-President, Technical: Editorial Review: Technical and Research Committee Chairperson:

Anthony W. Stutes, P.E., CIPE David Chin, P.E., CIPE ASPE Technical and Research Committee Norman T. Heinig, CIPE

CONTRIBUTORS

Chapter 1 Michael Granata, P.E. Timothy Smith, CIPE Patrick L. Whitworth, CIPE Chapter 2 Notman T. Heinig, CIPE Saum K. Nour, Ph.D., P.E., CIPE Chapter 3 Michael Granata, P.E. Timothy Smith, CIPE Patrick L. Whitworth, CIPE Chapter 4 Patrick L. Whitworth, CIPE Chapter 5 Michael Granata, P.E. Stephen E. Howe, P.E., CIPE Donald L. Sampler, Sr., P.E., CIPE Chapter 6 Anthony W. Stutes, P.E., CIPE

Chapter 7 Joseph J. Barbera, P.E., CIPE John P. Callahan, CIPE Paul D. Finnerty, CIPE Ronald W. Howie, CIPE Robert L. Love, P.E., CIPE Steven T. Mayer, CIPE, CET Jon G. Moore Rand J. Refrigeri, P.E. Chapter 8 A. R. Rubin, Professor of Biological and Agricultural Engineering, North Carolina State University Patrick L. Whitworth, CIPE Chapter 9 National Ground Water Association (NGWA), Westerville, OH Patrick L. Whitworth, CIPE Chapter 10 Clarke L. Marshall Chapter 11 Michael Frankel, CIPE Warren W. Serles Chapter 12 Michael Frankel, CIPE

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ASPE Data Book — Volume 1

ABOUT ASPE The American Society of Plumbing Engineers (ASPE) is the international organization for professionals skilled in the design and specification of plumbing systems. ASPE is dedicated to the advancement of the science of plumbing engineering, to the professional growth and advancement of its members, and to the health, welfare, and safety of the public. The Society disseminates technical data and information, sponsors activities that facilitate interaction with fellow professionals, and, through research and education programs, expands the base of knowledge of the plumbing engineering industry. ASPE members are leaders in innovative plumbing design, effective materials and energy use, and the application of advanced techniques from around the world.

WORLDWIDE MEMBERSHIP — ASPE was founded in 1964 and currently has 7,100 members. Spanning the globe, members are located in the United States, Canada, Asia, Mexico, South America, the South Pacific, Australia, and Europe. They represent an extensive network of experienced engineers, designers, contractors, educators, code officials, and manufacturers interested in furthering their careers, their profession, and the industry. ASPE is at the forefront of technology. In addition, ASPE represents members and promotes the profession among all segments of the construction industry. ASPE MEMBERSHIP COMMUNICATION — All members belong to ASPE worldwide and have the opportunity to belong and participate in one of the 57 state, provincial or local chapters throughout the U.S. and Canada. ASPE chapters provide the major communication links and the first line of services and programs for the individual member. Communications with the membership is enhanced through the Society’s bimonthly newsletter, the ASPE Report, and the monthly magazine, Plumbing Engineer.

TECHNICAL PUBLICATIONS — The Society maintains a comprehensive publishing program, spearheaded by the profession’s basic reference text, the ASPE Data Book. The Data Book, encompassing forty-five chapters in four volumes, provides comprehensive details of the accepted practices and design criteria used in the field of plumbing engineering. New additions that will shortly join ASPE’s published library of professional technical manuals and handbooks include: High-Technology Pharmaceutical Facilities Design Manual, High-Technology Electronic Facilities Design Manual, Health Care Facilities and Hospitals Design Manual, and Water Reuse Design Manual.

CONVENTION AND TECHNICAL SYMPOSIUM — The Society hosts biennial Conventions in even-numbered years and Technical Symposia in odd-numbered years to allow professional plumbing engineers and designers to improve their skills, learn original concepts, and make important networking contacts to help them stay abreast of current trends and technologies. In conjunction with each Convention there is an Engineered Plumbing Exposition, the greatest, largest gathering of plumbing engineering and design products, equipment, and services. Everything from pipes to pumps to fixtures, from compressors to computers to consulting services is on display, giving engineers and specifiers the opportunity to view the newest and most innovative materials and equipment available to them. CERTIFIED

IN PLUMBING ENGINEERING — ASPE sponsors a national certification program for engineers and designers of plumbing systems, which carries the designation “Certified in Plumbing Engineering” or CIPE. The certification program provides the profession, the plumbing industry, and the general public with a single, comprehensive qualification of professional competence for engineers and designers of plumbing systems. The CIPE, designed exclusively by and for plumbing engineers, tests hundreds of engineers and designers at centers throughout the United States biennially. Created to provide a single, uniform national credential in the field of engineered plumbing systems, the CIPE program is not in any way connected to state-regulated Professional Engineer (P.E.) registration.

ASPE RESEARCH FOUNDATION — The ASPE Research Foundation, established in 1976, is the only independent, impartial organization involved in plumbing engineering and design research. The science of plumbing engineering affects everything . . . from the quality of our drinking water to the conservation of our water resources to the building codes for plumbing systems. Our lives are impacted daily by the advances made in plumbing engineering technology through the Foundation’s research and development.

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American Society of Plumbing Engineers

Data Book

(4 Volumes — 45 Chapters)

Volume 1 Chapter 1 2 3 4 5 6 7 8 9 10

Volume 3 Chapter 1 2 3 4 5 6 7 8 9 10 11

Volume 4 Chapter 1 2 3 4 5 6 7 8 9 10 11 12

Fundamentals of Plumbing Engineering (Revised 1999) Plumbing Formulae, Symbols, and Terminology Standard Plumbing Materials and Equipment Plumbing Specifications Plumbing Cost Estimation Job Preparation, Plumbing Drawing, and Field Checklists Plumbing for Physically Challenged Individuals Energy Conservation in Plumbing Systems Corrosion Seismic Protection of Plumbing Equipment Acoustics in Plumbing Systems

Special Plumbing Systems (Estimated date: 2000) Fire Protection Systems (Chapter 7, looseleaf format) Plumbing Design for Health Care Facilities (Chapter 32, looseleaf format) Treatment of Industrial Waste (Chapter 23, looseleaf format) Irrigation Systems (Chapter 29, looseleaf format) Reflecting Pools and Fountains (Chapter 30, looseleaf format) Public Swimming Pools (Chapter 31, looseleaf format) Gasoline and Diesel Oil Systems (Chapter 33, looseleaf format) Steam and Condensate Piping (Chapter 38, looseleaf format) Compressed Air Systems (Chapter 39, looseleaf format) Solar Energy (Chapter 20, looseleaf format) Site Utility Systems

Plumbing Components and Equipment (Estimated revision date: 2002) Plumbing Fixtures (Chapter 8, looseleaf format) Piping Systems (Chapter 10, looseleaf format) Valves (Chapter 9, looseleaf format) Pumps (Chapter 11, looseleaf format) Piping Insulation (Chapter 12, looseleaf format) Hangers and Supports (Chapter 13, looseleaf format) Vibration Isolation (Chapter 14, looseleaf format) Grease Interceptors (Chapter 35, looseleaf format) Cross Connection Control (Chapter 24, looseleaf format) Water Conditioning (Chapter 28, looseleaf format) Thermal Expansion and Contractions (Chapter 5, looseleaf format) Potable Water Coolers and Central Water Systems (Chapter 27, looseleaf format)

(The chapters and subjects listed for these volume are subject to modification, adjustment and change. The contents shown for each volume are proposed and may not represent the final contents of the volume. A final listing of included chapters for each volume will appear in the actual publication.)

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Table of Contents CHAPTER 1 Sanitary Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Flow in Stacks, Building Drains, and Fixture Drains . . . . . . . . . . . . . . . . . . . . . . . . 1 Flow in Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Flow in Building Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Flow in Fixture Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Pneumatic Pressures in a Sanitary Drainage System . . . . . . . . . . . . . . . . . . . . . . . . 2 Fixture Discharge Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Drainage Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Stack Capacities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Capacities of Sloping Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Steady, Uniform Flow Conditions in Sloping Drains . . . . . . . . . . . . . . . . . . . . . . 6 Hazen and Williams Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Darcy-Weisbach Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Manning Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Slope of Horizontal Drainage Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Load or Drainage Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Components of Sanitary Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sumps and Ejectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Cleanouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Floor Drains and Floor Sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Grates/Strainers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Flashing Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Sediment Bucket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Backwater Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Oil Interceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Grease Interceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Trap Primers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Noise Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Building Sewer Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Sanitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Kitchen Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Waterproofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Floor Leveling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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Joining Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection from Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sovent Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CHAPTER 2 Gray-Water Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Design Criteria for Gray-Water Supply and Consumption . . . . . . . . . . . . . . . . . . . 23 Design Estimates for Commercial Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Gray-Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Gray-Water Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Design Estimates for Residential Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Design Estimates for Irrigation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Treatment Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Economic Analysis — An Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Public Concerns/Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 CHAPTER 3 Vents and Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Section I — Vents and Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Purposes of Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Vent Stack Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Traps and Trap Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Factors Affecting Trap Seal Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Suds Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Fixture Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Venting as a Means of Reducing Trap Seal Losses from Induced Siphonage . . . 39 Design of Vents to Control Induced Siphonage . . . . . . . . . . . . . . . . . . . . . . . . 40 Drainage Fixture Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Vent Sizes and Lengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 End Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Common Vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Stack Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Wet Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Circuit and Loop Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Relief Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Table of Contents

Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vent Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combination Waste and Vent Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section II — Several Venting Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Philadelphia System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sovent System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stack Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wet Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reduced-Size Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section III — Sizing of Several Venting Systems . . . . . . . . . . . . . . . . . . . . . . . . . Reduced-Size Venting Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sizing Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sovent Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerator Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deaerator Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sizing Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CHAPTER 4 Storm-Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 General Design Considerations for Buildings and Sites . . . . . . . . . . . . . . . . . . . . . 67 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Part One: Building Drainage System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Pipe Sizing and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Rainfall Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Rainfall Rate Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Secondary Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Roof Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Drain Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Roof Drain Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Piping Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Locating Vertical Leaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Horizontal Pipe Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Controlled-Flow Storm Drainage System . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Part Two: Site Drainage System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 General Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

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Site Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 The Rational Method of System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Exterior Piping and Inlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Subsurface Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Source of Subsurface Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Site Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Drainage Pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Trenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Selecting Pipe Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Disposal of Ground Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Storm-Water Detention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Standard Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Form 4-1 Storm-Drainage Calculations for Roof Drains and Vertical Leaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Form 4-2 Storm-Drainage System Sizing Sheet . . . . . . . . . . . . . . . . . . . . . . 110 Form 4-3 Storm-Water Drainage Worksheet 1 . . . . . . . . . . . . . . . . . . . . . . . 111 Form 4-3 Storm-Water Drainage Worksheet 2 . . . . . . . . . . . . . . . . . . . . . . . 112 Form 4-3 Storm-Water Drainage Worksheet 3 . . . . . . . . . . . . . . . . . . . . . . . 113 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 CHAPTER 5 Cold-Water Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Domestic Cold-Water Meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Meter Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Sizing the Water Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Sizing the Water Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Hazen-Williams Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Factors Affecting Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Velocity Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Water Hammer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Shock Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 System Protection and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Air Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Water Hammer Arresters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Backflow Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Types of Cross-Connection Control Device . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Assessment of Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Premise Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

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Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inadequate Water Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydropneumatic-Tank System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gravity-Tank System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Booster-Pump System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excess Water Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure-Regulating Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Pressure-Regulating Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sizing, Selection, and Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Testing, Cleaning, and Disinfection of Domestic, Water-Supply Systems . . . . . . Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cleaning and Disinfecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xi

. 148 . 149 . 150 . 150 . 152 . 152 . 152 . 152 . 152 . 153 . 154 . 154 . 154 . 155

CHAPTER 6 Domestic Water-Heating Systems . . . . . . . . . . . . . . . . . . . . . . 157 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Basic Formulae and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Heat Recovery — Electric Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Hot-Water Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Mixed-Water Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Stratification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Hot-Water Temperature Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Hot-Water Circulation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Self-Regulating Heat-Trace Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Relief Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Sizing Pressure and Temperature-Relief Valves . . . . . . . . . . . . . . . . . . . . . . . 167 Temperature Relief Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Pressure Relief Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Thermal Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Safety and Health Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Legionella Pneumophila (Legionnaires’ Disease) . . . . . . . . . . . . . . . . . . . . . . . 169 Scalding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

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CHAPTER 7 Fuel-Gas Piping Systems . . . . . . . . . . . . . . . . . . Low and Medium-Pressure Natural Gas Systems . . . . . . . . . . . . . Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laboratory Gas .................................. Gas Train Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Boosters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Boosters for Natural or Liquefied Petroleum Gas . . . . . Materials of Construction . . . . . . . . . . . . . . . . . . . . . . . . . Gas Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sizing a Gas Booster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liguefied Petroleum Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plastic Pipe and Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tubing Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flexible Gas Hose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indoor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outdoor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leak Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix B — Values of Fuel Gas . . . . . . . . . . . . . . . . . . . . . . . . . Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . 173 . . . . . . . . . . . 173 . . . . . . . . . . . 173 . . . . . . . . . . . 176 . . . . . . . . . . . 177 . . . . . . . . . . . 177 . . . . . . . . . . . 178 . . . . . . . . . . . 178 . . . . . . . . . . . 178 . . . . . . . . . . . 179 . . . . . . . . . . . 179 . . . . . . . . . . . 180 . . . . . . . . . . . 182 . . . . . . . . . . . 183 . . . . . . . . . . . 194 . . . . . . . . . . . 194 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 196 . . . . . . . . . . . 197 . . . . . . . . . . . 197 . . . . . . . . . . . 197 . . . . . . . . . . . 212 . . . . . . . . . . . 213 . . . . . . . . . . . 214

CHAPTER 8 Private Sewage-Disposal Systems Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary Collection and Treatment Systems . . . . . Soil-Absorption Systems . . . . . . . . . . . . . . . . . . . Guide for Estimating Soil Absorption Potential Soil Maps . . . . . . . . . . . . . . . . . . . . . . . . Clues to Absorption Capacity . . . . . . . . . . Procedure for Percolation Tests . . . . . . . . Soil-Absorption System Selection . . . . . . . . . Leaching Trenches . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . 217 . . . . . . . . . . . 217 . . . . . . . . . . . 217 . . . . . . . . . . . 217 . . . . . . . . . . . 217 . . . . . . . . . . . 218 . . . . . . . . . . . 218 . . . . . . . . . . . 219 . . . . . . . . . . . 220 . . . . . . . . . . . 221

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Table of Contents

Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 Serial Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Seepage Beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Seepage Pits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Mound Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Collection and Treatment Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Alternatives to Gravity Collection and Distribution . . . . . . . . . . . . . . . . . . . . 226 Alternatives to Conventional Primary-and-Secondary Treatment . . . . . . . . . . 227 Septic Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Functions of the Septic Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Biological Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Solids Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Septic Tank Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Invert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Outlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Tank Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Storage above Liquid Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Use of Compartments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 General Information on Septic Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Grease Interceptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Distribution Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Septic Tank/Soil-Absorption Systems for Institutions and Recreational and Other Establishments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Water Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Special Fixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Alternative Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Special Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Individual Aerobic Waste-Water Treatment Plants . . . . . . . . . . . . . . . . . . . . . . . . 232 Estimating Sewage Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 CHAPTER 9 Private Water Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Sources of Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

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Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dug Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bored Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Driven Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jetted Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulics of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection of Wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Softening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scale and Corrosion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taste and Odor Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prophylaxis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Well Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suction Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supply Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thrust Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depth of Bury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Operation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 240 . 240 . 241 . 241 . 241 . 241 . 243 . 243 . 244 . 244 . 244 . 244 . 245 . 245 . 245 . 245 . 245 . 245 . 247 . 248 . 248 . 249 . 250 . 250 . 251 . 251 . 251 . 252 . 252 . 252

CHAPTER 10 Vacuum Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Units of Measurement and Reference Points . . . . . . . . . . . . . . . . . . . . . . . . . 254 Standard Reference Points and Conversions . . . . . . . . . . . . . . . . . . . . . . 254 Flow-Rate Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Converting scfm to acfm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 General Vacuum Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Adjusting Vacuum-Pump Rating for Altitude . . . . . . . . . . . . . . . . . . . . . . . . . 257 Time for Pump to Reach Rated Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Adjusting Pressure Drop for Different Vacuum Pressures . . . . . . . . . . . . . . . 258

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Simplified Method of Calculating Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Vacuum Work Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Vacuum Source and Source Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Vacuum Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Gas-Transfer Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Seal Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Vacuum-Pressure Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Bourdon Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Diaphragm Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Ancillary Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Laboratory and Vacuum Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Vacuum Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Distribution Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Pipe Material and Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Sizing Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Vacuum-Cleaning Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Types of System and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Vacuum Producer (Exhauster) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Silencers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Inlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Control and Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Air-Bleed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Pipe and Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Detailed System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Inlet Location and Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Determining the Number of Simultaneous Operators . . . . . . . . . . . . . . . . 269 Inlet-Valve, Tool, and Hose Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Locating the Vacuum-Producer Assembly . . . . . . . . . . . . . . . . . . . . . . . . 270 Sizing the Piping Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Piping-System Friction Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Vacuum-Producer (Exhauster) Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 Separator Selection and Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 General Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

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CHAPTER 11 Water Treatment, Conditioning, and Purification . . . . . . . . . 279 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Basic Water Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Water Impurities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Suspended Matter (Particulates), Turbidity . . . . . . . . . . . . . . . . . . . . . . . 282 Dissolved Minerals and Organics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Dissolved Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Volatile Organic Compounds (VOC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Water Analysis and Impurity Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Specific Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Specific Conductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Total Suspended Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Total Dissolved Solids (TDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Total Organic Carbon (TOC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Silt Density Index (SDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Deposits and Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Scale and Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Biological Fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Predicting Scale Formation and Corrosion Tendencies . . . . . . . . . . . . . . . . . . . . . 290 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 Langelier Saturation Index (LSI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 Ryzner Stability Index (RI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Aggressiveness Index (AI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Treatment Methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Aeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Clarification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Deaeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Dealkalizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Decarbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Single-Stage Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Vapor-Compression Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Multi-Effect Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 Deep-Bed Sand Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 Cross-Flow and Tangential-Flow Filtration . . . . . . . . . . . . . . . . . . . . . . . . 300 Activated Carbon Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

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Ion Exchange and Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 Regenerable Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Regeneration Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 Service Deionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Continuous Deionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 Water Softening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Ion-Exchange System Design Considerations . . . . . . . . . . . . . . . . . . . . . . 308 Membrane Filtration and Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Reverse Osmosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Membrane Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Cross-Flow Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Microbial Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Ultraviolet Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 Ozone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Utility Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Initial Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Clarification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Biological Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Water Softening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Boiler Feed-Water Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Cooling-Water Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Biological Fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Potable Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Water Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Laboratory Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Pharmaceutical Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 Feed Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 Purification System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 Central Purification Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 Piping Distribution Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 System Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

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CHAPTER 12 Special-Waste Drainage Systems . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Approval Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Material and Joint Selection Considerations . . . . . . . . . . . . . Pipe Sizing Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pH Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General System Design Considerations . . . . . . . . . . . . . . . . . . . . . Acid-Waste Drainage and Vent Systems . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Health and Safety Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . Common Types of Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfuric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrochloric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrobromic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Perchloric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Laboratory Waste Piping and Joint Material . . . . . System Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . Acid Waste Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radioactive Waste Drainage and Vent System . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Nature of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Units of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allowable Radiation Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radioactive Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Approval Process and Application Requirements . . . . . General Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . Pipe Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . General Design Considerations . . . . . . . . . . . . . . . . . . . . . Infectious and Biological-Waste Drainage Systems . . . . . . . . . . . . Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biological Safety Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquid-Waste Decontamination System . . . . . . . . . . . . . . . . . . System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Design Considerations . . . . . . . . . . . . . . . . . . . . . . Chemical-Waste Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . 327 . . . . . . . . . . . 327 . . . . . . . . . . . 327 . . . . . . . . . . . 328 . . . . . . . . . . . 328 . . . . . . . . . . . 328 . . . . . . . . . . . 329 . . . . . . . . . . . 329 . . . . . . . . . . . 329 . . . . . . . . . . . 329 . . . . . . . . . . . 332 . . . . . . . . . . . 332 . . . . . . . . . . . 332 . . . . . . . . . . . 333 . . . . . . . . . . . 333 . . . . . . . . . . . 333 . . . . . . . . . . . 333 . . . . . . . . . . . 333 . . . . . . . . . . . 334 . . . . . . . . . . . 334 . . . . . . . . . . . 334 . . . . . . . . . . . 337 . . . . . . . . . . . 337 . . . . . . . . . . . 337 . . . . . . . . . . . 338 . . . . . . . . . . . 339 . . . . . . . . . . . 339 . . . . . . . . . . . 339 . . . . . . . . . . . 340 . . . . . . . . . . . 340 . . . . . . . . . . . 340 . . . . . . . . . . . 341 . . . . . . . . . . . 341 . . . . . . . . . . . 342 . . . . . . . . . . . 343 . . . . . . . . . . . 343 . . . . . . . . . . . 343 . . . . . . . . . . . 344 . . . . . . . . . . . 344 . . . . . . . . . . . 345 . . . . . . . . . . . 345 . . . . . . . . . . . 345

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Codes and Standards . . . . . . . . . . . . . . . Pipe Material and Joint Selection . . . . . . System Design Considerations . . . . . . . . Fire-Suppression Water Drainage . . . . . . . . . System Description . . . . . . . . . . . . . . . . . Flammable and Volatile Liquids . . . . . . . . . . Oil in Water . . . . . . . . . . . . . . . . . . . . . . Methods of Separation and Treatment References . . . . . . . . . . . . . . . . . . . . . . . . . .

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ILLUSTRATIONS Figure 1-1 Procedure for Sizing an Offset Stack . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 1-2 Basic Floor-Drain Components . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 1-3 Pattern Draft for Floor Gratings: (a) Sharp Edge, (b) Reverse Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 1-4 Types of Floor Drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 1-5 Various Types of Backwater Valve . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 1-6 Combination Floor Drain and Indirect Waste Receptor . . . . . . . . . 17 Figure 1-7 Inside-Caulk Drain Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 1-8 Spigot-Outlet Drain Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 1-9 No-Hub-Outlet Drain Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 1-10 IPS or Threaded-Outlet Drain Body . . . . . . . . . . . . . . . . . . . . . . 18 Figure 1-11 (A) Traditional Two-Pipe System, (B) Typical Sovent Single-Stack Plumbing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 2-1 Plumbing System Flow Charts: (A) Conventional Plumbing System; (B) Recycled-Water System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 2-2 Riser Diagrams: (A) Gray-Water Plumbing System; (B) RecycledWater-Waste System with System Treatment Plant (STP) . . . . . . . . . . . . . . 24 Figure 2-3 Water Treatment Systems: (A) Types of Gray-Water Treatment System; (B) Types of Black-Water Treatment System . . . . . . . . . . . . . . . . . 28 Figure 2-4 System Design Flow Chart Example (250-Room Hotel) . . . . . . . . . 30 Figure 2-5 Nomograph for Overview of Preliminary Feasibility of Gray-Water Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 3-1 Suds-Pressure-Zone Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 3-2 Suds Venting/Suds Pressure Zones . . . . . . . . . . . . . . . . . . . . . . . 39 Figure 3-3 Loop Vent, with Horizontal Branch Located (a) at Back Below Water Closets, (b) Directly Under Water Closets . . . . . . . . . . . . . . . . . . . . . 44 Figure 3-4 Circuit Vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Figure 3-5 Relief Vent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Figure 3-6 Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Figure 3-7 Combination Waste-and-Vent System . . . . . . . . . . . . . . . . . . . . . 47 Figure 3-8 Philadelphia System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Figure 3-9 Wet Venting and Stack Venting . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Figure 3-10 Pipe Layout Drawing — Two-Story Residential Building, Freezing

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Climate, Schedule 40 Plastic Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Figure 3-11 (A) Traditional Two-Pipe Plumbing System; (B) Typical Sovent Single-Stack Plumbing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Figure 3-12 Typical Sovent System Aerator Fitting . . . . . . . . . . . . . . . . . . . . 56 Figure 3-13 Typical Sovent System Deaerator . . . . . . . . . . . . . . . . . . . . . . . . 56 Figure 3-14 Sovent System Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Figure 3-15 Soil and Waste Branches Connected into a Horizontal Stack Offset. Waste Branches Connected into the Pressure-Relief Line . . . . . . . . 59 Figure 3-16 Soil and Waste Branches Connected below a Deaerator Fitting at the Bottom of the Stack . . . . . . . . . . . . . . . . . . . . . . . 61 Figure 3-17 Deaerator Fitting Located above Floor Level of Building Drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Figure 3-18 Sovent Fitting: (A) Single-Side Entry (Without Waste Inlets); (B) Double-Side Entry (with Waste Inlets) . . . . . . . . . . . . . . . . . . . . . . . . . 62 Figure 3-19 Two Alternative Design Layouts for Typical Back-to-Back Bathroom Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Figure 4-1 Piping Layout for Typical Building Elevation . . . . . . . . . . . . . . . . . 70 Figure 4-2 Piping Layout for Typical Building Site Plan . . . . . . . . . . . . . . . . . 70 Figure 4-3 Typical Roof Drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Figure 4-4 Typical Roof-Drain Installations . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Figure 4-5 4-In. (101-mm) Roof Drain Flow Chart . . . . . . . . . . . . . . . . . . . . . 84 Figure 4-6 Clear-Water Waste Branches for Connection to Storm System . . . 84 Figure 4-7 Typical Expansion Joint or Horizontal Offset . . . . . . . . . . . . . . . . 87 Figure 4-8 Typical Roof Drain and Roof Leader . . . . . . . . . . . . . . . . . . . . . . . 87 Figure 4-9 Example of a Controlled-Flow Storm-Drainage System . . . . . . . . . 94 Figure 4-10 Overland Flow Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Figure 4-11 Typical Intensity-Duration-Frequency Curves . . . . . . . . . . . . . . . 97 Figure 4-12 Sources of Subsurface Water . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Figure 4-13 Borings Revealing the Nature of the Ground, Water Table Elevations, and Rock Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Figure 4-14 Cross Section Illustrating the Concept of the K Factor . . . . . . . 101 Figure 4-15 Open Joint Pipe Surrounded by Filter Material . . . . . . . . . . . . . 102 Figure 4-16 Perforated Pipe in Trench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Figure 4-17 Pipe and Footing Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Figure 4-18 Pipe in Trench with Dimensions of Filter Layers . . . . . . . . . . . . 104 Figure 4-19 Sump-Pump Discharge to the Storm-Drainage System . . . . . . . 106 Figure 5-1 Friction Loss of Head Chart, Coefficient of Flow (C) = 140 . . . . . . 118 Figure 5-1 (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Figure 5-2 Conversion of Fixture Units, fu, to gpm (L/s) . . . . . . . . . . . . . . . 120 Figure 5-3 Conversion of Fixture Units, fu, to gpm (L/s), Design Load vs. Fixture Units, Mixed System . . . . . . . . . . . . . . . . . . . . . . 126 Figure 5-4 Typical Friction Losses for Disk-Type Water Meters . . . . . . . . . . 127 Figure 5-5 Establishing the Governing Fixture or Appliance . . . . . . . . . . . . 129 Figure 5-6 Determining Pressure Available for Friction . . . . . . . . . . . . . . . 130

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Figure 5-7 Pipe Sizing Data, Smooth Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Figure 5-8 Pipe Sizing Data, Fairly Smooth Pipe . . . . . . . . . . . . . . . . . . . . . 140 Figure 5-9 Pipe Sizing Data, Fairly Rough Pipe . . . . . . . . . . . . . . . . . . . . . . 141 Figure 5-10 Pipe Sizing Data, Rough Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Figure 5-11 Air Chambers: (a, b) Plain Air Chambers, (c) Standpipe Air Chamber, (d) Rechargeable Air Chamber . . . . . . . . . . . . . . . . . . . . . . 143 Figure 5-12 Hydropneumatic Pressure System Layout that Determines the Minimum Tank Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Figure 5-13 Typical Hydropneumatic Supply System . . . . . . . . . . . . . . . . . . 150 Figure 5-14 Piping Connections for a Gravity Water-Storage Tank with Reserve Capacity for Firefighting . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Figure 7-1 Variations of a Basic Simplex Booster System . . . . . . . . . . . . . . . . 181 Figure 7-3 Pipe Sizing, Low Pressure System with an Initial Pressure Up to 1 psi (6.9 kPa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Figure 7-4 Pipe Sizing, Any System with an Initial Pressure Between 1 and 20 psi (6.9 and 137.8 kPa) . . . . . . . . . . . . . . . . . . . . . . . . 193 Figure 7-5 Typical Diversity Curves for Gas Supply to High-Rise Apartments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Figure 7-6 Diversity Percentage for Multifamily Buildings (Average) . . . . . . . 195 Figure 8-1 Three Legs of Disposal Field Fed from Cross Fitting Laid on Its Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Figure 8-2 Disposal Lines Connected by Headers to Circumvent Stoppages . 221 Figure 8-3 Transverse and Lineal Sections of Drain Field Showing Rock and Earth Backfill around Drain Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Figure 8-4 Graph Showing Relation Between Percolation Rate and Allowable Rate at Sewage Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Figure 9-1 Well under (A) Static and (B) Pumping Conditions . . . . . . . . . . . 242 Figure 9-2 Typical Gravel Filter Well with a Vertical Turbine Pump . . . . . . . 246 Figure 9-3 Graph Indicating Minimum Storage-Tank Size . . . . . . . . . . . . . . 248 Figure 9-4 Storage-Tank Suction Piping Detail: (A) Sump Suction Alternate, (B) Anti-Vortex Alternate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Figure 10-1 Conversion of Vacuum-Pressure Measurements . . . . . . . . . . . . 255 Figure 10-2 Schematic Detail of a Typical Laboratory Vacuum-Pump Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Figure 10-3 Typical Process Vacuum-Pump Duplex Arrangement . . . . . . . . 261 Figure 10-4 Direct Reading Chart Showing Diversity for Laboratory Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Figure 10-5 Acceptable Leakage in Vacuum Systems . . . . . . . . . . . . . . . . . . 267 Figure 10-6 Vacuum-Cleaning Piping Friction Loss Chart . . . . . . . . . . . . . . 273 Figure 10-7 Schematic of a Typical Wet-Vacuum Cleaning Pump Assembly . 276 Figure 11-1 Typical Water Analysis Report . . . . . . . . . . . . . . . . . . . . . . . . . 286 Figure 11-2 pH of Saturation for Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Figure 11-3 Detail of Vapor Compression Still . . . . . . . . . . . . . . . . . . . . . . . 296 Figure 11-4 Detail of Multi-Effect Still . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Figure 11-5 Schematic Detail of Large-Scale, Granular-Activated

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Carbon Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 11-6 Typical Single-Bed Ion Exchanger . . . . . . . . . . . . . . . . . . . . . . Figure 11-7 Typical Dual-Bed Ion Exchanger . . . . . . . . . . . . . . . . . . . . . . . Figure 11-8 Typical Mixed-Bed Ion Exchanger . . . . . . . . . . . . . . . . . . . . . . Figure 11-9 Schematic Operation of a Continuous Deionization Unit . . . . . Figure 11-10 Hollow-Fiber Reverse-Osmosis Configuration . . . . . . . . . . . . Figure 11-11 Spiral-Wound Reverse-Osmosis Configuration . . . . . . . . . . . Figure 11-12 Tubular Reverse Osmosis Configuration . . . . . . . . . . . . . . . . Figure 11-13 Plate-and-Frame Reverse-Osmosis Configuration . . . . . . . . . Figure 11-14 UV Wavelength Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 11-15 Principle of Corona-Discharge Ozone Generator . . . . . . . . . . Figure 11-16 Typical Pharmaceutical Water-Flow Diagram . . . . . . . . . . . . Figure 12-1 Typical Acid-Resistant Manhole . . . . . . . . . . . . . . . . . . . . . . . Figure 12-2 Typical Large Acid-Neutralizing Basin . . . . . . . . . . . . . . . . . . . Figure 12-3 Typical Continuous Acid-Waste Treatment System . . . . . . . . . Figure 12-4 Typical Oil Interceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 12-5 Typical Gravity Draw-Off Installation (A) Plan and (B) Isometric

. 301 . 303 . 303 . 304 . 306 . 309 . 309 . 310 . 310 . 312 . 313 . 322 . 335 . 336 . 338 . 348 . 349

TABLES Table 1-1 Residential Fixture-Unit Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Table 1-2 Capacities of Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Table 1-3 Horizontal Fixture Branches and Stacks . . . . . . . . . . . . . . . . . . . . . 5 Table 1-4 Values of R, R2/3, AF, and AH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 1-5 Approximate Discharge Rates and Velocities in Sloping Drains, n = 0.015 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 1-6 Building Drains and Sewers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Table 1-7 Recommended Grate Open Areas for Various Outlet Pipe Sizes . . . . 10 Table 1-8 Relative Properties of Selected Plumbing Materials for Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 2-1 The National Sanitation Foundation’s Standard 41 . . . . . . . . . . . . 22 Table 2-2 Design Criteria of Six Typical Soils . . . . . . . . . . . . . . . . . . . . . . . . . 26 Table 2-2 (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Table 2-3 Location of the Gray-Water System . . . . . . . . . . . . . . . . . . . . . . . . 27 Table 2-4 Subsurface Drip Design Criteria of Six Typical Soils . . . . . . . . . . . . 27 Table 2-5 Gray-Water Treatment Processes for Normal Process Efficiency . . . 28 Table 2-6 Comparison of Gray-Water System Applications . . . . . . . . . . . . . . . 29 Table 2-7 Life-Cycle Economic Comparison: Gray-Water Systems for 250-Room Hotel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Table 3-1 Suds Pressure-Relief Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Table 3-2 Maximum Length of Trap Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Table 3-3 Maximum Distance of Fixture Trap from Vent . . . . . . . . . . . . . . . . 40 Table 3-4 Drainage-Fixture-Unit Values for Various Plumbing Fixtures . . . . . 41 Table 3-5 Size and Length of Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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Table 3-6 Size of Vent Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Table 3-7 Fixture Unit Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Table 3-8 Fixture Vents and Stack Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Table 3-9 Confluent Vents Serving Three Fixture or Stack Vents . . . . . . . . . . 51 Table 3-10 Confluent Vents Serving Four or More Fixture or Stack Vents, Schedule 40 Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Table 3-11 Confluent Vents Serving Four or More Fixture or Stack Vents, Copper Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Table 3-12 Flow Areas of Pipe and Tube, in2 (103 mm2) . . . . . . . . . . . . . . . . . 52 Table 3-13 Arterial Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Table 3-14 Fixture Unit Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Table 3-15 Maximum Fixture Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Table 3-16 Size Rules for Connecting Fixtures into the Sovent Single-Stack Drainage Plumbing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Table 3-17 Minimum Size of Equalizing Line . . . . . . . . . . . . . . . . . . . . . . . . . 61 Table 3-18 Maximum Sovent Stack Loadings . . . . . . . . . . . . . . . . . . . . . . . . . 63 Table 3-19 Loadings for Building Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Table 4-1 Maximum Rates of Rainfall for Various US Cities, in./h (mm/h) . . 71 Table 4-2 Sizes of Roof Drains and Vertical Pipes . . . . . . . . . . . . . . . . . . . . . 85 Table 4-3 Sizes of Semicircular and Equivalent Rectangular Gutters . . . . . . . 86 Table 4-4 Pipe Sizing Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Table 4-5 Sizes of Scuppers for Secondary Drainage . . . . . . . . . . . . . . . . . . . 93 Table 4-6 Some Values of the Rational Coefficient C . . . . . . . . . . . . . . . . . . . 95 Table 4-7 Size Ranges for Filter Material . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Table 5-1 Displacement-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Table 5-2 Compound-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Table 5-3 Turbine-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Table 5-4 Surface Roughness Coefficient (C) Values for Various Types of Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Table 5-5 Demand Weight of Fixtures, in Fixture Units . . . . . . . . . . . . . . . . 123 Table 5-6 Conversions—Gallons per Minute (Liters per Second) to Fixture Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Table 5-7 Allowance for Friction Loss in Valves and Threaded Fittings . . . . . 128 Table 5-7 (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Table 5-8 Flow and Pressure Required for Various Fixtures during Flow . . . 129 Table 5-9 Water Pipe Sizing—Fixture Units vs. psi/100 ft (kPa/100 m), Type L Copper Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Table 5-10 Water Pipe Sizing Fixture Units versus psi/100 ft. (kPa/100 m), Galvanized Fairly Rough Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Table 5-11 Required Air Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Table 5-12 Sizing and Selection of Water-Hammer Arresters . . . . . . . . . . . . 144

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Table 5-13 Guide to the Assessment of Hazard and Application of Devices—Isolation at the Fixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 5-14 Guide to the Assessment of Facility Hazard and Application of Devices—Containment of Premise . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 5-15 Minimum Flow Rates and Size of Minimum Area of RPBD . . . . Table 6-1 Typical Hot-Water Temperatures for Plumbing Fixtures and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 6-2 Hot-Water Multiplier, P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 6-2 (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 6-3 Thermal Properties of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 6-4 Time/Water Temperature Combinations Producing Skin Damage Table 7-1 Approximate Gas Demand for Common Appliances . . . . . . . . . . Table 7-2 Equivalent Lengths for Various Valve and Fitting Sizes . . . . . . . Table 7-3 Natural Gas Pipe Sizing Table for Gas Pressure < 1.5 psi . . . . . . Table 7-3(M) Natural Gas Pipe Sizing Table for Gas Pressure < 10.3 kPa . . Table 7-4 Natural Gas Pipe Sizing Table for Gas Pressure < 1.5 psi . . . . . . Table 7-4(M) Natural Gas Pipe Sizing Table for Gas Pressure < 10.3 kPa . . Table 7-5 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . . . Table 7-5(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa . Table 7-A1 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A1(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A2 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A2(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A3 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A3(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A4 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A4(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A5 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A5(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A6 Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi . . . . . . Table 7-A6(M) Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa Table 7-A7 Natural Gas Pipe Sizing Table for Gas Pressure < 1 psi . . . . . . Table 7-A7(M) Natural Gas Pipe Sizing Table for Gas Pressure < 6.9 kPa . . Table 7-B1 Typical Heating Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 7-B2 Typical Working Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 7-B3 Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 7-B4 Specific Gravity Multipliers . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 8-1 Minimum Absorption Area for Private Dwellings . . . . . . . . . . . . . Table 8-2 Recommended Distances Between Soil-Absorption System and Site Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 8-3 Liquid Capacity of Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 8-4 Allowable Sludge Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . Table 8-5 Average Waste-Water Flows from Residential Sources . . . . . . . .

. 146 . 147 . 148 . 159 . 161 . 163 . 168 . 170 . 175 . 184 . 186 . 187 . 188 . 189 . 190 . 191 . 198 . 199 . 200 . 201 . 202 . 203 . 204 . 205 . 206 . 207 . 208 . 209 . 210 . 211 . 212 . 212 . 213 . 213 . 218 . 220 . 227 . 229 . 233

Table of Contents

Table 8-6 Typical Waste-Water Flows from Commercial Sources . . . . . . . . Table 8-7 Typical Waste-Water Flows from Institutional Sources . . . . . . . . Table 8-8 Typical Waste-Water Flows from Recreational Sources . . . . . . . . Table 8-9 Quantities of Sewage Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 8-10 Estimated Distribution of Sewage Flows . . . . . . . . . . . . . . . . . . Table 8-11 Allowable Rate of Sewage Application to a Soil-Absorption System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 9-1 Curve Radii for Cast-Iron Pipe, ft (m) . . . . . . . . . . . . . . . . . . . . . Table 9-2 Thrust Block Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 9-3 Area of Bearing Face of Concrete Thrust Blocks, ft2 (m2) . . . . . . Table 9-4 Coefficients of Expansion, in/in/°F (mm/mm/°C) . . . . . . . . . . . Table 10-1 Basic Vacuum-Pressure Measurements . . . . . . . . . . . . . . . . . . Table 10-2 Conversions from Torr to Various Vacuum-Pressure Units . . . . Table 10-3 IP and SI Pressure Conversion . . . . . . . . . . . . . . . . . . . . . . . . . Table 10-4 Expanded Air Ratio, 29.92/P, as a Function of Pressure, P (in. Hg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 10-5 Direct Ratio for Converting scfm to acfm (nL/s to aL/s) . . . . . . Table 10-6 Barometric Pressure Corresponding to Altitude . . . . . . . . . . . . Table 10-7 Factor for Flow Rate Reduction Due to Altitude . . . . . . . . . . . . Table 10-8 Constant, C, for Finding Mean Air Velocity . . . . . . . . . . . . . . . . Table 10-9 Diversity Factor for Laboratory Vacuum Air Systems . . . . . . . . Table 10-10 Vacuum-Pump Exhaust Pipe Sizing . . . . . . . . . . . . . . . . . . . . Table 10-11 Pressure Loss Data for Sizing Vacuum Pipe . . . . . . . . . . . . . . Table 10-12 Recommended Sizes of Hand Tools and Hose . . . . . . . . . . . . . Table 10-13 Flow Rate and Friction Loss for Vacuum-Cleaning Tools and Hoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 10-14 Recommended Velocities for Vacuum-Cleaning Systems . . . . . Table 10-15 Pipe Size Based on Simultaneous Usage . . . . . . . . . . . . . . . . . Table 10-16 Equivalent Length (ft.) of Vacuum Cleaning Pipe Fittings . . . . Table 10-17 Classification of Material for Separator Selection . . . . . . . . . . Table 11-1 Important Elements, Acid Radicals, and Acids in Water Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 11-2 Converting ppm of Impurities to ppm of Calcium Carbonate . . . Table 11-3 Resistivity and Conductivity Conversion . . . . . . . . . . . . . . . . . . Table 11-4 Prediction of Water Tendencies by the Langelier Index . . . . . . . Table 11-5 Numerical Values for Substitution in Equation 11-3 to Find the pHs of Saturation for Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 11-6 Prediction of Water Tendencies by the Ryzner Index . . . . . . . . . Table 11-7 Typical Cations and Anions Found in Water . . . . . . . . . . . . . . . Table 11-8 Comparison of Reverse-Osmosis Polymers . . . . . . . . . . . . . . . . Table 11-9 Recommended Boiler Feed-Water Limits and Steam Purity . . . . Table 11-10 Water-Treatment Technology for Small Potable Water Systems Table 11-11 CAP and ASTM Reagent-Grade Water Specifications . . . . . . . .

xxv

. 234 . 234 . 235 . 236 . 237 . 237 . 250 . 251 . 251 . 252 . 254 . 254 . 256 . 256 . 257 . 257 . 258 . 259 . 263 . 264 . 265 . 270 . 271 . 271 . 272 . 274 . 275 . 281 . 285 . 287 . 291 . 291 . 292 . 301 . 311 . 315 . 318 . 319

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Table 11-12 NCCLS Reagent-Grade Water Specifications . . . . . . . . . . . Table 11-13 AAMI/ANSI Water-Quality Standards . . . . . . . . . . . . . . . . Table 11-14 ASTM Electronics-Grade Water Standarda . . . . . . . . . . . . Table 11-15 USP XXII Purified-Water and WFI Water-Purity Standards Table 12-1 Drainage Pipe Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 12-1 (M) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . .

. . . . . .

. . . . . .

. 319 . 319 . 320 . 321 . 330 . 331

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

Chapter 1 — Sanitary Drainage Systems

1 INTRODUCTION A sanitary drainage system generally consists of horizontal branches, vertical stacks, a building drain inside the building, and a building sewer from the building wall to the point of disposal. To economically design a sanitary drainage system is to use the smallest pipes that can rapidly carry away the soiled water from individual fixtures without clogging the pipes, without leaving solids in the piping, without generating excessive pneumatic pressures at points where the fixture drains connect to the stack (which might cause the reduction of trap water seals and force sewer gases back through inhabitable areas), and without creating undue noise. Since vents and venting systems are described in a separate chapter (Chapter 3 of this volume), the following discussion centers on the drain and waste systems’ design.

FLOW IN STACKS, BUILDING DRAINS, AND FIXTURE DRAINS

1

Sanitary Drainage Systems

of the stack at the level of entry. In any event, as soon as the water enters the stack, it is rapidly accelerated downward by the force of gravity, and before it falls very far, it assumes the form of a sheet around the wall of the stack, leaving the center of the pipe open for the flow of air. This sheet of water continues to accelerate until the frictional force exerted by the wall of the stack on the falling sheet of water equals the force of gravity. From that point on—if the distance the water falls is great enough and provided that no flow enters the stack at lower levels to interfere with the sheet—the sheet remains unchanged in thickness and velocity until it reaches the bottom of the stack. The ultimate vertical velocity the sheet attains is called the “terminal velocity,” and the distance the sheet must fall to attain this terminal velocity is called the “terminal length.” Following are the formulae developed for terminal velocity and terminal length: Equation 1-1 VT = 3.0

Q 2/5 ‰d

Flow in Stacks

LT = 0.052VT2

Flow in the drain empties into the vertical stack fitting, which may be a long-turn tee-wye or a short-turn or sanitary tee. Each of these fittings permits flow from the drain to enter the stack with a component directed vertically downward. Depending on the rate of flow out of the drain into the stack, the diameter of the stack, the type of stack fitting, and the flow down the stack from higher levels, if any, the discharge from the fixture drain may or may not fill the cross section

where VT = Terminal velocity in stack, fps (m/s) LT = Terminal length below point of flow entry, ft (m) Q = Quantity rate of flow, gpm (L/s) d

= Diameter of stack, in. (mm)

Terminal velocity is attained at approximately 10 to 15 fps (3.05 to 5.22 m/s), and this velocity

2

is attained within 10 to 15 ft (3.05 to 5.22 m) of fall from the point of entry. At the center of the stack is a core of air that is dragged along with the water by friction and for which a supply source must be provided if excessive pressures in the stack are to be avoided. The usual means of supplying this air is through the stack vent or vent stack. The entrained air in the stack causes a pressure reduction inside the stack, which is caused by the frictional effect of the falling sheet of water dragging the core of air along with it. If the sheet of water falling down the stack passes a stack fitting through which the discharge from a fixture is entering the stack, the water from the branch mixes with or deflects the rapidly moving sheet of water. An excess pressure in the drain from which the water is entering the stack is required to deflect the sheet of water flowing downward or mix the branch water with it. The result is that a back pressure is created in the branch, which increases with the flow rate and flow velocity down the stack and with the rate of flow out of the drain.

Flow in Building Drains When the sheet of water reaches the bend at the base of the stack, it turns at approximately right angles into the building drain. Flow enters the horizontal drain at a relatively high velocity compared to the velocity of flow in a horizontal drain under uniform flow conditions. The slope of the building drain is not adequate to maintain the velocity that existed in the sheet when it reached the base of the stack. The velocity of the water flowing along the building drain and sewer decreases slowly then increases suddenly as the depth of flow increases and completely fills the cross section of the drain. This phenomenon is called a “hydraulic jump.” The critical distance at which the hydraulic jump may occur varies from immediately at the stack fitting to ten times the diameter of the stack downstream. Less jump occurs if the horizontal drain is larger than the stack. After the hydraulic jump occurs and water fills the drain, the pipe tends to flow full until the friction resistance of the pipe retards the flow to that of uniform flow conditions.

ASPE Data Book — Volume 2

Flow in Fixture Drains Determination of the drain size required is a relatively simple matter, since the fixture drain must be adequate only to carry the discharge from the fixture to which it is attached. Because of the problem of self-siphonage, however, it is advisable to select the diameter of the drain so that the drain flows little more than half full under the maximum discharge conditions likely to be imposed by the fixture. For example, a lavatory drain capable of carrying the flow discharged from a lavatory may still flow full over part or all of its length. There are several reasons for this. The vertical component of the flow out of the trap into the drain tends to make the water attach itself to the upper elements of the drain, and a slug of water is formed, filling the drain at that point. The result is that, if there is not sufficient air aspirated through the overflow, the pipe will flow full for part of its length, the average velocity of flow being less than the normal velocity for the rate of flow in the drain at a given slope. If the fixture considered is a water closet, the surge of water from the closet will continue almost without change even along a very long drain until it reaches the stack. Thus, it can be assumed, for all practical purposes, that the surge caused by the discharge of a water closet through a fixture drain reaches the stack or horizontal branch with practically the same velocity it had when it left the fixture.

PNEUMATIC PRESSURES IN A SANITARY DRAINAGE SYSTEM Because of the pressure conditions in a stack and a building drain, the waste water does not fill the cross section anywhere, so that the air can flow freely along with the water. The water flowing down the wall of the stack drags air with it by friction and carries it through the building drain to the street sewer. The air is then vented throughout the main street sewer system so dangerous pressures are not build up. If air is to enter the top of the stack to replace that being carried along with the water, there must be a pressure reduction inside the stack. Because of the head loss necessary to accelerate the air and to provide for the energy loss at the entrance, however, this pressure reduction is very small; it amounts to only a small

Chapter 1 — Sanitary Drainage Systems

fraction of an inch (a millimeter) of water. What causes appreciable pressure reductions is the partial or complete blocking of the stack by water flowing into the stack from a horizontal branch. A small increase in pneumatic pressure will occur in the building drain even if there is no complete blocking of the air flow by a hydraulic jump or by submergence of the outlet and the building sewer. This is due to the decrease in cross-sectional area available for air flow when the water flowing in the drain has adapted itself to the slope and diameter of the drain.

FIXTURE DISCHARGE CHARACTERISTICS The discharge characteristic curves—flow rates as a function of time—for most water-closet bowls have the same general shape, but some show a much lower peak and a longer period of discharge. The discharge characteristics for various types of water-closet bowl, particularly low-flow water closets, have a significant impact on estimating the capacity of a sanitary drainage system. Other plumbing fixtures, such as sinks, lavatories, and bathtubs, may produce similar surging flows in drainage systems, but they do not have as marked an effect as water closets do.

DRAINAGE LOADS A single-family dwelling contains certain plumbing fixtures—one or more bathroom groups, each consisting of a water closet, a lavatory, and a bathtub or shower stall; a kitchen sink, dishwasher, and washing machine; and, possibly, a set of laundry trays. Large buildings also have other fixtures, for example, slop sinks and drinking water coolers. The important characteristic of these fixtures is that they are not used continuously. Rather, they are used with irregular frequencies that vary greatly during the day. In addition, the various fixtures have quite different discharge characteristics, regarding both the average rate of flow per use and the duration of a single discharge. Consequently, the probability of all the fixtures in the building operating simultaneously is small. The assigning of fixture-unit (fu) values to fixtures to represent their load-producing effect

3

on the plumbing system was originally proposed in 1923 by Dr. Roy B. Hunter. The fixture-unit values were designed for application in conjunction with the probability of simultaneous use of fixtures to establish the maximum permissible drainage loads expressed in fixture units rather than in gallons per minute (gpm) (L/s) of drainage flow. Table 1-1 gives the recommended fixture-unit values. The plumbing engineer must conform to local code requirements.

Table 1-1

Residential Fixture-Unit Loads

Fixture

Fixture Units (fu)

Bathtub Clothes washer

2 3

Dishwasher Floor drain

2 3

Laundry tray Lavatory

2 1

Shower Sink (including dishwasher and garbage disposer) Water closet (tank type)

2 3 4

A fixture unit (fu) is a quantity in terms of which the load-producing effects on the plumbing system of different kinds of plumbing fixtures are expressed on an arbitrarily chosen scale. Dr. Hunter conceived the idea of assigning a fixture-unit value to represent the degree to which a fixture loads a system when used at the maximum assumed flow and frequency. The purpose of the fixture-unit concept is to make it possible to calculate the design load on the system directly when the system is a combination of different kinds of fixtures, each having a loading characteristic different than the others. Current or recently conducted studies of drainage loads on drainage systems may change these values. These include studies of: (1) reduced flow from water-saving fixtures; (2) models of stack, branch, and house drain flows; and (3) actual fixture use.

STACK CAPACITIES The criterion of flow capacities in drainage stacks is based on the limitation of the water-occupied cross section to a specified fraction, rs, of the

ASPE Data Book — Volume 2

4

cross section of the stack where terminal velocity exists, as suggested by earlier investigations. Flow capacity can be expressed in terms of the stack diameter and the water cross section: Equation 1-2 Q = 27.8 × rs5/3 × D8/3 where Q = Capacity, gpm (L/s) rs

= Ratio of cross-sectional area of the sheet of water to cross-sectional area of the stack

D

= Diameter of the stack, in. (mm)

Values of flow rates based on r = ¼, 7/24, and 3 are tabulated in Table 1-2.

Table 1-2 Pipe Size, in. (mm) 2 (50)

Capacities of Stacks

r = 1 /4 18.5 (1.18)

3 (80) 4 (100)

54 112

(3.40) (7.07)

5 (125) 6 (150)

205 (12.93) 330 (20.82)

Flow, gpm (L/s) r = 7/24 23.5 (1.48) 70 145

r = 1 /3 —

(4.41) (9.14)

85 (5.36) 180 (11.35)

270 (17.03) 435 (27.44)

324 (20.44) 530 (33.43)

8 (200) 10 (250)

710 (44.8) 1300 (82.0)

920 (58.04) 1650 (104.1)

1145 (72.24) 2055 (129.65)

12 (300)

2050 (129.3)

2650 (167.2)

3365 (212.3)

Whether or not Equation 1-2 can be used safely to predict stack capacities remains to be confirmed and accepted. However, it provides a definite law of variation of stack capacity with diameter; and if this law can be shown to hold for the lower part of the range of stack diameters, it should be valid for the larger diameters. It should be remembered that both F.M. Dawson and Dr. Hunter, in entirely independent investigations, came to the conclusion that slugs of water, with their accompanying violent pressure fluctuations, did not occur until the stack flowed ¼ to 3 full. Most model codes have based their stack loading tables on a value of r = ¼ or 7/24. The recommended maximum permissible flow in a stack is 7/24 of the total cross-sectional area of the stack. Substituting r = 7/24 into Equation 1-2, the corresponding maximum permissible flow for the various sizes of pipe in gpm (L/s) can be determined. Table 1-3 lists the

maximum permissible fixture units to be conveyed by stacks of various sizes. The table was obtained by taking into account the probability of simultaneous use of fixtures. For example, the 500 fu is the maximum loading for a 4-in. (100mm) stack, thus 147 gpm (9.3 L/s) is equivalent to 500 fu. This is the total load from all branches. It should be noted that there is a restriction of the amount of flow permitted to enter a stack from any branch when the stack is more than three branch intervals. If an attempt is made to introduce too large a flow into the stack at any one level, the inflow will fill the stack at that level and will even back up the water above the elevation of inflow, which will cause violent pressure fluctuations in the stack—resulting in the siphoning of trap seals—and may also cause sluggish flow in the horizontal branch. This problem was solved in a study of stack capacities made by Wyly and Eaton at the National Bureau of Standards, for the Housing and Home Finance Agency, in 1950. The water flowing out of the branch can enter the stack only by mixing with the stream flowing down the stack or by deflecting it. Such a deflection of the high-velocity stream coming down the stack can be accomplished only if there is a large enough hydrostatic pressure in the branch, since a force of some kind is required to deflect the downward flowing stream and therefore change its momentum. This hydrostatic pressure is built up by the backing up of the water in the branch until the head thus created suffices to change the momentum of the stream already in the stack enough to allow the flow from the branch to enter the stack. The magnitude of the maximum hydrostatic pressure that should be permitted in the branch as a result of the backing up of the spent water is based on the consideration that this backing up should not be sufficiently great to cause the water to back up into a shower stall or to cause sluggish flow. It is half the diameter of the horizontal branch at its connection to the stack. That is, it is the head measured at the axis of the pipe that will just cause the branch to flow full near the exit. When a long-turn tee-wye is used to connect the branch to the stack, the water has a greater vertical velocity when it enters the stack than it does when a sanitary tee is used, and the back pressures should be smaller in this case for the same flows down the stack and in the branch.

Chapter 1 — Sanitary Drainage Systems

5

Table 1-3 shows the maximum permissible fu loads for sanitary stacks. The procedure for sizing a multistory stack (greater than three floors) is first to size the horizontal branches connected to the stack. This is done by totaling the fixture units connected to each branch and size in accordance with column 2 in Table 1-3. Next, total all the fixture units connected to the stack and determine the size from the same table, under column 4. Immediately check the next column, “Total at One Branch Interval,” and determine that this maximum is not exceeded by any of the branches. If it is exceeded, the size of the stack as originally determined must be increased at least one size, or the loading of the branches must be redesigned so that maximum conditions are satisfied. Take, for example, a 4in. (100-mm) stack more than three stories in height: The maximum loading for a 4-in. (100mm) branch is 160 fu, as shown in column 2 of Table 1-3. This load is limited by column 5 of the same table, which permits only 90 fu to be introduced into a 4-in. (100-mm) stack in any one branch interval. The stack would have to be increased in size to accommodate any branch load exceeding 90 fu.

Table 1-3 Horizontal Fixture Branches and Stacks

Any 1 Stack of Horizontal 3 or Fewer Fixture Branch Brancha Intervals

Stacks with More than 3 Branch Intervals Total Total at 1 for Stack Branch Interval

1½ (40)

3

4

8

2

2

(50)

6

10

24

6

2½ (65)

12

20

42

9

3

20b

48b

72b

20b

(80)

Sizing is computed as follows: Step 1. Compute the fixture units connected to the stack. In this case, assume there are 1200 fixture units connected to the stack from the street floor through the top floor. Step 2. Size the portion of the stack above the fifth-floor offset. There are 400 fixture units from the top floor down through the sixth floor. According to Table 1-3, column 4, 400 fixture units require a 4-in. (100-mm) stack. Step 3. Size the offset on the 5th floor. An offset is sized and sloped like a building drain. Step 4. Size the lower portion of the stack from the fifth floor down through the street floor. The lower portion of the stack must be large enough to serve all fixture units connected to it, from the top floor down, in this case, 1200 fixture units. According to Table 1-3, 1200 fixture units require a 6-in. (150-mm) stack. Step 5. Size and slope the offset below the street floor the same as a building drain.

Maximum Number of Fixture Units (fu) that May Be Connected to Diameter of Pipe, in. (mm)

To illustrate clearly the requirements of a stack with an offset of more than 45° from the vertical, Figure 1-1 shows the sizing of a stack in a 12-story building where there is one offset between the fifth and sixth floors and another offset below the street floor.

4 (100)

160

240

500

90

5 (125)

360

540

1100

200

6 (150)

620

960

1900

350

8 (200)

1400

2200

3600

600

10 (250)

2500

3800

5600

1000

12 (300)

3900

6000

8400

1500

15 (380)

7000

aDoes not include branches of the building drain. bNo more than 2 water closets or bathroom groups within each branch interval or more than 6 water closets or bathroom groups on the stack.

The fixture on the sixth floor should be connected to the stack at least 2 ft (0.6 m) above the offset. If this is not possible, then connect them separately to the stack at least 2 ft (0.6 m) below the offset. If this is not possible either, run the fixture drain down to the fifth or fourth floor and connect to the stack there.

CAPACITIES OF SLOPING DRAINS Capacities of horizontal or sloping drains are complicated by surging flow. The concept of flow on which the determination of drain sizes is based is that of a highly fluctuating or surging condition in the horizontal branches that carry the discharges of fixtures to the soil or waste stack. After falling down the vertical stack, the water is assumed to enter the building drain with the peaks of the surges leveled off somewhat but still in a surging condition. In a large building covering considerable ground area there are probably several primary

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branches and certainly at least one secondary branch. After the water enters the building drain, the surge continues to level off, becoming more and more nearly uniform, particularly after the hydraulic jump has occurred. If the secondary branch is long enough, and if the drain serves a large number of fixtures, the flow may become substantially uniform before it reaches the street sewer.

Figure 1-1

Steady, Uniform Flow Conditions in Sloping Drains Although the equations of steady, uniform flow in sloping drains should not be used to determine the capacities of sloping drains in which surging flow exists, flow computations based on these formulas afford a rough check on values obtained by the more complicated methods that

Procedure for Sizing an Offset Stack

Chapter 1 — Sanitary Drainage Systems

7

are applicable to surging flow. Hence, three of the commonly used formulas for flow in pipes will be considered: (1) Hazen and Williams, (2) Manning, and (3) Darcy-Weisbach.

The quantity of flow is equal to the crosssectional area of flow times the velocity of flow obtained from the above three equations. This can be expressed as:

Hazen and Williams formula This formula is usually written:

Equation 1-5a

Equation 1-3 V = 1.318 × C × R where

Q = AV where

0.63

×S

0.54

V

= Mean velocity of flow, fps (m/s)

C

= Hazen and Williams coefficient

R

= Hydraulic radius of pipe, ft (m)

S

= Slope of pressure gradient

The exponents of R and S in Equation 1-3 have been selected to make the coefficient C as nearly constant as possible for different pipe diameters and for different velocities of flow. Thus, C is approximately constant for a given pipe roughness. Darcy-Weisbach formula In this formula the dimensionless friction coefficient f varies with the diameter of the pipe, the velocity of flow, the kinematic viscosity of the fluid flowing, and the roughness of the walls. It is usually written:

Q = Quantity rate of flow, cfs (m3/s) A

= Cross-sectional area of flow, ft2 (m2)

V

= Velocity of flow, fps (m/s)

By substituting the value of V from Manning’s formula, the quantity of flow in variously sized drains of the same material can be calculated: Equation 1-5b Q = A ×

1.486 × R2/3 × S1/2 ‰ n 

This is the formula used by many plumbing engineers to deal with sloping drain problems. The significant hydraulic parameters used in the above equation are listed in Table 1-4. It should be noted that the units in the above equations should be converted to the proper units whenever utilizing Equations 1-5a or 1-5b.

Equation 1-4 fLV2 D 2g where hf =

hf = Pressure drop or friction loss, ft (m) f

= Friction coefficient

L

= Length of pipe, ft (m)

D

= Diameter of pipe, ft (m)

V

= Mean velocity of flow, fps (m/s)

g

= Acceleration of gravity, 32.2 fps2 (9.8 m/s2)

Manning formula The Manning formula, which is similar to the Hazen and Williams formula, is meant for open-channel flow and is usually written: Equation 1-5 V =

1.486 1.486 × R2/3 × S1/2 = × R0.67 × S0.50 n n

In this formula, n is the Manning coefficient and varies with the roughness of the pipe and the pipe diameter.

Slope of Horizontal Drainage Piping Horizontal drains are designated to flow at halffull capacity under uniform flow conditions to minimize the generation of pneumatic pressure fluctuations. A minimum slope of ¼ in./ft (6.4 mm/m) should be provided for pipe 3 in. (80 mm) and smaller, 8 in./ft (3.2 mm/m) for 4–6-in. (100–150-mm) pipe, and z in./ft (1.6 mm/m) for pipe 8 in. (200 mm) and larger. (The designer must confirm required slopes with the local code authority.) These minimum slopes are required to maintain a velocity of flow greater than 2 fps for scouring action. Table 1-5 gives the approximate velocities for given slopes and diameters of horizontal drains based on the Manning formula for ½-full pipe and n = 0.015.

Load or Drainage Piping The recommended design loads for building drains and sewers are tabulated in Table 1-6. This table shows the maximum number of fixture units that may be connected to any portion of the building drain or building sewer for given

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Table 1-4 Values of R, R2/3, AF, and AH Pipe Size, in. (mm)

D 4, ft (mm)

1½ (40)

0.0335 (1.02)

0.1040

(3.17)

0.01412 (0.0013)

0.00706 (0.0006)

2

(50)

0.0417 (1.27)

0.1200

(3.66)

0.02180 (0.0020)

0.01090 (0.0009)

2½ (65)

0.0521 (1.59)

0.1396

(4.24)

0.03408 (0.0031)

0.01704 (0.0015)

3

(80)

0.0625 (1.90)

0.1570

(4.78)

0.04910 (0.0046)

0.02455 (0.0023)

4 (100)

0.0833 (2.54)

0.1910

(5.82)

0.08730 (0.0081)

0.04365 (0.0040)

5 (125)

0.1040 (3.17)

0.2210

(6.74)

0.13640 (0.0127)

0.06820 (0.0063)

6 (150)

0.1250 (3.81)

0.2500

(7.62)

0.19640 (0.0182)

0.09820 (0.0091)

8 (200)

0.1670 (5.09)

0.3030

(9.23)

0.34920 (0.0324)

0.17460 (0.0162)

10 (250)

0.2080 (6.33)

0.3510 (10.70)

0.54540 (0.0506)

0.27270 (0.0253)

12 (300)

0.2500 (7.62)

0.3970 (12.10)

0.78540 (0.0730)

0.39270 (0.0364)

15 (380)

0.3125 (9.53)

0.4610 (14.05)

1.22700 (0.0379)

0.61350 (0.0570)

R =

R2/3, ft (mm)

AF (Cross-Sectional Area for Full Flow), ft2 (m2)

AH (Cross-Sectional Area for Half-Full Flow), ft2 (m2)

Table 1-5 Approximate Discharge Rates and Velocities in Sloping Drains, n = 0.015a Actual Inside Diameter of Pipe, in. (mm)

½-Full Flow Discharge Rate and Velocity 1/16

in./ft (1.6 mm/m) Slope

Disch., gpm (L/s)

Velocity, fps (mm/s)

1/8

in./ft (3.2 mm/m) Slope

Disch., gpm (L/s)

Velocity, fps (mm/s)

1/4

in./ft (6.4 mm/m) Slope

Disch., gpm (L/s)

Velocity, fps (mm/s)

14 (31.8)

1/2

in./ft (12.7 mm/m) Slope

Disch. gpm (L/s)

Velocity, fps (mm/s)

3.40 (0.21)

1.78

(45.5)

1a (34.9)

3.13 (0.20)

1.34 (0.41)

4.44 (0.28)

1.90

(48.3)

12 (38.9)

3.91 (0.247)

1.42 (0.43)

5.53 (0.35)

2.01

(51.1)

1s (41.28)

4.81 (0.30)

1.50 (0.46)

6.80 (0.38)

2.12

(53.9)

2

8.42 (0.53)

1.72 (0.52)

11.9 (0.75)

2.43

(61.8)

(50.8)

22 (63.5) 3

(76.3)

10.8 (0.68)

1.41 (0.43)

15.3 (0.97)

1.99 (0.61)

21.6 (1.36)

2.82

(71.7)

17.6 (1.11)

1.59 (0.49)

24.8 (1.56)

2.25 (0.69)

35.1 (2.21)

3.19

(81.1)

75.5 (4.76)

3.86

(98.2)

4 (101.6)

26.70 (1.68)

1.36 (34.6)

37.8 (2.38)

1.93 (0.59)

53.4 (3.37)

2.73 (0.83)

5 (127)

48.3 (3.05)

1.58 (40.2)

68.3 (4.30)

2.23 (0.68)

96.6 (6.10)

3.16 (0.96)

137.

6 (152.4)

78.5 (4.83)

1.78 (45.3)

111.

(7.00)

2.52 (0.77)

157. (10.)

3.57 (1.09)

222. (14.0)

5.04 (128.2)

8 (203.2)

170. (10.73)

2.17 (55.2)

240. (15.14)

3.07 (0.94)

340. (21.5)

4.34 (1.32)

480. (30.3)

6.13 (155.9)

10 (256)

308. (19.43)

2.52 (64.1)

436. (27.50)

3.56 (1.09)

616. (38.9)

5.04 (1.54)

872. (55.0)

7.12 (181.0)

12 (304.8)

500. (31.55)

2.83 (72.0)

707. (44.60)

4.01 (1.22)

999. (63.0)

5.67 (1.73)

1413. (89.15)

8.02 (204.0)

a n = Manning coefficient, which varies with the roughness of the pipe.

(8.64)

4.47 (113.7)

Chapter 1 — Sanitary Drainage Systems

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slopes and diameters of pipes. For example, an offset below the lowest branch with 1300 fu at ¼ in./ft (6.4 mm/m) slope requires an 8-in. (200mm) pipe. For devices that provide continuous or semicontinuous flow into the drainage system, such as sump pumps, ejectors, and air-conditioning equipment, a value of 2 fu can be assigned for each gpm (L/s) of flow. For example, a sump pump that discharges at the rate of 200 gpm (12.6 L/s) is equivalent to 200 × 2 = 400 fu.

COMPONENTS OF SANITARY DRAINAGE SYSTEMS

Building drains that cannot be discharged to the sewer by gravity flow may be discharged into a tightly covered and vented sump, from which the liquid is lifted and discharged into the building’s gravity drainage system by automatic pump equipment or by any equally efficient method approved by the administrative authority. A duplex pump system should be used, so that, in the event of the breakdown of one pump, an-

Diameter of Pipe, in. (mm)

Building Drains and Sewersa

Maximum Number of Fixture Units that May Be Connected to Any Portion of the Building Drain or Building Sewer 1/16

(1.6)

Slope, in./ft (mm/m) 1/8 (3.2) 1/4 (6.4)

1/2 (12.7)

2 (50)

21

26

2½ (65) 3 (80)

24 42b

31 50b

4 (100) 5 (125)

Incoming water is collected in the sump before it goes down the drain pipe. Heavy-flow drains require large sumps to retain greater than usual amounts of water, thereby creating more head pressure on the pipe inlet. Most manufacturers make their sumps with bottom, side, or angle outlets and with inside caulk, no-hub, push-on, spigot, or screwed connections.

Cleanouts

Sumps and Ejectors

Table 1-6

other will remain in operation and no damage will be caused by the cessation of system operation. When a duplex unit is used, each pump should be sized for 100% flow, and it is good practice to have the operation of the pumps alternate automatically.

180 390

216 480

250 575

6 (150) 8 (200)

1400

700 1600

840 1,920

1,000 2,300

10 (250) 12 (300)

2500 2900

2900 4600

3,500 5,600

4,200 6,700

15 (380)

7000

8300

10,000

12,000

aOn-site sewers that serve more than one building may be sized according to the current standards and specifications of the administrative authority for public sewers. bNo more than 2 water closets or 2 bathroom groups, except in single-family dwellings, where no more than 3 water closets or 3 bathroom groups may be installed.

The cleanout provides access to horizontal and vertical lines to facilitate inspection and provide a means of removing obstructions such as solid objects, greasy wastes, and hair. Cleanouts, in general, must be gas and water-tight, provide quick and easy plug removal, allow ample space for the operation of cleansing tools, have a means of adjustment to finished surfaces, be attractive in appearance, and be designed to support whatever traffic is directed over them. Some cleanouts are designed with a neoprene seal plug, which prevents “freezing” or binding to the ferrule. All plugs are machined with a straight or running thread and a flared shoulder for the neoprene gasket, permitting quick and certain removal when necessary. A maximum opening is provided for tool access. Recessed covers are available to accommodate carpet, tile, terrazzo and other surface finishes, and are adjustable to the exact floor level established by the adjustable housing or by the set screws. Waste lines are normally laid beneath the floor slabs at a distance sufficient to provide adequate backfill over the joints. Cleanouts are then brought up to floor-level grade by pipe extension pieces. Where the sewer line is at some distance below grade and not easily accessible through extensions, small pits or manholes with access covers must be installed. When cleanouts are installed in traffic areas, the traffic load must be considered when the materials of construction are selected. The size of the cleanout within a building should be the same size as the piping, up to 4 in. (100 mm). For larger size interior piping, 4in. (100-mm) cleanouts are adequate for their

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intended purpose; however, 6-in. (150-mm) cleanouts are recommended to allow for a larger variety of access for sewer video equipment. Cleanouts should be provided at the following locations: 1. Five ft 0 in. (1.5 m) outside or inside the building at the point of exit. 2. At every change of direction greater than 45°. 3. A maximum distance between cleanouts of 50 ft (15.1 m) should be maintained for piping 4 in. (100 mm) and smaller, and of 75 ft (22.9 m) for larger piping. Underground sanitary sewer piping larger than 10 in. (250 mm) in diameter should be provided with manholes at every change of direction and every 150 ft (45.7 m). 4. At the base of all stacks. 5. To comply with applicable codes. Optional locations include: 1. At the roof stack terminal. 2. At the end of horizontal fixture branches or waste lines. 3. At fixture traps. (Fixture traps can be premanufactured with cleanout plugs, although some codes prohibit the installation of this kind of trap.)

Table 1-7 Recommended Grate Open Areas for Various Outlet Pipe Sizes Recommended Minimum Grate Open Area Transverse Area of Pipe, in.2a (× 10 mm2)

Minimum Inside Area, in.2 (× 10 mm2)

1½ (40) 2 (50)

2.04 3.14

(1.3) (2.0)

2.04 3.14

(1.3) (2.0)

3 (80) 4 (100)

7.06 12.60

(4.6) (8.1)

7.06 12.06

(4.6) (8.1)

5 (125) 6 (150)

19.60 (12.7) 28.30 (18.3)

19.60 (12.7) 28.30 (18.3)

8 (200)

50.25 (32.4)

50.24 (32.4)

Nominal Pipe Size, in. (mm)

aBased on extra-heavy soil pipe, nominal internal diameter.

Floor Drains and Floor Sinks A large-diameter drain with a deep sump connected to a large-diameter pipe will pass more water more rapidly than a smaller drain will. However, economics do not allow the designer arbitrarily to select the largest available drain when a smaller, less-expensive unit will do a satisfactory job. High-capacity drains are intended for use primarily in locations where the flow reaches high rates, such as malls, washdown areas, and certain industrial applications. Table 1-7, which shows minimum ratios of open grate area based on pipe diameter, is offered as a guide for the selection of drains where the drain pipe diameter is known. The only drawback to using the open-areapipe-diameter-ratio method is that all drain manufacturers do not list the total open areas of grates in their catalogs. This information usually can be obtained upon request, however. For the sizing of floor drains for most indoor applications, the capacity of a drain is not extremely critical because the drain’s primary function is to handle minor spillage or fixture overflow. The exceptions are, of course, cases where equipment discharges to the drain, where automatic fire sprinklers may deluge an area with large amounts of water, and where flushing of the floor is required for sanitation. Generally located floor drains or drains installed to anticipate a failure may not receive sufficient water flow to keep the protective water seal or plumbing trap from evaporating; if it does evaporate, sewer gases will enter the space. Automatic or manual trap primers should be installed to maintain a proper trap seal. (A small amount of vegetable oil will dramatically reduce the evaporation rate of infrequently used floor drains and floor sinks.) Figure 1-2 shows the basic components of a floor drain.

Grates/Strainers The selection of grates is based on use and the amount of flow. Light-traffic areas may have a nickel-bronze-finished grate, while mechanical areas may have a large, heavy-duty, ductile iron grate. The wearing of spike-heeled shoes prompted the replacement of grates with a heel-proof, ¼-

Chapter 1 — Sanitary Drainage Systems

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Figure 1-2 Basic Floor-Drain Components: (A) Removable Grate; (B) Rust-Resistant Bolts; (C) Integral, One-Piece, Flashing Ring; (D) Cast Drain Body with Sump; (E) Sediment Bucket (optional).

in.-square (6.4-mm) hole design in public toilet rooms, corridors, passageways, promenade decks, patios, stores, theaters, and markets. Though this type of grating has less drainage capacity than the previous one, its safety feature makes it well worth the change.

into its original position. Ramp-drain gratings should be slightly convex because rapidly flowing ramp water has a tendency to flow across the grate. A better solution to this problem is to place flat-top grates on a level surface at the bottom of the ramp, rather than on the ramp slope.

Grates or strainers should be secured with stainless-steel screws in nickel-bronze tops. Vandal-proof fasteners are available from most manufacturers. Vandal-proofing floor drain grates is advisable. If there is public access to the roof, consideration must be given to protecting the vent openings from vandals.

A technique in casting grates is the reversal of pattern draft, which removes the razor-sharp edges created when grates are buffed. See Figure 1-3. The prevalent buffing technique is called “scuff-buff’ because it gives the grate a slightly used appearance. The use of slots in grates is becoming obsolete because of the slicing edges they create, which cause excess wear and tear

In school gymnasium shower rooms, where the blocking of flat-top shower drains with paper towels can cause flooding, dome grates in the corners of the room or angle grates against the walls can be specified in addition to the regular shower drains. Shower-room gutters and curbs have become undesirable because of code requirements and the obvious dangers involved. Therefore, the passageways from shower areas into locker areas need extended-length drains to prevent runoff water from entering the locker areas. Where grates are not secured and are subject to vehicular traffic, it is recommended that nontilting and/or tractor-type grates be installed. When a grate starts to follow a wheel or is hit on one edge and starts to tilt, the skirt catches the side of the drain body and the grate slides back

(a)

(b) Figure 1-3 Pattern Draft for Floor Gratings: (a) Sharp Edge, (b) Reverse Pattern.

12

ASPE Data Book — Volume 2

on the wheels of hand-trucks and other vehicles. Square openings are more desirable because they shorten this edge and provide greater drainage capacity than round holes.

Flashing Ring This component makes an effective seal, which prevents water from passing around the drain to the area below.

Sediment Bucket A “sediment bucket” is an additional internal strainer designed to collect debris that gets by the regular strainer; it is required wherever the drain can receive solids, trash, or grit that could plug piping. Locations include: 1. Toilet rooms in commercial buildings should be equipped with floor drains with sediment buckets to facilitate cleaning. 2. Floor drains with sediment buckets must also be provided in mechanical equipment rooms, where pumps, boilers, water chillers, heat exchangers, and HVAC equipment regularly discharge and/or must be periodically drained for maintenance and repairs. HVAC equipment requires the drainage of condensate from cooling coils, using indirect drains. 3. Boilers require drains with sediment buckets. Strategically located floor drains are also required in buildings with wet fire-protection sprinkler systems to drain water in case sprinkler heads are activated. The maximum temperature of liquids discharged should be 140°F (60°C). Floor drains shall connect into a trap so constructed that it can be readily cleaned and sized to serve efficiently the purpose for which it is intended. A deep-seal-type trap or an approved automatic priming device should be provided. The trap shall be accessible either from the floor-drain inlet or by a separate cleanout within the drain. Figure 1-4 illustrates several types of drain that meet these conditions.

Accessories A variety of accessories are available to make the basic drain adaptable to various types of structure. The designer must know the construction of the building, particularly the floor and deck structures, to specify the appropriate drain.

Figure 1-4 Types of Floor Drain: (A) Typical Drain with Integral Trap that May Be Cleaned Through Removable Strainer at Floor Level; (B) Floor Drain with Combination Cleanout and Backwater Valve, for Use Where Possibility of Backflow Exists; (C) Drain with Combined Cleanout, Backwater Valve, and Sediment Bucket.

Backwater Valves A backwater valve can be installed on a building sewer/house drain when the drain is lower than the sewer line, when unusual sewer surcharges may occur due to combined storm-water and sanitary sewer systems, or when older municipal sewers incur high rates of infiltration. A backwater valve reacts similarly to the way a check valve does. The device consists of a mechanical flapper or disc, which requires a certain amount of maintenance; therefore, attention must be given during the placement of these devices to a free area and access for maintenance. Sediment can accumulate on the flapper valve seat, preventing the flapper from closing tightly. Also, many valves employ a spring or mechanical device to exert a positive pressure on the flapper device, which requires occasional lubrication. Most manufacturers of backwater valves provide an access cover plate for maintenance, which may also be used as a building sewer cleanout. Figure 1-5 illustrates various types of backwater valve that may be installed where there is a possibility of backflow.

Oil Interceptors In commercial establishments such as service stations, garages, auto-repair shops, dry cleaners, laundries, industrial plants, and process industries having machine shops, metal-treating process rooms, chemical process or mixing

Chapter 1 — Sanitary Drainage Systems

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Grease Interceptors In the drainage from commercial kitchens, grease, fats, and oils must be separated from sewage. This function is performed by grease interceptors installed in drain lines where the presence of grease in the sewage is expected.

Figure 1-5 Various Types of Backwater Valve

rooms, etc., there is always the problem of flammable or volatile liquids entering the drainage system, which can contaminate the sewer line and cause a serious fire or explosive condition. Oil interceptors are designed to separate and collect oils and other light-density, volatile liquids, which would otherwise be discharged into the drainage system. An oil interceptor is required wherever lubricating oil, cutting oil, kerosene, gasoline, diesel fuel, aircraft fuel, naphtha, paraffin, trisodium phosphate, or other light-density and volatile liquids are present in or around the drainage system. The interceptor is furnished with a sediment bucket, which collects debris, small parts, chips, particles, and other sediment that are frequently present in industrial waste from these types of facility and could clog the drainage system. A gasketed, removable cover permits access for cleaning the interceptor. To eliminate pressure buildup inside the interceptor, a connection on each side of the body allows the venting of the interceptor. Oil interceptors are sized in accordance with the maximum anticipated gpm (L/s) flow rate of waste water that could be discharged through the drains they serve. A flow-control fitting of the exact gpm (L/s) interceptor rating ensures maximum oil interception efficiency. If this flow rating is exceeded, the separation of the oil from the waste water will not occur. Oil draw-off pipes, used in conjunction with a supplemental waste oil storage tank, can improve efficiency and prolong system maintenance and cleaning.

It is sometimes practical to discharge the waste from two or more sinks into a single interceptor. This practice is recommended only when all the fixtures are close together to avoid installing long piping runs to the interceptor. The closer the interceptor can be installed to the fixture(s) the better. The longer the run of pipe, the cooler the waste water is. As the waste water cools, the grease congeals, coating and clogging the interior of the pipe. The procedures for sizing grease interceptors are as follows: 1. Determine the cubic content of the fixtures by multiplying length by width by depth. 2. Determine the capacity in gallons (1 gal = 231 in.3) (liters [1 L = 1000 cm3]). 3. Determine the actual drainage load. The fixture is usually filled to about 75% of capacity with waste water. The items being washed displace about 25% of the fixture content. Therefore, actual drainage load = 75% of fixture capacity. 4. Determine the flow rate and the drainage period. In general, good practice dictates a 1-min drainage period; however, where conditions permit, a 2-min period is acceptable. The drainage period is the actual time required to completely empty the fixture. 5. Flow rate =

Actual drainage load Drainage period

6. Select the interceptor that corresponds to the flow rate calculated. It is recommended to provide the automatic removal of grease from the interceptor to a storage tank that can be cleaned regularly.

Trap Primers In lieu of deep-seal P-traps, many jurisdictions require trap primers on floor and fixture drains that are consistently used on an infrequent basis. General-purpose, mechanical-room drains; toilet-room drains; and seasonable, condensate drains fall into this category. A trap primer allows

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small amounts of water to trickle into the device to prevent the loss of the trap seal through evaporation. Maintaining proper water-trap seals is critical to keeping sewer gases from entering occupied spaces. (Refer to Chapter 3 of this volume, “Vents and Venting Systems.”) Some jurisdictions allow manual trap primers, which consist of a manual valve on a domestic water supply diverting water to, or directly connected to, the fixture trap. Automatic trap primers are widely accepted. Following are some of the different types: 1. Electric-operated, solenoid valves. These can be programmed to operate at predetermined and regular intervals. They require a power source and should be specified to fail in the closed position. 2. Pressure-differential-actuated valves. These are connected to or installed in-line on a domestic water line. They discharge a small amount of water each time there is a change in the domestic-water-line pressure. Pressure fluctuates upon fixture use and/or flushvalve operation. 3. Fixture supply-water type. These devices are mounted on the tailpiece of a flushometer valve to collect a small portion of water as it cascades toward the bowl. The flushometer tailpiece is typically protected from back-siphonage by the vacuum breaker mounted at the tailpiece entrance. 4. Fixture waste-water type. These devices are mounted on the trap of frequently used fixtures. A tapping at the overflow line will allow small amounts of waste water to enter an adjacent, infrequently used drain as the trap surges during use. Automatic trap primers can be obtained as pre-engineered devices, which have approvals that are widely accepted. All direct connections between the sewer system and the potable water system must be protected from contamination potential. The above-referenced primers can be manufactured with, or fitted with, devices that are approved to prevent cross-contamination.

Supports The location of pipe supports is usually specified by code. They are located to maintain a slope that is as uniform as possible and will not change with time. In this regard, the rigidity of pipe and joints and the possibility of creep and bedding settlement are primary considerations. When

building settlement may be significant, special hanging arrangements may be necessary. Underground piping should be continuously and firmly supported, but blocking below metal pipe is usually acceptable. Consult the manufacturer for recommendations for piping materials not covered in the code and for special problems. Hangers should be designed adequately. To protect from damage by building occupants, allow at least a 250-lb (113.4-kg) safety factor when designing hangers. See Data Book, Volume 4, Chapter 6 for further information. Seismic restraint must also be considered.

MATERIALS Materials recommended for soil and waste piping, installed above ground within buildings, are copper alloy, copper, cast iron (hub-and-spigot or hubless), galvanized steel, lead, or PVC plastic pipe. Underground building drains should be cast-iron soil pipe, hard-temper copper tube, ABS or PVC, PVDF, DWV pattern schedule 40 plastic pipe with compression joints or couplings, installed with a minimum cover of 12 in. (300 mm). Corrosive wastes require suitably acid-resistant materials such as high-silicon cast iron, borosilicate glass, polypropylene, etc. (Note: Some blood analyzers disharge sodium azide. It forms a very dangerous, explosive compound with copper pipes. Either other piping must be used or the sodium azide must be kept out of the system.) The materials used for pipe fittings must be compatible with the materials utilized for piping. Fittings should sweep in the direction of flow and have smooth interior surfaces without ledges, shoulders, or reductions that may obstruct the flow in piping. Drains specified with cast-iron or PVC bodies should be suitable for most installations. Where extra corrosion resistance is required, high-silica cast iron, polypropylene, borosilicate glass, stainless steel, galvanized iron, or other acid-resisting material should be selected. Where a sediment bucket is used, it should be bronze or galvanized or stainless steel. Enameled sediment buckets are impractical because they chip when cleaned. In the selection of materials for top surfaces, such as grates, where floor drains are visible in finished areas, appearance is a prime consideration. As cast iron will rust and galvanizing and

Chapter 1 — Sanitary Drainage Systems

chrome plating will eventually be worn off by traffic, the preferred material is solid, cast nickel-bronze, which maintains its attractive appearance. In a swimming pool, however, chlorine necessitates the use of chlorine-resistant materials. For large grates that will be subject to hand-truck or forklift traffic, a ductile iron grate with or without a nickel-bronze veneer is recommended. Polished brass or bronze for floor service has the disadvantage of discoloring unless there is constant traffic over it. Cast aluminum has also been found inadequate for certain floor-service applications due to excessive oxidation and its inability to withstand abrasion.

Noise Transmission Noise transmission along pipes may be reduced by avoiding direct metal-to-metal connections. Noise transmission through pipe walls is generally reduced by using heavier materials. Noise transmission to the building may be reduced by isolating piping with resilient materials, such as rugs, belts, plastic, or insulation. See Table 1-8 for relative noise-insulation absorption values.

BUILDING SEWER INSTALLATION The installation of building sewers (house drains) is very critical to the operation of the sewer. Inadequate bedding in poor soils may allow the sewer to settle, causing dips and low points in the sewer. The settlement of sewers interrupts flow, diminishes minimum cleansing velocity, reduces capacity, and creates a point where solids can drop out of suspension and collect. The following are some guidelines for installing building sewers/drains: 1. Compacted fill. Where natural soil or compacted fill exists, the trench must be excavated in alignment with the proposed pitch and grade of the sewer. Depressions need to be cut out along the trench line to accept the additional diameter at the piping joint or bell hub. A layer of sand or pea gravel is placed as a bed in the excavated trench because it is easily compacted under the pipe, allowing more accurate alignment of the pipe pitch. The pipe settles into the bed and is firmly supported over its entire length.

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2. Shallow fill. Where shallow amounts of fill exist, the trench can be over excavated to accept a bed of sand, crushed stone, or similar material that is easily compacted. Bedding should be installed in lifts (layers), with each lift compacted to ensure optimum compaction of the bedding. The bed must be compacted in alignment with the proposed pitch and grade of the sewer. It is recommended that pipe joints or bell hub depressions be hand prepared due to the coarser crushed stone. The soil bearing weight determines trench widths and bedding thickness. 3. Deep fill. Where deep amounts of fill exist, the engineer should consult a geotechnical engineer, who will perform soil borings to determine the depths at which soils with proper bearing capacities exist. Solutions include compacting existing fill by physical means or removing existing fill and replacing it with crushed stone structural fill. 4. Backfilling. Backfilling of the trench is just as critical as the compaction of the trench bed and the strength of existing soils. Improper backfill placement can dislodge pipe and cause uneven sewer settlement, with physical depressions in the surface. The type of backfill material and compaction requirements need to be reviewed to coordinate with the type of permanent surface. Landscaped areas are more forgiving of improper backfill placement than hard surface areas, such as concrete or bituminous paving. Care must be taken when using mechanical means to compact soils above piping. Mechanical compaction of the first layer above the pipe by vibrating or tamping devices should be done with caution. Compacting the soil in 6-in. (150-mm) layers is recommended for a good backfill. Proper sewer bedding and trench backfill results in an installation that can be counted upon for long, trouble-free service.

SANITATION All drains should be cleaned periodically, particularly those in markets, hospitals, foodprocessing areas, animal shelters, morgues, and other locations where sanitation is important.

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Where sanitation is important, an acid-resisting enameled interior in floor drains is widely accepted. The rough surfaces of either brass or iron castings collect and hold germs, fungusladen scum, and fine debris, which usually accompany drain waste. There is no easy or satisfactory way to clean these rough surfaces; the most practical approach is to enamel them. The improved sanitation compensates for the added expense. However, pipe threads cannot be cut into enameled metals because the enameling will chip off in the area of the machining. Also, pipe threads themselves cannot be enameled; therefore, caulked joints should be specified on enameled drains. Most adjustable floor drains utilize a threaded head that allows elevation adjustments. The drains cannot be enameled because of this adjusting thread. However, there are other adjustable drains that use sliding lugs on a cast thread and may be enameled. Another point to remember is that a grate or the top ledge of a drain can be enameled, but the enamel will not tolerate traffic abrasion without showing scratches and, eventually, chipping. The solution to this problem is a stainless-steel or nickel-bronze rim and grate over the enameled drain body, a common practice on indirect waste receptors, sometimes referred to as “floor sinks.” Specifiers seem to favor the square, indirect waste receptor, but the round receptor is easier to clean and has better antisplash characteristics. For cases where the choice of square or round is influenced by the floor pattern, round sinks with square tops are available.

ASPE Data Book — Volume 2

ter-supply line to a drain, a vacuum breaker installed according to code must be provided.

KITCHEN AREAS When selecting kitchen drains, the designer must know the quantity of liquid and solid waste the drains will be required to accept, as well as which equipment emits waste on a regular basis and which produces waste only by accidental spillage. Floor-cleaning procedures should be ascertained to determine the amount of water used. If any amount of solid waste is to be drained, receptors must be specified with removable sediment buckets made of galvanized or stainless steel. Also, there must be enough vertical clearance over these drains to conveniently remove the sediment buckets for cleaning. Many kitchen planners mount kitchen equipment on a 5-in. (125-mm) curb. Placing the drain on top of the curb and under the equipment makes connection of indirect drain lines difficult and the receptor inaccessible for inspection and cleaning. Mounting the receptor in front of the curb takes up floor space, and the myriad indirect drains that discharge into it create a potential hazard for employees who may trip over them. The solution requires close coordination between the engineer and the kitchen designer.

In applications such as hospital morgues, cystoscopic rooms, autopsy laboratories, slaughterhouses, and animal dens, the enameled drain is fitted with a flushing rim. This is most advisable where blood or other objectionable materials might cling to the side walls of the drain. Where the waste being drained can create a stoppage in the trap, a heel inlet on the trap with a flushing connection is recommended in addition to the flushing rim, which merely keeps the drain sides clean. (This option may not be allowed by certain codes.) A 2-in. (50-mm) trap flushes more effectively than a 3-in. (80-mm) trap because it allows the flushing stream to drill through the debris rather than completely flush it out. A valve in the water line to the drain is the best way to operate the flushing-rim drain. Flush valves have been used and save some water; however, they are not as convenient or effective as a shutoff valve. In any flushing wa-

Figure 1-6 Combination Floor Drain and Indirect Waste Receptor

Chapter 1 — Sanitary Drainage Systems

Figure 1-6 shows an arrangement whereby any spillage in front of the curb can be drained by half of the receptor, while indirect drains are neatly tucked away. Where equipment is on the floor level and an indirect waste receptor must be provided under the equipment, a shallow bucket that can easily be removed is recommended.

WATERPROOFING Whenever a cast-iron drain is cemented into a slab, separation due to expansion and contraction occurs and creates several problems. One is the constant wet area in the crevice around the drain that promotes mildew odor and the breeding of bacteria. Seepage to the floor below is also a possibility. This problem can be corrected by a seepage or flashing flange. Weep holes in the flashing flange direct moisture into the drain. Also, this flange accepts membrane material and, when used, the flashing ring should lock the membrane to the flange. One prevalent misconception about the flashing flange is that it can have weep holes when used with cleanouts. In this case, there can be no weep holes into the cleanout for the moisture to run to. Weep holes should also be eliminated from the flashing flanges of drains, such as reflection-pool drains, where the drain entrance is shut off by an overflow standpipe to maintain a certain water level. The term “nonpuncturing,” used in reference to membrane-flashing, ring-securing methods, is now obsolete as securing bolts have been moved inboard on flashing L flanges and the membrane need not be punctured to get a seal. Of the various arrangements, this bolting method allows the greatest squeeze pressure on the membrane.

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with adjustable tops to attain an installation that is flush with the finished floor.

JOINING METHODS Drain and cleanout outlets are manufactured in four basic types: 1. Inside caulk. In this arrangement, the pipe extends up into the drain body and oakum is packed around the pipe tightly against the inside of the outlet. Molten lead is then poured into this ring and later stamped or caulked to correct for lead shrinkage. Current installation methods use a flexible gasket for a caulking material. See Figure 1-7. 2. Spigot outlet. This type utilizes the caulking method as outlined above, except that the spigot outlet is caulked into the hub or bell of the downstream pipe or fitting. See Figure 1-8. 3. Push-seal gasketed outlet. This type utilizes a neoprene gasket similar to standard ASTM C564 neoprene gaskets approved for huband-spigot, cast-iron soil pipe. A ribbed neoprene gasket is applied to the accepting pipe thus allowing the drain outlet to be pushed onto the pipe. 4. No-hub. This type utilizes a spigot (with no bead on the end) that is stubbed into a neoprene coupling with a stainless-steel bolting band (or other type of clamping device), which, in turn, accepts a downstream piece of pipe or headless fitting. See Figure 1-9. 5. IPS or threaded. This type is a tapered female thread in the drain outlet designed to accept the tapered male thread of a downstream piece of pipe or fitting. See Figure 1-10.

FLOOR LEVELING A major problem in setting floor drains and cleanouts occurs when the concrete is poured level with the top of the unit, ignoring the fact that the addition of tile on the floor will cause the drain or cleanout to be lower than the surrounding surface. To solve the problem, cleanouts can be specified with tappings in the cover rim to jack the top part of the cleanout up to the finished floor level. Floor drains can be furnished Figure 1-7 Inside-Caulk Drain Body

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THERMAL EXPANSION When excessive thermal expansion is anticipated, the pipe movement should be controlled to avoid harmful changes in slope or damage. This may be done by anchoring, using expansion joints, or using expansion loops or bends. When anchoring, avoid excessive stress on the structure and the pipe. Piping or mechanical engineering handbooks should be consulted if stress analy-

sis is to be performed due to excessive stresses or to the differing expansion characteristics of materials. See Data Book, Volume 2, Chapter 5 for further information.

PROTECTION FROM DAMAGE Following are some common types of damage to anticipate and some methods of protection: Hazard

Protection

Abrasion

Plastic or rubber sleeves. Insulation where copper pipe leaves slab.

Condensation

Insulation on piping.

Corrosion

See Data Book, Vol. 1, Ch. 8, “Corrosion.”

Earth loads

Stronger pipe or pipe sleeves.

Expansion and contraction

Flexible joints, loops, swing joints, or offsets.

Fire

Building construction around pipe. Some jurisdictions require metal piping within 2 ft (0.6 m) of an entry into a firewall. Must maintain fire ratings.

Heat

Keeping thermoplastic pipe away from sources of heat or using insulation.

Nails

Using ferrous pipe, steel sleeves, steel plates or space pipe away from possible nail penetration zone.

Seismic

Bracing pipe and providing flexible joints at connection between piping braced to walls or structure and piping braced to the ceiling and between stories (where there will be differential movements).

Settlement

Sleeves or flexible joints. When embedded in concrete, covering with three layers of 15-lb (6.8-kg) felt.

Sunlight

Protecting thermoplastic pipe by insulation and jacket or shading to avoid warping.

Figure 1-8 Spigot-Outlet Drain Body

Figure 1-9 No-Hub-Outlet Drain Body

Figure 1-10 IPS or ThreadedOutlet Drain Body

Chapter 1 — Sanitary Drainage Systems

Vandals

Installing pipe above reach or in areas protected by building construction. Support piping well enough to withstand 250 lb (113.4 kg) hanging on the moving pipe.

Wood shrinkage

Providing slip joints and clearance for pipe when wood shrinks. Approximately s in. (16 mm)/floor is adequate for usual frame construction, based on 4% shrinkage perpendicular to wood grain. Shrinkage along the grain does not usually exceed 0.2%.

SOVENT SYSTEMS The sovent single-stack plumbing system is a sanitary drainage system developed to improve and simplify soil, waste, and vent plumbing in multistory buildings. The basic design criteria for sovent drainage plumbing systems for multistory buildings is based on experience gained in the design and construction of sovent systems serving many living units and on extensive experimental work on a plumbing test tower. The criteria to be used as guidelines in design work must be obtained from the designer and/or manufacturer of sovent systems. The sovent system has four parts: a drain, waste, and vent (DWV) stack; a sovent aerator fitting at each floor level; drain, waste, and vent (DWV) horizontal branches; and a sovent deaerator fitting at the base of the stack. The two special fittings, the aerator and deaerator, are the basis for the self-venting features of the sovent system. The functions of the aerator are (1) to limit the velocity of both liquid and air in the stack, (2) to prevent the cross section of the stack from filling with a plug of water, and (3) to mix efficiently the waste flowing in the branches with the air in the stack. The deaerator fitting separates the air flow in the stack from the liquid, ensuring smooth entry into the building drain and relieving the positive pressure at the bottom of the stack. The result is a single stack that is self venting with the fittings balancing positive

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and negative pressures at or near the zero line throughout the system. Soil stack and vent combine into a single sovent stack. Figure 1-11 illustrates a typical sovent single-stack plumbing system.

RESEARCH The advent and use of ultra-low-flow water closets, and to some extent other water-saving fixtures, has brought into question the loading on drainage systems and how the reduced amount of water “carries” solids in the system. Still to be confirmed is that the slope of conventional drainage piping allows solids to remain in suspension until mixed with other flows in the drainage system. Further research is required to determine the proper slopes of drainage piping and that the release of water from fixtures is properly timed to ensure that solids are carried sufficient distances. There have been numerous studies, particularly in the United Kingdom, of reduced-size venting. These studies are discussed in more depth in Chapter 3 of this volume, “Vents and Venting Systems.”

REFERENCES 1.

Daugherty, Robert L., Joseph B. Franzini, and E. John Finnemore. 1985. Fluid mechanics with engineering applications. 8th ed. New York: McGraw-Hill.

2.

Dawson, F.M., and A.A. Kalinske. 1937. Report on hydraulics and pneumatics of plumbing drainage systems. State University of Iowa Studies in Engineering, Bulletin no. 10.

3.

Wyly and Eaton. 1950. National Bureau of Standards, Housing and Home Finance Agency.

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(A)

(B)

Figure 1-11 (A) Traditional Two-Pipe System, (B) Typical Sovent Single-Stack Plumbing System.

Chapter 2 — Gray-Water Systems

2 INTRODUCTION One of the means of conserving water is to recycle it. Nonpotable water systems that use recycled water are commonly referred to as “graywater systems.” There is no single definition of gray water. The definitions of a variety of recycled waters are interchangeable. In general, the term “gray water” is intended to include appropriately treated water that has been recovered from typical fixtures, such as lavatories, bathtubs, showers, and clothes washers. Waste potentially containing grease, such as that from kitchens and dishwashers, as well as waste from food disposals in kitchens is excluded due to the possibility of solid articles. Recycled water is intended to include “clean” water additionally treated to remove bacteria, heavy metals, and organic material. “Black water,” on the other hand, is water recovered from plumbing fixtures discharging human excrement, such as water closets and urinals, and cooling-tower water (because of the chemicals involved in its treatment). Rainwater is another excellent source of water. It can be collected in cisterns for use in a wide variety of nonpotable uses with little or no treatment. Rainwater in cisterns can also be used for an emergency supply of drinking water if it is appropriately treated prior to use. This chapter is limited to the discussion of gray water only.

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Gray-Water Systems

Gray-water systems have been used in various areas of the world. In many regions, water is a critical resource and extreme measures to optimize the use of water are sometimes necessary. Water reuse offers a considerable savings of water resources, which is appealing in localities where the underground aquifers are in danger of depletion or where adequate supplies of water are not available. Waste-water management is also a significant reason for the use of gray-water systems. On-site reclamation and recycling of relatively clean, nonpotable water is considered for the following reasons: 1. In areas where the code mandates that gray water be used where the availability of potable water is in short supply or restricted. 2. For projects where public liquid sewage disposal capacity is either limited or inadequate. 3. For economic reasons because obtaining potable water or disposing of liquid waste is very costly. 4. For economic reasons, where payback will occur in less than 2 years and where recycling will reduce sewer and water usage fees, resulting in substantial savings in operating costs. Appropriately treated gray water is commonly used for the following proposes: 1. Flushing water for water closets and urinals.

Note: This chapter is written primarily to familiarize the reader with the general subject area. It is not intended to be used for system design without reference and adherence to other technical data and local code requirements.

2. Landscape irrigation. 3. Cooling-tower makeup.

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4. Decorative pool and fountain fill water. 5. Floor and general hard surface wash down. 6. Laundry prerinse water. The most common purpose is to provide water for the flushing of urinals and water closets, especially in high-rises, hotels, and large dwellings.

CODES AND STANDARDS There are no nationally or regionally established model codes that mandate the use of gray water. The Uniform Plumbing Code discusses gray water but limits the discussion to single-family dwellings. Many specific local areas have established standards and guidelines for the use of gray water in facilities and homes. Where graywater use is permitted, local health departments have established minimum-treatment standards. In these localities, the engineer must check for regulations applicable to gray water, as is done for plumbing and building codes. The National Sanitation Foundation’s Standard 41, which regulates the minimum water quality for recycled waste water, is shown in Table 2-1. The gray-water quality must be verified against Table 2-1 and existing local regulations, if any, before use.

Table 2-1 The National Sanitation Foundation’s Standard 41 Component

Maximum Limits

Biological oxygen demand 5 ppm (5 mg/L) Suspended solids Total coliform Nitrogen removal

5 ppm (5 mg/L) 2.2 counts/26.4 gal (2.2 counts/100 mL) 85–95%

SYSTEM DESCRIPTION Gray-water systems collect the dilute waste water discharged from lavatories, service sinks, baths, laundry tubs, showers, and other similar types of fixtures. This water is then filtered and/or treated until it reaches a level of quality consistent with its intended reuse. The piping network distributes it to sources not used for human consumption in a safe and distinctive manner.

Figure 2-1 shows flow charts for a conventional plumbing system and a recycled water system. In the recycled-water flow system, the gray water and black water sources are clearly defined. The use of the gray-water system is also defined, namely, for all nonpotable water systems, cooling-tower water requirements, and the irrigation system. Figure 2-2(A) shows single-line diagrams of a gray-water plumbing system to bathtubs and lavatories and a recycled, gray-water system with a gray-water treatment plant from bathtubs, lavatories, and water closets. The reused water (gray water) from the fixtures is pumped for reuse in the water closets. This figure shows the isometric piping of a gray-water system with the supply and drainage piping arrangement. The basic plumbing supply with hot water system feeds the lavatories and the bathtubs, which, in turn, act as a source for the gray-water system. In Figure 2-2(B), the effluent storage as well as the sewage treatment plant (STP) utilize the gray water to route to the cooling tower, irrigation, and wash-down systems, and the water-closet fixtures. A gray-water system requires modifications to the standard plumbing systems throughout a facility. There will be duplicate drainage systems. Instead of all the liquid discharged from all the plumbing fixtures going to the sanitary sewer, selected fixtures will have their effluent routed for recovery by the gray-water treatment system. The remainder will go to the sanitary sewer. There also will be duplicate water supplies: potable water will go to lavatories, sinks, showers, etc., and gray water to water closets, urinals, and other fixtures, depending on the quality of the gray-water treatment. Special care must be taken during the installation of a gray-water system. Clear identification and labeling of the gray-water system is mandatory. This will minimize the risk of cross connection during installation or repair of the system. Many newly formed, planned communities have adopted gray-water systems for their irrigation systems. Warning signs of “nonpotable water” or colored PVC piping are now visible across city landscapes. Blue dye has become a clear identification of the use of gray water.

Chapter 2 — Gray-Water Systems

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(A)

(B) Figure 2-1 Plumbing System Flow Charts: (A) Conventional Plumbing System; (B) Recycled-Water System.

System Components The following components are generally used for most systems. Their arrangement and type depend on the specific treatment system selected. 1. A separate gray-water collection piping system. 2. A primary waste-treatment system consisting of turbidity removal, storage, biological treatment, and filtering. 3. Disinfecting systems consisting of ozone, ultraviolet irradiation, chlorine, or iodine. 4. Treated water storage and system distribution pressure pumps and piping.

DESIGN CRITERIA FOR GRAYWATER SUPPLY AND CONSUMPTION It is estimated that q of the waste water discharged from a typical household in 1 day is gray water. The remaining waste water (that is, 3 of the discharge) is black water from water closets. The discharge from the separate piping system supplying the gray-water system should be sized based on the applicable plumbing code. The following issues should be considered in the design of any gray-water system: 1. The design flow is based on the number of people in a facility.

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(A)

(B) Figure 2-2 Riser Diagrams: (A) Gray-Water Plumbing System; (B) Recycled-Water-Waste System with System Treatment Plant (STP). Notes, Figure 2-2(A):1. Gray water can also be utilized for other uses, such as irrigation, cooling tower makeup, etc., provided treatment is adequate. 2. Common vent for both drainage stacks.

Chapter 2 — Gray-Water Systems

2. Lavatory use is estimated at 0.25 gal/use (0.95 L/use). 3. Men use urinals 75% of the time and water closets 25% of the time. 4. The average person uses a toilet 3 times a day.

Design Estimates for Commercial Buildings Gray-water supply Estimates of gray-water supply sources vary in commercial buildings. In an office building, fixtures such as lavatories, water coolers, mop sinks, and coffee sinks are estimated to generate 1 gal/day/person (3.79 L/day/person). For an office building with 500 employees, we would expect to be able to recover 500 gal/ day (1823 L/day) for gray-water reuse. Based on 5 working days/week and 50 weeks/year annual use, 125,000 gal/yr (473 175 L/yr) could be available for gray-water reuse. Gray-water demand The gray-water demand for an office building is estimated based on 3 toilet or urinal uses/day/person. For calculation purposes, assume the population is 50% male and 50% female, and that men use urinals 75% of the time and water closets 25% of the time. For an office building with 500 employees, we would estimate the gray-water demand as follows: 250 males × 3 flushes/day × 0.5 gal/flush (urinals ) × 75% usage = 281 gal/day 250 males × 3 flushes/day × 1.6 gal/flush (water closets ) × 25% usage = 300 gal/day 250 women × 3 flushes/day × 1.6 gal/flush (water closets) = 1200 gal/day TOTAL gray-water demand = 1781gal/day = approx. 445,250 gal/yr [250 males × 3 flushes/day × 1.89 L/flush (urinals ) × 75% usage = 1063 L/day 250 males × 3 flushes/day × 6.06 L/flush (water closets ) × 25% usage = 1136 L/day 250 women × 3 flushes/day × 6.06 L/flush (water closets) = 4545 L/day TOTAL gray-water demand = 6744 L/day = approx. 1 686 000 L/yr] This example shows that approximately 3.6 gal/person/day (13.5 L/person/day) is needed to supply gray water to toilets and urinals for a

25

500-employee office. This demand could be supplied in part by the 1 gal/person/day available from the fixtures identified in the gray-water supply section above. In shopping centers, flow rates are based on square feet (m2) of space, not the number of persons. The flow demand is gallons per day per square foot (0.06 gpd/ft2 [0.23 L/day/0.1 m2]). The calculations in food service resemble those for grease interceptor sizing. The number of seats, the hours of operation, single-serving utensils, and other, similar factors change the equations for gray-water calculations.

Design Estimates for Residential Buildings (a) The number of occupants of each dwelling unit shall be calculated as follows: Occupants, first bedroom: 2 Occupants, each additional bedroom: 1 (b) The estimated gray-water flows for each occupant shall be calculated as follows: Showers, bathtubs, and wash basins: 25 gpd (95 L/day)/occupant Laundry: 15 gpd (57 L/day)/occupant (c) The total number of occupants shall be multiplied by the applicable estimated gray-water discharge as provided above, and the type of fixtures connected to the gray-water system. Example 2-1 Single-family dwelling, 3 bedrooms with showers, bathtubs, wash basins, and laundry facilities all connected to the gray-water system: Total number of occupants = 2 + 1 + 1 = 4 Estimated gray-water flow = 4 × (25 + 15) = 160 gpd [4 × (95 + 57) = 608 L/day] Example 2-2 Single-family dwelling, 4 bedrooms with only the clothes washer connected to the gray-water system: Total number of occupants = 2 + 1 + 1 + 1 = 5 Estimated gray-water flow = 5 × 15 = 75 gpd (5 × 57 = 285 L/day)

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Design Estimates for Irrigation Systems Gray-water system design and selection depends on a variety of elements: location, soil type, the source of water supply, the type of treatment facility, and the application of reuse. Additional requirements are noted for the reuse of graywater systems for irrigation systems. Some of the parameters are ground-water level, geological stability of the region, plot plan, and distances of irrigation from adjacent properties, lakes, lot lines, drainage channels, water supply lines, surface slope, wells, and interaction of gray-water systems with private sewage disposals. Inspection and testing is an inherent part of the design. System components must be securely installed and the manufacturer properly identified. The holding tanks must be installed in dry levels, and, if underground, contamination issues must be accounted for. The authorities having jurisdiction shall review all plans, and qualified and experienced contractors shall install the system in accordance with the contract documents. To design a gray-water system, one must estimate the source of water supply. Separate design parameters become important for reuse in buildings or in irrigation systems. For irrigation systems, the required area of subsurface must be designed based on soil analysis. The following paragraph clearly defines the design issues for irrigation facilities: Each valved zone shall have a minimum effective irrigation area in square feet (square meters) as determined by Table 2-2 for the type of soil found in the excavation. Table 2-2 gives the design criteria for the use of gray-water systems in various types of soil (coarse sand or gravel, fine sand, sandy loam, sandy clay, mixed clay). As the soil weight decreases and the soil becomes less porous, the minimum square feet (square meters) needed for leaching increases. Coarse sand or gravel needs a 20-ft2 irrigation area per 100 gal (1.86 m2 per 379 L) of estimated gray-water discharge per day. Clay with a small amount of sand or gravel requires 120 ft2 per 100 gal (11.15 m2 per 379 L) of estimated gray water per day. The area of the irrigation/disposal field shall be equal to the aggregate length of the perforated pipe sections within the valved zone times the width of the proposed irrigation/disposal field. Each proposed gray-water system shall include at least three valved zones, and each zone shall be in compliance with the provisions

of the section. No excavation for an irrigation/ disposal field shall extend within 5 vertical ft (1.5 m) of the highest known seasonal ground water, nor shall it extend to a depth where gray water may contaminate the ground water or ocean water. The applicant shall supply evidence of ground-water depth to the satisfaction of the administrative authority.

Table 2-2 Design Criteria of Six Typical Soils Type of Soil

Minimum Minimum Irrigation Area Absorption Capacity (ft2/100 gal of (min/in. estimated gray-water of irrigation area/ discharge/day) day)

Coarse sand or gravel

20

5.0

Fine sand Sandy loam

25 40

4.0 2.5

Sandy clay Clay with considerable sand or gravel Clay with small amount of sand or gravel

60

1.7

90

1.1

120

0.8

Source: IAPMO, 1997, Uniform Plumbing Code, Appendix G.

Table 2-2 (M) Design Criteria of Six Typical Soils Type of Soil

Minimum Minimum Irrigation/Leaching Absorption Capacity Area (min/m2 (m2/ L of of irrigation/ estimated gray-water leaching area/ discharge/day) day)

Coarse sand or gravel

0.005

5.0

Fine sand Sandy loam

0.006 0.010

4.0 2.5

Sandy clay Clay with considerable sand or gravel Clay with small amount of sand or gravel

0.015

1.7

0.022

1.1

0.030

0.8

Source: IAPMO, 1997, Uniform Plumbing Code, Appendix G.

Chapter 2 — Gray-Water Systems

27

Table 2-3 identifies the location and separation distances from a variety of structures and environments. For example, any building or structure shall be a minimum of 5 ft (1.5 m) from a gray-water surge tank. The minimum distance from any property lines to a gray-water surge tank is 5 ft (1.5 m). Critical areas such as streams, lakes, seepage pits, or cesspools shall

Table 2-3 Location of the Gray-Water System Element

Minimum Horizontal Distance from Holding Tank, ft (mm)

Irrigation Disposal Field, ft (mm)

Buildings or structures

5.2 (1524)

2.3 (610)

Property line adjoining private property

5 (1524)

5 (1524)

Water supply wells

50 (15 240)

100 (30 480)

Streams and lakes

50 (15 240)

50.5 (15 240)

Seepage pits or cesspools 5 (1524) Disposal field and 100% expansion area

5 (1524)

5 (1524)

4.6 (1219)

0 (0)

5 (1524)

On-site domestic water service line

5 (1524)

5 (1524)

Pressurized public water main

10 (3048)

10.7 (3048)

Septic tank

Table 2-4 Subsurface Drip Design Criteria of Six Typical Soils Type of Soil

Minimum Emitter Discharge, gal/day (L/day)

Minimum Number of Emitters per gal/day (L/day) of Gray-Water Production

Sand

1.8 (6.8)

0.6

Sandy loam Loam

1.4 (5.3) 1.2 (4.5)

0.7 0.9

Clay loam Silty clay

0.9 (3.4) 0.6 (2.3)

1.1 1.6

Clay

0.5 (1.9)

2

be a minimum of 50 ft (15.2 m) from surge tanks and 100 ft (30.5 m) from irrigation fields. Similarly, the distance from the public water main to a surge tank shall be a minimum of 10 ft (3.1 m). The table also identifies additional restrictions. See Table 2-4 for the design of the gray-water distribution in subsurface drip systems for various types of soil. This table gives the minimum discharge, in gallons/day, for effective irrigation distribution. “Emitters” are defined as orifices with a minimum flow path of 120 microns (µ) and shall have a tolerance of manufacturing variation equal to no more than 7%.

TREATMENT SYSTEMS Treatment systems vary widely. The treatment system conditions the recovered water to a degree consistent with both the intended use of the conditioned water and the design requirements of the design engineer, the applicable code, or the responsible code official—whichever is the most stringent. Typical waste-water (gray-water and black-water) treatments used for various types of project are depicted in Figure 2-3. The size of the treatment systems available vary from those installed for individual private dwellings to those serving multiple facilities. As the treatment facility becomes more complex, the number of treatment activities increases and the quality of the water improves. Some of the treatment activities are basic screening, flow equalization, biological treatment, filtration, coagulation, sedimentation, disinfections, reclaimed water tank, membrane filtration, and activated carbon filtration. The selection of a treatment system also depends on the quality and type of the influent water. To decide which is the most appropriate treatment, the kinds of fixture discharge to be used for reclaiming and the treatment requirements of the authorities must be determined. Table 2-5 describes the types of filtration and water-treatment processes most commonly used in the gray-water treatment process. Depending on the types of filtration, the degree and types of components filtered vary. Basic filtration concentrates on reducing suspended solids and does not absorb nitrogen or phosphates. Coagulation assists in building up the solid filtration and adds phosphates to the list. Chlorination is signifi-

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(A)

(B) Figure 2-3 Water Treatment Systems: (A) Types of Gray-Water Treatment System; (B) Types of Black-Water Treatment System

Table 2-5 Gray-Water Treatment Processes for Normal Process Efficiency Suspended Solids

Biological Oxygen Demand

Chemical Oxygen Demand

Phosphates, P0-4

Nitrogen

Total Dissolved Solids

Filtration Coagulation / filtration

80 90

40 50

35 40

0 85

0 0

0 15

Chlorination Tertiary treatment

0 95

20a 95

20a 910

0 15-60

0 50-70

0 80

Absorphan (carbon filtration)

0

60-80

70

0

10

5

Process

a Nominal, additional removals possible with super chlorination and extended contact time.

Chapter 2 — Gray-Water Systems

29

cant only on oxygen demand issues. Tertiary treatment includes filtration of all categories. Absorphan, or carbon filtration, concentrates primarily on biological and chemical oxygen demands. Table 2-6 shows the design elements of graywater system treatments. In the type A treatment, separate gray-water riser piping and water-closet piping is required. This type of treatment consists of filtration, chlorination, and color modifications. The system re-feeds the water closets. The enhanced version of the type A treatment adds color as well as chemical treatments. If the water source contains high percentages of soaps or foaming agents, the addition of defoaming agents is highly recommended. Increased conditioning of the water will increase the use of the water for other applications, such as cooling towers. Type B treatments give the complete tertiary treatment of the water and permit the use of water for a wide variety of reuse applications. The biological and chemical oxygen treatments are mandatory for the high concentrations of fecal matter. The addition of chemical treatment, filtration, and/or carbon absorption conditions the water for a wide variety of applications. Treatment quality also must take into account the chemical compound of the water required for use in piping, cooling towers, industrial applications,

and plant life to prevent scaling of pipes and fouling of valves or equipment.

ECONOMIC ANALYSIS— AN EXAMPLE Table 2-7 gives the life cycle economic comparison of a gray-water system for a 250-room resort hotel. The cost of the conventional system is based on water and sewer annual consumption. The minimum gray-water system, Type A treatment facility, would have an initial fixed estimated cost of $87,500.00. This cost amortized over 15 years with 12% interest will result in an annual cost for payment of the initial capital cost. This annual cost, plus the water and sewer cost, plus the treatment equipment maintenance cost is near the annual cost for the hotel management. With maximum gray-water treatment, Type B, the total annual cost does not decrease very much. In fact, statistically they are nearly the same. Given this data, the only reasons to provide gray water in facilities are governmental or institutional incentives. In addition, the cost of sewage as well as the cost of water consumption may become the decisive factors. Any increase in the cost of sewage or water, caused perhaps by a drought in a region, can alter the life-cycle economics.

Table 2-6 Comparison of Gray-Water System Applications System

Piping

Treatment

Potential Gray-Water Uses

Water Savingsa

Sewage Savingsa

Conventional

Base

None

N/A

0

0

Type A (minimal treatment)

Separate gray-water riser/separate WC stack

Filtration, chlorination, color

Water closets

20,000 gal/day (75 708 L/day) 17% (inc. irrigation), 22% (without irrigation)

20,000 gal/day (75 708 L/day) 26%

Type A (enhanced treatment)

Separate gray-water riser/separate WC stack

Chemical filtration, chlorination, color

Water closets, cooling towers, irrigation (pos.)

35,000 gal/day, (132 489 L/day) 30% (incl. irrigation), 38% (without irrigation)

35,000 gal/day (132 489 L/day) 46%

Type B

Separate gray-water riser

Tertiary sewage treatment

All nonpotable uses

61,000 gal/day, (230 909 L/day) 52% (incl. irrigation)

N/A

a Values for savings noted are based on the 250-room resort hotel example. Percentages based on normal usage of 117,850 gal/day, Including irrigation, and 91,150 gal/day, without irrigation.

30

ASPE Data Book — Volume 2

(A)

(B)

(C)

(D)

Figure 2-4 System Design Flow Chart Example (250-Room Hotel): (A) Conventional Plumbing System; (B) Recycling for Water Closets; (C) Recycling for Water Closets and Cooling Tower; (D) Recycling for Water Closets, Cooling Tower, and Irrigation

Chapter 2 — Gray-Water Systems

31

Table 2-7 Life-Cycle Economic Comparison: Gray-Water Systems for 250-Room Hotel Installed System Type A (Minimal Conventional Gray System Water)

Type B (Gray Water)

To use the nomograph, proceed as follows: 1. Enter the lower right portion of the nomograph with the anticipated total potable water consumption for all users (based on a conventional system). 2. Move vertically up to the combined utility cost for water purchase and sanitary sewage charges (e.g., $1.25/1000 gal [3785 L] for water, and $0.75/1000 gal [3785 L] for sewage).

Fixed Cost

0.000

$87,500

$259,000

Life

20 yr

15 yr (Base system)

15 yr

Cost of money

12%

12%

12%

Capital recovery factor

N/A

0.1468.2

0.14682

Amortized first cost

0

$12,846

$38,026

Utility costs

0

0

0

5. Move vertically down to the annual interest rate (cost of money) used in the analysis.

Water ($1.40/ 1000 gal [3785 L])

$59,395

$49,315

$28,299

6. Move horizontally to the left to form baseline Y.

Sewage ($0.50/ 1000 gal [3785 L])

$13,706

$10,106

0

Operational cost

0

0

0

Treatment equipment

0

$1,240

$6,305

$73,101

$73,507

$72,630

Total Annual Cost

The complete water flow chart of the 250room hotel is shown in Figure 2-4. As depicted in Table 2-6, the water-flow-rate savings are clearly defined. Before one considers using a gray-water system, it is desirable to be able to evaluate quickly, on a preliminary basis, the potential economic feasibility of the proposed scheme. To facilitate this, a nomograph such as that shown in Figure 2-5 can be used. This analysis shows the variation in interest rates, variation in cost of combined water and sewage, the water daily use, and cost of total systems based on two types of treatments, A and B. Movement through the chart from an interest rate (based on the current economy) to the combined cost of sewage and water (based on municipalities) to the water consumption (based on building occupancy) and to the type of treatment facility (based on the purity required) can provide an approximate cost for a gray-water system.

3. Move horizontally to the left to form baseline X. 4. Enter the upper right portion of the nomograph with the estimated additional cost of the gray-water system (additional piping, storage, and treatment equipment).

7. If the proposed system is a Type A gray-water system, go to the intersection of baseline X and the system A curve (lower left quadrant) of the nomograph. 8. If a Type B gray-water system is being studied, go to the intersection of baseline X and the system B curve. 9. From the appropriate intersection, move vertically up to the horizontal separation line and then up and left at the indicated 45° angle to an intersection with baseline Y. 10. From this intersection point, move vertically down once again to the intersection with baseline X. 11. If this final (circled) intersection is in the lower right field, the system appears preliminarily feasible and should be subjected to a more detailed economic analysis. 12. If the final intersection falls to the left and above the sector dividing line, then the economic feasibility of the scheme is strongly suspect. Note: Obviously, the many variable inputs that must be considered in a detailed economic analysis do not lend themselves to an easy-to-use nomograph. Many of these inputs have been simplified by making normal assumptions about such things as ratios of reuse, relative quantities of water consumption, and sewage discharge. Thus, while the nomograph does give a quick and relatively good indication of feasibility, it does not replace a detailed economic evaluation. This is particularly true if the scheme under consideration has anticipated hydraulic flow patterns that differ markedly from the relative uses outlined in Figure 2-5.

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Figure 2-5 Nomograph for Overview of Preliminary Feasibility of Gray-Water Systems

As a region’s population grows, the utilization of limited water supplies becomes more critical, and the need for conservation becomes more obvious, evidenced by regulation, a change in the types of plumbing fixtures, public education and voluntary participation, or an increase in water and sewage system charges. In addition, the economic capabilities of a municipality determine its capability for adding sewage-treatment facilities and meeting the demands of the community.

PRECAUTIONS Since gray water poses a potential health hazard, a great deal of care must be exercised once such a system is installed. One of the greatest dangers is the possibility that the gray water will be inadvertently connected to the potable-water system. To avoid this possibility, the water itself and the piping must be made easily distinguishable, anti-cross-connection precautions must be taken, and appropriate alarms must be installed.

Chapter 2 — Gray-Water Systems

Treated water could be colored by food dye that is biodegradable. Fixtures could be bought in the color of the water if the water color will be found objectionable. The piping system itself must be clearly identified with labels placed visibly along the run of the pipe. If possible, the piping material should be different so that the possibility of mistaking and interconnecting the two systems will be unlikely. The most important consideration is the education of individuals and the staff of a facility with a gray-water system. An explanation of the dangers and proper operating instructions will ensure that an informed staff will operate and maintain the system in a correct manner.

PUBLIC CONCERNS/ACCEPTANCE Although gray-water systems have been approved for general use in different parts of the world and have been designed in a variety of forms, it is still unfamiliar to many city and county governments, plumbing and facility engineers, and the general public. An exception is the Bahamas, where the local code mandates dual or gray-water systems in all occupancies. Although the use of gray water is a proven cost-effective alternative to the use of potable water in various systems, there is reluctance on the part of authorities to approve it. Some reasons include: 1. There is no generally accepted standard for the quality of recycled water. Several states in the US, Japan, and the Caribbean have adopted codes and guidelines, but for most of the world there is no standard. This has resulted in rejection of the systems or long delays during the approval process of projects while the quality of the water is in question. 2. Regulatory and plumbing codes that do not have any specific restrictions against using gray water or have ambiguous language that could be interpreted for its use but whose officials impose special standards due to their lack of experience. Although the use of gray water is ideal in certain circumstances, the success of gray water will depend solely on public acceptance, and that will require an adequate educational effort. The use of colored water in water closets may

33

not be attractive to the occupants of a newly occupied high-rise. Educating the users of gray water is imperative. An understanding of the source and the associated dangers and limitations of gray water is essential to acceptance by the general public. To draw a parallel, the general public is now fully aware of the dangers of electricity, yet life without electricity is considered to be abnormal. An economic analysis of gray-water systems in health-care facilities may favor dual plumbing systems. However, the presence of viruses, bacteria, and biological contamination in healthcare gray-water systems (through lavatories, bathtubs, showers, and sinks) may increase the cost of water treatment. Also there is a legitimate concern regarding the spread of disease through such gray-water systems that must not be overlooked. Therefore, the application of graywater systems in health-care facilities may be a less attractive option because of the possibility of biological contamination.

CONCLUSION This Data Book chapter began with the definition of gray water and ended with a discussion of its public acceptance. It touched briefly on the design elements of the plumbing system and identified the variations among different facilities. The economic analysis of the gray-water system can become the decisive issue that determines whether a gray-water system is even considered for a project. This analysis can be extrapolated for any other projects and variations. For the full design of gray-water systems, the reader should refer to other technical data books. Water treatment is one of the backbones of the gray-water system. For the water-flow calculations with all the required pumps, piping, and controls, the reader is referred to the ASPE Manual on Gray Water (forthcoming). Finally, water shortages, government subsidies, tax incentives, the facility limitations of local governments, and population growth will be the primary motivators for designers and project engineers to consider gray-water system selections in their designs.

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REFERENCES 1.

Atienze, J., and J. Craytor. 1995. Plumbing efficiency through gray-water recycling. Consulting Specifying Engineer. (March): 58.

2.

Baltimore, MD, Dept. of Public Works. June 1966. Commercial water use research project, by J. B. Wolf, F. P. Linaweaver, and J.C. Center.

3.

Dumfries Triangle and Occoquan-Woodbridge Sanitary District, Woodbridge, VA. Water uses study, by G. D. Gray and J. J. Woodcock.

4.

International Association of Plumbing and Mechanical Officials (IAPMO). 1998. California plumbing code. Walnut, CA.

5.

IAPMO. 1997. Uniform plumbing code.

6.

Konen, Thomas P. 1986. Water use in office buildings. Plumbing Engineer Magazine. July/August.

7.

Lehr, Valentine A. 1987. Gray-water systems. Heating/Piping/Air Conditioning. January.

8.

n.a. 1997. Water: Use of treated sewage on rise in state. Los Angeles Times, August 17: A36.

9.

Siegrist, R., and W. C. Boyle. 1976. Characteristics of rural household waste water. Journal of the Environmental Engineering Division, (June): 533.

10. US Dept. of Commerce, National Information Services. 1978. Management of small waste flows, by Wisconsin University, PB-286-560. 11. US General Services Administration. 1995. Water management: A comprehensive approach for facility managers.

Chapter 3 — Vents and Venting

3 Venting systems are often the least understood of the basic plumbing design concepts. The complete venting of a building drainage system is a very complicated subject, as can be seen from the great variety of venting systems that may be involved. It is not feasible to cover all the venting variations in this chapter. However, to foster understanding, the preparation of venting tables for stacks and for horizontal branches for various venting systems is discussed. Owing to the fact that the conditions that tend to produce pneumatic pressures in the venting system that exceed or are below atmospheric pressure by considerable amounts vary so greatly from case to case, and since the building drain may be wholly or partly submerged—or not submerged at all—where it enters the street sewer, it is not feasible to lay down rules that will apply to the venting of all designs.

SECTION I — VENTS AND VENTING Purposes of Venting Vent systems are installed to eliminate trap siphonage, reduce back pressure and vacuum surges, promote the rapid and silent flow of wastes, and ventilate the sewer. Trap siphonage reduces or eliminates the trap seal and leads to an insanitary and hazardous condition. Pressure and vacuum surges cause objectionable movements of the water in the highly visible water closet traps as well as affect the trap seals in all fixtures. Excessive pressure causes bubbles of sewer gas to flow through traps. Unvented traps

35

Vents and Venting

lead to gurgling noises and sluggish waste flow. Sewer ventilation is required by some local authorities to promote flow in the sewer and to reduce the concentration of dangerous and corrosive gases.

Vent Stack Terminal A “vent stack terminal” is the part of the venting system that extends through the roof, thus keeping the drainage system open to atmospheric pressure. Though it may be small by comparison to the overall sanitary drainage piping, the vent stack terminal is an important portion of the system. Through the terminal vent, air at atmospheric pressure enters the drainage system to hold in balance the water seal contained in each fixture trap. The balance of atmospheric air pressure and gravitational pull on the wastewater mass follows the principles outlined in Chapter 1 of this volume, “Sanitary Drainage Systems.” Vent stack terminals need to be sized in accordance with local codes and/or good engineering practices. Good engineering practices include the following: 1. Increase the terminal pipe by two sizes at 18 in. (455 mm) below the roof line. This allows for the interior building space (which is usually warmer) to provide a convecting flow of interior building heat, keeping the vent terminal at the roof from freezing closed. 2. Project the vent terminal in accordance with jurisdictional building codes and in a distant relationship from air intake louvers, windows, doors, and other roof openings, 10 ft (3 m)

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minimum. Sewer gases will be forced upward through the terminal stack by the weight of the waste water, therefore, the vent pressures versus the air intake volumes need to be considered. 3. Provide minimum 4-in. (101.6-mm) diameter vent stack terminals. Experience has proved that a 4-in. (101.6-mm) terminal allows an adequate volume of air to enter the plumbing system, and its effective opening is not as easily constricted by foreign matter, ice, snow, or vermin as the opening of a smaller diameter pipe would be. (It should be noted that most codes require only that one 3-in. [76-mm] vent to atmosphere be provided for each building drain.)

extent as the fixture gradually empties after the siphon is broken. Glass plumbing is a convenient way to observe this phenomenon. Water-closet traps must always be siphoned to achieve a flush. Water closets are designed so that the watercloset trap is refilled. Traps can also be siphoned when there is excessive vacuum in the system.

Factors Affecting Trap Seal Loss Based on the preceding, the following will reduce the danger of seal siphonage of the trap: 1. Reduce the depth of the overflow rim in fixtures. 2. Flatten the bottoms of fixtures.

Winds of sufficient force can affect the function of the venting system. A strong wind blowing across the effective opening of the vent stack terminal can create unbalanced air pressures within the system. Protective devices are available but may be susceptible to frost closure. Care must also be taken in locating the vent terminals with respect to building walls, higher adjacent roofs, parapet walls, etc., as these may affect the proper flow of air into and out of the venting system.

3. Avoid high-suds detergents.

Traps and Trap Seals

There are three predominant ways in which traps seals are reduced. The first way occurs when the pneumatic-pressure fluctuations caused by the discharge of fixtures other than the fixture to which a particular trap is attached siphon water out of the trap until the positive part of the fluctuation occurs. The second way is by the discharge of the fixture to which the trap is attached. The third way of reducing trap seals is by the buildup of high-suds detergents. It is recommended that the first phenomenon described be called “induced siphonage” and the second “self-siphonage.”

Traps are installed at the plumbing fixtures to prevent sewer gas and odors from escaping into the building and to keep insects and vermin outside. They are usually required to be of the water-seal, self-scouring type. Other types may be necessary to save precious metal or to keep harmful material out of the drainage system. Special code approvals may be necessary in these cases. The trap seal may be lost when a fixture is drained. During drainage, water drops through the fixture outlet down the tailpiece, acquiring momentum. This momentum is transferred to trap-seal water. The combined water then flows out of the trap down the trap arm at a rate depending on slope and momentum. The momentum will be increased if there is a vacuum in the drainage system. If the trap arm fills with water (either actually or effectively because of suds in the trap arm), the trap water may siphon. (For this reason, most codes limit the distance from the fixture to the trap weir to 24 in. [0.6 m].) Some water will remain in the trap, but the water seal will be lost or reduced. The trap is usually replenished to some

4. Provide smaller discharge openings on the fixtures. 5. Reduce the distance (tailpiece length) between the fixture and the trap. 6. Increase the size of the trap and trap arm. 7. Reduce the vacuum on the discharge side of the trap. 8. Provide a vent near the trap outlet.

Suds Venting High-sudsing detergents may be expected to be used in kitchen sinks, dishwashers, and clotheswashing machines in residential occupancies. These suds disrupt the venting action and spread through the lower portions of multistory drainage systems. The more turbulence, the greater the suds. In some cases, suds back up through the traps and even spill out on the floor. They cause an increase in the pressure and vacuum levels in the systems. They affect both singlestack and conventional systems. Solutions to the

Chapter 3 — Vents and Venting

37

problem may involve avoiding suds pressure zones, connecting the suds-producing stack downstream of all other stacks, and increasing the size of the horizontal building drain to achieve less restrictive flow of air and water. Using streamline fittings, such as wyes, tends to reduce suds formation. Check valves in fixture tailpieces have been used to fix problem installations.

sudsy detergents are used, a zone shall be considered to exist downstream in the horizontal drain from the base of the stack and both upstream and downstream of the next offset fitting downstream. Zone 4. In a soil or waste system, which serves fixtures on two or more floors and receives wastes from fixtures wherein sudsy detergents are used, a zone shall be considered to exist in the vent stack extending upstream from the point of connection to the base of the soil or waste stack. See Figure 3-2.

The National Standard Plumbing Code, one of the traditional codes, lists the following special requirements to avoid suds problems: 1. Where required. Where kitchen sinks, laundry trays, laundry washing machines, and similar fixtures in which sudsy detergents are normally used, discharge at an upper level into a soil or waste stack which drainage and vent piping for such lower fixtures shall be arranged so as to avoid connection to suds pressure zones in the sanitary drainage and vent systems, or a suds relief vent, relieving to a nonpressure zone shall be provided at each suds pressure zone where such connections are installed. In multistory buildings, with more than six branch intervals of fixtures described above, separate waste and vent stacks for the lower four branch intervals of fixtures shall be required. See Table 3-1. 2. Suds pressure zones. Suds pressure zones shall be considered to exist at the following locations in sanitary drainage and vent systems as indicated in Table 3-1. See Figure 3-1. Zone 1. In a soil or waste stack, which serves fixtures on two or more floors and receives wastes from fixtures wherein sudsy detergents are used, a zone shall be considered to exist in the vertical portion upstream of an offset fitting and the riser to the upper section of the system, in the horizontal portion downstream of this fitting and in the horizontal portion upstream of the offset immediately preceding the next offset fitting. See Table 3-1.

Fixture Vents The discharge of a lavatory or sink is quite high at first, decreasing a little as the depth in the basin decreases, until suddenly the rate of discharge falls rapidly to nearly zero, with the

Table 3-1 Suds Pressure-Relief Vents Waste Size, in. (mm)

Relief Vent Size, in. (mm)

1½ (38)

2 (51)

2

(51)

2 (51)

2½ (63)

2 (51)

3

2 (51)

(76)

4

(101)

3 (76)

5

(127)

4 (101)

6

(152)

5 (127)

8

(203)

6 (152)

Extent of Suds Pressure Zones for Various Size Soil and Waste Piping, Extent of Zone (Measured from Fittings) Stack Size, in. (mm)

Upstream, U, ft (m)

Downstream, D, ft (m)

1½ (38)

5 (1.5)

1½ (0.45)

Zone 2. In a soil or waste stack, which serves fixtures on two or more floors and receives wastes from fixtures wherein sudsy detergents are used, a zone shall be considered to exist at the base of the stack and extending upstream. See Table 3-1.

2

Zone 3. In a soil or waste system, which serves fixtures on two or more floors and receives wastes from fixtures wherein

(51)

7 (2.1)

1½ (0.45)

2½ (63)

8 (2.4)

2

3

(0.61)

(76)

10 (3.0)

2½ (0.76)

4 (101)

13 (4.0)

3½ (1.1)

5 (127)

17 (5.2)

4

(1.2)

6 (152)

20 (6.1)

5

(1.5)

Note: For use with Figure 3-1.

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38

Figure 3-1 Suds-Pressure-Zone Diagram

coincidental formation of a vortex which allows air to be sucked down into the drain. Air that is drawn through the fixture passes down the drain in the form of bubbles that are dragged along the highest element of the drain. If there is enough air traveling with the water, when the flow from the fixture falls off, the bubbles enable the water to break loose from the upper element of the drain, so that the piston effect of water that would otherwise occur is often prevented. If the slug of water continues to fill the cross section as the flow decreases, it moves downstream slowly, creating a reduced pressure behind it that sucks the water out of the trap just as happens when the reduced pressure is due to induced siphonage. Only a limited amount of data on the selfsiphonage of plumbing-fixture traps have been

published. Tests of the siphonage of fixture traps were made as early as 1880, but no record of investigations of self-siphonage at such an early date has been found. Perhaps the most systematic investigation of the subject was made by John L. French and Herbert N. Eaton. A fullscale test was conducted by them to determine the factors that affect self-siphonage and, more particularly, to establish limits on drain lengths, slopes, diameters, and other pertinent variables that would ensure that excessive trap-seal losses due to self-siphonage would not occur. Based on these early research results, lengths of nominally sized, horizontal, unvented waste pipes believed to be safe against self-siphonage have been established. For example, the Uniform Plumbing Code has a section on the maximum length of the trap arm stating as follows:

Chapter 3 — Vents and Venting

39

Figure 3-2 Suds Venting/Suds Pressure Zones

“Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in Table 3-2, but in no case less than two (2) times the diameter of the trap arm.”

It should be noted that the International Plumbing Code requirements differ significantly from these. They are set forth as follows:

Table 3-2 Maximum Length of Trap Arm

“Each fixture trap shall have a protecting vent located so that the slope and the developed length in the fixture drain from the trap weir to the vent fitting are within the requirements set forth in Table 3-3.”

Diameter of Trap Arm, in. (mm)

Venting as a Means of Reducing Trap Seal Losses from Induced Siphonage

Distance— Trap to Vent, ft (m)

1¼ (32)

2½ (0.76)

1½ (38) 2 (51)

3½ (1.1) 5 (1.5)

3 4

(76) (101)

6 10

(1.8) (3.0)

Spent water and other wastes from plumbing fixtures enter vertical stacks through branch drains where the flow is described as separated flow. The waste water travels along the lower portion of the drain allowing the free movement of air in the upper portion of the conduit. Shortly after

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Table 3-3 Maximum Distance of Fixture Trap from Vent

Size of Trap, in. (mm)

Size of Fixture Drain, in. (mm)

Slope, in./ft (cm/m)

Distance from Trap, ft (m)

14 (32) 14 (32)

14 (32) 12 (40)

4 (12.5) 4 (12.5)

32(1.07) 5 (1.52)

12 (40) 12 (40)

12 (40) 2 (51)

4 (12.5) 4 (12.5)

5 (1.52) 6 (1.83)

2 3

2 3

4 (12.5) 8 (25)

8 (2.44) 10 (3.05)

8 (25)

12 (3.66)

(51) (76)

4 (101)

(51) (76)

4 (101)

entering the stack, the waste water attaches itself to the walls of the vertical pipe forming an annular flow. The falling water drags with it air that in a conventional plumbing drainage system is removed through the extensive network of vents in addition to the building drain. The capacity of a given design is governed by the system’s ability to manage the incoming air in such a way that the pressure excursions, positive and negative, will be within certain acceptable limits. Positive pressures are high and often the cause of failure in systems with complex building drains. The main vent stack is designed to remove the expected air with a pressure loss less than 1 in. (25.4 mm) of water column. In tall buildings, the falling water develops large negative pressures, which cause failures by siphoning the water from traps.

Design of Vents to Control Induced Siphonage In most plumbing codes a loading table for vents is provided. The purpose of such a table is to give the information necessary to design the vent stack for the delivery of the amount of air required for the control of pneumatic pressures at critical points in the drainage system within limits of ±1 in. (25.4 mm) of water column from atmospheric pressure. If this range of pressure can be maintained, the effects of pneumatic-pressure fluctuations on the fixture-trap seals will be negligible. The dimensions of pipes required to deliver given quantities of air at a pressure drop of 1 in. (25.4 mm) of water column can be computed from the Darcy-Weisbach Formula combined with the

conventional formula for expressing losses other than those associated with flow in long, straight pipes. This can be expressed as: Equation 3-1 hf =

fLV2 D2g

where hf =

Head loss due to friction, ft (m) of air column

f

=

Coefficient of friction corresponding to the roughness of the pipe surface and the diameter of the pipe

L

=

Length of piping, ft (m)

V

=

Velocity of flow, fps (m/s)

D

=

Diameter of piping, ft (m)

g

=

Gravitational acceleration, 32.2 ft/ s2 (9.8 m/s2)

The maximum permissible length of vent piping is expressed as: Equation 3-2 hfd5 (0.03109)fq2

L = where L

=

Length of piping, ft (m)

hf =

Head loss due to friction, ft (m) of fluid column

d

=

Diameter of piping, in. (mm)

f

=

Coefficient of friction corresponding to the roughness of the pipe surface and the diameter of the pipe

q

=

Quantity rate of flow, gpm (L/s)

Drainage Fixture Units The selection of the size and length of vent piping requires design or installation information about the size of the soil and/or waste stack and the fixture unit (derived from the supply system design) loads connected to the stack. Total fixture units connected to the stack can be computed in accordance with Table 3-4. Fixture units are really weighting factors that effectively convert the various types of fixture, having different probabilities of use, to equivalent numbers of an arbitrarily chosen type of fixture with a single probability of use. In other words, the fix-

Chapter 3 — Vents and Venting

41

Table 3-4 Drainage-Fixture-Unit Values for Various Plumbing Fixtures Type of Fixture or Group of Fixtures

Drainage-FixtureUnit Value (dfu)

Automatic clothes washer (2-in. [51 mm] standpipe) Bathroom group consisting of a water closet, lavatory, and bathtub or shower stall: Flushometer valve closet Tank-type closet Bathtub (with or without overhead shower)a Bidet Clinic Sink Combination sink-and-tray with food-waste grinder Combination sink-and-tray with one 1½-in. (38 mm) trap Combination sink-and-tray with separate 1½-in. (38 mm) trap Dental unit or cuspidor Dental lavatory Drinking fountain Dishwasher, domestic Floor drains with 2-in. (51 mm) waste Kitchen sink, domestic, with one 1½-in. (38 mm) trap Kitchen sink, domestic, with food-waste grinder Kitchen sink, domestic, with food-waste grinder and dishwasher 1½-in. (38 mm) trap Kitchen sink, domestic, with dishwasher 1½-in. (38 mm) trap Lavatory with 1¼-in. (32-mm) waste Laundry trap (1 or 2 compartments) Shower stall, domestic Showers (group) per headb Sinks: Surgeon’s Flushing rim (with valve) Service (trap standard) Service (P trap) Pot, scullery, etc.b Urinal, pedestal, syphon jet blowout Urinal, wall lip Urinal, stall, washout Urinal, trough (each 6-ft [1.8 m] section) Wash sink (circular or multiple) each set of faucets Water closet, tank-operated Water closet, valve-operated Fixtures not listed above: Trap size 1¼ in. (32 mm) or less Trap size 1½ in. (38 mm) Trap size 2 in. (51 mm) Trap size 2½ in. (63 mm) Trap size 3 in. (76 mm) Trap size 4 in. (101 mm)

3

8 6 2 1 6 4 2 3 1 1 ½ 2 3 2 2 3 3 1 2 2 2 3 6 3 2 4 6 4 4 2 2 4 6 1 2 3 4 5 6

a A shower head over a bathtub does not increase the fixture-unit value. b See Chapter 1 of this volume for the method of computing equivalent fixture values for devices or equipment that discharges continuous or semicontinuous flows into sanitary drainage systems.

ture unit assigned to each kind of fixture represents the degree to which it loads the system. The designer should confirm or adjust this data based on the local code.

Vent Sizes and Lengths The above two equations are useful for computing lengths and diameters of vent pipes required to carry given rates of air flow. Appropriate values of the friction coefficient should be used in applying these equations. For any particular pipe, “f” is an inverse function of the Reynold’s number (turbulence) and increases with the roughness of pipe material relative to diameter. The size of vent piping shall be determined from its length and the total number of fixture units connected thereto, as set forth in Table 3-5. Note, in Table 3-5, that some codes limit the maximum length located in the horizontal position due to higher friction losses in horizontal piping. On average, codes may limit that 20-50% of maximum length be located in the horizontal position.

End Venting “End venting” is a system of floor drains whose branch arms do not exceed 15 ft (4.5 m) and are sloped at 8 in./ft (3.2 mm/m) (1%) to a main drain that is sized two pipe diameters larger, therefore allowing the main drain to be end vented. The theory is that the system is oversized allowing the sewer always to flow partially full, thus permitting air to circulate above. (This configuration is similar to a combination wasteand-vent system.)

Common Vent A common vent may be used for two fixtures set on the same floor level but connecting at different levels in the stack, provided that the vertical drain is one pipe diameter larger than the upper fixture drain but in no case smaller than the lower fixture drain, or whichever is the larger, and that both drains conform to the distances from trap to vent for various size drains.

Stack Venting A group of fixtures, consisting of one bathroom group and a kitchen sink or combination fixtures, may be installed without individual fixture vents

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Table 3-5 Size and Length of Vents Size of Soil or Waste Stack, in. (mm)

Fixture Units Connected

1¼ (32)

1½ (38)

2 (51)

Diameter of Vent Required, in. (mm) 2½ (63) 3 (76) 4 (101) 5 (127)

6 (152)

8 (203)

Maximum Length of Vent, ft (m)

1½ (38)

8

50 (15.2) 150 (45.7)

2 (51)

12

30 (9.1)

75 (22.8)

200 (61)

2 (51)

20

26 (7.9)

50 (15.2)

150 (45.7)

2½ (63)

42

30 (9.1)

100 (30.5)

300 (91.4)

3 (76)

10

30 (9.1)

100 (30.5)

100 (30.5)

600 (182.9)

3 (76)

30

60 (18.3)

200 (61)

500 (152.4)

3 (76)

60

50 (15.2)

80 (27.8)

4 (101)

100

35 (10.7)

100 (30.5)

260 (79.2)

1000 (304.8)

4 (101)

200

30 (9.1)

90 (27.4)

250 (76.2)

900 (274.3)

4 (101)

500

20 (6.1)

70 (21.3)

180 (54.9)

700 (213.4)

5 (127)

200

35 (10.7)

80 (27.8)

350 (106.7)

1000 (304.8)

5 (127)

500

30 (9.1)

70 (21.3)

300 (91.4)

900 (274.3)

5 (127)

1100

20 (6.1)

50 (15.2)

200 (61)

700 (213.4)

6 (152)

350

25 (7.6)

50 (15.2)

200 (61)

400 (122)

6 (152)

620

15 (4.6)

30

(9.1)

125 (38)

300 (91.4) 1100 (335.3)

6 (152)

960

24

(7.3)

100 (30.5)

250 (76.2) 1000 (304.8)

6 (152)

1900

20

(6.1)

70 (21.3)

200 (61)

700 (213.0)

8 (203)

600

50 (15.2)

150 (43.7)

500 (152.4)

1300 (396.6)

8 (203)

1400

40 (12.2)

100 (30.5)

400 (122)

1200 (365.8)

8 (203)

2200

30

(9.1)

80 (27.8)

350 (106.7)

1100 (335.3)

8 (203)

3600

25

(7.6)

60 (18.3)

250 (76.2)

800 (243.8)

10 (254)

1000

75 (22.9)

125 (38)

10 (254)

2500

50 (15.2)

100 (30.5)

500 (152.4)

10 (254)

3800

30

(9.1)

80 (27.8)

350 (106.7)

10 (254)

5600

25

(7.6)

60 (18.3)

250 (76.2)

400 (122)

1300 (396.6)

1000 (304.8)

Chapter 3 — Vents and Venting

in a one-story building or on the top floor of a building, provided each fixture drain connects independently to the stack, and the water closet and bathtub or shower-stall drain enters the stack at the same level and in accordance with trap-arm requirements. When a sink or combination fixture connects to the stack-vented bathroom group and when the street sewer is sufficiently overloaded to cause frequent submersion of the building sewer, a relief vent or back-vented fixture shall be connected to the stack below the stack-vented water closet or bathtub.

Wet Venting If allowed by local codes, a single-bathroom group of fixtures may be installed with a drain from a back-vented lavatory, kitchen sink, or combination fixture serving as a wet vent for a bathtub or shower stall and for the water closet, provided that: 1. Not more than one fixture unit is drained into a 1½-in. (38-mm) diameter wet vent or not more than four fixture units drain into a 2-in. (51-mm) diameter wet vent. 2. The horizontal branch connects to the stack at the same level as the water-closet drain or below the water-closet drain when installed on the top floor. Bathroom groups consisting of two lavatories and two bathtubs or shower stalls back to back on a top floor may be installed on the same horizontal branch with a common vent for the lavatories and with no back vent for the bathtubs or shower stalls and for the water closets, provided the wet vent is 2 in. (51 mm) in diameter and the length of the fixture drain conforms to Table 3-2. On the lower floors of a multistory building, the waste pipe from one or two lavatories may be used as a wet vent for one or two bathtubs or showers, provided that: 1. The wet vent and its extension to the vent stack is 2 in. (51 mm) in diameter. 2. Each water closet below the top floor is individually back-vented. 3. The vent stack is sized as shown in Table 3-6.

43

Table 3-6 Size of Vent Stacks Diam. of Vent Stacks No. of Wet-Vented Fixtures

in.

mm

1 or 2 bathtubs or showers 3–5 bathtubs or showers

2 2½

50.8 63.5

6–9 bathtubs or showers 10–16 bathtubs or showers

3 4

76.2 101.6

Circuit and Loop Venting A branch soil or waste pipe to which two but not more than eight water closets (except blowout type), pedestal urinals, trap standard to floor, shower stalls, or floor drains are connected in battery may be vented by a circuit or loop vent which takes off in front of the last fixture connection. In addition, lower-floor branches serving more than three water closets shall be provided with a relief vent taken off in front of the first fixture connection. When lavatories or similar fixtures discharge above such branches, each vertical branch shall be provided with a continuous vent. Figure 3-3 represents a typical loop-vented, water-closet row installed on the top floor of a building or in a one-story building. Figure 3-3(a) shows the horizontal branch installed at the back below the water closet. Figure 3-3(b) is the same toilet room, except that the horizontal branch is directly under the water closets. Figure 3-4 illustrates a toilet arrangement similar to that shown in Figure 3-3 except that the installation applies to a multistory building. A circuit vent is similar to a loop vent except that a circuit vent connects into the vent stack. When the circuit, loop, or relief vent connections are taken off the horizontal branch, the vent branch connection shall be taken off at a vertical angle or from the top of the horizontal branch. In sizing, the diameter of a circuit or loop vent shall be made not less than the size of the diameter of the vent stack, or one half the size of the diameter of the horizontal soil or waste branch, whichever is smaller. When fixtures are connected to one horizontal branch through a double wye or a sanitary tee in a vertical position, a common vent for each two fixtures back to back with a double connec-

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Figure 3-4 Circuit Vent Figure 3-3 Loop Vent, with Horizontal Branch Located (a) at Back Below Water Closets, (b) Directly Under Water Closets.

tion shall be provided. The common vent shall be installed in a vertical position as a continuation of the double connection.

Relief Vents Soil and waste stacks in buildings having more than ten branch intervals shall be provided with a relief vent at each tenth interval installed, beginning with the top floor. The size of the relief vent shall be equal to the size of the vent stack to which it connects. The lower end of each relief vent shall connect to the soil or waste stack through a wye below the horizontal branch serving the floor, and the upper end shall connect to the vent stack through a wye not less than 3 ft (0.9 m) above the floor level. In order to balance the pressures that are constantly changing within the plumbing system, it is necessary to provide a relief vent at various intervals, particularly in multistory buildings. Figure 3-5 illustrates important requirements for the installation of a relief vent.

Offset An offset in a run of piping consists of a combination of elbows or bends that brings one section

of the pipe out of line but into a line approximately parallel with the other section. The offset distance can be estimated according to the following: Pipe Size, in. (mm) 2 3

Horizontal Offset, in. (mm)

(51) (76)

5 (127) 7 (177)

4 (101) 5 (127)

10 (254) 12 (303)

6 (152) 8 (203)

14 (354) 18 (455)

Offsets less than 45° from the horizontal in a soil or waste stack shall comply with the following: 1. Offsets may be vented as two separate soil or waste stacks, namely, the stack section below the offset and the stack section above the offset. 2. Offsets may be vented by installing a relief vent as a vertical continuation of the lower section of the stack or as a side vent connected to the lower section between the offset and the next lower fixture or horizontal

Chapter 3 — Vents and Venting

45

branch. The upper section of the offset shall be provided with a yoke vent. The diameter of the vents shall be not less than the diameter of the main vent or of the soil and waste stack, whichever is smaller. Figure 3-6 illustrates the requirements for installation.

with the requirements of Table 3-5, the number of units being the sum of all units on all stacks connected thereto, and the developed length being the longest vent length from the intersection at the base of the most distant stack to the vent terminal in the open air as a direct extension of one stack.

Vent Headers

Combination Waste and Vent Systems

Stack vents and vent stacks may be connected into a common vent header at the top of the stacks and then extended to the open air at one point. This header shall be sized in accordance

These are horizontal wet-vented systems. They are used where walls are not available for vents. They depend on oversized drainage pipes to prevent loss of trap seal. Surge loads are not allowed.

Figure 3-5 Relief Vent

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Grease-producing fixtures are not allowed, as scouring action is poor. They are used primarily for extended floor or shower-drain installations, for floor sinks for markets or restaurants, and for worktables in schools. See Figure 3-7. Some codes also allow sinks and lavatories to be installed with this type of system. Check the local code for requirements.

SECTION II — SEVERAL VENTING SYSTEMS Philadelphia System Philadelphia or one pipe system refers to using one stack instead of having separate drainage and vent stacks. These systems depend on relieving the pressures by making the pipe larger than required for drainage pipe in a two-pipe system. These systems also use unvented traps (“s” traps) that depend on oversized traps and refill from flat bottom fixtures to maintain the trap seal.

Figure 3-6

This system limits the trap arm length to reduce suction buildup. The size of the main stack is increased to limit pressure and vacuum buildup. See Figure 3-8. Check with the local authorities to see if this system is allowed. Contact the City of Philadelphia for specific requirements.

Sovent System The performance of the sovent plumbing system is based mainly on the aerator, which is required on each floor level, and the deaerator at the base of the stack. The aerator provides an offset and entrance chamber to divert the main flow around the branch inlet and permit a gradual mixing of the branch flow with the main stack flow. These fittings limit the velocity of both liquid waste and air in the stack and create minimum turbulence inside the fitting chamber. The resulting air flow and associated pressure fluctuation are therefore less. The deaerator installed at the base and at every change of direction of the stack from vertical to horizontal acts to separate the air flow from the fixture in the stack, ensuring the smooth

Offset

Chapter 3 — Vents and Venting

entry of liquid into the building drain and relieving the positive pressure generated in the stack’s base. It is obvious that these fittings balance positive and negative pressure at or near zero throughout the entire system under conditions of normal usage.

Stack Venting In stack venting the fixtures are connected independently through their fixture drains to the drainage stack without any venting other than what is afforded through the stack and stack vent. Since no back venting is used when the

47

fixtures are stack vented, economy of installation is achieved. However, with this type of venting, certain precautions must be observed if the trap seals of the stack-vented fixtures are not to be depleted excessively by the pneumatic-pressure variations within the stack. One precaution that must be observed is to connect the fixtures on the floor in question to the stack in the proper order vertically upward. They should be connected in order of decreasing rate of discharge in the upward direction. Thus the lavatory drain should be the drain that is highest on the stack. The reason

Figure 3-7 Combination Waste-and-Vent System

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Figure 3-8

Philadelphia System

Chapter 3 — Vents and Venting

49

for this is that the discharge of a fixture drain into the stack causes pressure reduction for some distance below the point of entry, and this pressure reduction is greater the greater the rate of discharge. (See Figure 3-9.) Another precaution that is observed in the United States is to permit stack venting only in single-story structures or on the top floor of multistory buildings. It should be noted, however, that the British have installed some systems with stack venting on every floor of multistory buildings and report that it is working satisfactorily.

Wet Venting A “wet vent” is one that vents a particular fixture and at the same time receives the discharge from other fixtures (see Figure 3-9). In practice, such a vent receives the discharge only from lowrate fixtures, such as lavatories, sinks, etc., never from a water closet or from a number of fixtures. The principal object of using wet vents is to reduce the vent piping required for a given installation by making individual pipes serve two purposes. Because wet venting simplifies the drainage system and thereby decreases the cost of installation, there is an increasing tendency among code-writing authorities to permit its use under suitable restrictions that are necessary to prevent excessive trap seal losses. Dr. R. Hunter, at the National Bureau of Standards, conducted tests on wet venting and reported the results in Recommended Minimum Requirements for Plumbing in Dwellings and Similar Buildings. He pointed out that, under certain conditions, wet venting could be used without danger of reducing trap seals excessively. In a later publication he indicated that bathroom fixtures back to back can be wet vented satisfactorily, provided the bathtub drains between the wet vent and the bathtub trap are laid on a uniform slope and otherwise comply with the conditions necessary to prevent excessive selfsiphonage.

Reduced-Size Venting In 1972, a laboratory study of one-story and splitlevel experimental drainage systems where the vents varied from one to six pipe sizes smaller than those presently specified by codes showed satisfactory hydraulic and pneumatic perfor-

Figure 3-9 Wet Venting and Stack Venting mance under various loading conditions (National Bureau of Standards 1974). At the same time, the ten-story wet-vent system in Stevens’s Building Technology Research Laboratory had been modified by reducing the vents one to three pipe sizes in accordance with plans and specifications furnished by the National Bureau of Standards (NBS) and the conducting of a series of tests under various loading conditions. Based on the test loads imposed, the reduced-size vents selected for use in this study appear to be adequate with regard to trap-seal retention and blow-back for a ten-story building (Stevens Institute of Technology 1973). In 1976, a report described the experimental findings of tests on a full-scale, two-story plumbing system with reduced-size vents under a range of operating conditions including having the vent terminals closed and the building drain submerged. Results indicate that dry-vent piping in one and two-story housing units can safely be made smaller than presently allowed by design without jeopardizing the trap seals.

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SECTION III— SIZING OF SEVERAL VENTING SYSTEMS Reduced-Size Venting Design This system may allow economies in venting design in low-rise residential buildings. It is similar to traditional codes, but allows smaller size vents. It is limited to special conditions and requires that vent pipes not be restricted by products of corrosion. General limitations Reduced-size venting is limited to water fall from the highest fixture to the building drain or its horizontal branches of 15 ft (4.6 m) for residential occupancies and residential-type fixtures. Reduced-size vents must be of corrosion-resistant materials, such as copper or plastic; must slope to the drain; must not be located where a stoppage could cause waste to back up into them (e.g., a single-compartment sink with a garbage disposer that could pump waste into the vent pipe in the event of stoppage below the vent); must not be installed within 1½ ft (0.5 m) developed length from a clothes-washer trap arm; and must be independent of other systems. (Exception: The drains from these systems may connect to any other system in gravity-flow building sewers.) Fixture and stack vents are traditional sizes up to at least 6 in. (152 mm) above the flood

Table 3-8 Type of Vent

level rim of the fixture served. An arterial vent is installed for systems with more than one floor of fixtures (the drainage piping between the arterial vent and the street sewer is at least the same size as the arterial vent). Vents that are subject to freezing are of traditional size; vent terminals are screened (free openings are at least 150% of the required flow area and openings face down); and drainage pipes are the size required by traditional codes. Always consult with the local plumbing code enforcement agency or other governmental department having jurisdiction before designing the system to be sure this sizing method is acceptable under the applicable code.

Table 3-7 Fixture

8–16 (2.4–4.9) Up to 8 (2.4)

8–16 (2.4–4.9) Stack vent

Up to 8 (2.4)

8–16 (2.4–4.9)

aIncrease one pipe size for two-story systems.

2 3 2 3 2 1 3 4

Fixture Vents and Stack Vents

Up to 8 (2.4)

Fixture vent for two traps

Fixture Units

Bathtub or shower Clothes washer Dish washer Floor drain Laundry tray Lavatory Sink (including dishwasher and garbage disposer) Water closet (tank type)

Elevation of Trap Centerline, Arm above Centerline of Its Horizontal Drain, ft (m)

Fixture vent for one trap

Fixture Unit Loads

Load Served by Vent (fixture units)

Nominal Size of Fixture or Stack Vent, in. (mm)

3 or less 4 3 or less 4

½ ¾ ¾ 1

(12.7)a (19)a (19) (25.4)

3 or less 4–6 7 and 8 6 or less 7 and 8

¾ 1 1¼ 1 1¼

(19)a (25.4) (32) (25.4) (32)

6 or less 7–15 16–29 6 or less 7–15 16–29

1 1¼ 1½ 1¼ 1½ 2

(25.4) (32) (38) (32) (38) (51)

Chapter 3 — Vents and Venting

51

Sizing procedure The following steps should be followed in the design of reduced-size venting:

Table 3-9 Confluent Vents Serving Three Fixture or Stack Vents Nominal Size of Fixture or Stack Vent, in. (mm)

1. Prepare a pipe layout drawing. 2. Determine the fixture units for each fixture vent and each stack vent using Table 3-7.

Largest

3. Size fixture and stack vents using Table 3-8.

½

4. Size confluent vents, beginning at the vents farthest from their termination. A. When a confluent vent serves two fixture vents, two stack vents, or one fixture vent and one stack vent, make the confluent vent one pipe size larger than the vents served. B. When a confluent vent serves any combination of three fixture vents and stack vents, size the confluent vent using Table 3-9. C. When a confluent vent serves any combination of four or more fixture and stack vents, size the confluent vent using Table 3-10 or 3-11. For flow areas of pipe and tube, use Table 3-12.

¾

(12.7) (19)

Next to Largest ½ ¾

(12.7) a

(19)

a

Nominal Size of Confluent Vent,

Smallest

in (mm.)

½

(12.7)

¾

(19)

¾

(19)a

1

(25.4)

1¼ (31)

1

(25.4)

1

(25.4)

¾

(19)a

1

(25.4)

1

(25.4)

1

(25.4)

1½ (38)

¾

(19)a

1½ (38)

a

1¼ (31)

¾

(19)

1¼ (31)

1

(25.4)

½

(12.7)

1½ (38)

1¼ (31)

1

(25.4)

¾

(19)

2

1¼ (31)

1¼ (31)

½

(12.7)

1½ (38)

1¼ (31)

1¼ (31)

¾

(19)

2

(51)

1½ (38)

1¼ (31)a

1¼ (31)a

2

(51)

1½ (38)

1½ (38)

1

2

(51)

1½ (38)

1½ (38)

1¼ (31)

3

(76)

(25.4)a

(51)

aOr smaller.

Table 3-10 Confluent Vents Serving Four or More Fixture or Stack Vents, Schedule 40 Pipe Size of Largest Vent Served, in. (mm) ½ (12.7)

1 (25.4)

1¼ (31)

Nominal Size of Confluent Vent, in. (mm) 1½ (38) 2(51) 2½ (63)

3(76)

4 (101)

Total Flow Area of Vents Served, in2 (103 mm2) 2.5–7.5 (1.6–4.8)

7.5–14 (4.8–9.0)

¾ (19)

1.4–4.2 (0.9–2.7)

4.2–7.9 (2.7–5.1)

7.9– 21 (5.1–13.6)

1 (25.4)

1.8–2.6 (1.2–1.7)

2.6–4.8 (1.7–3.1)

4.8–13 (3.1–8.4)

13–27 (8.4–17.4)

2.4–2.8 (1.6–1.8)

2.8–6.7 (1.8–4.3)

6.7–15 (4.3–9.7)

15–36 (9.7–23.2)

2.9–5.5 (1.9–3.6)

5.5–11 (3.6–7.1)

11–27 (7.1–17.4)

27 to 79 (17.4 to 51.0)

3.8–6.8 (2.5–4.4)

6.8–16 (4.4–10.3)

16 to 48 (10.3 to 31.0)

5.7–11 (3.7–7.1)

to 34 (7.1 to 21.9)

1¼ (31) 1½ (38) 2 (51) 2½ (63) 3 (76)

1.2–2.5 (0.8–1.6)

8.3 to 22 (5.4 to 14.2)

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Table 3-11 Confluent Vents Serving Four or More Fixture or Stack Vents, Copper Tube Size of Largest Vent Served, in. (mm) ½ (12.7) ¾ (19) 1 (25.4)

Nominal Size of Confluent Vent, in. (mm) Type DWV

Type M ¾ (19)

1 (25.4)

1¼ (31) 1½ (38) 2 (51) 2 Total Flow Area of Vents Served, in (103 mm2)

1.0–1.1 (0.6–0.7)

1.1–3.0 (0.7–1.9)

3.0–7.0 (1.9–4.5)

7.0–14 (4.5–9.0)

1.3–1.5 (0.8–1.0)

1.5–3.4 (1.0–2.2)

3.4–6.7 (2.2–4.3)

6.7–21 (4.3–13.6)

1.6–2.0 (1.0–1.3)

2.0–4.0 (1.3–2.6)

4.0–12 (2.6–7.7)

12–60 (7.7–38.7)

2.1–2.7 (1.4–1.7)

2.7–8.1 (1.7–5.2)

8.1–40 (5.2–25.8)

40–120 (25.8–77.4)

2.6–5.7 (1.7–3.7)

5.7–28 (3.7–18.1)

28–85 (18.1–54.8)

4.1–16 (2.7–10.3)

16–49 (10.3–31.6)

1¼ (31) 1½ (38) 2 (51)

3 (76)

4 (101)

3 (76)

5. When a vent is longer than 25 ft (7.6 m) developed length between the trap arm and the roof termination, increase the vent one pipe size over its entire length. 6. When serving more than one floor level of fixtures, provide an arterial vent, connected to the largest drain and near the building sewer. Size the arterial vent using Table 313. The arterial vent may also serve as a confluent vent and fixture vent. Increase the connecting drain size to equal the arterial vent size to vent the system properly. 7. When a portion of the vent is subject to freezing, increase that portion to the traditional size. Installation The design engineer should explain the special requirements of the reduced-size venting method to the installer, who may be unfamiliar with them. More detailed drawings may be necessary to describe the system completely. The engineer should make regular inspections to be sure that the design conditions are met in the field. Also, the owner should be given copies of the plumbing drawings for permanent records so that future additions can be properly sized.

8–22 (5.2–14.2)

Table 3-12

Flow Areas of Pipe and Tube, in2 (103 mm2)

Nominal Size, in. (mm)

Schedule 40 Pipe

¼ (12.7)

0.3 (0.2)

Copper Tube Type M

Type DWV

0.25 (0.2)

—

½ (19)

0.53 (0.3)

0.52 (0.3)

—

1

0.86 (0.6)

0.87 (0.6)

—

1¼ (31)

1.5 (1.0)

—

1.32 (0.9)

1½ (38)

2.04 (1.3)

—

1.87 (1.2)

2

(51)

3.36 (2.2)

—

3.27 (2.1)

2½ (63)

4.79 (3.1)

—

—

3

(76)

7.39 (4.8)

—

7.24 (4.7)

4 (101)

12.7 (8.2)

—

12.6 (8.1)

(25.4)

Table 3-13 Load on System (fixture units)

Arterial Vents

Length of Arterial Vent, ft (m)

Nominal Size of Arterial Vent, in. (mm)

10 or less

36 (11) or less over 36 (11) to 120 (36.6)

1½ (38) 2 (51)

11–30

30 (9.1) or less over 30 (9.1) to 100 (30.5)

1½ (38) 2 (51)

Chapter 3 — Vents and Venting

53

Example. The following design example illustrates the reduced-size venting method: Conditions. Two-story residential building, freezing climate, Schedule 40 plastic vents. Step 1. Prepare a pipe layout. See Figure 3-10. Step 2. Determine fixture and stack vent sizes by using Table 3-8. Vent Pipe

Number of Fixture Traps

Vent Stack

Elevation, ft (m)

Load (from Table 3-7) (fixture units)

Size, in. (mm)

1

1

no

5 (1.5)

3

2

2

no

5 (1.5)

5

1

3

2

yes

15 (4.6)

5

1¼ (31)

4

3

yes

15 (4.6)

7

1½ (38)

5

1

no

4 (1.2)

3

½ (12.7) (25.4)

½ (12.7)

Step 3. Determine confluent vent size. Vent Pipe

Number

Sizes, in. (mm)

Area (from Table 3-12), in2 (mm2)

Size, in. (mm)

20

2

1, 1 (25.4, 25.4) (vents 1 & 2)

—

1¼ (31) (one size over 1)

21

3

1¼, 1, 1 (31, 25.4, 25.4) (vents 1, 2, and 3)

—

2 (51) (from Table 3-10)

22

4

1 (25.4) (vent 1)

0.86 (0.6)

1 (25.4) (vent 2)

0.86 (0.6)

1¼ (31) (vent 3)

1.5 (1.0)

1½ (38) (vent 4)

2.04 (1.3)

2 (51) (from Table 3-10)

Step 4. No vent is longer than 25 ft (7.6 m); therefore, no increase is necessary. Step 5. Determine arterial vent size from Table 3-13. Vent Pipe

Load (fixture units)

Length, ft (m)

Size, in. (mm)

4, 22, and 23

23

5 (1.5)

1½ (38)

Step 6. Increase all vents that are subject to freezing conditions to traditional sizes. Vent Pipe

Load (fixture units)

Length ft, (m)

Size, in. (mm)

22

23

4½ (1.4)

2 (51)a

23

23

1½ (0.5)

3 (76)b

a Traditional size. b Size required to prevent frost closure.

Vent 22 was 2 in. (51 mm), Step 3. Vent 23 (extension of vent 22) should be increased from 2 in. (51 mm), Step 4, to 3 in. (76 mm). Increase bathtub drain to 2 in. (51 mm).

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Figure 3-10 Pipe Layout Drawing – Two-Story Residential Building, Freezing Climate, Schedule 40 Plastic Vents

Sovent Systems The sovent system is a single-stack system that may allow economies in drainage and vent systems. There are no limits to heights or occupancies, but there are special design rules. The effects of excess suds should be considered. Always consult with the local plumbing code enforcement agency or other governmental department having jurisdiction before designing the system to make sure this system is acceptable under the local code. The sovent system has four parts: a drain, waste, and vent (DWV) stack; a sovent aerator

fitting at each floor level; DWV horizontal branches; and a sovent deaerator fitting at the base of the stack. The two special fittings, the aerator and the deaerator, are the basis for the self-venting features of the sovent system. Soil stack and vent combine into a single sovent stack. Figure 3-11 illustrates a typical sovent single-stack plumbing system and a traditional two-pipe system. Aerator fittings The sovent system aerator fitting consists of an offset at the upper stack inlet connection, a mixing chamber, one or more branch inlets, one or more waste inlets for the connection of smaller waste branches, a baffle

Chapter 3 — Vents and Venting

(A)

55

(B)

Figure 3-11 (A) Traditional Two-Pipe Plumbing System; (B) Typical Sovent Single-Stack Plumbing System.

ASPE Data Book — Volume 2

56

in the center of the chamber with an aperture between it and the top of the fitting, and the stack outlet at the bottom of the fitting. The aerator fitting provides a chamber where the flow of soil and waste from horizontal branches can unite smoothly with the air and liquid already flowing in the stack. The aerator fitting performs this function efficiently so that no plug of water forms across the stack to cause pressure and vacuum fluctuations that could blow or siphon fixture trap seals. The aerator also slows the flow down the stack at each floor level.

is designed to overcome the tendency of the falling waste to build up excessive back pressure at the bottom of the stack when the flow is decelerated by the bend into the horizontal drain. The deaerator provides a method of separating air from system flow and equalizing pressure buildups. The configuration of the deaerator fitting causes part of the air falling with the liquid and solid in the stack to be ejected through the pressure relief line to the top of the building drain while the balance goes into the drain with the soil and waste.

Aerator fittings are installed in the sovent system at every floor level, where there is a soil branch or where there is no soil branch but a waste branch equal in diameter to, or one size smaller than, the stack. At a floor level where the aerator fitting is not needed (e.g., on a 4-in. [101-mm] stack where there is no soil branch and only a 2-in. [51-mm] waste branch enters), a double in-line offset is used in place of the aerator fitting. This offset reduces the vertical velocity in the stack between floor intervals in a manner similar to the aerator fitting (see Figure 3-12). Deaerator fittings The sovent system deaerator fitting consists of an air separation chamber having an internal nose piece, a stack inlet, a pressure-relief outlet at the top, and a stack outlet at the bottom. (See Figure 3-13.) The deaerator fitting at the bottom of the stack functions in combination with the aerator fittings above to make the single stack self venting. The deaerator

Figure 3-12 Typical Sovent System Aerator Fitting

Figure 3-13 Typical Sovent System Deaerator

Chapter 3 — Vents and Venting

57

Sizing procedure The following steps should be followed in the design of this system:

must be one pipe size larger than the size of the larger stack below the tie line.

1. Prepare a layout drawing.

An aerator fitting is required at each level where one of the following horizontal branches enters the sovent stack: (1) a soil branch, (2) a waste branch the same size as the sovent stack, or (3) a waste branch one DWV tube size smaller than the sovent stack. A 2-in. (51-mm) horizontal waste branch may be entered directly into a 4-in. (101-mm) sovent soil stack. At any floor level where an aerator fitting is not required, a double in-line offset is built into the stack at the nominal floor interval. This maintains the lowered fall rate of the sovent system within the stack.

2. Determine the loading on each section of pipe. 3. Size the stack. 4. Size the branches. 5. Select the fittings above the building drain. 6. Design the connections to the building drain. 7. Size the building drain. (For additional illustrations of requirements, see Copper Development Association listing in References.) Stack The stack must be carried full size through the roof to the atmosphere. Two stacks can be tied together at the top, above the highest fixture, with only one stack extending through the roof. If the distance between the two stacks is 20 ft (6.1 m) or less, the horizontal line that ties the two verticals together, pitched at ¼ in./ft (20.8 mm/m), can be the same diameter as the stack that terminates below the roof level. If the distance is greater than 20 ft (6.1 m), the line must be one size larger than the terminated stack. An inverted long-turn fitting is used at the junction. The common stack extending through the roof

The size of the stack is determined by the number of fixture units connected, as with traditional sanitary systems. (See Tables 3-14 and 3-15.) Branches The starting point in sizing the horizontal soil and waste branches is to determine the fixture-unit loading based on the various fixtures and appliances in the system design. According to traditional practice, the maximum number of fixture-units that may be connected to branches and branch arms of various sizes is shown in Table 3-14. Tailpiece, trap, trap arm, and branch sizes for the individual fixture connections are shown in Table 3-16 (see Figures 3-14 and 3-15).

Figure 3-14 Sovent System Branches

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Table 3-14

Fixture Unit Loads Fixture-Unit Value as Load Factor

Fixture Type

1 bathroom group (water closet, lavatory, and bath tub or shower stall) . Tank-type closet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flush-valve closet Bathtuba (with or without overhead shower) . . . . . . . . . . . . . . . . . . . . . . . Bathtuba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bidet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combination sink and tray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Combination sink and tray with food-disposal unit . . . . . . . . . . . . . . . . . . Dental unit or cuspidor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dental lavatory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drinking fountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dishwasher,b domestic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Floor drainsc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kitchen sink, domestic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kitchen sink, domestic, with food-disposal unit . . . . . . . . . . . . . . . . . . . . Lavatory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lavatory, barber, beauty parlor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lavatory, surgeon’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laundry tray (1 or 2 compartments) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shower stall, domestic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Showers (group) per head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinks Surgeon’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flushing rim (with valve) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service (trap standard) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service (P trap) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pot, scullery etc.b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urinal, pedestal, syphon, jet, blowout . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urinal, wall lip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urinal stall, washout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urinal troughb (each 2-ft section) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wash sinkb (circular or multiple, each set of faucets) . . . . . . . . . . . . . . . . Water closet Tank-operated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Valve-operated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Minimum Size of Trap, in. (mm)

6 8 2 3 3 3 4 ½ 1 ½ 2 1 2 3 1 2 2 2 2 3

1½ (38) 2 (51) Nominal 1½ (38) 1½ (38) Separate 1½ (38) traps 1¼ (31) 1¼ (31) 1 (25.4) 1½ (38) 2 (51) 1½ (38) 1½ (38) 1¼ (31) 1½ (38) 1½ (38) 1½ (38) 2 (51)

3 8 3 2 4 8 4 4 2 2

1½ (38) 3 (76) 3 (76) 2 (51) 1½ (38) Nominal 3 (76) 1½ (38) 2 (51) 1½ (38) Nominal 1½ (38)

6 8

Nominal 3 (76) 3 (76)

a A shower head over a bathtub does not increase the fixture value. b See following note for method of computing unit value of fixtures. c Size of floor drain shall be determined by the area of surface water to be drained.

Table 3-14

Fixture Unit Loads (cont’d)

Note: Fixtures not listed in the above table shall be estimated as follows:

Fixture Drain or Trap Size, in. (mm) 1¼ (32) and smaller 1½ (38) 2 (51) 2½ (63) 3 (76) 4 (101)

Fixture-Unit Value 1 2 3 4 5 6

Table 3-15 Branch Size, in. (mm)

Fixture Units

2 (51) 3 (76)

6a 35

4 (101)

180

Maximum Fixture Units

Exception No 6-unit fixtures or traps Only two 6-unit fixtures or traps

a4, if simultaneous discharge of more than 4 fu is probable.

Chapter 3 — Vents and Venting

59

Figure 3-15 Soil and Waste Branches Connected into a Horizontal Stack Offset. Waste Branches Connected into the Pressure-Relief Line.

Branch sizes must be increased over the sizes shown in Tables 3-15 and 3-16 under the following conditions: 1. A second vertical drop downstream from a trap arm or any vertical drop of more than 3 ft (0.9 m) requires an increase of one pipe size at the

Table 3-16 Size Rules for Connecting Fixtures into the Sovent Single-Stack Drainage Plumbing System Tailpiece, in. (mm)

Trap, in. (mm)

Trap Arm, in. (mm)

Branch, in. (mm)

1¼ (31)

1¼ (31)

1½ (38)

2 (51)

1¼ (31) 1½ (38)

1½ (38) 1½ (38)

2 2

(51) (51)

2 (51) 2 (51)

2

2

3 (76)a

3 (76)

(51)

(51)

Note: Diameter is shown for each permitted combination of elements. a2 in. (51 mm) for stall shower, floor drain, or automatic washing machine standpipe drain.

downstream side of the fitting at the beginning of the vertical drop in question. 2. When three 90° changes in direction (using 90° elbows or similar one-diameter radius turns) occur in a horizontal branch, it must be increased one pipe size at the upstream side of the third 90° change in direction. If a 90° change in direction in the horizontal can be made with two 45° elbow fittings, or with an extra long-term elbow (more than one and one half diameter radius), this rule does not apply. 3. When a branch serves two water closets and one or more additional fixtures, the soil line must be increased to 4 in. (101 mm). Starting at the most remote fixture and moving toward the stack, the branch size is increased to 4 in. (101 mm) at the point where it has picked up one water closet and one additional fixture closer to the stack. 4. When a soil branch exceeds 12 ft (3.7 m) in horizontal length, it should be increased one pipe size.

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60

5. When a waste branch exceeds 15 ft (4.6 m) in horizontal length, it should be increased one pipe size. Note: It is best to install a secondary pressureequalizing line when the horizontal length exceeds 27 ft (8.2 m) in cases (4) and (5) above. Fittings An aerator fitting is required at each level where one of the following horizontal branches enters the sovent stack: (1) a soil branch, (2) a waste branch the same size as the sovent stack, or (3) a waste branch one DWV tube size smaller than the sovent stack. A 2-in. (51-mm) horizontal waste branch may be entered directly into a 4-in. (101-mm) sovent soil stack. At a floor level where the aerator fitting is not needed (e.g., on a 4-in. [101-mm] stack where there is no soil branch and only a 2-in. [51-mm] waste branch enters), a double in-line offset is used in place of the aerator fitting. At the deaerator outlet, the stack is connected into the horizontal drain through a long-turn fitting arrangement. Downstream, at least 4 ft (1.2 m) from this point, the pressure relief line from the top of the deaerator fitting is connected into the top of the building drain. A deaerator fitting, with its pressure-relief line connection, is installed in this way at the base of every sovent stack and also at every offset (vertical-horizontal-vertical) in a stack. In the latter case, the pressure-relief line is tied into the stack immediately below the horizontal portion. Waste branches at least one pipe size smaller than the stack may be led directly into the sovent aerator fitting through a waste entry. Smaller waste branches may be led directly into a stack fitting. Where there is an offset (vertical-horizontalvertical) in the stack, a deaerator fitting, with its pressure-relief line, must be installed. This eliminates the need for a deaerator fitting at the base of the stack if no branches enter the stack below the stack offset and provided that double in-line offsets occur at every nominal floor interval. At a stack offset of less than 60° with the vertical no deaerator fitting is needed. The following must be observed with regard to fittings in sovent systems:

Connection

DWV Fitting

From trap arm to upper vertical branch terminal

Single 90° elbow; for two lavatories double elbow (short turn); for two sinks 90° elbow plus a 45° elbow

From vertical branch to horizontal branch (exception: soil branches require long turn 90° elbows for all 90° changes in direction)

Long turn T-Y, 45° wye and 45° or 90° elbow

From horizontal branch to vertical branch

Single 90° elbow or double elbow

From horizontal to horizontal (exception: soil branches require long turn 90° elbows for all 90° changes in direction)

45° wye and 45° elbow, long turn T-Y or 90° elbow

From waste branch to stack Sanitary tee From branch below the deaerator fitting to stack, to building drain, to horizontal offset or to pressure relief line

Long turn T-Y or a 45° wye and a 45° elbow

Pressure-equalizing lines As an alternative to the sizing procedures previously outlined and increasing the branch sizes, a pressure-equalizing line may be used. Where this is done, a 1-in. (25.4-mm) or larger line is used to equalize the pressure in the branch by connecting it from the top of the discharge side of the trap to one of the following locations: 1. The top of the sovent aerator, using a special inlet in the top of the fitting. 2. The atmosphere, via a run that may also connect with similar upper floor fixtures. 3. The stack, at least 3 ft (0.9 m) above the aerator at that floor level or immediately below one at a higher level, using a DWV tee fitting. Of the three locations, the top of the aerator is the preferred one. The minimum size of the pressure-equalizing line depends on the branch length, as shown in Table 3-17. The three recommended vent connection points are based on the formula of Prandtl-Colebrook (drain half full, roughness Kb = 0.04 in. [1.0 mm]). Fixture units are according to Hunter’s curve for peak load (NBS Monograph 31). Building drain connections Each sovent stack normally empties through a deaerator,

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61

Table 3-17 Minimum Size of Equalizing Line Branch Length, ft (m)

Up to 8 Fixture Units, in. (mm)

8–353 Fixture Units, in. (mm)

Up to 30 (up to 9.1)

1 (25.4)

1½ (38)

30–40 (9.1–12.2)

1¼ (31)

2 (51)

40–50 (12.2–15.2)

1½ (38)

2 (51)

Over 50 (over 15.2)

2 (51)

3 (76)

which should be installed as close as possible to the building drain. The deaerator outlet is connected to the building drain through a long-turn 90° elbow (radius of at least 1½ diameter), through two 45° elbows or wyes, or through a long-turn (more than 1½ diameter) T-Y fitting. The relief line venting the deaerator chamber into the horizontal drain should be 3 in. (76 mm) and should be connected into the top of the horizontal drain at least 4 ft (1.2 m) downstream from the base of the stack. Connection of the pressure-relief line into the

top of the building drain is through a 45° wye fitting. (See Figures 3-16 and 3-17.) The deaerator fitting may be installed at a floor level above the base of the stack if design conditions dictate and no fixtures are attached into the stack below it. Where this is done, the traditional rules for connecting the deaerator fitting are followed; however, a longer relief line will be required to reach the prescribed connection point in the horizontal drain. Double in-line offsets must be installed in the stack at normal floor intervals below the deaerator. Two stacks may be combined before they enter the building drain. The size of the continuing common stack is determined by the total fixture loading on the combined stacks. Fixtures may be connected into the stack immediately below the deaerator fitting and into the building drain between the base of the stack and the point where the pressure-relief line ties into the building drain. Fixtures may also be connected below a deaerator fitting into a horizontal offset in a stack. Two-in. (51-mm) waste branches may be connected into the 3-in. (76-mm) deaerator pressure-relief line by using a Y-branch fitting.

Figure 3-16 Soil and Waste Branches Connected below a Deaerator Fitting at the Bottom of the Stack

ASPE Data Book — Volume 2

62

Sovent fitting Two basic types of sovent aerator fitting meet the needs of most stack designs: the double-side-entry fitting and the single-sideentry fitting. Face-entry fittings and top-entry fittings are used in special cases. (See Figure 3-18.) Branch inlets can be of any size to accommodate standard DWV tube. When using the single-entry fitting, the inlet connections are normally 3 in. (76 mm). When the double-sideentry fitting is used, the branch inlet connections may be 4 or 3 in. (101 or 76 mm), depending on the branch loading. Branches under 3 in. (76 mm) in size can be connected into the aerator fittings with 3 and 4-in. (76 and 101-mm) entries by using appropriate reducer fittings. Alternatively, fittings can be ordered to accommodate smaller branches. However, economical design is more likely to dictate the use of fittings with waste inlets to take smaller branches. Consider a typical apartment-house, backto-back bathroom grouping, as shown in Plan A of Figure 3-19, and assume a ten-story building. Stack size will be 4 in. (101 mm). The branches are sized and designed as follows:

Figure 3-17 Deaerator Fitting Located above Floor Level of Building Drain

1. The lavatories, with a trap arm size of 1½ in. (38 mm), are joined into a vertical waste branch of 2-in. (51-mm) size, according to Table 3-16. Since there is only one vertical drop in the branch serving the lavatories, it remains 2 in. (51 mm) all the way to the aerator fitting waste inlet. 2. Water closets require a minimum soil-branch size of 3 in. (76 mm). Since the branch serving the two water closets also serves an additional fixture, it must be increased to 4 in. (101 mm) for entry into the aerator fitting. An alternative design for the branches is shown in Plan B of Figure 3-19, which assumes that a drop ceiling is not possible and the four bathrooms must be served by two 4-in. (101-mm) stacks.

(A)

(B)

Figure 3-18 Sovent Fitting: (A) Single-Side Entry (Without Waste Inlets); (B) DoubleSide Entry (with Waste Inlets)

Installation The design engineer should explain the special requirements of the sovent system to the installer, who may be unfamiliar with them. More detailed drawings may be necessary to describe the system completely. The engineer should make regular inspections to be sure that the design conditions are met in the field. Also, the owner should be given copies of the plumbing drawings for permanent records so that future additions can be properly sized.

Chapter 3 — Vents and Venting

63

Table 3-18 Maximum Sovent Stack Loadings Stack Size, in. (mm)

Maximum Fixture Units

Table 3-19 Drain Size, in. (mm)

4 (101) 5 (127)

500 1100

6 (152)

1900

aIncluding no more than 8 water closets.

Suggested Maximum Fixture Units /8-in./ft (12.5 cm/m) Fall (1%)

¼-in./ft (25 cm/m) Fall (2%)

½-in./ft (50 cm/m) Fall (4%)

4 (101) 5 (127)

36 150

100 350

200 650

6 (152) 8 (203)

430 1700

850 2700

1400 3900

64a

3 (76)

Loadings for Building Drains

1

Figure 3-19 Two Alternative Design Layouts for Typical Back-to-Back Bathroom Arrangements

64

GLOSSARY For the purposes of this chapter, the following terms have the meanings indicated. Air admittance valve This is a mechanical device that allows the introduction of air into the venting system but prevents the discharge of air from the venting system. It reduces the volume of the venting system and may reduce the number of vents required to terminate to atmosphere. This device can be used only when the system experiences negative pressure fluctuations. Battery of fixtures Any group of two or more similar adjacent fixtures that discharge into a common horizontal waste or soil branch. Branch interval The distance along a soil or waste stack, corresponding in general to a story height but in no case less than 8 ft (2.4 m), within which the horizontal branches from one floor or story of a building are connected to the stack. Building drain That part of the lowest piping of a drainage system that receives discharges from the soil, waste, and other drainage pipes inside the walls of the building and conveys them to the building sewer beginning 3–5 ft (1–1.5 m) outside the building wall. Circuit vent A branch vent that serves two or more traps and extends from the downstream side of the highest fixture connection of a horizontal branch to the vent stack. Combination waste-and-vent system A specially engineered system of waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe adequately sized to provide free movement of air above the flow line of the drain. Common vent A vent connected at the common connection of two fixture drains and serving as a vent for both fixtures. Continuous vent A vertical vent that is a continuation of the drain to which it connects. Drainage fixture unit (dfu or fu) A measure of the probable discharge into the drainage system by various types of plumbing fixture. The drainage-fixture-unit value for a particular fixture depends on its volume rate of drainage discharge, on the duration of a single drainage operation, and on the average time between successive operations.

ASPE Data Book — Volume 2

Horizontal branch drain A drain branch pipe extending laterally from a soil or waste stack or building drain, with or without vertical sections or branches, that receives the discharge from one or more fixture drains and conducts it to the soil or waste stack or to the building drain. Insanitary (unsanitary) A condition that is contrary to sanitary principles or is injurious to health. Loop vent A circuit vent that loops back to connect with a stack vent instead of a vent stack. Offset A combination of elbows or bends that brings one section of the pipe out of line but into a line approximately parallel with the other section. Relief vent An auxiliary vent that permits additional circulation of air in or between drainage and vent systems. Stack venting A method of venting a fixture or fixtures through the soil or waste stack. Trap arm That portion of a fixture drain between a trap and its vent. Trap seal The maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap. Vent stack A vertical vent pipe that is installed to provide circulation of air to and from the drainage system and that extends through one or more stories. Vent stack terminal The vertical termination point that normally extends up through the roof of the building, thus venting to the atmosphere. Wet vent A vent that receives the discharge of wastes from sources other than water closets and kitchen sinks.

Chapter 3 — Vents and Venting

REFERENCES 1.

American Society of Plumbing Engineers (ASPE) Research Foundation. 1978. Reduced-size venting design, by E. Brownstein. Westlake Village, CA.

2.

Copper Development Association, Inc. Copper sovent single-stack plumbing system handbook supplement. New York.

3.

Manas, Vincent T. 1957. National plumbing code handbook. New York: McGraw-Hill.

4.

National Association of Home Builders Research Foundation. 1971. Performance of reduced-size venting in residential drain, waste and vent system. Report LR 210-17.

5.

National Association of Plumbing-Heating-Cooling Contractors and American Society of Plumbing Engineers. 1973. National standard plumbing code.

6.

National Bureau of Standards. 1923. Recommended minimum requirements for plumbing in dwellings and similar buildings, by Dr. R. Hunter.

7.

National Bureau of Standards. 1974. Laboratory studies of the hydraulic performance of one-story and split-level residential plumbing systems with reduced-size vents, by R. S. Wyly, G. C. Sherlin, and R. W. Beausoliel. Report no. BBS 49.

8.

National Bureau of Standards. n.d. Monograph no. 31.

9.

Stevens Institute of Technology. 1973. An investigation of the adequacy of performance of reduced-size vents installed on a ten-story drain, waste and vent system, by T. K. Konen and T. Jackson. Report SIT-DL-73-1708.

65

66

ASPE Data Book — Volume 2

Chapter 4 — Storm-Drainage Systems

4 GENERAL DESIGN CONSIDERATIONS FOR BUILDINGS AND SITES Storm-drainage systems convey rainwater from buildings, surface runoff from all types of precipitation, ground water, and subsurface water. The drainage may include rainwater from parking lots, roadways, roofs of structures, and undeveloped areas of a site. Depending on the approval of the local administrative authority, some clear-water wastes, such as condensate from HVAC units, untreated cooling-tower water, ice-machine discharge, and pond overflow, may be allowed to be conducted to the storm-drainage system. These discharges must exclude any chemicals or sanitary flow. If any oils are directed to the storm system, an oil separator must be provided to separate the oils prior to discharge to a public storm system. The local authority must approve all drainage plans, including detention and outfall structures, and must issue permits. Building sites should be provided with a means for draining water from roofs, paved areas, areaways, yards, and all other areas where the collection or uncontrolled flow of rainwater could cause damage to a building, overload local streams, or present a hazard to the public. The storm-drainage systems should provide a conduit or channel from the point of collection to an approved point of disposal, usually a public storm sewer system or drainage canals. If the building storm-drainage system is at a lower elevation than the public storm sewer sys-

67

StormDrainage Systems

tem, not allowing for gravity drainage, the drainage must be pumped. When a public means of disposal is not available, the discharge should be directed to a safe point of disposal as approved by the jurisdictional authority for storm-water control. The storm sewer should be separate from the sanitary sewer system unless there is an approved combined storm/sanitary sewer system available. Such systems have become a rarity because of the additional loads imposed on the municipal sewage disposal plants; also, overflow could cause direct contamination of the local streams and waterways. Federal government regulations prohibit the use of combined sewers for any public system that receives federal funding. Controlled-flow storm-drainage systems should be considered in all combined storm/sanitary sewer systems. If the storm-drainage piping does connect to the sanitary sewer, the storm drain must be properly trapped prior to its connection. Storm-drainage stacks do not require venting because there is no need to control hydraulic or pneumatic pressures within any fixed limits. Negative pressures occur at the top of the stack and positive pressures exist at the bottom of the stack. Because the stack is not vented, pressures can become rather high, creating turbulence at the base of the stack known as the “hydraulic jump” phenomenon. In general, supercritical flow can be changed to subcritical flow only by passing through a hydraulic jump. The extreme turbulence in a hydraulic jump will dissipate energy rapidly, causing a sharp drop in the total head between the supercritical and subcritical states

68

of flow. No connections should be made within the area where hydraulic jump may occur. It may be more advantageous to route the storm and sanitary mains separately to the exterior of the building before they are tied together in the combined system, with a trap separating the systems. Traps should be either located inside the building or buried, with access, below the frostline to prevent freezing. Connection of the storm leaders to the sanitary sewer should be a minimum of 10 ft (3.1 m) downstream from any sanitary connection to prevent the hydraulic jump from disrupting flow when the storm drains are discharging and causing backups in the sanitary system. Rainwater is normally conveyed from the area being drained at the same rate at which it is collected, unless controlled-flow systems are utilized to alleviate overtaxation of the public storm sewers. The rate of the water flow to be drained is determined by the size of the area being drained, the roughness coefficient and infiltration rate of the area being drained, and the rate of rainfall. Rainfall intensity charts published by the National Weather Service and the administrative authority having jurisdiction should be consulted when determining the rate of rainfall for the area of the country in which a building is being constructed. Ponding may be allowable in areas such as a paved schoolyard, where it would cause few problems because of the normal inactivity in a schoolyard during rainy periods. If the structure cannot tolerate the additional weight imposed by the ponding of the water or if the ponding of water may cause a hazard to the public, the more stringent of design considerations may be appropriate.

ASPE Data Book — Volume 2

pable of withstanding all anticipated abuses, corrosion, weather, and expected expansion and contraction. Underground piping should be of cast iron (service or extra-heavy weight, depending on the loads exerted on the pipe), ductile iron, hardtemper copper, aluminum, ABS, PVC-DWV, concrete or extra-strength vitrified clay. If plastic piping is used, a proper class B bedding must be provided for adequate laying and support of the pipe. Plastic piping does not have the scour resistance of metal piping, especially at the base elbow. Aluminum pipe and other metallic pipe in corrosive soils must be wrapped or coated. Piping cast in columns should be type L copper or plastic. All materials must be approved by the local code body. See other Data Book chapters on piping and drainage for data on pipe schedules, joining methods, plumbing drains, etc.

PART ONE: BUILDING DRAINAGE SYSTEM DESIGN The design of drainage systems should be based on sound engineering judgment with standard engineering methods governing the basic aspects of drainage systems. Special local conditions, building and site characteristics, and code authority requirements may necessitate a unique design. The designer should keep in mind that the codes are minimum standards only. All designs must meet, or exceed, the local code requirements.

Design Criteria The following items should be considered when establishing the design criteria:

Similar to the requirements for sanitary systems and per the local code authority, all systems must be properly tested upon completion.

1. Local climatic conditions. Rainfall rate, snow depth, freezing conditions, frost line, etc., as determined from National Weather Service publications.

MATERIALS

2. Building construction. Type of roof, pattern of drainage slopes, vertical wall heights, parapet heights, scupper sizes and locations, emergency drain requirements and locations, pipe space allocations in the ceiling space, wall and chase locations, etc.

Materials for aboveground piping in buildings should be brass, copper pipe or tube type DWV, cast-iron, galvanized or black steel, lead, aluminum, ABS or PVC-DWV. Care should be taken in the use of plastic piping because of its higher expansion and contraction characteristics, required supports, and possible noise problems. Exposed leaders or downspouts should be ca-

3. Departments having jurisdiction. Design rainfall rate, minimum pipe size and slope, overflow requirements, extent of overflow pipe and discharge requirements, method of connec-

Chapter 4 — Storm-Drainage Systems

tion to the public storm sewer, safe method of disposal if the public storm sewer is not available, controlled-flow roof drainage, retention/detention, etc. 4. Site conditions. Location, size, topography and elevation, soil conditions and type, water table, location and pipe material of public storm sewer, location of existing manholes, location of other utilities within the site, etc.

Pipe Sizing and Layout The storm-drainage system(s) required for a building and site of simple design are shown in Figures 4-1 and 4-2. The following points should be considered: 1. Roof drains and pipe sizing are based on the collection areas, the slope of the pipe, and the rainfall rate. 2. Overflow drains and piping are equivalent to the roof drains served, and the basis of the sizing is the same as it is for roof drains. These drains should be piped separately from the primary system to a separate disposal point so that blockage of the primary drainage system will not affect the overflow drainage system. 3. The collection area for deck and balcony drains, where there is an adjacent vertical wall face, is based on the horizontal collection area plus a percentage of the adjacent vertical wall areas. 4. The sizes of the mains are based on the accumulated flows of the drains and drain leaders upstream. 5. The building storm-drain size is based on the total of the horizontal collection areas plus a percentage of the vertical wall areas on the one side of the building that contributes the greatest flow. 6. Sizes of mains downstream of sump pumps are based on the accumulated flows of gravity drains upstream plus the discharge capacity of any sump pumps upstream. 7. The pipe size of the sump pump discharge is based on the capacity of the pump but is normally the same as the discharge pipe size of the pump. For duplex pumps that may operate simultaneously, the combined discharge capacity should be used. The discharge pipe should connect to the horizontal storm main a minimum of 10 ft (3.3 m) downstream of

69

the base of any stack, as high pressure can exist in this zone due to hydraulic jump. 8. The size of the building overflow storm drain is based on the accumulated flow from the overflow drain leaders upstream. Means for the disposal of the overflow drain discharge must meet the requirements of the local codes. Local codes may not allow open discharge on the street, especially in northern climates; therefore, it may be necessary to tie to the public storm sewer separately from the primary drainage system. Both may be routed to the same manhole but with separate inlets. 9. The size of the area drain piping is based on the collection area plus a percentage of the adjacent wall areas draining into the collection area. 10. The size of an areaway or stairwell drain piping is based on the collection area plus a percentage of the adjacent wall areas not previously calculated draining into the areaway or stairwell. 11. The size of the catch basin piping is based on the “rational method” (see discussion under “Site Drainage” in Part Two of this chapter). 12. The size of the storm drain from the catch basins is based on the cumulative flows from the catch basins upstream. 13. The drain from the lower-level deck drain should connect to the horizontal storm main a minimum of 10 ft (3.3 m) downstream of the base of any stack, as high pressure can exist in this zone due to hydraulic jump.

Rainfall Rates Rainfall rate tables Table 4-1 lists the maximum rainfall rates for various US cities. These rates are also listed for various rainfall intensities, both in duration length and in return period. Table 4-1 allows the selection of a precipitation-frequency value for a 10-year or 100-year return period with durations of 5 min, 15 min, or 60 min. Other return periods and durations can be selected by interpolation between the values listed, as follows: Equation 4-1 10-min value = 0.59 (15-min value) + 0.41 (5-min value)

ASPE Data Book — Volume 2

70

Figure 4-1 Piping Layout for Typical Building Elevation

Figure 4-2 Piping Layout for Typical Building Site Plan

Note: A = Roof drains and pipe, B = Overflow drains and piping, C = Collection area for deck and balcony drains, D = Storm leaders, E = Building storm drain, F = Main downstream of sump pump, G = Sump pump discharge, H = Building overflow storm drain, I = Area drain piping, J = Area-way/stairwell drain piping, M = Connection of lower deck drain to horizontal storm main.

Note: E = Building storm drain, H = Building overflow storm drain, I = Area drain piping, J = Area-way/stairwell drain piping, K = Catch basin piping, L = Storm drain from the catch basin.

Equation 4-2

rainfall rate is averaged over the period, is significantly heavier than a 60-min duration total for a 60-min period.

30-min value = 0.49 (60-min value) + 0.51 (15-min value) The “return period” determines the rainfall history used in the calculations and is the estimated average period of time between occurrences of a rainfall rate that equals or exceeds the design condition. A 100-year return period will include heavier storms than a 10-year return period and requires the use of a heavier rainfall intensity. The “duration” determines the length of time to be utilized in the rainfall calculations. Normally, the intensity of a storm is much heavier taken over a shorter duration and decreases as the storm progresses. During a flash flood or summer storm, a deluge of precipitation may occur for a short duration and taper off. Therefore, the amount of rainfall for a 5-min duration, projected over a 60-min period where the

The local code having jurisdiction should be consulted to determine the rate of rainfall that is applicable for the design areas. A minimum design should be for a 10-year, 5-min storm for the building roof and for the site. Design for the most stringent rainfall intensities may not be necessary if a secondary drainage system is provided, such as scuppers in a parapet wall or a separately piped secondary drainage system, that will accept the overflow. Therefore, the design may be based on a more liberal design storm of a 100-year return period, 60-min duration, as opposed to a more conservative 100-year return period, 5-min duration. Secondary drainage systems Some codes require that the primary drainage system be designed for the less stringent value, with the

Chapter 4 — Storm-Drainage Systems

71

Table 4-1 Maximum Rates of Rainfall for Various US Cities, in./h (mm/h) Frequency and Duration of Storm 100-Yr., 5 Min.

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

10.08 (256.0)

7.28 (184.9)

3.7

(94.0)

7.50 (190.5)

Alabama: Birmingham Huntsville

9.96 (253.0)

7.08 (179.8)

3.3

(83.8)

7.30 (185.4)

Mobile

10.80 (274.3)

8.00 (203.2)

4.5 (114.3)

8.18 (207.8)

Montgomery

10.26 (260.6)

7.60 (193.0)

3.8

7.73 (196.4)

Alaska: Fairbanks

Use NOAA atlas for detailed

1.00

(25.4)

3.70

(94.0)

Juneau

state precipitation map.

0.60

(15.2)

1.70

(43.2)

2.2

(55.9)

4.30 (109.2)

Arizona: Phoenix

Use NOAA atlas for detailed state precipitation map.

Arkansas: Bentonville

10.20 (259.1)

7.24 (183.9)

3.62

(91.9)

7.38 (187.4)

Ft. Smith

10.20 (259.1)

7.28 (184.9)

3.9

(99.1)

7.41 (188.1)

9.96 (253.0)

7.16 (181.9)

3.7

(94.0)

7.36 (186.9)

Eureka

1.5

(38.1)

2.70

(68.6)

Fresno

1.90

(48.3)

3.60

(91.4)

Little Rock California:

Los Angeles

2.00

(50.8)

3.60

(91.4)

Mt. Tamalpais

1.50

(38.1)

2.50

(63.5)

Pt. Reyes

1.50

(38.1)

2.40

(61.0)

Red Bluff

Use NOAA atlas for detailed

1.75

(44.5)

3.80

(96.5)

Sacramento

state precipitation map.

1.30

(33.0)

3.00

(76.2)

San Diego

1.50

(38.1)

3.30

(83.8)

San Francisco

1.50

(38.1)

3.00

(76.2)

San Jose

1.50

(38.1)

2.00

(50.8)

1.5

(38.1)

3.10

(78.7)

San Luis Obispo Colorado: Denver

Use NOAA atlas for detailed

Grand Junction

state precipitation map.

2.2

(55.9)

5.70 (144.8)

1.70

(43.2)

3.00

Pueblo

2.50

(63.5)

5.00 (127.0)

Wagon Wheel Gap

1.90

(48.3)

3.60

2.8

(71.1)

6.23 (158.2)

(76.2) (91.4)

Connecticut: Hartford

8.70 (221.0)

5.96 (151.4)

(Continued)

ASPE Data Book — Volume 2

72

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min. New Haven

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

9.00 (228.6)

6.00 (152.4)

3.0

6.42 (163.1)

9.48 (240.8)

7.00 (177.8)

3.5

(88.9)

6.93 (176.1)

9.72 (246.9)

7.22 (183.4)

4.0 (101.6)

7.10 (180.4)

10.08 (256.0)

8.08 (205.2)

4.3 (109.2)

7.86 (199.6)

Delaware: Dover District of Columbia: Washington Florida: Jacksonville Key West

9.12 (231.6)

7.24 (183.9)

4.28 (108.7)

7.07 (179.6)

Miami

9.84 (249.9)

8.80 (223.5)

4.5 (114.3)

7.69 (195.4)

Orlando

10.80 (274.3)

8.40 (213.4)

4.50 (114.3)

8.42 (213.9)

Pensacola

10.80 (274.3)

8.08 (205.2)

4.60 (116.8)

8.18 (207.8)

Tampa

10.80 (274.3)

8.40 (213.4)

4.2 (106.7)

8.33 (211.6)

Tallahassee

10.50 (266.7)

8.04 (204.2)

4.1

8.05 (204.4)

Georgia: Atlanta

9.90 (251.5)

7.12 (180.9)

Augusta

9.84 (249.9)

7.20 (182.9)

10.08 (256.0)

7.40 (188.0)

3.7

(94.0)

7.62 (193.6)

9.60 (243.8)

7.60 (193.0)

4.0 (101.6)

7.44 (188.9)

10.44 (265.2)

7.88 (200.2)

4.0 (101.6)

7.96 (202.2)

Macon Savannah Thomasville Hawaii: Honolulu

Use NOAA atlas for detailed

(88.9)

7.33 (186.2)

4.00 (101.6)

3.5

7.33 (186.2)

3.00

(76.2)

5.2 (132.1)

state precipitation map.

Idaho: Boise

Use NOAA atlas for detailed

1.0

(25.4)

2.7

(68.6)

Lewiston

state precipitation map.

1.0

(25.4)

3.1

(78.7)

1.20

(30.5)

3.7

(94.0)

Pocatello Illinois: Cairo

9.84 (249.9)

6.96 (176.8)

3.40

(86.4)

7.16 (181.8)

Chicago

9.30 (236.2)

6.60 (167.6)

2.7

(68.6)

6.76 (171.8)

Peoria

9.72 (246.9)

6.88 (174.8)

2.9

()

7.04 (178.9)

Springfield

9.84 (249.9)

7.12 (180.9)

3.0

(76.2)

7.10 (180.3)

Evansville

9.72 (246.9)

6.80 (172.7)

3.0

(76.2)

7.04 (178.9)

Ft. Wayne

9.24 (234.7)

6.48 (164.6)

2.85

(72.4)

6.65 (168.9)

Indiana:

(Continued)

Chapter 4 — Storm-Drainage Systems

73

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min.

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

Indianapolis

9.42 (239.3)

6.60 (167.6)

2.8

(71.1)

6.82 (173.2)

Terre Haute

9.66 (245.4)

6.72 (170.7)

3.18

(80.8)

7.02 (178.2)

Iowa: Charles City

9.96 (253.0)

7.08 (179.8)

3.35

(85.1)

7.06 (179.4)

Davenport

9.84 (249.9)

7.00 (177.8)

3.0

(76.2)

7.04 (178.7)

10.32 (262.1)

7.28 (184.9)

3.4

(86.4)

7.31 (185.7)

Dubuque

9.84 (249.9)

6.94 (176.3)

3.30

(83.8)

7.01 (178.0)

Keokuk

9.96 (253.0)

7.08 (179.8)

3.30

(83.8)

7.15 (181.6)

10.44 (265.2)

7.32 (185.9)

3.6

(91.4)

7.34 (186.3)

Concordia

10.44 (265.2)

7.48 (190.0)

3.75

(95.3)

7.37 (187.1)

Dodge City

10.20 (259.1)

7.24 (183.9)

3.45

(87.6)

7.20 (182.8)

Des Moines

Sioux City Kansas:

Goodland

9.96 (253.0)

6.80 (172.7)

3.5

(88.9)

6.85 (174.1)

Iola

10.44 (265.2)

7.32 (185.9)

3.62

(91.9)

7.40 (187.9)

Topeka

10.50 (266.7)

7.40 (188.0)

3.8

(96.5)

7.39 (187.8)

Wichita

10.50 (266.7)

7.50 (190.5)

3.9

(99.1)

7.51 (190.8)

Kentucky: Lexington

9.36 (237.7)

6.56 (166.6)

2.9

()

6.82 (173.3)

Louisville

9.36 (237.7)

6.56 (166.6)

2.8

(71.1)

6.88 (174.8)

10.50 (266.7)

7.96 (202.2)

4.30 (109.2)

7.99 (202.9)

Louisiana: Alexandria New Orleans

10.92 (277.4)

8.20 (208.3)

4.5 (114.3)

8.30 (210.7)

Shreveport

10.44 (265.2)

7.60 (193.0)

4.0 (101.6)

7.81 (198.4)

Eastport

6.60 (167.6)

4.60 (116.8)

2.20

(55.9)

4.63 (117.6)

Portland

7.56 (192.0)

5.12 (130.1)

2.25

(57.2)

5.36 (136.1)

Presque Isle

6.96 (176.8)

4.68 (118.9)

2.05

(52.1)

4.91 (124.7)

Baltimore

9.72 (246.9)

7.24 (183.9)

3.5

(88.9)

7.11 (180.7)

Cambridge

9.60 (243.8)

7.24 (183.9)

3.25

(82.6)

7.05 (179.0)

Cumberland

9.30 (236.2)

6.56 (166.6)

2.75

(69.9)

6.76 (171.8)

Boston

7.20 (182.9)

5.20 (132.1)

2.7

(68.6)

5.26 (133.5)

Nantucket

7.20 (182.9)

5.12 (130.1)

2.50

(63.5)

5.32 (135.0) (Continued)

Maine:

Maryland:

Massachusetts:

ASPE Data Book — Volume 2

74

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min. Springfield

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

8.64 (219.5)

6.00 (152.4)

2.70

(68.6)

6.20 (157.5)

Alpena

8.64 (219.5)

5.60 (142.2)

2.50

(63.5)

6.02 (153.0)

Detroit

8.88 (225.6)

5.92 (150.4)

2.5

(63.5)

6.37 (161.7)

Escanaba

8.88 (225.6)

5.60 (142.2)

2.40

(61.0)

6.22 (158.0)

Grand Rapids

9.00 (228.6)

6.00 (152.4)

2.6

(66.0)

6.48 (164.6)

Houghton

8.40 (213.4)

5.20 (132.1)

2.40

(61.0)

6.00 (152.5)

Lansing

9.24 (234.7)

6.10 (154.9)

2.80

(71.1)

6.62 (168.1)

Marquette

8.40 (213.4)

5.20 (132.1)

2.40

(61.0)

5.97 (151.7)

Port Huron

8.76 (222.5)

5.80 (147.3)

2.70

(68.6)

6.31 (160.4)

Ste. Marie

7.80 (198.1)

5.20 (132.1)

2.25

(57.2)

5.59 (141.9)

Duluth

9.48 (240.8)

6.40 (162.6)

2.6

(66.0)

6.70 (170.1)

Minneapolis

9.96 (253.0)

6.88 (174.8)

3.0

(76.2)

7.00 (177.8)

Michigan:

Minnesota:

Moorhead

10.02 (254.4)

6.88 (174.8)

3.20

(81.3)

6.88 (174.7)

Worthington

10.50 (266.7)

7.30 (185.4)

3.4

(86.4)

7.29 (185.2)

Biloxi

11.04 (280.4)

8.10 (205.7)

4.5 (114.3)

8.35 (212.1)

Meridian

10.32 (262.1)

7.64 (194.1)

4.05 (102.9)

7.82 (198.6)

Mississippi:

Tupeto

9.96 (253.0)

7.20 (182.9)

3.60

(91.4)

7.72 (196.0)

10.44 (265.2)

7.68 (195.1)

4.20 (106.7)

7.87 (199.9)

Columbia

10.08 (256.0)

7.20 (182.9)

3.80

(96.5)

7.20 (183.0)

Hannibal

10.02 (254.5)

7.08 (179.8)

3.75

(95.3)

7.18 (182.3)

Kansas City

10.44 (265.2)

7.34 (186.4)

3.65

(92.7)

7.37 (187.1)

Vicksburg Missouri:

Poplar Bluff

9.96 (253.0)

7.08 (179.8)

3.55

(90.2)

7.27 (184.6)

St. Joseph

10.44 (265.2)

7.36 (186.9)

3.65

(92.7)

7.37 (187.1)

9.90 (251.5)

7.00 (177.8)

3.2

(81.3)

7.12 (180.9)

10.14 (257.6)

7.20 (182.9)

3.7

(94.0)

7.23 (183.7)

1.60

(40.6)

4.30 (109.2)

1.50

(38.1)

3.80

(96.5) (83.8)

St. Louis Springfield Montana: Havre Helena

Use NOAA atlas for detailed

Kalispell

state precipitation map.

1.20

(30.5)

3.30

Miles City

2.15

(54.6)

7.00 (177.8)

Missoula

1.30

(33.0)

2.70

(68.6)

(Continued)

Chapter 4 — Storm-Drainage Systems

75

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min.

100-Yr., 15-Min.

100-Yr., 60-Min.

10.50 (266.1)

7.44 (189.0)

3.80

10-Yr., 5-Min.

Nebraska: Lincoln

(96.5)

7.39 (187.8)

North Platte

10.02 (254.5)

6.80 (172.7)

3.35

(85.1)

6.88 (174.7)

Omaha

10.50 (266.1)

7.38 (187.5)

3.6

(91.4)

7.39 (187.8)

Scottsbluff

9.60 (243.8)

6.40 (162.6)

3.15

(80.0)

6.41 (162.7)

Valentine

9.96 (253.0)

6.84 (173.7)

3.25

(82.6)

6.78 (172.2)

1.2

(30.5)

3.20

(81.3)

1.00

(25.4)

3.00

(76.2)

1.00

(25.4)

2.70

(68.6)

Nevada: Reno

Use NOAA atlas for detailed

Tonopah

state precipitation map.

Winnemucca New Hampshire: Berlin

7.80 (198.1)

5.36 (136.1)

2.2

(55.9)

5.64 (143.4)

Concord

7.92 (201.2)

5.60 (142.2)

2.50

(63.5)

5.73 (145.5)

Atlantic City

9.36 (237.7)

6.72 (170.7)

3.4

(86.4)

6.82 (173.3)

Paterson

9.24 (234.7)

6.52 (165.6)

3.00

(76.2)

6.65 (168.9)

Trenton

9.30 (236.2)

6.72 (170.7)

3.2

(81.3)

6.71 (170.3)

2.00

(50.8)

3.70

New Jersey:

New Mexico: Albuquerque

Use NOAA atlas for detailed

Roswell

state precipitation map.

Santa Fe

(94.0)

2.60

(66.0)

5.40 (137.2)

2.00

(50.8)

4.40 (111.8)

New York: Albany

9.12 (231.6)

6.24 (158.5)

2.50

(63.5)

6.48 (164.5)

Binghamton

8.82 (224.0)

5.72 (145.3)

2.4

(61.0)

6.34 (161.1)

Buffalo

8.40 (213.4)

5.34 (135.6)

2.30

(58.4)

5.97 (151.7)

Canton

8.10 (205.7)

5.24 (133.1)

2.25

(57.2)

5.84 (148.3)

Messena

7.86 (199.6)

5.20 (132.1)

2.25

(57.2)

5.61 (142.6)

New York

9.24 (234.7)

6.40 (162.6)

3.1

(78.7)

6.65 (168.9)

Oswego

8.28 (210.3)

5.50 (139.7)

2.20

(55.9)

5.81 (147.6)

Rochester

8.28 (210.3)

5.20 (132.1)

2.20

(55.9)

5.80 (147.3)

Syracuse

8.64 (219.5)

5.32 (135.1)

2.4

(61.0)

6.06 (154.0)

Asheville

9.60 (243.8)

6.84 (173.7)

3.2

(81.3)

6.99 (177.5)

Charlotte

9.84 (249.9)

6.92 (175.8)

3.4

(86.4)

7.24 (183.9)

Greensboro

9.84 (249.9)

7.00 (177.8)

3.30

(83.8)

7.22 (183.4) (Continued)

North Carolina:

ASPE Data Book — Volume 2

76

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min.

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

Hatteras

9.36 (237.7)

6.88 (174.8)

4.15 (105.4)

7.07 (179.6)

Raleigh

9.84 (249.9)

7.28 (184.9)

4.0 (101.6)

7.29 (185.1)

Wilmington

9.48 (240.8)

7.36 (186.9)

4.4 (111.8)

7.14 (181.4)

Bismarck

9.84 (249.9)

6.40 (162.6)

2.7

(68.6)

6.57 (166.9)

Devil’s Lake

9.96 (253.0)

6.48 (164.6)

2.82

(71.6)

6.67 (169.5)

Williston

9.00 (228.6)

6.00 (152.4)

2.60

(66.0)

6.00 (152.5)

Cincinnati

9.30 (236.2)

6.52 (165.6)

2.8

(71.1)

6.79 (172.4)

Cleveland

8.76 (222.5)

5.92 (150.4)

2.4

(61.0)

6.31 (160.4)

Columbus

9.00 (228.6)

6.42 (163.1)

2.7

(68.6)

6.57 (166.9)

Steubenville

8.88 (225.6)

6.00 (152.4)

2.70

(68.6)

6.44 (163.7)

Toledo

8.94 (227.1)

6.04 (153.4)

2.6

(66.0)

6.46 (164.1)

Hooker

10.08 (256.0)

7.12 (180.8)

3.30

(83.8)

7.08 (180.0)

Oklahoma City

10.50 (266.7)

7.42 (188.5)

4.1

()

7.58 (192.6)

Tulsa

10.38 (263.7)

7.40 (188.0)

3.80

(96.5)

7.52 (190.9)

0.90

(22.9)

3.30

North Dakota:

Ohio:

Oklahoma:

Oregon: Baker

Use NOAA atlas for detailed

Portland

state precipitation map.

Roseburg

(83.8)

1.3

(33.0)

3.00

(76.2)

1.40

(35.6)

3.60

(91.4)

Pennsylvania: Bradford

8.64 (219.5)

5.60 (142.4)

2.50

(63.5)

6.11 (155.2)

Erie

8.64 (219.5)

5.68 (144.3)

2.4

(61.0)

6.14 (156.0)

Harrisburg

9.36 (237.7)

6.92 (175.8)

2.9

()

6.76 (171.8)

Philadelphia

9.36 (237.7)

6.88 (174.8)

3.2

(81.3)

6.76 (171.8)

Pittsburg

8.82 (224.0)

5.96 (151.4)

2.5

(63.5)

6.40 (162.6)

Reading

9.36 (237.7)

6.80 (172.7)

3.05

(77.5)

6.81 (172.9)

Scranton

9.12 (231.6)

6.20 (157.5)

2.8

(71.1)

6.56 (166.8)

2.50

(63.5)

5.70 (144.8)

Puerto Rico: San Juan

Use NOAA atlas for detailed state precipitation map.

Rhode Island: Block Island

8.16 (207.3)

5.54 (140.7)

2.75

(69.9)

Providence

7.80 (198.1)

5.40 (137.2)

2.9

()

5.90 (149.8) 5.64 (143.4) (Continued)

Chapter 4 — Storm-Drainage Systems

77

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min.

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

South Carolina: Charleston

9.36 (237.7)

7.48 (190.0)

4.1

()

7.24 (183.8)

Columbia

9.90 (251.5)

6.40 (162.6)

3.5

(88.9)

7.35 (186.6)

Greenville

9.84 (249.9)

7.36 (186.9)

3.3

(83.8)

7.17 (182.1)

10.02 (254.5)

7.08 (179.8)

3.30

(83.8)

6.82 (173.2)

9.90 (251.5)

6.80 (172.7)

3.10

(78.7)

6.69 (169.9)

South Dakota: Aberdeen Pierre Rapid City Yankton

9.84 (249.9)

6.36 (161.5)

2.7

(68.6)

6.51 (165.4)

10.44 (265.2)

7.28 (184.9)

3.62

(91.9)

7.25 (184.1)

9.84 (249.9)

7.00 (177.8)

3.50

(88.9)

7.32 (188.9)

Tennessee: Chattanooga Knoxville

9.00 (228.6)

6.60 (167.6)

3.1

(78.7)

6.66 (169.2)

Memphis

9.96 (253.0)

7.14 (181.4)

3.5

(88.9)

7.37 (187.3)

Nashville

9.84 (249.9)

6.92 (175.8)

3.0

(76.2)

7.10 (180.3)

Abilene

10.38 (263.7)

7.32 (185.9)

3.70

(94.0)

7.43 (188.7)

Amarillo

10.20 (259.1)

7.24 (183.9)

3.55

(90.2)

7.30 (185.4)

Austin

10.50 (266.7)

7.68 (195.1)

4.25 (108.0)

7.69 (195.3)

Brownsville

10.68 (271.3)

7.92 (201.2)

4.40 (111.8)

7.89 (200.4)

Texas:

Corpus Christi

10.68 (271.3)

8.00 (203.2)

4.6 (116.8)

7.92 (201.2)

Dallas

10.50 (266.7)

7.50 (190.5)

4.2 (106.7)

7.63 (193.8)

Del Rio

10.20 (259.1)

7.29 (185.1)

4.00 (101.6)

7.32 (186.0)

El Paso

6.60 (167.6)

5.60 (142.2)

2.0

(50.8)

4.57 (116.1)

10.50 (266.7)

7.50 (190.5)

3.90

(99.1)

7.60 (193.1)

Fort Worth Galveston

10.92 (277.4)

8.10 (205.7)

4.70 (119.4)

8.30 (210.7)

Houston

10.80 (274.3)

8.04 (204.2)

4.5 (114.3)

8.18 (207.8)

Palestine

10.44 (265.2)

7.60 (193.0)

4.00 (101.6)

7.79 (197.8)

Port Arthur

10.92 (277.4)

8.08 (205.2)

4.65 (118.1)

8.30 (210.7)

San Antonio

10.50 (266.7)

7.70 (195.6)

4.4 (111.8)

7.61 (193.2)

Tyler

10.38 (263.7)

7.52 (191.0)

3.90

(99.1)

7.76 (197.0)

Utah: Modena

Use NOAA atlas for detailed

1.50

(38.1)

3.80

(96.5)

Salt Lake City

state precipitation map.

1.30

(33.0)

3.40

(86.4)

Vermont: Brattleboro

8.40 (213.4)

5.88 (149.4)

2.40

(61.0)

6.02 (152.9)

Burlington

8.16 (207.3)

5.52 (140.2)

2.3

()

5.75 (146.0)

(Continued)

ASPE Data Book — Volume 2

78

Frequency and Duration of Storm

(Table 4-1 continued) 100-Yr., 5 Min. Rutland

100-Yr., 15-Min.

100-Yr., 60-Min.

10-Yr., 5-Min.

8.28 (210.3)

5.60 (142.2)

2.4

(61.0)

5.92 (150.4)

9.60 (243.8)

6.56 (166.6)

2.75

(69.9)

7.06 (179.3)

Virginia: Lynchburg Norfolk

9.54 (242.3)

7.20 (182.9)

4.0 (101.6)

7.11 (180.6)

Richmond

9.84 (249.9)

7.28 (184.9)

4.0 (101.6)

7.23 (183.6)

Winchester

9.48 (240.8)

6.68 (169.7)

2.75

(69.9)

6.88 (174.6)

Wytheville

9.30 (236.2)

6.50 (165.1)

3.25

(82.6)

6.76 (171.8)

North Head

1.00

(25.4)

2.80

(71.1)

Port Angeles

1.10

(27.9)

2.20

(55.9)

Washington:

Seattle

Use NOAA atlas for detailed

Spokane

state precipitation map.

Tacoma

1.0

(25.4)

2.20

(55.9)

1.00

(25.4)

3.10

(78.7)

1.00

(25.4)

2.80

(71.1)

Tatoosh Island

1.00

(25.4)

3.20

(81.3)

Walla Walla

1.00

(25.4)

2.70

(68.6)

Yakima

1.10

(27.9)

2.60

(66.0)

West Virginia: Charleston

9.00 (228.6)

6.34 (161.0)

2.9

()

6.57 (166.9)

Elkins

8.94 (227.1)

6.32 (160.5)

2.75

(69.9)

6.53 (165.8)

Parkersburg

9.06 (230.1)

6.34 (161.0)

2.75

(69.9)

6.62 (168.0)

Green Bay

9.00 (228.6)

6.12 (155.4)

2.5

(63.5)

6.42 (163.1)

LaCrosse

9.84 (249.9)

6.90 (175.3)

2.9

()

6.98 (177.2)

Madison

9.48 (240.8)

6.70 (170.2)

3.12

(79.2)

6.79 (172.4)

Wisconsin:

Milwaukee

9.12 (231.6)

6.48 (164.6)

2.7

(68.6)

6.60 (167.7)

Spooner

9.66 (245.4)

6.52 (165.6)

2.85

(72.4)

6.81 (172.9)

2.5

(63.5)

5.60 (142.2)

Wyoming: Cheyenne Lander

Use NOAA atlas for detailed

1.50

(38.1)

3.70

Sheridan

state precipitation map.

1.70

(43.2)

5.20 (132.1)

1.40

(35.6)

2.50

Yellowstone Park

(94.0) (63.5)

Sources: Table 4-1 is based on the National Oceanic and Atmospheric Administration Technical Memorandum NWS HYDRO-35, except for the 12 western states. NWS Technical Paper no. 25 was used for the following 12 western states: Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. The NOAA Atlas 2: Precipitation–Frequency Atlas of the Western United States (11 Volumes, 1973) should also be utilized in the design for the 12 western states.

Chapter 4 — Storm-Drainage Systems

secondary drainage system handling any overflow that may occur when heavier storms arise. These same codes may require that the secondary drainage systems be designed for the more stringent values, for when the primary drainage systems may be clogged. The Standard Plumbing Code, effective in 1990, requires that the primary drainage system be designed for a 100-year, 60-min rainfall frequency; also, the secondary drainage system must be designed for a 100-year, 15-min rainfall frequency. The two systems’ combined capacities would exceed the required capacity for a 100-year, 5-min storm. If a rainfall heavier than the design rainfall occurred, the two systems would work together to carry the increased load. An argument can be made for using the most conservative rainfall rates in the design of roof drainage systems. The shortcomings of underdesigned roof drainage systems have had dramatic results when roofs collapsed. The designer must weigh the liabilities of an under-designed drainage system against the economic benefit of maybe only one pipe size. In consideration for the safety of life and the protection of the owner’s property, use of the most conservative design may be appropriate.

Roof Drainage Coordination The building roof transfers the combined weight of live and dead loads to the supporting structure. The supporting structure may be constructed of steel, concrete, wood, or other materials. Live loads include snow, rain, wind, etc. Dead loads include HVAC units, roof drains, and the roof deck. Locating the roof drains should be a cooperative effort among the architect, the structural engineer, and the plumbing engineer. The architect is familiar with the building construction, parapets, walls, chase locations, available headroom for pipe runs, roof construction, and the waterproofing membrane. The structural engineer is familiar with the structural support layout, roof slopes, column orientation, footing sizes and depths, and the maximum allowable roof loading. The plumbing engineer can provide information concerning the maximum roof areas per drain, wall and column furring-out requirements, headroom requirements, ceiling space requirements, minimum footing depths, and the pos-

79

sible benefits of ponding. The plumbing engineer should also ensure that the drains are located in the low points of the roof to limit deflection— which could cause ponding and shifting of the roof low point—and located to minimize the horizontal piping runs. Drain location The first roof drain should not be farther than 50 ft (15.2 m) from the end of a valley, the maximum distance between drains should be 200 ft (61 m). With a roof slope of ¼ in./ft (21 mm/m) and a distance of 20 ft (6.1 m) from the roof high point to the roof drain, the depth of water at the drain would be approximately 5 in. (12.7 cm). The parapet wall scuppers would be set at 5 in. (12.7 cm) above the roof low point. A maximum weight at the drain that would be transmitted to the roof structural supports would be 26 psf (126.9 kg/m2) live load, which would exceed the capacity of a normal 20 psf (97.7 kg/m2) roof live load (30 psf [146.5 kg/ m2] live load in snow areas). The designer must closely coordinate the drainage system design with the roof structural design. All penetrations through the roof must be sealed watertight. Metal flashing, 18–24 in. (0.460.61 m) square or round, is often suggested around the roof drain because of the heavy wear and the likelihood that it will be a leakage problem area; it is usually placed between the roofing plies. This flashing may also be used to form a roof sump to collect the storm water prior to its entering the drain. (A square opening is easier to cut into the roof than a round opening.) Most codes require a minimum of two roof drains on roofs with areas less than 10,000 ft2 (929 m2), and four drains on roofs exceeding 10,000 ft2 (929 m2). Some codes allow a maximum roof area per drain of 10,000 ft2 (929 m2), but this may require that the drains and associated piping be excessively large. To control labor costs and avoid potential furring and footing depth problems with the piping, a maximum area of 5000 ft2 (465 m2)per drain and a maximum drain and leader size of 8 in. (203 mm) should be considered. The designer must be aware of the location of roof expansion joints. These joints may prohibit rainwater flow across the roof, thus dividing the roof into fixed drainage areas. At least two roof drains should be provided for each roof drainage area, no matter how small.

80

The roof drain should be a minimum of 12– 18 in. (0.30-0.61 m) from any parapet wall or other obstruction to allow for proper flashing. The drains should be located a minimum of 10 ft (3.05 m) from any building opening or air intake. The minimum roof drain size should be 2 in. (50.8 mm) for decks and 3 in. (76.2 mm) where leaves are possible. In selecting the size of the roof drain, all of the horizontal roof area from adjacent high points sloping to the drain must be taken into account. Adjacent surfaces The roof drain must also receive drainage of rainwater from other roof areas, such as penthouses, that dump onto the roof area being calculated and from the adjacent vertical walls that discharge onto the horizontal roof surface. Some codes require that 50% of all vertical wall areas be added to the horizontal roof area. Other codes use complex formulae for various wall configurations. These formulae are normally excessive for roof areas that have more than one vertical wall or multiple-story walls with runoff directed to the horizontal roof surface. Rain seldomly falls in a totally vertical direction. Depending on the wind conditions, the angle of rainfall could be as much as 60° to the vertical or more. The wind, particularly in high-rise buildings, can blow the rain off a vertical wall and away from the building surfaces.

ASPE Data Book — Volume 2

a terrace, used as a parking deck with heavy traffic, or used to retain rainwater to limit the effluent to the storm sewer system. Roof drains, other than for flat decks, should have strainers that extend a minimum of 4 in. (100 mm) above the roof surface immediately adjacent to the drain. Strainers for the roof drains shall have an available inlet area not less than 1½ times the area of the leader that serves the drain. Dome-type strainers are required to prevent the entrance of leaves, debris, birds, and small animals. Flat-deck strainers, for use on sun decks, promenades, and parking garages where regular maintenance may be expected, shall have an available inlet area not less than 2 times the area of the leader that serves the drain. Heel-proof strainers may be required if subjected to pedestrian traffic. The flashing ring is used to attach the roof waterproofing membrane to the drain body to maintain the watertight integrity of the roof. An underdeck clamp should be utilized for securing the drain to the metal or wood decking; poured concrete roofs do not require these clamps. Drain receivers should be used on drains for concrete

The height above a horizontal surface at which the wind removes more than 50% of the rainwater from the wall surfaces has not been determined. Further study is required before local codes can be contradicted; therefore, the local code concerning vertical wall contribution of rainwater to horizontal surfaces should be complied with as a minimum. Roof drain construction Standard roof drains have three basic parts: the strainer, the flashing ring with gravel stop, and the drain body or sump. The strainers may be cast-iron coated or polyethylene dome type (for use where leaves may be encountered) or flat type (for sunroofs, areaways, and parking decks). Standard roof drain construction is shown in Figure 4-3. The roof drain types for all the common roof types are depicted in Figure 4-4. When selecting the type of drain to be used, the engineer must know the roof construction and thickness. The roof may be flat or pitched, used to retain water for cooling purposes, have a sprinkler system for cooling purposes, used as

Figure 4-3

Typical Roof Drain

Source: Reprinted, by permission, from the Jay R. Smith catalog.

Chapter 4 — Storm-Drainage Systems

decks. Drains that may receive sand and grit should be provided with sediment buckets. Piping system design Once the rainfall rate has been determined, the drains must be selected and the piping system designed. Determining the rate of rainfall for a system’s design requires researching the requirements for the particular structure under consideration. Secondary (overflow) drainage systems are required on buildings with parapet walls–or any other construction around the perimeter of the roof that would entrap rainwater on the roof. Conventional roof drainage systems are designed to remove rainwater as rapidly as it falls on a roof. Example 4-1. For Greenville, South Carolina, for a 100-year return period with a 5-min duration, Table 4-1 shows a precipitation-frequency value of 9.84 in./h/ft2 (249.9 mm/h/ft2). If a roof area of 1850 ft2 (172 m2) per drain is used, the roof drain and vertical pipe section (roof drain leader or downspout) would be sized for a rainfall intensity of 9.84 in./h/ft2 × 1850 ft2 = 18,204 in./h (249.9 mm/h/ft2 × 172 m2 = 42 982.8 mm/ h). To convert in./h to gallons per minute (gpm), multiply by the value of 0.0104 gpm/in./h: 18,204 in./h × 0.0104 gpm/in./h = 189.3 gpm per drain. As seen in the engineering sheet for a 4-in. roof drain (Figure 4-5), the drain can handle varied flow rates depending on the developed head of water at the drain. If the purpose of the drain design is to drain the rainwater from the roof as quickly as it collects, the design must be capable of handling the peak flow rate with a low head of water at the drain. Therefore, the maximum flow rates per drain shown in Table 4-2 are to be considered conservative. After calculating the peak flow to the roof drains, refer to Table 4-2 for sizing the roof drains and the vertical pipe sections. The roof drain leader should be sized at least to match the roof drain connection. Round and rectangular leaders are shown. Rectangular leaders A rectangular leader, because of its four sides and corners, experiences a greater friction loss than the equivalent round leader, which diminishes its carrying capacity. To compensate for this increased friction loss, a rectangular leader should be at least 10% larger than a round leader to provide the same capacity. Table 4-2 has been adjusted to include the 10% increase for rectangular leaders. If the 10%

81

increase resulted in an unavailable rectangular size, the next larger stock size was shown. The ratio of width to depth of rectangular leaders should not exceed 3:1. Use Form 4-1, found in the Appendix at the end of this chapter, for project roof drain and vertical leader sizing calculations that can be maintained in the project files. Gutters and downspouts For sizing horizontal gutters, refer to Table 4-3. This table depicts semicircular gutters and the equivalent rectangular gutters. The method of selecting sizes is similar to that used for round and rectangular leaders. Gutters should be a minimum of 4 in. (100 mm) wide—the more the roof slope, the wider the gutter should be to prevent the rainwater from planing over the gutter without entering. The minimum slope the gutter should maintain is z in./ft (1.6 mm/m). Downspouts from the gutter should be sheet metal (which is less susceptible to freezing than nonmetal materials) to 5 ft (1.5 m) above grade and cast iron or ductile iron to the tie-in with the underground piping, as this type of piping is more resistant to damage. Downspouts should be a minimum size of 1¾ × 2¼ in. (44.4 × 57.2 mm) and should be a maximum of 75 ft (22.8 m) apart (the American Bridge Co. recommends 40 ft [12.2 m]). Outlets that dump onto grade on splashbacks or are indirectly tied to the underground piping may be provided with screens or strainers for filtering debris and sediment. For residential construction, 5½-in. (139.7-mm) minimum semicircular gutters should be used, and leaders/downspouts should be 3 or 4 in. (76.2 or 101.6 mm) round, or 2 × 3 in. (50.8 × 76.2 mm) or 2 × 4 in. (50.8 × 101.6 mm) rectangular. Piping coordination Any piping layout must be coordinated with the other trades that may be affected, such as architecture for furring-in the proper columns for vertical leaders (also known as conductors or downspouts)–and structural engineering for pipe support and footing depths. Other utilities, such as piping, ductwork, and conduit runs, may also be affected. If interior floor/hub drains, drains from lower roofs, clear-water wastes, or areaway drains are connected to the storm system inside the building (if allowed by the jurisdictional authority), the drains must connect at least 10 pipe diameters (10 ft [3.0 m] minimum) downstream of the

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82

(A)

(B)

(C)

Chapter 4 — Storm-Drainage Systems

83

(D)

(E)

(F) Figure 4-4 Typical Roof-Drain Installations: (A) Steel or Concrete Roof Deck with Insulation Tapered to the Drain; (B) Precast or Steel Substrate with an Inverted-Membrane Type Roof; (C) Parapet Drain in Poured Concrete Deck with Downspout Elbow; (D) Planting Area Drain in Raised Planter Box; (E) Indirect Waste for HVAC Equipment on Concrete Roof Deck; (F) Promenade Drain in Precast Deck with Synthetic Flooring and Underdeck Clamp. Source: Reprinted by permission of Tyler Pipe/The Wade Division, Tyler, Texas.

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84

Figure 4-5

4-In. (101-mm) Roof Drain Flow Chart

Source: Reprinted by permission of the Josam Company from the Design Engineering Sheet.

last offset fitting. Clear-water wastes should be properly trapped and vented (see Figure 4-6). Traps must be the same size as the horizontal drain to which they are connected and should be provided with 4-in. (102-mm) minimum, deepseal p-traps, or with water from trap primers or frequently used fixtures to maintain the trap seal for drains not receiving water on a regular basis. Because of the excessive pressure that may exist in the leader, a low-level drain may become the vent to relieve the pressure, blowing water and air from the drain. These drains are subject to backflow and should be provided with backwater valves and vented, or routed separately to tie to the system beyond the point of excess pressure. If backwater valves are used, they can cause the areas affected not to allow drainage and a

Figure 4-6 Clear-Water Waste Branches for Connection to Storm System Source: Reprinted, by permission, from The Illustrated National Plumbing Code Design Manual (Ballanco & Shumann 1987).

Chapter 4 — Storm-Drainage Systems

Table 4-2 Diameter of Leader, in. (mm) Dimensions of Leader, in. (mm) 2 (50.8) 2 × 2 (50.8 × 50.8) 1½ × 2½ (38.1 × 63.5) 2½ (63.5) 2½ × 2½ (63.5 × 63.5) 3 (76.2) 2 × 4 (50.8 × 101.6) 2½ × 3 (63.5 × 76.2) 4 (101.6) 3 × 4¼ (76.2 × 107.6) 3½ × 4 (88.9 × 101.6) 5 (127) 4 × 5 (101.6 × 127) 4½ × 4½ (114.3 × 114.3) 6 (152.4) 5 × 6 (127 × 152.4) 5½ × 5½ (139.7 × 139.7) 8 (203.2) 6 × 8 (152.4 × 203.2)

85

Sizes of Roof Drains and Vertical Pipes

Cross-Sectional Area, in.2 (cm2) 3.14 (20.3) 4.00 (25.8) 3.75 (24.2) 4.91 (31.7) 6.25 (40.3) 7.07 (45.6) 8.00 (51.6) 7.50 (48.4) 12.57 (81.1) 12.75 (82.3) 14.00 (90.3) 19.06 (123.0) 20.00 (129.0) 20.25 (130.6) 28.27 (183.4) 30.00 (193.5) 30.25 (195.2) 50.27 (324.3) 48.00 (309.7)

Water Contact Area, in.2 (cm2) 6.28 (40.5) 8.00 (51.6) 8.00 (51.6) 7.85 (50.6) 9.00 (58.1) 9.42 (60.8) 12.00 (77.4) 11.00 (71.0) 12.57 (81.1) 14.50 (93.6) 14.00 (90.3) 15.07 (97.2) 18.00 (116.1) 18.00 (116.1) 18.85 (121.6) 22.00 (141.9) 22.00 (141.9) 25.14 (162.2) 28.00 (180.6)

Maximum Discharge Capacity, gpm (L/s)a 30 (1.2) 30 (1.2) 30 (1.2) 54 (3.4) 54 (3.4) 92 (5.8) 92 (5.8) 92 (5.8) 192 (12.1) 192 (12.1) 192 (12.1) 360 (22.7) 360 (22.7) 360 (22.7) 563 (35.5) 563 (35.5) 563 (35.5) 1208 (76.2) 1208 (76.2)

a With approximately 1¾-in. (45-mm) head of water at the drain.

buildup of water may occur. Horizontal piping of clear-water wastes and vents should be sized as a sanitary drainage branch is. When such piping is tied to a leader, an upright wye should be utilized. Expansion Expansion and improper anchoring of the vertical pipe have caused roof drains to be pushed up above the roof deck, destroying the integrity of the roof waterproofing by tearing the flashing and the waterproofing membrane. This problem can be more apparent in high-rise buildings and buildings where the exposed leader is subjected to cold rainwater or melting snow and ice that enters piping at the ambient temperature of the building. An expansion joint at the roof drain or a horizontal section of the branch line should be provided to accommodate the movement of the leader without affecting the roof drain. See Figure 4-7. Insulation The horizontal section of pipe and the roof-drain body should be insulated, per cold water installations with a vapor barrier, to control condensation. See Figure 4-8. Low-temperature liquid flow in the piping will cause condensation to form on the outside of the piping, possibly causing stain damage to the ceil-

ings or, where exposed, drip marks on the flooring. Locating vertical leaders Locating the vertical leaders within the building has several advantages: convenience, safety, appearances, and freeze protection. However, leaders located on the exterior can be installed at a much lower cost and do not take up any valuable floor space. To keep the number of leaders to a minimum, the leaders may combine flows from more than one roof drain, from a roof drain and a lowerdeck drain, from a roof drain and clear-water wastes, or from any combination of the above. The engineer must include the additional flows when calculating the leader size. This method is especially beneficial in keeping the costs of highrise buildings contained. If the leaders are to be located at the building columns, the column footings must be dropped correspondingly to accommodate the elbow at the base of the leader (stack). The base elbow should be a long sweep bend to help alleviate any excess pressures in the downstream pipe, and the elbow should be properly supported. The elbow may rest directly on the column footing to act as a support (see Figure 4-8).

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86

A riser clamp should be provided at each floor line for support of the leader. Also a cleanout should be provided at the base of all stacks to allow the base elbow to be rodded out.

be protected by metal or concrete guards or recessed in the wall and constructed of a ferrous alloy pipe, such as cast iron, to 5 ft (1.5 m) above the paving or loading platforms.

If blockage occurs in the drainage system and backs up in the vertical leader, the piping system may be subjected to a head pressure that is greater than the joining system is designed for. To prevent joint failure, pressure pipe may be considered for the piping system. All exterior leaders that may be exposed to damage, such as occurs in parking or truck-loading areas, should

If an offset is 45° or less, the leader can be sized as a vertical pipe. If the offset is greater than 45°, the pipe must be sized as a horizontal pipe. To avoid stoppages due to leaves, ice, etc., the leader cannot be reduced in size in the direction of flow throughout its length. For example, an 8-in. (203-mm) horizontal line must

Table 4-3

Sizes of Semicircular and Equivalent Rectangular Gutters

Diameter of Gutter, in. (mm) Dimensions of Gutter, in. (mm)

Cross-Sectional Area, in.2 (mm2)

Water Contact, Area, in.2 (cm2)

Slope,a in./ft (mm/m)

Capacity, gpm (L/min)

3

(76.2)

3.53

(22.83)

4.70

(30.32)

z

(1.6)

—

3

(76.2)

3.53

(22.83)

4.70

(30.32)

8

(3.2)

—

1½ × 2½

(38.1 × 63.4)

3.75

(24.25)

5.50

(35.48)

¼

(6.4)

26

1½ × 2½

(38.1 × 63.5)

3.75

(24.25)

5.50

(35.48)

½ (12.7)

40

4

(101.6)

6.28

(40.61)

6.28

(40.52)

z

(1.6)

—

4

(101.6)

6.28

(40.61)

6.28

(40.52)

8

(3.2)

39

(146.25)

2¼ × 3

(57.2 × 76)

6.75

(43.65)

7.50

(48.50)

¼

(6.4)

55

(206.25)

2¼ × 3

(57.2 × 76)

6.75

(43.65)

7.50

(48.50)

½ (12.7)

87

(326.25)

5

(127)

9.82

(63.50)

7.85

(50.76)

z

(1.6)

—

5

(127)

9.82

(63.50)

7.85

(50.76)

8

(3.2)

74

(277.5)

4 × 2½

(101.6 × 63.4)

10.00

(64.67)

9.00

(58.20)

¼

(6.4)

106

(397.5)

3 × 3½

(76 × 88.9)

10.00

(64.67)

9.00

(58.20)

½ (12.7)

156

(585)

6

(152)

14.14

(91.44)

9.43

(60.9)

z

(1.6)

—

6

(152)

14.14

(91.44)

9.43

(60.9)

8

(3.2)

110

(97.5) (150)

(412.5)

3×5

(76 × 127)

15.00

(97.00)

11.00

(71.14)

¼

(6.4)

157

(588.75)

3×5

(76 × 127)

15.00

(97.00)

11.00

(71.14)

½ (12.7)

225

(843.75)

8

(203.2)

25.27 (163.42)

12.57

(81.29)

z

(1.6)

172

(645)

8

(203.2)

25.27 (163.42)

12.57

(81.29)

8

(3.2)

247

(926.25)

4½ × 6 (114.3 × 152.4)

27.00 (174.6)

15.00

(97.00)

¼

(6.4)

348 (1305)

4½ × 6 (114.3 × 152.4)

27.00 (174.6)

15.00

(97.00)

½ (12.7)

494 (1852.5)

10

(254)

39.77 (257.19)

15.70 (101.52)

z

(1.6)

331 (1241.25)

10

(254)

39.77 (257.19)

15.70 (101.52)

8

(3.2)

472 (1770)

5×8

(127 × 203.2)

40.00 (258.7)

18.00 (116.40)

¼

(6.4)

651 (2440.25)

4 × 10

(101.6 × 254)

40.00 (258.7)

18.00 (116.40)

½ (12.7)

1055 (3956.25)

Note: Figures are based on the Chezy Formula for Discharge of Circular Sewers, n = 0.013, and gutter flowing full. aMinimum velocity of 2 fps (0.6 m/s).

Chapter 4 — Storm-Drainage Systems

Figure 4-7

Typical Expansion Joint or Horizontal Offset

Source: Reprinted, by permission, from Plumbing Design and Installation Reference Guide (Hicks 1986).

Figure 4-8

Typical Roof Drain and Roof Leader

Source: Reprinted, by permission, from Cast Iron Soil Pipe and Fittings Engineering Manual (Cast-Iron Soil Pipe Institute 1976).

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tie to an 8-in. (203-mm) vertical leader, even if Table 4-2 requires a smaller size. Vertical leaders should be tied to the horizontal main with single-wye fittings; double-wye fittings should be avoided. Horizontal pipe sizing The horizontal piping should be sized to flow full under uniform flow conditions at the peak flow rate, as opposed to sanitary sewers, which are designed to flow ½ to Q full. A minimum velocity of 2 ft/s (fps) (0.61 m/s) should be maintained to properly scour the pipe of grit, sand, and debris. (Some authorities recommend a minimum velocity of 3 fps [0.91 m/s] to keep the sediment in suspension.) The horizontal piping must be properly supported, with bell holes provided for underground bell-and-spigot piping. Use Form 4-2, in the Appendix at the end of this chapter, to calculate the storm-drain horizontal main size. Cleanouts should be provided at any change in direction exceeding 45° and at any change in pipe size, and to meet any applicable local code requirements for distances between cleanouts. The cleanouts should be extended up to grade or the floor above, or out to the wall face with a wall plate. The location of cleanout plugs above ceilings may cause damage to the ceiling when the pipe must be cleaned. Avoid running horizontal piping above the ceilings of computer rooms, kitchens, and foodpreparation areas. A pipe rupture above one of these areas could cause major damage and contamination. Piping under building slabs should be avoided if feasible; as pipe leaks could erode the fill below slabs and cause the slab to crack. Once the peak flow has been determined, the Manning Formula (Equation 4-3) should be used for sizing; refer to Table 4-4. Equation 4-3 1.486 × A × R.67 × S.5 Q = ‰ n  where Q =

Flow rate, ft3/s (m3/s)

A

=

Area, ft2 (m2)

R

=

Hydraulic radius of pipe = D/4, ft (m)

[D =

Diameter of pipe, ft (m)]

S

Hydraulic slope, ft/ft (m/m)

=

n

=

Coefficient of roughness, constant

The roughness coefficient of the pipe can be affected by age, corrosion, misalignment of the pipe, solid deposits in the pipe, and tree roots or other obstructions. Table 4-4 shows the types of pipe material that are available for each of the listed sizes. It also shows the various capacities of the piping at different slopes. The greater the slope is, the higher the capacity, but the greater the slope, the deeper the line and the more excavation required. This may cause significant problems when the engineer is trying to tie in to an existing storm sewer or “daylight” (i.e., discharge to the open atmosphere as opposed to into an underground pipe) to a ditch or canal. Secondary drainage systems may be either scuppers, which allow the entrapped rainwater to overflow the roof, or a separately piped drainage system to a separate point of discharge. Scuppers shall be sized in accordance with Table 4-5. The secondary piping system shall be designed similarly to the way the primary drainage system was designed. Some codes and designers prefer that the discharge from secondary drainage systems be readily noticeable, to ensure the prompt repair of the primary drainage systems. If the storm-drainage system receives continuous or intermittent flow from sump pumps, air-conditioning units, or similar devices, the flow should be added to the drainage system, either on the roof if the discharge is onto the roof, or in the piping if the discharge ties directly to the drainage system. After the system has been laid out and sized, the designer should review the proposed system to determine if revisions to the layout would improve the system from the standpoint of ease of installation, cost of materials and/or coordination with other trades. Controlled-flow storm-drainage system In lieu of sizing the storm-drainage system on the basis of the actual maximum projected roof areas, the roof drainage system (or a part of it) may be sized on the equivalent or adjusted projected roof areas that result from the controlled flow and the storage of storm water on the roof. Controlled-flow systems collect the rainwater on the roof and release the flow slowly to the drainage system. These systems can provide significant installation savings by requiring smaller roof drains, smaller diameter piping and smaller

Chapter 4 — Storm-Drainage Systems

Table 4-4

89

Pipe Sizing Chart

Slope Pipe Material

Discharge Capacity

Pipe Size, in. (mm)

in./ft (cm/m)

%

gpm (L/s)

Cast iron PVC-DWV Steel

2 (50) 2 (50) 2 (50)

¼ (25) ½ (50) 1 (100)

2.1 4.2 8.3

19 (1.199) 27 (1.703) 39 (2.460)

Cast iron Ductile iron PVC-DWV Steel

3 (80) 3 (80) 3 (80) 3 (80)

8 (12.5) ¼ (25) ½ (50) 1 (100)

1.0 2.1 4.2 8.3

40 (2.523) 57 (3.596) 81 (5.109) 114 (7.191)

Cast iron Ductile iron PVC-DWV Steel Concrete Vitrified clay

4 (100) 4 (100) 4 (100) 4 (100)

8 (12.5) ¼ (25) ½ (50) 1 (100)

1.0 2.1 4.2 8.3

Cast iron Ductile iron PVC-DWV Steel Concrete Vitrified clay

6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 6 (150)

z (6.3) 8 (12.5) x (18.8) ¼ (25) c (31.3) a (37.5) v (43.8) ½ (50) s (62.5) ¾ (75) d (87.5)

0.5 1.0 1.5 2.1 2.5 3.0 3.5 4.2 5.0 6.0 7.0

Cast iron Ductile iron PVC-DWV Steel Concrete Vitrified clay

8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200) 8 (200)

Cast iron Ductile iron PVC-DWV Steel Concrete Vitrified clay

10 (250) 10 (250) 10 (250) 10 (250) 10 (250) 10 (250) 10 (250) 10 (250) 10 (250) 10 (250)

Cast iron Ductile iron

12 (300) 12 (300)

z (6.3) 8 (12.5) x (18.8) ¼ (25) c (31.3) a (37.5) v (43.8) ½ (50) b (56.3)

z (6.3) 8 (12.5) x (18.8) ¼ (25) c (31.3) a (37.5) v (43.8)

0.2 0.4 0.5 0.8 1.0 1.5 2.1 2.5 3.0 3.5 4.2 4.5

cfs (L/s)

Velocity fps (m/s)

0.043 (1.217) 0.061 (1.726) 0.086 (2.434)

1.97 (0.591) 2.80 (0.840) 3.94 (1.182)

0.090 0.127 0.180 0.254

(2.547) (3.594) (5.094) (7.188)

1.83 2.59 3.67 5.17

(0.549) (0.867) (1.101) (1.551)

87 (5.488) 123 (7.759) 174 (10.976) 247 (15.581)

0.194 (5.490) 0.274 (7.754) 0.390 (11.037) 0.550 (15.565)

2.22 3.14 4.47 6.30

(0.666) (0.942) (1.341) (1.890)

178 (11.228) 257 (16.212) 309 (19.492) 363 (22.898) 398 (25.106) 436 (27.503) 471 (29.711) 514 (32.423) 563 (35.514) 617 (38.920) 666 (42.011)

0.397 0.572 0.687 0.808 0.887 0.972 1.050 1.145 1.255 1.375 1.485

(10.726) (16.188) (19.442) (22.866) (25.102) (27.508) (29.715) (32.404) (35.517) (38.913) (42.026)

2.02 2.91 3.50 4.11 4.52 4.95 5.35 5.83 6.39 7.00 7.56

(0.606) (0.873) (1.050) (1.233) (1.356) (1.485) (1.605) (1.749) (1.917) (2.100) (2.268)

0.541 0.765 0.937 1.082 1.234 1.481 1.742 1.912 2.095 2.263 2.467 2.566

(15.291) (21.650) (26.517) (30.621) (34.922) (41.912) (49.299) (54.110) (59.289) (64.043) (69.816) (72.618)

1.55 2.19 2.68 3.10 3.53 4.24 4.99 5.48 6.00 6.48 7.06 7.35

(0.465) (0.657) (0.804) (0.930) (1.059) (1.272) (1.497) (1.644) (1.800) (1.944) (2.118) (2.205)

1.80 2.53 3.12 3.59 4.09 4.91 5.78 6.34 6.95 7.50

(0.540) (0.759) (0.936) (1.077) (1.227) (1.473) (1.734) (1.902) (2.085) (2.250)

243 343 420 485 554 665 782 858 940 1,015 1,107 1,152

(15.328) (21.636) (26.494) (30.594) (34.946) (41.948) (49.329) (54.123) (59.295) (64.026) (69.830) (72.668)

0.2 0.4 0.5 0.8 1.0 1.5 2.1 2.5 3.0 3.5

439 (27.692) 621 (39.173) 761 (48.004) 879 (55.447) 1,002 (63.206) 1,203 (75.885) 1,414 (89.195) 1,553 (97.963) 1,701 (107.299) 1,837 (115.878)

0.980 (27.751) 1.380 (39.054) 1.700 (48.110) 1.960 (55.468) 2.230 (63.109) 2.680 (75.844) 3.150 (89.145) 3.460 (97.918) 3.790 (107.257) 4.090 (115.747)

0.2 0.4

715 (45.102) 1,012 (63.837)

1.590 (44.997) 2.250 (63.675)

2.02 (0.606) 2.86 (0.600)

(Continued)

ASPE Data Book — Volume 2

90

(Table 4-4 continued) Pipe Material

PVC-DWV Steel Concrete Vitrified clay

Ductile iron PVC-DWV Steel

Cast iron Ductile iron Concrete Vitrified clay

Ductile iron PVC-DWV Steel

Slope Pipe Size, in. (mm)

12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 12 (300) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 14 (350) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 15 (375) 16 (400) 16 (400) 16 (400) 16 (400) 16 (400)

in./ft (cm/m)

z (6.3) 8 (12.5)

¼ (25)

z (6.3)

8 (12.5)

x (18.8)

z (6.3)

8 (12.5)

x (18.8)

z (6.3)

Discharge Capacity %

gpm (L/s)

cfs (L/s)

Velocity fps (m/s)

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.1 2.2 2.4

1,239 (78.156) 1,431 (90.267) 1,632 (102.947) 1,752 (110.516) 1,893 (119.410) 2,024 (127.674) 2,146 (135.370) 2,304 (145.336) 2,373 (149.689) 2,478 (156.312)

2.760 (78.108) 3.190 (90.277) 3.640 (103.012) 3.900 (110.370) 4.220 (119.426) 4.510 (127.633) 4.780 (135.274) 5.130 (145.179) 5.290 (149.707) 5.520 (156.216)

3.51 4.06 4.63 4.97 5.37 5.74 6.09 6.53 6.74 7.03

(1.053) (1.218) (1.389) (1.491) (1.611) (1.722) (1.827) (1.959) (2.022) (2.109)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

760 (47.941) 1,074 (67.748) 1,316 (83.013) 1,519 (95.819) 1,699 (107.173) 1,861 (117.392) 2,010 (126.791) 2,149 (135.559) 2,279 (143.759) 2,450 (154.546) 2,519 (158.899) 2,631 (165.963) 2,739 (172.776) 2,842 (179.273) 2,942 (185.581) 3,039 (191.700) 3,132 (197.567)

1.690 (47.827) 2.390 (67.637) 2.930 (82.919) 3.380 (95.654) 3.780 (106.974) 4.150 (117.445) 4.480 (126.784) 4.790 (135.557) 5.080 (143.764) 5.460 (154.518) 5.610 (158.763) 5.860 (165.838) 6.100 (172.630) 6.330 (179.139) 6.560 (185.648) 6.770 (191.591) 6.980 (197.534)

1.58 2.24 2.74 3.16 3.54 3.88 4.19 4.48 4.75 5.11 5.25 5.48 5.71 5.92 6.14 6.33 6.53

(0.474) (0.672) (0.822) (0.948) (1.062) (1.164) (1.257) (1.344) (1.425) (1.533) (1.575) (1.644) (1.713) (1.776) (1.842) (1.899) (1.959)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

918 (57.907) 1,298 (81.878) 1,590 (100.297) 1,835 (115.752) 2,052 (129.440) 2,248 (141.804) 2,428 (153.158) 2,596 (163.756) 2,753 (173.659) 2,960 (186.717) 3,044 (192.016) 3,179 (200.531) 3,309 (208.732) 3,434 (216.617) 3,554 (224.186) 3,671 (231.567) 3,784 (238.695)

2.040 (57.766) 2.890 (81.787) 3.540 (100.182) 4.090 (115.747) 4.570 (129.331) 5.010 (141.783) 5.410 (153.103) 5.780 (163.574) 6.130 (173.479) 6.600 (186.780) 6.780 (191.874) 7.080 (200.364) 7.370 (208.571) 7.650 (216.495) 7.920 (224.136) 8.180 (213.494) 8.430 (238.569)

1.66 2.36 2.89 3.33 3.72 4.08 4.41 4.71 5.00 5.38 5.53 5.77 6.01 6.23 6.45 6.67 6.87

(0.498) (0.708) (0.867) (0.999) (1.116) (1.224) (1.323) (1.413) (1.500) (1.614) (1.659) (1.731) (1.803) (1.869) (1.935) (2.001) (2.061)

0.1 0.2 0.3 0.4 0.5

1,049 (66.171) 1,484 (93.611) 1,817 (114.616) 2,099 (132.405) 2,346 (147.986)

2.340 (66.222) 3.310 (93.673) 4.050 (114.615) 4.680 (132.444) 5.230 (148.009)

1.66 2.35 2.87 3.32 3.71

(0.498) (0.705) (0.861) (0.996) (1.113)

(Continued)

Chapter 4 — Storm-Drainage Systems

(Table 4-4 continued) Pipe Material

Slope Pipe Size, in. (mm)

16 16 16 16 16 16 16 16 16 16 Ductile iron Steel Concrete Vitrified clay

Ductile iron Steel

Concrete Vitrified clay

Ductile iron Steel Concrete

91

(400) (400) (400) (400) (400) (400) (400) (400) (400) (400)

18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 18 (450) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 20 (500) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 21 (520) 24 (600) 24 (600) 24 (600)

in./ft (cm/m)

8 (12.5)

x (18.8)

z (6.3)

8 (12.5)

z (6.3)

8 (12.5)

z (6.3)

8 (12.5)

Discharge Capacity %

gpm (L/s)

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

2,570 2,776 2,968 3,148 3,385 3,480 3,635 3,783 3,926 4,064

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

(162.116) (175.110) (187.221) (198.576) (213.526) (219.518) (229.296) (238.632) (247.652) (256.357)

cfs (L/s)

5.730 6.190 6.610 7.010 7.540 7.750 8.100 8.430 8.750 9.050

Velocity fps (m/s)

(162.159) (175.177) (187.063) (198.383) (213.382) (219.325) (229.230) (238.569) (247.625) (256.115)

4.06 4.39 4.69 4.97 5.35 5.50 5.74 5.98 6.21 6.42

(1.218) (1.317) (1.407) (1.491) (1.605) (1.650) (1.722) (1.794) (1.863) (1.957)

1,486 (93.737) 2,101 (132.531) 2,574 (162.368) 2,972 (187.474) 3,322 (209.552) 3,640 (229.611) 3,931 (247.967) 4,203 (265.125) 4,458 (281.211) 4,793 (302.342) 4,928 (310.858) 5,147 (324.673) 5,357 (337.920) 5,560 (350.725)

3.310 (93.673) 4.680 (132.444) 5.730 (162.159) 6.620 (187.346) 7.400 (209.420) 8.110 (229.513) 8.760 (247.908) 9.360 (264.888) 9.930 (281.019) 10.680 (302.244) 10.980 (310.734) 11.470 (324.601) 11.940 (337.902) 12.390 (350.637)

1.87 2.65 3.24 3.75 4.19 4.59 4.96 5.30 5.62 6.04 6.21 6.49 6.76 7.01

(0.561) (0.795) (0.972) (1.125) (1.257) (1.377) (1.488) (1.590) (1.686) (1.812) (1.863) (1.947) (2.028) (2.103)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

1,971 2,787 3,414 3,942 4,407 4,828 5,215 5,575 5,913 6,357 6,537 6,828

(124.331) (175.804) (215.355) (248.661) (277.994) (304.550) (328.962) (351.671) (372.992) (401.000) (412.354) (430.710)

4.390 6.210 7.610 8.780 9.820 10.760 11.620 12.420 13.170 14.160 14.560 15.210

(124.237) (175.743) (215.363) (248.474) (277.906) (304.508) (328.846) (351.486) (372.711) (400.728) (412.048) (430.443)

2.01 2.85 3.49 4.03 4.50 4.93 5.33 5.69 6.04 6.49 6.68 6.97

(0.603) (0.855) (1.064) (1.209) (1.350) (1.479) (1.599) (1.707) (1.812) (1.947) (2.004) (2.091)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

2,242 3,171 3,884 4,485 5,014 5,493 5,933 6,343 6,727 7,233 7,437

(141.425) (200.027) (245.042) (282.914) (316.283) (346.498) (374.254) (400.116) (424.339) (456.258) (469.126)

5.000 7.070 8.650 9.990 11.170 12.240 13.220 14.130 14.990 16.120 16.570

(141.500) (200.081) (244.795) (282.717) (316.111) (346.392) (374.126) (399.879) (424.217) (456.468) (469.210)

2.08 2.94 3.60 4.15 4.64 5.09 5.50 5.88 6.23 6.70 6.89

(0.624) (0.882) (1.080) (1.245) (1.392) (1.527) (1.650) (1.764) (1.869) (2.010) (2.067)

0.05 0.1 0.2

2,265 (142.876) 3,204 (202.108) 4,531 (285.815)

5.040 (142.632) 7.140 (202.062) 10.090 (285.547)

1.60 (0.480) 2.27 (0.681) 3.21 (0.963)

(Continued)

ASPE Data Book — Volume 2

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(Table 4-4 continued) Pipe Material

Vitrified clay

Concrete

Ductile iron Steel Concrete Vitrified clay

Concrete Vitrified clay

Ductile iron Steel Concrete Vitrified clay

Slope Pipe Size, in. (mm)

24 24 24 24 24 24

(600) (600) (600) (600) (600) (600)

27 (685) 27 (685) 27 (685) 27 (685) 27 (685) 27 (685) 27 (685) 27 (685) 30 (760) 30 (760) 30 (760) 30 (760) 30 (760) 30 (760) 30 (760) 33 (840) 33 (840) 33 (840) 33 (840) 33 (840) 33 (840) 33 (840) 36 (915) 36 (915) 36 (915) 36 (915) 36 (915) 36 (915)

in./ft (cm/m)

z (6.3)

z (6.3)

z (6.3)

z (6.3)

z (6.3)

Discharge Capacity %

gpm (L/s)

cfs (L/s)

Velocity fps (m/s)

0.3 0.4 0.5 0.6 0.7 0.8

5,549 6,408 7,164 7,848 8,477 9,062

(350.031) (404.217) (451.905) (495.052) (534.729) (571.631)

12.360 14.280 15.960 17.480 18.890 20.190

(349.788) (404.124) (451.668) (494.684) (534.587) (571.377)

3.93 (1.179) 4.54 (1.362) 5.08 (1.524) 5.56 (1.668) 6.01 (1.803) 6.43 1.929)

0.05 0.1 0.2 0.3 0.4 0.5 0.6 0.7

3,102 4,387 6,204 7,599 8,774 9,810 10,746 11,607

(195.674) (276.732) (391.348) (749.345) (553.464) (618.815) (677.858) (732.170)

6.910 9.770 13.820 16.930 19.550 21.860 23.940 25.860

(195.553) (276.491) (391.106) (479.119) (553.265) (618.638) (677.502) (731.838)

1.74 2.46 3.48 4.26 4.92 5.50 6.02 6.50

(0.522) (0.738) (1.044) (1.278) (1.476) (1.650) (1.806) (1.950)

0.05 0.1 0.2 0.3 0.4 0.5 0.6

4,111 5,813 8,221 10,069 11,626 12,999 14,239

(259.322) (366.684) (518.581) (635.153) (733.368) (819.977) (898.196)

9.160 12.950 18.320 22.430 25.900 28.960 31.730

(259.228) (366.485) (518.456) (634.769) (732.970) (819.568) (897.959)

1.87 2.64 3.73 4.57 5.28 5.90 6.46

(0.561) (0.792) (1.119) (1.371) (1.584) (1.770) (1.938)

0.05 5,302 (334.450) 0.1 7,498 (472.974) 0.2 10,603 (668.837) 0.3 12,986 (819.157) 0.4 14,995 (945.885) 0.5 16,765 (1057.536) 0.6 18,365 (1158.464)

11.810 (334.223) 16.700 (472.610) 23.620 (668.446) 28.930 (818.719) 33.410 (945.503) 37.350 (1057.005) 40.920 (1158.036)

1.99 2.81 3.98 4.87 5.62 6.29 6.89

(0.597) (0.843) (1.194) (1.461) (1.686) (1.887) (2.067)

0.05 6,688 (421.879) 0.1 9,458 (596.611) 0.2 13,376 (843.758) 0.3 16,382 (1033.377) 0.4 18,917 (1193.284) 0.5 21,149 (1334.079)

14.900 (421.670) 21.070 (596.281) 29.800 (843.340) 36.500 (1032.950) 42.150 (1192.845) 47.120 (1333.496)

2.11 2.98 4.22 5.16 5.96 6.67

(0.633) (0.894) (1.266) (1.548) (1.788) (2.001)

Notes: 1. Calculations for the discharge of circular sewers are based on the Manning Formula: Q = 1.486 AR2/3 S1/2 η 2. Pipe capacities for sewers are based on an “η” value of 0.013. This may vary somewhat with depth of flow and with pipe materials as follows: Vitrified clay, concrete, unlined ductile iron η = 0.013 Cast iron, uncoated η = 0.015 Steel η = 0.012 PVC-DWV η = 0.009 Corrugated η = 0.024 3. Pipe capacities are based on the pipe flowing full. 4. Velocity of flow shall not be less than 2 fps (0.61 m/s).

Chapter 4 — Storm-Drainage Systems

Table 4-5

93

Sizes of Scuppers for Secondary Drainage Length, L, of Weir, in. (cm)

Head, H, in. (cm)

4 (10.2)

6 (15.2)

8 (20.3)

10 (25.4)

12 (30.5)

18 (45.7)

24 (61.0)

30 (76.2)

36 (91.4)

48 (121.9)

1 2

10.7 (0.7) 30.5 (1.9)

3 4

52.9 (3.3) 84.1 (5.3) 115.2 (7.3) 146.3 (9.2) 177.8 (11.2) 271.4 (17.1) 364.9 (23.0) 458.5 (28.9) 552.0 (34.8) 739.0 (46.6) 76.7 (4.8) 124.6 (7.9) 172.6 (10.9) 220.5 (13.9) 269.0 (17.0) 413.3 (26.1) 557.5 (35.2) 701.8 (44.3) 846.0 (53.4) 1135.0 (71.6)

6

123.3 (7.8) 211.4 (13.3) 299.5 (18.9) 387.5 (24.4) 476.5 (30.1) 741.1 (46.8) 1005.8 (63.5) 1270.4 (80.1) 1535.0 (96.8) 2067.5 (130.4)

Capacity, gpm (L/s) 17.4 (1.1) 47.5 (3.0)

23.4 (1.5) 64.4 (4.1)

29.3 (1.8) 81.4 (5.1)

35.4 (2.2) 53.4 (3.4) 71.5 (4.5) 89.5 (5.6) 107.5 (6.8) 143.7 (9.1) 98.5 (6.2) 149.4 (9.4) 200.3 (12.6) 251.1 (15.8) 302.0 (19.1) 404.0 (25.5)

Source: Reprinted by permission of the Ingersol-Rand Co.1981. 16th ed. Note: Calculations are based on the Francis Formula: Q = 3.33 (L – 0.2H) H1.5 where Q = Flow rate, ft3/s (m3/s) L = Length of scupper opening, ft (m) (Should be 4 to 8 times H.) H = Head on scupper, ft (m) (Measured 6 ft [1.83 m] back from opening.)

diameter storm sewers. These systems also help to alleviate flooding in overtaxed public storm sewers or drainage canals during heavy rainfalls. The impact on the sewage treatment plant for a combined storm/sanitary sewer is considerably lessened by the use of controlled-flow roof-drainage systems. Controlled-flow systems should not be used if the roof is used for functions precluding water storage, such as a sundeck or a parking level, or if not allowed by the authority having jurisdiction. Holding the water on the roof increases the structural costs and may require a different roofcovering material.

The flow-control devices must be acceptable to the administrative authority. Valves, orifices, or mechanical devices are not permitted to restrict or control flow. The roof drains are provided with weirs, which are either parabolic, adjustable rectangular, or triangular, and which act like small dams to control flow into the drains. For standard, controlled-flow roof-drain construction, see Figure 4-9. Certain roof-design details must be incorporated into the finished roof. The water depth on the roof must not exceed 3 in. (80 mm) on deadflat roofs and an average maximum depth of 3 in. (80 mm) for pitched roofs (6 in. [150 mm]

ASPE Data Book — Volume 2

94

maximum from the high point to the low point of the roof) during the storm. The depth of water must be representative of the depth over all the roof and must assume the primary drains are blocked. The drain-down time is the time, measured in hours, for the roof to completely drain after the storm has reached its maximum intensity and duration and has ceased. The drain-down time must be in accordance with the local code but should not exceed 24 hours (12– 17 hours maximum recommended). The flow-control device should be installed so that the rate of discharge of the water should not exceed the rate allowed. The roof design for controlled-flow roof drainage should be based on

a minimum of 30 lb/ft2 (psf) (1.44 kPa) loading to provide a safety factor above the 15.6 psf (0.75 kPa) represented by the 3-in. (76.2-mm) design depth of water. The roof should be level and 45° cants should be installed at any wall or parapet. The flashing should extend at least 6 in. (152.4 mm) above the roof level. Doors opening onto the roof must be provided with a curb at least 4 in. (101 mm) high. Flow-control devices should be protected by strainers and in no case should the roof surface in the vicinity of the drain be recessed to create a reservoir. Roof-drain manufacturers have done much research on engineering criteria and parameters regarding the head of water on the roof for the weir design in controlled-flow roof drains, and they have established suggested design procedures with flow capacities and charts. Secondary roof drainage is required in case the primary drains are blocked, as is discussed earlier in this chapter. Secondary drainage systems can reduce the savings potential of controlled-flow roof drainage systems. If scuppers are utilized, they should be placed ½ in. (12.7 mm) above the maximum designated head, 3½ in. (88.9 mm) above the roof level. One scupper, or secondary drain, should be provided for each roof drain.

Figure 4-9 Example of a Controlled-Flow Drain Source: Reprinted, by permission, from the Jay R. Smith catalog.

Chapter 4 — Storm-Drainage Systems

PART TWO: SITE DRAINAGE SYSTEM DESIGN General Design Considerations Part One of this chapter discussed general criteria that must be considered in the design of both roof and site drainage systems, including materials, rainfall rates, and pipe sizing. These general design considerations apply to Part Two also. The tables and figures used to illustrate the chapter are consecutive from Part One to Part Two.

Site Drainage When large areas with fewer drainage points– such as commercial or industrial sites, parking lots, highways, airports or whole cities–require storm drainage, the methods and tables found in most codes are not applicable. The solutions obtained using those methods would result in systems that are oversized for the flows involved and are far too large to be economically feasible.

95

applied to the surface, and it assumes that the runoff coefficient would remain constant. The Rational Method of storm-drainage design states that the peak discharge is approximately equal to the product of the area drained, the runoff coefficient, and the maximum rainfall intensity, or: Equation 4-4 Q = CIA where Q =

Rainfall runoff, ft3/s (m3/s)

C

=

Surface runoff, coefficient (dependent on the surface of the area drained)

I

=

Rainfall intensity, in./h (mm/h)

A

=

Drainage area, acres (m2)

Note: 1 acre = 43,560 ft2 (4047 m2)

The reason is that, in large systems, time is required for flows to peak at the inlets and accumulate in the piping system. Because of this time factor, the peak flow in the piping does not necessarily coincide with the peak rainfall. The design of large storm-drainage systems usually is the responsibility of the civil engineer; however, the applicable theories and principles are often used by the plumbing engineer.

The “runoff coefficient” is that portion of rain that falls on an area and flows off as free water and is not lost to infiltration into the soil, ponding in surface depressions, or evaporation (expressed as a decimal). Construction increases have increased the number of impervious surfaces, which also increases the quantity of runoff. Table 4-6 lists some values for the runoff coefficient as reported in the American Society of Civil Engineers’ Manual on the Design and Construction of Sanitary and Storm Sewers.

The rate of runoff from an area is influenced by many factors, such as:

The rate of runoff is hard to accurately evaluate and is impacted by the precipitation rate,

1. Intensity and duration of the rainfall. 2. Type, imperviousness, and moisture content of the soil.

Table 4-6 Some Values of the Rational Coefficient C

3. Slope of the surfaces. 4. Type and amount of vegetation. 5. Surface retention. 6. Temperature of the air, water, and soil.

The Rational Method of System Design The “Rational Method” is the most universally applied and recommended way of calculating runoff because it takes all these factors into account. This method assumes that, if rain were to fall on a totally impervious surface at a constant rate long enough, water would eventually run off of the surface at the same rate as it was

Surface Type

C Value

Bituminous streets Concrete streets Driveways, walks Roofs Lawns, sandy soil Flat, 2% Average, 2–7% Steep, 7% Lawns, heavy soil Flat, 2% Average, 2–7% Steep, 7% Unimproved areas

0.70–0.95 0.80–0.95 0.75–0.85 0.75–1.00 0.05–0.10 0.10–0.15 0.15–0.20 0.13–0.17 0.18–0.22 0.25–0.35 0.10–0.30

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surface composition and slope, duration of the precipitation, and the degree of saturation of the soil. The infiltration rate is much greater for loose sandy soils than for hard clay type soils. Once saturated, the soil will not absorb any more water, which causes greater runoff. The longer the duration of the precipitation and the steeper the slope of the ground, the lower are the rate of infiltration and the amount of water held in depressions. Most engineering designers make use of information reported in tabular or graphic form, inserting local conditions per their experience and practice. Most sites have various surface com-

Figure 4-10

positions. The runoff coefficient can be weighted and calculated as follows: Equation 4-5 Cw =

(A1 × C1) + (A2 × C2) + (A3 × C3) +...(An × Cn) A1 + A2 + A3 +...An

where Cw =

Surface runoff

A1 =

Drainage area, by surface type, ft2 (m2)

C1 =

Runoff coefficient, by surface type

Overland Flow Time

Chapter 4 — Storm-Drainage Systems

The weighted runoff coefficient must be recalculated for each drainage point because the variables may change. The time of concentration is the sum of the overland flow time plus the time of flow in the pipe above the section of the pipe being designed. The overland flow time is usually taken from a nomograph adapted from sources such as the Engineering Manual of the War Department. See Figure 4-10 for an example. Water travels faster across impervious surfaces, such as roofs or parking areas, than across absorbent surfaces such as grassy or wooded areas. Flow time in piping is usually determined by using the Manning Formula to find the velocity in the piping. If the velocity and the distance of flow are known, the time can be calculated. The time of concentration is needed to determine the rainfall intensity affecting the flow at that point in the system, a minimum of 10 min. In the application of the Rational Method, a rainfall intensity, I, must be used, which represents the average intensity of a storm of given frequency for the time of concentration, tc. The frequency chosen is largely a matter of economics. Factors related to the choice of a design frequency have already been discussed. Frequencies of 1 to 10 years are commonly used where residential areas are to be protected. For higher-

Figure 4-11

97

value districts, 10 to 20 years or higher return periods often are selected. Local conditions and practice normally dictate the selection of these design criteria. After tc and the rainfall frequency have been ascertained, the rainfall intensity, I, may be obtained from Table 4-1. For values different than those listed in Table 4-1, the rainfall intensity is usually obtained by making use of a set of rainfall intensity-duration-frequency curves for the area of design, such as those shown in Figure 4-11. The tributary area can be accurately measured from a site plan showing contours and noting that water can only flow from higher elevations to the drain inlet under consideration. The total tributary area may extend beyond property lines. Example 4-2 Calculate the storm-water runoff into one inlet from a tributary area having a grassy area of 0.5 acres, a pavement area of 0.5 acres, and a roof area of 0.2 acres, for a total area of 1.20 acres. The water must flow across 100 ft (30.5 m) of grassy area and across 100 ft (30.5 m) of pavement from the most remote point of the tributary area. The slope of the grass surface is 2%. The slope of the pavement is 1%. The design storm frequency is 20 years. The roof drains flow

Typical Intensity-Duration-Frequency Curves

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onto the grassy area at the most remote point of the tributary area. Solution The weighted coefficient of runoff for the entire area will be calculated using Equation 4-5. The time of concentration will then be determined. The runoff rate will then be calculated using the Rational Method Formula (Equation 4-4). Assume coefficients of runoff for the various portions of the tributary area to be as follows: grassy area = 0.15, pavement = 0.90, and the roof = 1.00. Therefore, the weighted runoff coefficient is: Cw =

(0.50 × 0.15) + (0.50 × 0.90) + (0.20 × 1.00) 0.50 + 0.50 + 0.20

Cw =

0.725 = 0.60 1.20

Time of concentration Distance—Inlet to Most Remote Point, ft (m) Grass Pavement Roof Total

Time for Overland Flow (min)

100 (30.5) 100 (30.5)

15 3

—

5 23

Rainfall intensity Using Figure 4-11 and entering the bottom of the graph at a time concentration of 23 min, and following the vertical axis of the graph to where the vertical line intersects the 20-year frequency curve then horizontally to the left, a rainfall intensity of approximately 5.1 in./h (129.5 mm/h) is obtained. Runoff The runoff from this tributary area is calculated using the Rational Method Formula (Equation 4-4): Q =

0.60 × 5.1 × 43,560 = 3.1 ft3/s 3600 × 12

Q = ‰

0.60 × 129.5 × 4047 = 0.9 m3/s  3600 × 1000

Exterior Piping and Inlets The designer should obtain drawings of the public storm sewer available at the project site that depict materials, locations, sizes, and depths. The local authority should be contacted to ascertain

that the public storm system has the capacity for the projected flow. If the available capacity is not sufficient to handle the additional flow, either a controlled-flow roof drainage system or a retention basin, or both, may be required. The designer must coordinate the piping layout with other underground utilities. The pipe should have a minimum exterior size of 10 in. (254 mm) unless otherwise noted by the local code authority and should maintain a minimum velocity of 2–3 ft/s (fps) (0.61-0.91 m/s); maximum velocity should be 30 fps (9.1 m/s) to limit erosion of the pipe interior. Use Table 4-4 for sizing the exterior piping, this sizing is based on the Manning Formula. The flow rates from other inlets should be accumulated through the piping system. Use Form 4-3 (Sheets 1-3) in the Appendix at the end of this chapter for record keeping. The overland flow time to the first inlet must be added to the pipe flow time. The pipe flow time is determined by dividing the length of pipe between two points by the velocity of flow in the pipe. The size is controlled by either the existing storm sewer size or by the allowable slope. There are three basic inlets to the stormdrainage system: 1. Drainage inlets. Structures that admit storm water into the storm-drainage system, located in areas generally free of sediment or debris. Bottom is level with outlet pipe invert. 2. Catch basins. Similar to inlets except for space below the inlet and outlet pipes for retention of sediment. Located in paved areas; require good maintenance. 3. Manholes. Provide ease of access to pipe connections; use a drop manhole if there is a difference of 2 ft (0.61 m) or more between the inlet and the outlet. Catch basins should be provided at the inlet to drains, with strainer openings equal to at least twice the area of the drains. Use site contour lines to locate site low points; these areas must be provided with drains to prevent ponding. Parking area and street gutter drains should be openthroat, curb type drains and should be provided with hoods. Grate type inlets can become fouled, decreasing the capacity of the drain. Street inlets should be located upstream of flow at the intersection of streets and so that the maximum water depth at the curb is approximately Q the height of the curb and the width of water in the

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gutter does not exceed ½ the width of the adjacent driving lane.

proper traffic load, and have an impact slab if the storm water cascades 10 ft (3.1 m) or more.

Street gutters should use a roughness coefficient of 0.015. If trenches are utilized, the trenches must be wide enough for a drain of the proper size to connect to the trenches. Location of drain inlets should be done so as to avoid pedestrian crossing zones and to prevent water from crossing a street or sidewalk to reach the drain. Inlets should be in grassy areas to prevent water from flowing from the grassy area onto paved areas and especially to prevent water from freezing on the paved areas in colder climates. Further, they should be adjacent to buildings to ensure positive drainage away from the buildings. Inlet flow capacities should be limited to approximately 5 ft3/s (0.14 m3/s). The maximum distance between inlets should be 300 ft (91.4 m).

The layout of the piping system should attempt to keep excavation to a minimum by following the slope of the ground above the pipe and by limiting manhole depths to a maximum of 15 ft (4.6 m), if possible, by locating the manholes closer together. The layout should also attempt to avoid tree locations because of root problems, and piping below paving should be kept to a minimum. The layout should avoid railroad tracks. The exfiltration of water from bad joints and cracks in the pipe can erode the subgrade of roads or railways. When piping must cross a road or railway, joints with very little or no leakage should be selected and the strength of the pipe must be proper for the trench loads it will endure.

Culvert pipes are storm sewers that are usually open on both ends. They are commonly placed in a creek bed or ditch and used to transport storm water from one side of a road or embankment to the other side. Culvert inlets and outlets should be provided with head walls composed of straight walls for culverts less than 24 in. (0.61 m) in diameter and with wing walls for culverts greater than 24 in. (0.61 m) in diameter. Head walls tend to improve the hydraulic characteristics of the culvert and should be provided with vertical sloped bar strainers to reduce clogging. The culvert should be sized to pass the design flow rate without building up an excessive water depth on the upstream end of the culvert, a minimum of 15 in. (381 mm). The culvert design should provide reasonable freeboard to prevent the water from running over the road or embankment, yet it cannot allow the water to build up high enough to cause damage upstream of the culvert.

Subsurface Drainage The importance of subsurface water-conveying systems cannot be overemphasized. Each system is designed to solve a specific problem. Some systems are installed to prevent the earth from losing bearing resistance by water erosion of the soil, others to prevent uplifting of the building slabs by hydrostatic pressure. Another reason for installing subsurface drainage systems is to prevent the slab or walls below grade from becoming wet by capillary action if the ground water is too close to the slab. In each case, the objective of this type of system is to prevent subsurface water from rising above a predetermined elevation. Source of subsurface water The source of all subsurface water is rain, hail, snow, or sleet. Some precipitation finds its way to streams, rivers, lakes, and oceans by surface runoff. Much

Manholes should be provided for cleanout purposes on exterior piping at changes in direction, changes in pipe size, and changes in slope; at multiple pipe connections; and at intervals as required by the local code, but they should not be more than 250–500 ft (76.2-152.4 m) apart. Manholes should have a minimum opening of 24 in. (0.61 m) in diameter, have a 48-in. (1.22m) minimum base diameter, have a 1–3-in. (25.4– 76.2-mm) drop in invert across the base, be provided with cast-iron steps at 9 in. (228.6 mm) on center, have a cast-iron frame and cover for Figure 4-12 Sources of Subsurface Water

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of it seeps into the ground, percolates through the pores of the soil, and, eventually, spills into large surface bodies of water through underground passages or by becoming surface-borne again. See Figure 4-12. There are two basic types of subsurface water: 1. Perched water is a local accumulation that has seeped into the ground from previous rains and is trapped in small pockets by impervious substances, such as clay or rock. The water accumulates because these substances form a basin. Because perched water does not flow in the absence of rainfall, the upper surface of the water (called the water table) is approximately level and the absence of a constant inflow makes control of the water straightforward. Pumping will completely remove this water and local rainfall is necessary to replenish it. 2. Flowing water occurs when subsurface water passes from deposit to deposit by percolation (constant flowing water table). This body of water can be a small brook or a large river. The flow is constant in one direction. The top of the water table is never level because of the resistance of the soil to the flow of water. The quantity of water flowing is related to the rate of water overflowing the deposits, which, in turn, is related to the amount of percolation entering the deposits. During regional droughts, there may be no flow at all. Site investigation Economics and feasibility are the bases of all analytical studies. The location of a structure is accepted only after a survey has proven that it is both technically feasible and economically practical. The contours of the land have an important bearing on the amount of excavation and backfilling required. Underground conditions, such as rock and water, can also be deciding factors. Land contours and conditions above ground can easily be determined by direct observation; underground conditions are more difficult to ascertain and require special equipment and experience. The most common method of determining subsurface conditions is to bore a hole into the ground and record the texture and strata elevation of the various types of soil found. Borings can also reveal water-table elevations, the strength of the soils, and rock conditions. See Figure 4-13.

Figure 4-13 Borings Revealing the Nature of the Ground, Water Table Elevations, and Rock Conditions

While rock can be useful in providing a good bearing for the structure, its presence may be the one factor that prevents the use of the site due to excessive excavation costs. The soil may be of a texture that will not sustain the weight of the structure and piles may have to be driven. Also, ground water contributes to foundation problems. The level of the ground water may cause poor soil bearing values, and often a high ground-water table will necessitate costly pressure foundation slabs. Determining capacities of ground water Prior to designing drainage systems, it is necessary to determine the quantity of subsurface water that must be removed to lower the water table to a safe elevation. These tests are normally performed by a soils engineer or done at the request of the civil or structural engineer. As is common with the majority of hydraulic formulae and the methods devised to ascertain characteristics of fluids, determination of subsurface water quantities involves an educated guess. With all the necessary factors for various conditions that must be used in the formulae, it is improbable that an accurate answer will be attained. However, an answer that can be used with the assurance that it is the best available can be obtained by considering the information from the great number of tests conducted in the laboratory and in the field. Two factors are used to determine quantities of subsurface water: 1. Coefficient of permeability, or K factor, de-

Chapter 4 — Storm-Drainage Systems

fined as gallons (liters) of water per day through 1 square foot (0.09 m2) of soil, with an increasing head of 1 foot (0.3 m) every linear foot (0.3 m). See Figure 4-14. 2. Coefficient of transmissibility, or Q factor, defined as gallons (liters) of water per day through the entire area, with the actual increasing head every linear foot (0.3 m). Excavation prior to testing is considered the most accurate method for determining subsurface water flows, as the excavation largely eliminates the resistance of the soil to flow. This method can easily be the most expensive: when contractors are chosen before the design of the subsurface drainage system, the advantage of competitive bidding is lost. With Q directly determined, K can be estimated by using the following relationship, which will enable the design of the pipe and trench system (see also Figure 4-14). Equation 4-6 K =

velocity × 7.5 gal/ft3 slope

velocity × 1002.4 L/m3 K = slope ‰ 

101

Information derived from borings include texture and strata of soils, water, rock and samples of specimens encountered. Direction of the flow can be determined by the elevation of the water table in the various borings. Knowing the various strata and the texture of the soil, an average K factor can be determined. A cross-section sketch of the strata information obtained from the borings can be drawn and the area of each layer determined. Laboratory tests or published charts will indicate the K factor for each texture of soil, and the average K factor of the cross section can be obtained. If the table is flowing, it is important to choose the proper cross section in relation to the direction of flow. If the water is a deposit (not flowing), an average K for two cross sections, at right angles to each other, must be determined and the larger one used. The following industry standards for K factors are used: K Factors of Various Soil Textures, gal/day/ ft2/ ft of head/l ft (L/day/m2/m of head/l m) Clean gravel

100,000–1,000,000 (43 852 977–438 529 774)

Mixture, sand and gravel

100–10,000 (43 853–4 385 298)

Mixture, sand, silt, clay, fine sand

0.01–10 (4.38–4385)

Clay

0.0001–0.001 (0.044–0.438)

where Velocity = Q/area, ft2/day (m2/day) Slope = Head per length, ft/ft (m/m) The term “slope” refers to the hydraulic gradient in the soil. It is difficult to determine; for most purposes, however, the slope is 1.

It can readily be observed from the above table that the chance of error with this method is great. To eliminate as much error as possible, samples of the soils, taken during borings, should be taken to a laboratory to obtain the proper K factor. The possibility of error will then be limited to calculating an average K for the proper cross section of the site area. It must be realized that the K factor measures the capacity of the soil to conduct water not the actual amount flowing. The quantity of water infiltrating the soil may be less than K but is never more. Thus, the K factor is a safe criterion for use with the boring method. After the average K is determined, Q must be established. Figure 4-14 Cross Section Illustrating the Concept of the K Factor

Equation 4-7 Q = K × area × slope

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Q should not be modified to reflect local weather conditions because K reflects the peak flow possible. Drainage pipe Drainage pipe is rated according to its allowable infiltration rate, in gal/min/ in. of diameter/ft of length (L/s/mm of diameter/m of length). The total infiltration rate of the piping system must exceed Q. The selection of a piping system becomes a matter of economics, with due consideration given to subsoil conditions, cost of materials, and labor. The following piping systems are available for use as subsurface drainage systems: Open joint pipe This pipe uses a 4-in. (100 mm) minimum separation between the pipe sections. Care in the bedding of the pipe is required to prevent soil seepage into the piping. This pipe should be used when a large quantity of drainage is desired and the soil consists of relatively large particles. The infiltration rate of this material can be as high as 25,000 gal/day/ft2 of pipe surface/ft of head/l ft (10 962 500 L/day/m2/ m/l m), depending upon the opening of the joints. The amount of soil that can enter the open joint and, ultimately, render the system useless by clogging the pipe is great. To prevent washout, several layers of filter material, carefully graduated in size, must be installed between the base soil and the pipe. See Figure 4-15. Perforated pipe This is the most commonly used method; it provides good drainage capability

Figure 4-15 Open Joint Pipe Surrounded by Filter Material

ASPE Data Book — Volume 2

and allows less soil seepage. This pipe should be used where a large quantity of drainage is required and the soil is not too coarse. The allowable infiltration rate of this material ranges from 15,000 to 20,000 gal/day/ft2 of pipe surface/ft of head/l ft (6 577 500 to 8 770 000 L/day/m2/m/l m), depending upon the size of the perforations. Washout of base soil is also common with this method, and carefully chosen graduations of filter materials must be used. The pipe can be obtained with various size perforations and the filter material must be selected to satisfy the diameters of the perforations. See Figure 4-16. Porous pipe This pipe is the easiest of the three to clog. It is used when it is imperative that washout be prevented and the length of trenching is not a major consideration. The infiltration rate is 9000 to 10,000 gal/day/ft2 of pipe surface/ft of head/l ft (3 946 500 to 4 385 000 L/day/m2/ m/l m). A filter material is not necessary to prevent washout. The value of this piping material is its ability to prevent washout; however, its K factor may necessitate almost twice the length of trenching or pipe diameter used with others. Trenching The purpose of trenching is to permit ground water to be transmitted to the drainage piping with the least amount of resistance possible and to accommodate the filter material. The location of all drainage systems must be coordinated with the foundation/structural engineer and other underground utilities. It is important in the system design to give consideration to trench loading on the pipe, which requires proper bedding, backfill, and tamping. Refer to the Concrete Pipe Handbook by the American

Figure 4-16 Perforated Pipe in Trench

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103

Concrete Institute and Data Book, Volume 1, Chapter 2. To enable the greatest amount of water to flow into the piping, a filter material is placed between the pipe and the wall of the trench. If no filter material were installed between the pipe and the base soil material, the amount of water entering the pipe would be only as great as the amount of water coming through the soil adjacent to the pipe, which depends on the K factor of the soil. The amount of water filtering through 1 linear foot (0.3 m) of trench should be less than the amount of water 1 linear foot (0.3 m) of pipe can receive. The foundation drainage piping should be placed at the same elevation as the lowest floor and should be a minimum of 3 ft (0.9 m) from the foundation wall. The foundation drainage system should be placed on all sides of the building, or at least on all sides from which ground water is expected. A basic rule of spacing between trenches for below-slab drainage is that this distance should be no greater than twice the vertical distance of the adjacent trenches but should not exceed 10– 15 ft (3.0–4.5 m) on center. The more porous the soil, the farther apart and the deeper the trenches should be. The vertical distance is measured from the bottom of the pipe to the top of the filter material, normally a few inches (mm) to 18 in. (0.45 m) below the slab. This rule is designed to prevent the water table from rising above the elevation required for safety between the trenches. During trenching, care must be observed not to undermine the building footings. A “no-man zone” exists from the lower edge of a footing in a 45° angle (angle of repose) down and away from

Table 4-7 Filter Material

Figure 4-17 Pipe and Footing Locations

the footing (see Figure 4-17). To prevent undermining the footing, piping should not be placed within this zone—unless the foundation/structural engineer’s approval to do so is obtained. Filter materials The piping must be surrounded with gravel or another loose, non- absorbent material and should be backfilled with a similar material to at least 1 ft (0.3 m) below the pipe. Porous materials should be used above the pipe to direct ground water to the drain and should be extended up as close as possible to grade. Filter materials can be obtained in mixtures ranging from coarse gravel to fine sand and in any composition. With each mixture, a grain size curve can be developed to determine the general size of the mixture, at various percentages, by weight. The filter material must be tamped to reduce washout of the base material.

Size Ranges for Filter Material

Size Range, in. (mm) (1.–10.2) (1.3–7.6)

15% Size, in. (mm)

85% Size, in. (mm)

K factora

0.09 0.07

(2.3) (1.8)

0.25 (6.4) 0.20 (5.1)

29,000 (12.7) 18,000 (7.9)

Pea gravel Coarse sand

0.04–0.40 0.05–0.30

Fine sand and medium gravel Coarse sand and medium gravel

0.03–0.35 (0.8–8.9) 0.025–0.35 (0.6–8.9)

0.055 (1.4) 0.03 (0.8)

0.25 (6.4) 0.24 (6.1)

17,000 (7.5) 14,000 (6.1)

Concrete sand

0.03–0.30

0.05

0.20 (5.1)

10,000 (4.4)

(0.8–7.6)

aIn gal/day/ft2 of pipe surface/ft of head/l ft (L/day/m2/m/m x 106).

(1.3)

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Figure 4-18

Pipe in Trench with Dimensions of Filter Layers

For open-joint and perforated pipe, the filter material must be carefully selected to graduate from twice the size of the pipe openings to the fine size of the base material at the site. The thickness of each layer of filter material around the pipe and in the trench should be at least 4 in. (101.6 mm). It is sometimes used as the criterion of trench width, if the K factor of the soil does not require the width to be broader. See Figure 4-18. Table 4-7 includes some common filtering materials and their size ranges. Selecting pipe diameter Pipe diameter affects the functioning of the subsurface drain in two ways. First, there must be sufficient surface to permit the required infiltration, and second, the pipe must be large enough to convey the infiltrated water but not smaller than 4 in. (101.6 mm).

For example, assume a soil to have a K factor of 1000 gal/day/ft2 of pipe surface/ft of head/ l ft (438 500 L/day/m2/m/l m) and a trench with 8 ft2 of surface (sides and bottom)/l ft (0.74 m2/ 0.3 l m) of trench . Assuming a hydraulic slope of 1, the infiltration rate will be 8000 gal/day/ft (99345 L/day/m) of trench . Using a trial-and-error method of solution, assume a 4-in. (101.6-mm) pipe. The pipe surface is approximately 1 ft2/l ft (0.3 m2/l m) for a 4-in. (101.6-mm) porous pipe. Assume an infiltration capability of 10,000 gal/day/ft2/l ft of pipe (4 385 000 L/day/m2/l m), then the pipe infiltration rate will be 10,000 gal/day/l ft (4 385 000 L/day/l m) of pipe. This is greater than the required infiltration rate of 8000 gal/day/l ft (99 345 L/day/m). Now it must be determined whether this 4in. (101.6-mm) pipe is able to convey the water. In order to solve the problem, certain simplify-

Chapter 4 — Storm-Drainage Systems

ing assumptions must be made. In most cases, the drainage piping will be installed flat. However, water will flow in a flat pipe if the end of that pipe is open to atmospheric pressure. A conservative assumption is that the water acts as if the pipe had a slope of 0.01 ft/ft (0.01 m/m) or 1%. This enables the use of standard charts for the discharge of circular pipes based on the Manning formula. Such a pipe chart would show that at a 0.01 ft/ft (0.01) slope, a 4-in. (101.6mm) pipe will accommodate 150,000 gal/day (567 750 L/day). With an infiltration rate of 8000 gal/day/l ft (99 345 L/day/m), the 4-in. (101.6mm) pipe will be flowing full in 150,000/8000 or 20 ft (6.1 m). If the trench were 100 ft (30.5 m), requiring a capacity of 800,000 gal/day (3 028 000 L/day), then the chart would indicate that an 8-in. (203-mm) pipe would be required. Disposal of ground water Ground water very often becomes surface borne and a source of supply to streams, brooks, and rivers. If the natural flow of ground water is disrupted, a waterway, important to some individuals, may be deprived of its supply. After the contours of the land and the adjacent property are studied, the ground water may be directed to daylight, a stream, a ditch, or another natural waterway; or put back into the ground with diffusion wells, which may defeat the purpose of the drainage system. For many installations, it is neither feasible nor desirable to return the water into the ground. The effect of additional ground water on an adjacent structure may be deleterious. Discharge of subsurface water into municipal storm sewers requires permission from the authorities having jurisdiction. Storm sewers are often available and, if the capacity allows it, discharge into them is usually approved. It is a good practice to install a sediment pit to prevent washout material from entering municipal sewers and to provide an acceptable backwater valve in the discharge to the public storm sewer. If the subsoil drainage system is lower than the public storm sewer, pumping may be required. If the drainage must be pumped, the subsurface drainage pipe should terminate with a ¼ bend down into a sump (minimum 18 in. [0.45 m] diameter and 24 in. [0.6 m] deep) with the end submerged 3 in. (76.2 mm) or less. Venting of the sump is not required. The sump cover should be of proper traffic loading, flush with

105

the floor, and loose fitting, or, if used as an area drain, it can be open grating. The sump construction should be tile, plastic, fiberglass, steel, cast iron, concrete, or another approved material. The pump should be a duplex unit and, if considered critical, may require emergency power or a diesel backup pump. The capacity and head for the pump must meet the anticipated requirements. Subsurface water often contains sand and silt sediment. Pumps must be designed to accept some sediment, or damage to the pump components will occur. The pump head must be sufficient to lift the water from the low-water pump-off level in the pit (normally 6 in. [127 mm] above the sump bottom) to the necessary elevation to tie into the gravity storm main, plus make up for the friction losses in the pump discharge piping, including fittings and valves. A full-flow check valve is required in the pump discharge piping and an isolation valve should be provided for servicing the check valve. If the lift is 35–40 ft (10.7–12.2 m), the check valve should be the spring-loaded type. The discharge piping should be the same size as the pump connection, or larger to reduce the friction losses, and should be of galvanized steel with cast-iron, screwed fittings. An individual branch electrical circuit should be provided for the pump, with proper waterproof provisions. See Figure 4-19. Some subsoil drainage water can have offensive odors or can carry pollutants. Under these conditions, discharge to the sanitary sewer may be preferable, or required, and the sump may be required to be upright. However, directing the discharge to the sanitary sewer may overload the public sewer. The designed system should be reviewed by the jurisdictional authority.

Storm-Water Detention Within the drainage basins of streams with a history of flooding, along outfalls with limited capacities, and in areas where the discharge could cause overloading of the public storm sewer, the local authority may require an onsite storm water detention system with an established slow release rate as part of the drainage plan for a proposed development. A change in the use of a site, from a wooded or grassy area to a paved commercial or industrial area, causes a severe impact to natural waterways including a decrease in infiltration and

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Figure 4-19 Sump-Pump Discharge to the Storm-Drainage System

overland travel time and an increase in peak discharges and rainwater runoff. The increase in runoff also causes problems with soil erosion and sedimentation. Natural waterways are replaced or supplemented by paved gutters, storm sewers, channels with predetermined widths and depths, or other elements of artificial drainage.

undisturbed and developed conditions, and the rate of release from the site is limited to the runoff rate for the undisturbed conditions. The excess runoff created by the development must be detained with a storage system acceptable to the local authority, the owner, and the designer.

This urbanization causes higher peak flow rates, which necessitate that either the municipality install a drainage system with a higher capacity or the developer install a detention system. Because of the significant costs involved and ever-increasing development, improvement of the drainage systems may be impractical. Therefore, on-site detention systems are required in many instances.

The intent of a detention system is to minimize the discharge rate and consequent flooding by controlling the release rate. Rainwater can be held passively by shallow ponding in grassy strips of land, in parking areas if appropriate, and on the roofs of buildings (see the discussion in Part One of “Controlled-Flow Drainage System”). Water can also be held in the piping system by the installation of weirs or orifices at inlet points such as manholes, etc.

The theory of a detention system is that peak runoff rates for a site are determined for both

Three variables in the design require calculation:

Chapter 4 — Storm-Drainage Systems

1. Outflow from the basin (varies as a function of time). 2. Inflow to the basin (varies as a function of time). 3. Storage (the difference between items 1 and 2 above). There are basically two design approaches to the design of detention basins. The Rational Method should be utilized for sites that are less than 1 acre (4046.724 m2) (some designers use it for 10 acres [40,467.24 m2] or less), using a 10-year frequency design rainfall rate. For larger areas, the Soil Conservation Service (SCS) Technical Release Number 55 (TR-55) Method should be used for calculating runoff rates and storage capacity requirements.

107

Equation 4-9 Gravity outflow, Vo = 40 × Qo × T where Vo =

Outlet flow per acre imperviousness (based on the water level rising at a constant rate), ft3/s/acre (m3/s/ acre)

Qo =

Maximum outflow per acre imperviousness, ft3/s/acre (m3/s/acre)

T

Storage time, from time storage begins until the peak storage is attained, min

=

Equation 4-10 Allowable outflow acreage × runoff coefficient

The detention basin is installed at or below ground level, with the depth limited by either the invert of the public storm sewer that is being tied to or by the depth of the stream or ditch. A pond may be used in an area of the site that is less obtrusive. Detention basins may require paved overflow spillways and small-diameter dewatering drains. Trash guards should be provided on the outlet pipe(s) from the basin. Fences are often required around ponds and basins for security and the protection of the public.

Qo =

One problem with calculating the required storage is that the gravity outflow rate is dependent upon the amount and the depth of the water in the pond. The outflow changes instantaneously as the head varies, and the peak outflow only occurs when the basin is at peak volume. A constant outflow, such as that provided by a pump, is much easier to calculate: the storage is simply the inflow to the basin minus the pumped outflow.

Equation 4-12

Note: For runoff coefficient, see Table 4-6. Equation 4-11 T = −25 +

√ 6562.5 Q o

Once the outflow rate has been determined, the volume of storage required can be calculated, as follows:

Vs = Vn − Vo therefore Vs =

10,500T − 40 QoT T + 25

where Vs =

Maximum water volume stored per acre imperviousness, ft3/s/acre (m3/s/acre)

STANDARD EQUATIONS Equation 4-13 Equation 4-8 Gravity inflow, Vn =

Vt = Vs × A × C 10,500T T + 25

where Vt =

Maximum total water volume stored, ft3 (m3)

A

=

Area, acres

C

=

Runoff coefficient (see Table 4-6)

where Vn =

Inlet flow per acre imperviousness, ft3/s/acre (m3/s/acre)

T

Storage time, from time storage begins until the peak storage is attained, min

=

If the outlet is to be an orifice operating under a head, select a depth of retention and a corresponding outflow pipe that will yield an outflow

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108

in ft3/s (m3/s) equal to the maximum allowable operating condition under the head as determined by the depth of retention. Equation 4-14 Orifice area, A =

Q 0.62 × 2GH

where A

=

Area of outlet orifice or pipe, ft2 (m3)

Q =

Allowable outflow rate, ft3/s (m3/s)

G

=

Acceleration due to gravity = 32.2 ft/s2 (9.8 m/s2)

H

=

Head, distance of water level to centerline of the outflow pipe, ft (m).

If the outlet flow is constant, select a depth of retention and a pump that will yield an outflow in ft3/s (m3/s) equal to the maximum allowable. The constant outflow rate implies that the total outflow is the outflow rate multiplied by the duration of the storm. Equation 4-15 Pumped outflow, Vo = 60 QoT Once the pumped (constant) outflow rate has been determined, the volume of storage required can be calculated, as follows: Equation 4-16 Vs = Vn − Vo therefore Vs =

10,500T − 60 QoT T + 25

Equation 4-17 T = − 25 +

√ 4375 Q o

All systems should be permitted and should be submitted to the local authority for approval.

Chapter 4 — Storm-Drainage Systems

APPENDIX Form 4-1 Storm-Drainage Calculations for Roof Drains and Vertical Leaders

109

110

ASPE Data Book — Volume 2

Form 4-2 Storm-Drainage System Sizing Sheet

Chapter 4 — Storm-Drainage Systems

Form 4-3 Storm-Water Drainage Worksheet 1

111

112

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Form 4-3 Storm-Water Drainage Worksheet 2

Chapter 4 — Storm-Drainage Systems

Form 4-3 Storm-Water Drainage Worksheet 3

113

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114

REFERENCES 1.

American Concrete Institute. Concrete pipe handbook. Washington, DC.

2.

American Society of Civil Engineers. n.d. Manual on the design and construction of sanitary and storm sewers.

3.

Ballanco, Julius, and Eugene R. Shumann. 1987. The illustrated national plumbing code design manual. Ballanco and Shumann—Illustrated Plumbing Codes, Inc.

4.

Building Officials and Code Administration (BOCA). 1981. BOCA basic plumbing code.

5.

Cast-Iron Soil Pipe Institute. 1976. Cast-iron soil pipe and fittings engineering manual. Vol. 1. Washington, DC.

6.

Church, James C. 1979. Practical plumbing design guide. New York: McGraw-Hill.

7.

Frankel, Michael. 1981. Storm water retention methods. Plumbing Engineer March/April and May/June.

8.

Frederick, Ralph H., Vance A. Meyers, and Eugene P. Auciello. NOAA, National weather service 5-60 minute precipitation frequency for the eastern and central United States. NWS tech. memo. HYDRO-35. NTIS Publication PB-272 112. Silver Spring, MD: National Technical Information Service.

9.

Hicks, Tyler G., ed. 1986. Plumbing design and installation reference guide. New York: McGrawHill.

10. Manas, Vincent T. 1968. National plumbing code, illustrated. St. Petersburg, FL: Manas Publications. 11. Sansone, John R. 1978. Storm drainage design and detention using the rational method. Plumbing Engineer July/ August. 12. SBCCI. 1988. Standard plumbing code. Birmingham, AL. 13. Soil Conservation Service, Engineering Division. 1986. Urban hydrology for small watersheds. Technical release no. 55, June. NTIS publication PB87-101580. Silver Spring, MD: National Technical Information Service. 14. Steele, Alfred. 1982. Engineered plumbing design. Chicago: Delta Communications. (Now available through ASPE.) 15. Steele, Alfred. High-rise plumbing. Plumbing Engineer. Chicago: Delta Communications. 16. US War Department. Engineering manual of the War Department. Misc. publication no. 204. 17. US Department of the Army. Plumbing design manual no. 3.01.

18. Yrjanainen, Glen, and Alan W. Warren. 1973. A simple method for retention basin design. Water and Sewage Works December.

Chapter 5 — Cold-Water Systems

5 INTRODUCTION Proper design of a building’s water-distribution system is necessary so that the various fixtures function properly, that excessive pressure and pressure fluctuations are prevented, and that supply failure under normal conditions is avoided. The amount of cold water used in a building is a function of structure type, usage, occupancy, and time of day. It is necessary to provide the most economical pipe sizes to meet the peak demand without wasteful excess in piping or cost. There are at least five reasons why proper sizing of the piping in a water-distribution system is essential: 1. Health. This factor is of great importance. Inadequate sizing can cause negative pressures in a piping system and lead to contamination of the water supply by backflow or backsiphonage. 2. Pressure. If adequate residual pressure cannot be maintained at equipment and fixtures because of inadequate pipe sizing, improper operation will result. Excessive pressures will cause erosion and noise problems in the piping and accelerate deterioration of the seals in faucets. 3. Flow. If flow rates cannot be maintained at adequate levels because of inadequate pipe sizing, equipment performance will deteriorate. 4. Water service. Improper sizing can accelerate erosion, corrosion, and scale buildup. 5. Noise. High velocities cause noise and increase the danger of surge pressure shock.

115

Cold-Water Systems

(The accepted maximum velocity is 8 fps [2.4 m/s].)

DOMESTIC COLD-WATER METERS Many major municipalities furnish and/or install a particular type of water meter. In such locations, the meter characteristics (type, size, flow, pressure drops, remote readouts, costs, etc.) can be obtained through the local water department. Depending on the type of project being contemplated, a utility may request a particular meter (e.g., compound meter vs. turbine meter.) Whether a utility company’s meter or a meter from another source is used, the above-mentioned characteristics must be taken into consideration. The location of the meter is of prime importance. The meter shall not be subjected to freezing or submerged conditions. To discourage tapping of the piping ahead of the meter, it may be required that the meter be located directly inside the building wall. Some jurisdictions want the meter immediately adjacent to the tap to prevent illegal connections between the meter and the tap. Where job conditions mandate such a location, a meter in an outside pit or manhole should be watertight against both surface and ground-water conditions. A reduced-pressure backflow preventer is recommended at the building meter and is required by some codes and municipalities. Water meters for plumbing use are usually classified as the positive-displacement type, which indicate direct flow and record water passage in gal (L) or ft3 (m3).

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Meter Types

3. Water pressure available.

1. Disc meter. These meters are normally s, w, 1, 1½, and 2 in. (16, 19.1, 25, 40, and 50 mm) in size; are manufactured to meet the requirements of AWWA Standard C700; have a 150 psi (1034 kPa) maximum working pressure; and measure flow in one direction. This type of meter is common to residential and small commercial installations and is adaptable for remote readout systems.

4. Size of building service.

2. Compound meter. These meters are normally 2, 3, 4, and 6 in. (50, 80, 100, and 150 mm) in size; are manufactured to meet the requirements of AWWA Standard C700; have a 150 psi (1034 kPa) maximum working pressure; and measure flow in one direction. This type of meter is used when most of the flow is low but high flows are anticipated. It is capable of recording low flows and has the capacity for high flow rates. 3. Turbine meter. The sizes of this meter are 2, 3, 4, 6, and 10 in. (50, 80, 100, 150, and 250 mm). This type of meter has the characteristics of a compound meter but is more suitable for encountering a variety of flows. (A strainer should be installed upstream of the meter.) 4. Propeller meter. The sizes of this meter are 2–72 in. (51–1829 mm). Propeller meters are used where low flows never occur. 5. Fire-line meters or detector-check meters. This type of meter may be required by local codes in a water service that feeds a fire-protection sprinkler system or fire-hydrant system. In such a case, the installation must meet the requirements of the local fire official and the appropriate insurance company. The design should include a minimum of 8 pipe diameters of straight pipe upstream of the meter before any change in direction or connections. Various types of meter can be equipped with optional accessories. Remote-readout systems, strip-chart recorders, etc. are available for specific applications.

5. Piping, valve, meter, and elevation losses. 6. Meter costs and tap fees. 7. Maintenance costs and fees. Tables 5-1 to 5-3 from AWWA Standard M22 are reprinted as additional guidelines for water meters.

SIZING THE WATER LINE In practically all cases, water can be regarded as an incompressible fluid and, for calculations at approximately atmospheric temperature, it is customary to assume that water has a uniform density of 62.4 lb/ft3 (1 kg/L), which holds nearly constant through a temperature range of 32–60°F (0–15.6°C). For calculations involving water-heating systems such as boiler-feed pump discharge heads, it is necessary to take into account the changes in density, vapor pressure, and viscosity with temperature. Application of the common empirical equations for water flow is limited to water at usual atmospheric temperatures in the 32–l00°F (0–37.8°C) range. At higher temperatures, the changes in density and viscosity have a considerable bearing on flow relations; where accurate results are desired, use of the common empirical formulae is not recommended.

Hazen-Williams Formula Among the many empirical formulae for friction losses that have been proposed, the Hazen-Williams equation is the most widely used. In a convenient form, it reads as follows: Equation 5-1 100 1.85 q1.85  f = 0.2082  ‰ C  ‰ d4.8655  where f = Friction head, ft of liquid/100 ft

Sizing the Water Meter

of pipe (m/100 m)

The following design criteria may be used as a guide for selecting the proper meter:

C = Surface roughness constant

1. Building occupancy type.

d = Inside diameter of pipe, in. (mm)

2. Minimum and maximum demand.

q = Fluid flow, gpm (L/s)

Chapter 5 — Cold-Water Systems

Table 5-1

Size, in. (mm)

117

Displacement-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages

Maximum Capacity— AWWA Flow Criteria gpm (L/s)

psi (kPa)

Recommended Design Criteria—80% of Maximum Capacity gpm (L/s)

psi (kPa)

Recommended for Continuous Flow— 50% of Maximum Capacity gpm (L/s)

Brands of Meters Avgs.

psi (kPa)

s×w (16 × 19.1)

20 (1.26)

10.4 (71.76)

16 (1.00)

6.1 (42.19)

10 (0.63)

1.0 (6.9)

6

w (19.1)

30 (1.89)

10.6 (73.13)

24 (1.51)

6.9 (47.61)

15 (0.95)

1.05 (7.24)

6

1 (25.4)

50 (3.15)

9.3 (64.14)

40 (2.52)

6.3 (43.47)

25 (1.58)

1.0 (6.9)

6

1½ (38.1)

100 (6.30)

11.3 (77.10)

80 (5.05)

8.6 (59.34)

50 (3.15)

0.9 (6.21)

6

2 (50.8)

160 (10.08)

10.4 (71.76)

128 (8.08)

6.5 (44.85)

80 (5.04)

0.5 (3.45)

6

3 (76.2)

300 (18.93)

13.1 (90.39)

240 (15.14)

8.3 (57.27)

150 (9.46)

1.1 (7.59)

3

Source:AWWA Standard M22.

Table 5-2

Size in. (mm)

Compound-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages

Maximum Capacity— AWWA Flow Criteria

Recommended Design Criteria—80% of Maximum Capacity

gpm (L/s)

Brands of Meters Avgs.

gpm (L/s)

psi (kPa)

gpm (L/s)

2 (30)

160 (10.08)

9.2 (63.48)

128 (8.07)

6.1 (42.09)

80 (5.04)

2.6 (17.94)

3

3 (80)

320 (20.19)

13.4 (92.46)

250 (15.77)

8.9 (61.36)

160 (10.08)

4.2 (28.98)

5

4 (100)

500 (31.54)

9.6 (66.24)

400 (25.23)

6.3 (43.47)

250 (15.77)

3.5 (24.15)

5

6 (150)

1000 (63.09)

9.4 (64.86)

800 (50.46)

5.8 (40.02)

500 (31.54)

2.5 (17.25)

4

8 (203)

1600 (100.94)

1280 (80.75)

7.8 (53.82)

800 (50.46)

4.0 (27.60)

3

12.0 (82.8)

psi (kPa)

Recommended for Continuous Flow— 50% of Maximum Capacity psi (kPa)

Source:AWWA Standard M22.

Table 5-3

Size in. (mm)

Turbine-Type Meters Meeting AWWA Specifications— Flow-Pressure Loss Averages

Maximum Capacity— AWWA Flow Criteria gpm (L/s)

psi (kPa)

Recommended Design Criteria—80% of Maximum Capacity gpm (L/s)

psi (kPa)

Recommended for Continuous Flow— 50% of Maximum Capacity gpm (L/s)

Brands of Meters Avgs.

psi (kPa)

2 (50)

160 (10.08)

4.5 (31.05)

128 (7.57)

2.8 (19.32)

80 (5.04)

1.0 (6.9)

5

3 (80)

350 (22.37)

4.6 (31.74)

280 (17.66)

3.0 (20.69)

175 (11.04)

1.2 (8.3)

4

4 (100)

600 (37.85)

3.5 (24.15)

480 (30.28)

2.1 (14.5)

300 (18.93)

0.8 (5.5)

4

6 (150)

1250 (78.86)

3.5 (24.15)

1000 (69.09)

2.0 (13.8)

625 (39.43)

0.7 (4.9)

4

Source:AWWA Standard M22.

Figure 5-1

Friction Loss of Head Chart, Coefficient of Flow (C) = 140 (derived from the Hazen and Williams Formula)

118 ASPE Data Book — Volume 2

Figure 5-1 (M)

Friction Loss of Head Chart, Coefficient of flow (C) = 140 (derived from the Hazen and Williams Formula)

Chapter 5 — Cold-Water Systems 119

120

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Figure 5-2 Conversion of Fixture Units, fu, to gpm (L/s)

Chapter 5 — Cold-Water Systems

This formula is most accurate for the flow of water in pipes larger than 2 in. (5 cm) and at velocities less than 10 fps (3 m/s). Equation 5-1 yields accurate results only when the kinematic viscosity of the liquid is about 1.1 centistokes, which is the case of water at 60°F (15.6°C). However, the kinematic viscosity of water varies with temperature, from 1.8 centistokes at 32°F (0°C) to 0.29 centistokes at 212°F (100°C); therefore, the tables are subject to this error, which may increase the friction loss by as much as 20% at 32°F (0°C) and decrease it by as much as 20% at 212°F (100°C). Values of C, for various types of pipe, are shown in Table 5-4, together with the corresponding multipliers that should apply to the values of the head loss, f. Figure 5-1 shows the friction loss of head chart, C = 140, derived from the Hazen-Williams formula (Equation 5-1). Figure 5-2 illustrates the conversion of fixture units to gallons per minute (liters per second).

Factors Affecting Sizing The three factors affecting the sizing of a water line are the demand flow rate (gpm) (L/s), the velocity (fps) (m/s), and the pressure available for friction loss. Demand The first factor, flow rate, is the water demand of the system, in gpm (L/s). There is a vast difference in the water demand flow rates of flush valves in different types of occupancy. For example, ten water closets with flush valves in an apartment building may have a demand flow rate of 60 gpm (3.8 L/s), while ten water closets with flush valves in a public school may have a demand flow rate of 90 gpm (5.7 L/s). The judgment and experience of the designer plays an important part in accommodating such differences in the design of water systems. Another problem encountered in establishing flow rates is the practice of counting fixtures that are not normally in use. For example, a service sink in an office building is normally used only by the janitors at night; therefore, it should not be counted as a fixture in the total demand. Hose bibbs are other fixtures that should not be figured at 100% of their number. For example, the systems of large buildings may have many hose bibbs installed but only a few will be operated simultaneously. Individual branch lines should be sized to handle all the fixtures on the branch; however, the presence of these infre-

121

quently used fixtures should not be reflected in the total demand. After the designer has determined which fixtures to include in the water demand calculation, the maximum demand can be obtained. Fixture unit (fu) values for each fixture can be assigned by using Table 5-5 and a total fu value can be obtained by adding the fu values of all water-using fixtures with a normal domestic diversity. The total fu value can be converted into a gpm (L/s) flow rate by using Table 5-6 or Figures 5-2 or 5-3, each of which includes a diversity factor. The demand flow rates of all constant-use fixtures must be added to this flow rate. A constant-use fixture uses water continuously and does not have normal diversity. Air-conditioning cooling towers, booster pumps, commercial laundry or dishwashing equipment, lawn sprinklers, and industrial processes are examples of constant-use fixtures. Any such equipment must be figured separately and added to the gpm (L/s) flow rate obtained from the conversion of all fixture units. This combined figure is the peak demand flow rate for the project. (Note: Fixtures that are timed to operate during “off” hours should not be added.) The fixture-unit listings in Table 5-5 are for the total water consumption of the fixture. For the purposes of sizing either the hot or cold-water line, the fixture-unit loading for a fixture that uses both hot and cold water would be 75% of the total value. The 75% figure applies only to fixtures served by hot and cold water. It does not apply to single-service fixtures, such as water closets, urinals, and dishwashers. Velocity The second factor affecting the sizing of a water line is velocity. A maximum velocity of 15 fps (4.6 m/s), which is suggested by some model plumbing codes, is much too high for many installations. A velocity above 6 or 7 fps (1.8 or 2.1 m/s) normally creates noise. Also, depending on the piping material used and the temperature, hardness, and pH of the water, velocities above 4 fps (1.2 m/s) can cause erosion of the piping material. Another justification for lower velocities in a system is water hammer. Water hammer is the pounding force created by the sudden starting or stopping of water flow, which can be caused by quick-opening or closing valves. The impact of water hammer is directly proportional to the change in velocity and is equal to approximately 60 times the velocity change. For instance, if

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water traveling at 15 fps (4.6 m/s) is stopped suddenly, the increase in pressure within the pipe line will be approximately 900 psi (6205.3 kPa). This increased pressure can do considerable damage to piping systems and connected equipment.

sure. If the maximum pressure is above 80 psi, and a pressure-regulating device is installed, the pressure regulator will introduce an additional loss in the piping system when the water system is at minimum pressure. The water pressure should be determined from a fire-hydrant flow test, which is taken as close to the site as possible and includes static and residual pressures at a flow rate.

Pressure The third factor affecting the sizing of a water line is the pressure available for friction loss. The first step in ascertaining pressure available for friction loss is determining (from the local water department) the maximum and minimum water pressures and flow rate to be encountered at the project site. The maximum and minimum pressures may be nearly the same or they may vary greatly; care must be taken to handle the high pressure as well as the low pres-

Many model plumbing codes state that, if a pressure-regulating device is installed, the available pressure must be considered as 80% of the reduced pressure setting. Spring-operated, pressure-regulating devices have a fall-off pressure that is below the system pressure setting. Many engineers design a system incorporating the falloff pressure of the equipment they are using;

Table 5-4 Surface Roughness Coefficient (C) Values for Various Types of Pipe Values of C Range Average Value (High = Best, smooth, well-laid for Good, Low = Poor or corroded) Clean, New Pipe

Type of Pipe

Value Commonly Used for Design Purposes

Asbestos cement Fiber

160–140 —

150 150

140 140

Bitumastic-enamel-lined iron or steel centrifugally applied

160–130

148

140

Cement-lined iron or steel centrifugally applied Copper, brass, lead, tin or glass pipe and tubing

— 150–120

150 140

140 130

Wood stave Welded and seamless steel

145–110 150–80

120 140

110 100

—

139

100

Wrought iron Cast iron

150–80 150–80

130 130

100 100

Tar-coated cast iron Girth-riveted steel (projecting rivets in girth seams only) Concrete

145–80

130

100

— 152–85

130 120

100 100

Continuous-interior, riveted steel (no projecting rivets or joints)

Full-riveted steel (projecting rivets in girth and horizontal seams)

—

115

100

Vitrified clay Spiral-riveted steel (flow with lap)

— —

115 110

100 100

Spiral-riveted steel (flow against lap) Corrugated steel

— —

110 60

90 60

Value of C Multiplier to Correct Tables

150 0.47

140 0.54

130 0.62

120 0.71

110 0.84

100 1.0

90 1.22

80 1.50

70 1.93

60 2.57

Chapter 5 — Cold-Water Systems

123

Table 5-5 Demand Weight of Fixtures, in Fixture Unitsa Weight (fixture units)c Fixture Typeb Private Public Bathtubd

Minimum Connections, in. (mm) Cold Water

Hot Water

2

4

2 (13)

—

10

1 (25)

Bidet

2

4

2 (13)

2 (13)

Combination sink and tray

3

—

2 (13)

2 (13)

—

1

a (10)

Dental lavatory

1

2

2 (13)

Drinking fountain

1

2

a (10)

Kitchen sink

2

4

2 (13)

2 (13)

Lavatory

1

2

a (10)

a (10)

Laundry tray (1 or 2 compartments)

2

4

2 (13)

2 (13)

Shower, each headd

2

4

2 (13)

2 (13)

Sink, service

2

4

2 (13)

2 (13)

Urinal, pedestal

—

10

1 (25)

—

Urinal (wall lip)

—

5

2 (13)

—

Urinal stall

—

5

w (20)

—

Urinal with flush tank

—

3

Wash sink, circular or multiple (each set of faucets)

—

2

2 (13)

Flush valve

6

10

1 (25)

—

Tank

3

5

a (10)

—

Bedpan washer

Dental unit or cuspidor

—

2 (13) —

— 2 (13) —

—

2 (13)

Water closet:

a For supply outlets likely to impose continuous demands, esti-

mate the continuous supply separately and add to the total demand for fixtures. b For fixtures not listed, weights may be assumed by comparing the fixture to a listed one then using water in similar quantities and at similar rates. c The given weights are for the total demand of fixtures with both hot and cold-water supplies. The weights for maximum separate demands may be taken as 75% of the listed demand for the supply. d A shower over a bathtub does not add a fixture unit to the group.

however, the 80% factor is a rule of thumb that should not apply to an engineered system. If the available water pressure at a project site is high enough to require the use of a pressure-regulating device, the pressure-regulating valve is considered the starting point of the system for the purposes of calculation. The next step in obtaining the pressure available for friction loss is to determine the residual pressure required at the governing fixture or appliance (not necessarily the farthest fixture). “Residual pressure” is the pressure required at the fixture for it to operate properly with water flowing. Normally, but not always, 8 psi (55.2 kPa) is required for a flush-tank system and 15 psi (103.4 kPa) is required for a flush-valve system. Some flush-valve fixtures require 20 or 25 psi (137.9 or 172.4 kPa); some water closets require 40 psi (275.8 kPa); commercial dishwashers require 20 or 25 psi (137.9 or 172.4 kPa). It is evident, then, that the residual pressure should be figured as the actual pressure needed at the governing fixture. The third step is to determine the static pressure loss required to reach the governing fixture or appliance. The static loss (or gain) is figured at 0.433 psi/ft (9.8 kPa/m) of elevation difference, above or below the water main. The difference in elevation is usually a pressure loss to the system, as fixtures are normally at a higher elevation than the source. If the fixture is lower than the source, there will be an increase in pressure and the static pressure is added to the initial pressure. Another pressure loss is created by the water meter. This loss of pressure, for a disc type meter, can be determined from Figure 5-4 or from the manufacturer’s flow charts. The flow is determined from charts indicating the total flow rate, in gpm (L/s), the size and type of the meter, and the pressure drop for the corresponding flow. The loss is given in pounds per square inch (psi) and kilopascals (kPa). The selection of meter size is very important in the final sizing of the piping system and is one variable the designer can control. Many other factors, such as the height of the building, city water pressure, and requirements for backflow protection or water treatment, are dictated by codes or by the particular situation. The designer must review the system very closely prior to the selection of a meter size. Usually, the larger the meter, the higher the initial installation price and monthly charge. On the

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Table 5-6 Conversions—Gallons per Minute (Liters per Second) to Fixture Units Flow, gpm (L/s) 1 (0.06) 2 (0.13) 3 (0.19) 4 (0.25) 5 (0.32) 6 (0.38) 7 (0.44) 8 (0.50) 9 (0.57) 10 (0.63) 11 (0.69) 12 (0.76) 13 (0.82) 14 (0.88) 15 (0.95) 16 (1.01) 17 (1.07) 18 (1.13) 19 (1.20) 20 (1.26) 21 (1.32) 22 (1.39) 23 (1.45) 24 (1.51) 25 (1.58) 26 (1.64) 27 (1.70) 28 (1.76) 29 (1.83) 30 (1.89) 31 (1.95) 32 (2.02) 33 (2.08) 34 (2.14) 35 (2.21) 36 (2.27) 37 (2.33) 38 (2.39) 39 (2.46) 40 (2.52) 41 (2.58) 42 (2.65) 43 (2.71) 44 (2.77)

Fixture Units Flush Tank

Flush Valve

0 1 3 4 6 7 8 10 12 13 15 16 18 20 21 23 24 26 28 30 32 34 36 39 42 44 46 49 51 54 56 58 60 63 66 69 74 78 83 86 90 95 99 103

— — — — — — — — — — — — — — — — — — — — — 5 6 7 8 9 10 11 12 13 14 15 16 18 20 21 23 25 26 28 30 31 33 35

Flow, gpm (L/s) 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 105 110 115 120 125 130 135 140

(2.84) (2.90) (2.96) (3.02) (3.09) (3.15) (3.21) (3.28) (3.34) (3.40) (3.47) (3.53) (3.59) (3.65) (3.72) (3.78) (3.91) (4.03) (4.16) (4.28) (4.41) (4.54) (4.66) (4.79) (4.91) (5.04) (5.17) (5.29) (5.42) (5.54) (5.67) (5.80) (5.92) (6.05) (6.17) (6.30) (6.62) (6.93) (7.25) (7.56) (7.88) (8.19) (8.51) (8.82)

Fixture Units Flush Tank

Flush Valve

107 111 115 119 123 127 130 135 141 146 151 155 160 165 170 175 185 195 205 215 225 236 245 254 264 275 284 294 305 315 326 337 348 359 370 380 406 431 455 479 506 533 559 585

37 39 42 44 46 48 50 52 54 57 60 63 66 69 73 76 82 88 95 102 108 116 124 132 140 148 158 168 176 186 195 205 214 223 234 245 270 295 329 365 396 430 460 490

Flow, gpm (L/s) 145 (9.14) 150 (9.45) 155 (9.77) 160 (10.08) 165 (10.40) 170 (10.71) 175 (11.03) 180 (11.34) 185 (11.66) 190 (11.97) 200 (12.60) 210 (13.23) 220 (13.86) 230 (14.49) 240 (15.12) 250 (15.75) 260 (16.38) 270 (17.01) 280 (17.64) 290 (18.27) 300 (18.90) 310 (19.53) 320 (20.16) 330 (20.79) 340 (21.42) 350 (22.05) 360 (22.68) 370 (23.31) 380 (23.94) 390 (24.57) 400 (25.20) 410 (25.83) 420 (26.46) 430 (27.09) 440 (27.72) 450 (28.35) 500 (31.50) 550 (34.65) 600 (37.80) 700 (44.10) 800 (50.40) 900 (56.70) 1000 (63)

Fixture Units Flush Tank

Flush Valve

611 638 665 692 719 748 778 809 840 874 945 1018 1091 1173 1254 1335 1418 1500 1583 1668 1755 1845 1926 2018 2110 2204 2298 2388 2480 2575 2670 2765 2862 2960 3060 3150 3620 4070 4480 5380 6280 7280 8300

521 559 596 631 666 700 739 775 811 850 931 1009 1091 1173 1254 1335 1418 1500 1583 1668 1755 1845 1926 2018 2110 2204 2298 2388 2480 2575 2670 2765 2862 2960 3060 3150 3620 4070 4480 5380 6280 7280 8300

Chapter 5 — Cold-Water Systems

other hand, a larger meter may mean a smallersized piping system, which might prove to be more economical in the long run. These two factors are evaluated by the designer and economic considerations guide the selection. Furthermore, if a system does not have ample pressure, a means of preserving the available pressure is to use a larger meter, thereby decreasing pressure loss. This fact may well enable the designer to eliminate the use of a water-pressure booster system, thereby substantially reducing the plumbing system costs. The last step is to determine the other pressure losses encountered between the meter and the governing fixture. These could be caused by a water softener, a backflow preventer, a filter, or any other device that creates a pressure loss in the system. The “governing fixture” or appliance is the device that has the highest total when the residual pressure, static pressure, and all other pressure losses are added. Take, for example, the system shown in Figure 5-5. To find the governing fixture or appliance, determine which device requires the most pressure. Knowing that the meter loss is the same for all parts of the system, it can be temporarily ignored. Going from the meter to the flush-valve water closet, there are 15 psi (103.4 kPa) residual and no static loss for a total of 15 psi (103.4 kPa). As a total going through the backflow preventer, there are 16 psi (110.3 kPa) residual and 8.66 psi (59.7 kPa) static for a total loss of 24.66 psi (170 kPa). Going to the dishwasher, there is a total of 40 psi (275.8 kPa)—25 psi (172.4 kPa) residual plus 5 psi (34.5 kPa) loss through the water heater plus 10 psi (69 kPa) loss through the softener. Therefore, the dishwasher is the governing fixture, for it has the highest total when the residual, static, and other losses are added. Summarizing the steps, all the system needs or losses are subtracted from the minimum water pressure. The remainder is the pressure available for friction, defined as the total energy (or force) available to push the water through the pipes to the governing fixture or appliance. How this force is used is up to the designer, who may decide to use it evenly over the entire system, as an average pressure loss, or unevenly over the system. In designing the system, as long as the designer does not exceed the pressure available for friction, the system will work. A certain amount of pressure may be held in reserve, however, to allow for aging of the piping or decreases

125

in available water supply pressures as an area incurs growth. As previously determined, the governing appliance in the example in Figure 5-5 is the dishwasher. For the same example, assume that the minimum incoming water pressure is 60 psi (413.7 kPa). To determine the pressure available for friction, start with 60 psi (413.7 kPa) and subtract 3 psi (20.7 kPa) for the meter loss, 10 psi 69 kPa) for the softener, 5 psi (34.5 kPa) for the water-heater coil, and 25 psi (172.4 kPa) residual for the dishwasher. This leaves a remainder of 17 psi (117.2 kPa), which is the pressure available for friction. The losses for the backflow preventer and the static do not occur on the line between the meter and the governing fixture or appliance; therefore, they are not included in the calculations at this time. Only losses that occur on the line between the meter and the governing fixture or appliance are to be included in the initial calculations to determine the pressure available for friction. The other losses will enter into subsequent calculations. After obtaining the pressure available for friction, the next step is to calculate the “average pressure drop.” This is the pressure available for friction divided by the equivalent length of the run. The quotient is multiplied by l00 to obtain an answer in terms of loss in psi/100 ft (kPa/ l00 m). In determining the equivalent length of run, an allowance must be made for fittings. This can be determined from Table 5-7 or by adding a percentage to the developed length. The average pressure drop is an average loss over the system and should be used only as a guide in sizing piping. Part of the system can be designed to exceed the average pressure drop, while another part is designed to be less than the average. The average pressure drop can be exceeded—as long as the total pressure available for friction is not exceeded. The average pressure drop calculation, which is made initially, pertains only to the line from the meter to the governing fixture or appliance. Care should be taken to account for the average pressure drop calculations for the other lines. The branches off the main line should be sized on a different pressure-loss basis, or the branches closest to the meter may take pressure away from the farthest branches. Table 5-8 shows typical flow and pressure required during flow for various fixtures.

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Figure 5-3 Conversion of Fixture Units, fu, to gpm (L/s), Design Load vs. Fixture Units, Mixed System Example 5-1 Figure 5-6 illustrates how to determine the pressure available for friction. In the system shown (with a main line running from the meter, point A, to the governing fixture or appliance, point L), each section of the

line is equivalent to 10 ft (3.1 m) in length. This includes an allowance for fittings. The allowable pressure drop for friction is 10 psi (69 kPa). The first tabulation is the friction loss in the system. Section A–B has an equivalent length of 10 ft (3.1 m). The average pressure drop is 10 psi/ 100 ft (226.2 kPa/100 m). If it is assumed that

Chapter 5 — Cold-Water Systems

127

precisely sized pipe is obtained to give a pressure loss (due to friction) of exactly 10 psi/100 ft (226.2 kPa/l00 m), the pressure loss in this section is 1 psi (6.9 kPa) and the pressure for friction at point B is 9 psi (62.1 kPa). In section K–L, at point L, there is 0 pressure left for friction. This is the governing fixture.

each fixture is used up as friction loss, it tends to cause more water than necessary to flow through the branches to use the excess available pressure. Method B illustrates the ideal system. All the available frictional pressure in each of the branches is used. In actual practice, this method can not be utilized. The average pressure loss in each section is very high, far higher than is normally accepted in modern construction. Many engineers and designers would be concerned with the high pressure loss as well as with the high velocity shown by this example.

The next tabulation illustrates the sizing of branches (using a different friction-loss basis than was used for the main). 10 psi (69 kPa) available for friction loss; longest run: A–L, 100 ft (30.5 m); average pressure drop: (10 × 100)/100 = 10 psi/100 ft (226.2 kPa/ 100 m).

Method C is a modified header system. The main was sized on the average pressure drop of the system and the branches sized on their allowable frictional pressure drop. At section M–J, the total allowable pressure drop over the entire system (point A to point M) is 10 psi (69 kPa). Point M has an equivalent length of 90 ft (27.4 m) from point A. This gives an average pressure

Method A uses the same average pressure loss in the branches as was used in the line to the governing fixture. The pressure available for friction at the end of each branch is not 0. At point M, it is 1 psi (6.9 kPa); at point R, it is 5 psi (34.5 kPa); and at point U, it reaches a maximum of 8 psi (55.2 kPa). Unless the pressure to

63.0

50.4

37.8

25.2

18.9

12.6

6.30

5.04

3.15 3.78

2.52

1.89

1.26

0.38 0.44 0.50 0.57 0.63

0.32

6"

4"

1"

1-1

" 3/4

5/8 10 9 8 7 6

3"

110.3

2"

16

/2"

137.9

"

20

69.0 62.1 55.2 48.3 41.4

5

34.5

4

27.6

3

20.7

2

13.8

1

6.9 4

5

6 7 8 9 10

20

30

40 50 60

80 100

200

300 400

600 800 1000

Flow, gallons per minute Figure 5-4 Typical Friction Losses for Disk-Type Water Meters

Pressure Loss, kiloPascals

Pressure Loss, pounds per inch squared

0.25

Flow, liters per second

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128

Table 5-7

Allowance for Friction Loss in Valves and Threaded Fittings Equivalent Length of Pipe for Various Fittings (ft)

Diameter of Fitting (in.)

90° Standard Elbow

45° Standard Elbow

Standard T 90°

Coupling or Straight Run of T

Gate Valve

Globe Valve

Angle Valve

a

1

0.6

1.5

0.3

0.2

8

4

½

2

1.2

3

0.6

0.4

15

8

¾

2.5

1.5

4

0.8

0.5

20

12

1

3

1.8

5

0.9

0.6

25

15

1¼

4

2.4

6

1.2

0.8

35

18

1½

5

3

7

1.5

1

45

22

2

7

4

10

2

1.3

55

28

2½

8

5

12

2.5

1.6

65

34

3

10

6

15

3

2

80

40

4

14

8

21

4

2.7

125

55

5

17

10

25

5

3.3

140

70

6

20

12

30

6

4

165

80

Note: Allowances based on nonrecessed threaded fittings. Use ½ the allowances for recessed threaded fittings or streamline solder fittings.

Table 5-7 (M)

Allowance for Friction Loss in Valves and Threaded Fittings Equivalent Length of Pipe for Various Fittings (m)

Diameter of Fitting (mm)

90° Standard Elbow

45° Standard Elbow

Standard T 90°

Coupling or Straight Run of T

9.5

0.3

0.2

0.5

0.09

12.7

0.6

0.4

0.9

19.1

0.8

0.5

25.4

0.9

31.8

Gate Valve

Globe Valve

Angle Valve

0.06

2.4

1.2

0.18

0.12

4.6

2.4

1.2

0.24

0.15

6.1

3.7

0.6

1.5

0.27

0.18

7.6

4.6

1.2

0.7

1.8

0.4

0.24

10.7

5.5

38.1

1.5

0.9

2.1

0.5

0.3

13.7

6.7

50.8

2.1

1.2

3.1

0.6

0.4

16.8

8.5

63.5

2.4

1.5

3.7

0.8

0.5

19.8

10.4

76.2

3.1

1.8

4.6

0.9

0.6

24.4

12.2

101.6

4.3

2.4

6.4

1.2

0.8

38.1

16.8

127

5.2

3.1

7.6

1.5

1.0

42.7

21.3

152.4

6.1

3.7

9.1

1.8

1.2

50.3

24.4

Note: Allowances based on nonrecessed threaded fittings. Use ½ the allowances for recessed threaded fittings or streamline solder fittings.

Chapter 5 — Cold-Water Systems

Table 5-8

129

Flow and Pressure Required for Various Fixtures during Flow Pressure, psi (kPa)a

Fixture Basin faucet Basin faucet, self-closing Sink faucet, a in. (9.5 mm) Sink faucet, ½ in. (12.7 mm) Dishwasher

8

(55.2)

3

12 10

(82.7) (69)

2.5 (0.16) 4.5 (0.28)

(34.5) (103.4–172.4)

4.5 (0.28)

5 5

(34.5) (34.5)

6 5

12 15

(82.7) (103.4)

5 15–25

Bathtub faucet Laundry tub cock, ¼ in. (6.4 mm) Shower Water closet, ball cock Water closet, flush valve Urinal flush valve

10–20 15

Garden hose, 50 ft (15.2 m), and sill cock

Flow, gpm (L/s)

30

(69–137.9) (103.4) (206.8)

(0.19)

b

(0.38) (0.32)

3–10 3

(0.19–0.6) (0.19)

15–40 15

(0.95–2.5) (0.95)

5

(0.32)

aResidual pressure in the pipe at the entrance of the fixture considered. bSee manufacturer’s data.

Figure 5-5

Establishing the Governing Fixture or Appliance

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METHOD A Developed Length in Section, Section ft (m)

Developed Length from Point A, ft (m)

Friction Loss, psi/100 ft (kPa/100 m)

Friction Loss in Section, psi (kPa)

Total Pressure Pressure at End Loss from Friction, of Section for psi (kPa) Friction, psi (kPa)

A–B B–C

10 (3.1) 10 (3.1)

10 (3.l) 20 (6.1)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

1 (6.9) 2 (13.8)

9 (62.1) 8 (552)

C–D D–E

10 (3.1) 10 (3.1)

30 (9.1) 40 (12.2)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

3 (20.7) 4 (27.6)

7 (48.3) 6 (41.4)

E–F F–G

10 (3.1) 10 (3.1)

50 (15 2) 60 (18.3)

10 (226.2) 10 (226.2)

1 (6 9) 1 (6.9)

5 (34.5) 6 (41.4)

5 (34.5) 4 (27.6)

G–H H–J

10 (3.1) 10 (3.1)

70 (21.3) 80 (24.4)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

7 (48.3) 8 (55.2)

3 (20.7) 2 (13.8)

J–K K–L

10 (3.1) 10 (3.1)

90 (27.4) 100 (30.5)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

9 (62.1) 10 (69)

1 (6.9) 0 (0)

METHOD B Developed Length in Section, Section ft (m)

Developed Length from Point A, ft (m)

Pressure at Start, psi (kPa)

Friction Loss, psi/100 ft (kPa/100 m)

Friction in Section, psi (kPa)

Pressure at End, psi (kPa)

M–J N–H

10 (3.1) 10 (3.1)

90 (27.4) 80 (24.4)

2 (13.8) 3 (20.7)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

1 (6.9) 2 (13.8)

P–G Q–F R–E

10 (3.1) 10 (3.1) 10 (3.1)

70 (21.3) 60 (18.3) 50 (15.2)

4 (27.6) 5 (34.5) 6 (41.4)

10 (226.2) 10 (226.2) 10 (226.2)

1 (6.9) 1 (6 9) 1 (6.9)

3 (20.7) 4 (27.6) 5 (34 5)

S–D T–C

10 (3.1) 10 (3.1)

40 (12.2) 30 (9.1)

7 (48.3) 8 (55.2)

10 (226.2) 10 (226.2)

1 (6.9) 1 (6.9)

6 (41.4) 7 (48.3)

U–B

10 (3.1)

20 (6.1)

9 (62.1)

10 (226.2)

1 (6.9)

8 (55.2)

Friction in Section, psi (kPa)

Pressure at End, psi (kPa)

Friction Loss, psi/100 ft Section (kPa/100 m)

Friction in Section, psi (kPa)

METHOD C Pressure Friction at End, Loss, psi/100 ft psi (kPa) (kPa/100 m)

M–J

20 (452.4)

2 (13.8)

0 (0)

11.1 (251.1)

1.1

(7.6)

0.90 (6.2)

N–H P–G

30 (678.6) 40 (904.8)

3 (20.7) 4 (27.6)

0 (0) 0 (0)

12.5 (282.8) 14.3 (323.5)

1.25 (8.6) 1.43 (9.9)

1.75 (12.1) 2.57 (17.7)

Q–F R–E

50 (1131) 60 (1357.2)

5 (34.5) 6 (41.4)

0 (0) 0 (0)

16.6 (375.5) 20 (452.4)

1.66 (11.5) 2 (13.8)

3.34 (23) 4 (27.6)

S–D T–C

70 (1583.5) 80 (1809.7)

7 (48.3) 8 (55.2)

0 (0) 0 (0)

25 (565.5) 33.3 (753.3)

2.5 (17.2) 3.33 (23)

4.5 (31) 4.66 (32.1)

U–B

90 (2035.9)

9 (62.1)

0 (0)

50 (1131)

5

4

(34.5)

Figure 5-6 Determining Pressure Available for Friction

(27.6)

Chapter 5 — Cold-Water Systems

drop of 11.1 psi (7.6 kPa) and an unused frictional pressure of 0.9 psi (6.2 kPa). By going through all the branches in the same manner, one can see that the unused frictional pressure varies from 0.9 psi (6.2 kPa) to a maximum of 4.66 psi (32.1 kPa). These pressures are far less than those resulting from Method A and the average pressure drops are far less than those resulting from Method B. Consequently, Method C is the one most widely used by designers. In actual practice, it is not necessary to calculate the average pressure drop for each branch; usually, the branches are close together and the changes in the average pressure drop are very small. The last step is to take advantage of all available pressure. For example, a water heater could be located on the roof of a building. If the water system was designed to have a residual pressure on the roof of 15 psi (103.4 kPa), then the hot water piping system can be sized with a static pressure gain available, to be used for friction loss in the hot water piping. Another example of utilizing available pressure is an installation with a combination of flush valves and flush-tank water closets sized on the basis of a flush-valve system having a residual pressure of 15 psi (103.4 kPa). Within this system, the branches that have only flush-tank fixtures have an additional 7 psi (48.3 kPa) of pressure, which can be used for friction. The 7 psi (48.3 kPa) is the difference between the 15 psi (103.4 kPa) and 8 psi (55.2 kPa) residual pressures. Velocity Method Another method designers use to size water piping is the velocity method. The average pressure drop available for friction is calculated and, if it is greater than 7 or 8 psi/ 100 ft (158.4 or 181 kPa/100 m), the lines are sized on the basis of a 5 or 6-fps (1.5 or 1.8 m/s) velocity. In this method, the main line is conservatively sized and the short branches may slightly exceed the average pressure drop. However, the total pressure drop of the system does not exceed the allowable pressure loss for friction.

Summary The following items must be determined and calculated when sizing a system: 1. The maximum flow rate of the system. 2. The maximum and minimum water pressure in the main. 3. The residual pressure required at the gov-

131

erning fixture or appliance. 4. The static pressure loss to get to the governing fixture or appliance. 5. The meter loss. 6. Other losses between the meter and the governing fixture or appliance. 7. The pressure available for friction. 8. The average pressure drop from the meter to the governing fixture or appliance. 9. The average pressure drop for the other systems. 10. The size of the line from the meter to the governing fixture or appliance. 11. The size of the branch line. For the convenience of the designer in sizing water systems, the following tables and figures are provided: •

Table 5-9. Water pipe sizing, fixture units vs. psi/100 ft (kPa/100 m), Type L copper tubing.

•

Table 5-10. Water pipe sizing, fixture units vs. psi/100 ft (kPa/l00 m), galvanized, fairly rough pipe.

•

Figure 5-7. Pipe sizing data, copper tubing, smooth pipe.

•

Figure 5-8. Pipe sizing data, fairly smooth pipe.

•

Figure 5-9. Pipe sizing data, fairly rough pipe.

•

Figure 5-10. Pipe sizing data, rough pipe.

WATER HAMMER “Water hammer” is the term used to define the destructive forces, pounding noises, and vibrations that develop in a piping system when a column of noncompressible liquid (water) flowing through a pipeline at a given pressure and velocity is stopped abruptly. The surge pressure (or pressure wave) generated at the point of impact or stoppage travels back and forth through the piping system until the destructive energy is dissipated in the piping system. This violent action accounts for the piping noise and vibration. The common cause of shock is the quick closing of electrical, pneumatic, spring-loaded valves or devices, as well as the quick, hand closure of valves or fixture trim. The valve closure time is

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132

directly related to the intensity of the surge pressure.

Shock Intensity Quick valve closure may be defined as a closure time equal to or less than 2L/a seconds, where “L” is the length of pipe (ft) (m) from the point of closure to the point of relief (the point of relief is usually a larger pipe riser or main or a water tank), and “a” is the velocity of propagation of elastic vibration in the pipe (fps). The expression “2L/a” is the time interval required for the pressure wave to travel from the point of closure to the relief point and back to the point of closure. Maximum pressure rise can be calculated by the following, known as Joukowsky’s formula: Equation 5-2 Pr =

wav 144g

where Pr = Pressure rise above flow pressure, psi (kPa) w = Specific weight of liquid, lb/ft3 (kg/m3) a = Velocity of pressure wave, fps (4000– 4500 average for water) (m/s [1219– 1372 average]) v = Change in flow velocity, fps (m/s) g = Acceleration due to gravity, 32 ft/s2 (10 m/s2) This action produces a pressure rise of approximately 60 times the change in velocity. Engineers generally employ a velocity between 5 and 10 fps (1.5 and 3.1 m/s), which may produce a shock pressure of 300–600 psi (2068–4137 kPa). The resultant water-hammer shock wave travels back and forth in the piping, between the point of quick closure and the point of relief, at a rate of 4000–4500 fps (1219–1372 m/s). Although noise is generally associated with the occurrence of water hammer, water hammer can occur without audible sound. Quick closure always creates some degree of shock—with or without noise. Therefore, the absence of noise does not indicate that water hammer or shock is nonexistent in a water-distribution system.

System Protection and Control Water hammer arresters prolong the life and service of piping, valves, fittings, trim, equipment, apparatus, and other devices that are part of, or connected to, a water-distribution system. To reduce shock pressure and confine its action to the section of piping in which it occurs, a suitable means of control must be provided to absorb and dissipate the energy causing the shock. Water hammer arresters provide a diaphragm that moves with the pressure fluctuations, absorbing the shock wave. Air or another gas is the most effective medium to use for this purpose since it is highly compressible, thereby offering the maximum displacement cushion for absorbing the shock. Air chambers The air chamber has been utilized for controlling shock for many years. The unit consists of a capped piece of pipe having the same diameter as the line it serves; its length ranges from 12 in. to 24 ft (304.8–609.6 mm). The air chamber is constructed in several different shapes. Figure 5-11 shows a few examples of air chambers. Plain air chambers, Figure 5-11(a) and (b), are generally placed on the supply lines to fixtures or equipment. A standpipe type of air chamber, Figure 5-11(c), is generally placed on a piping main. A rechargeable type of air chamber, Figure 5-11(d), is generally placed at the end of a branch line or on a piping main. The air chambers shown are made of pipe and fittings. Unless devices are of the correct size and contain a prescribed volume of air, however, they cannot be regarded as suitable even for the temporary control of shock. Most valves and fittings used in plumbing water-distribution systems are designed and constructed for normal maximum working pressures of 150 psig (1034 kPa). Therefore, unless an air chamber can reduce shock pressures to some degree less than 250 psig (1724 kPa), serious damage to the valves, fittings, and other components of the piping system may result. The commonly used air chamber, even when correctly sized, controls shocks only temporarily after its initial installation. Although a correctly sized air chamber temporarily controls shock to within safe limits of pressure, its performance is effective only while

Chapter 5 — Cold-Water Systems

133

Table 5-9 Water Pipe Sizing—Fixture Units vs. psi/100 ft (kPa/100 m), Type L Copper Tubing Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

Pipe Size, in. (mm)

2½ (63.5)

15

69

1.0 (22.6)

0

2

6

12

21

58

155

17

73

1.1 (24.9)

0

2

7

13

22

62

170

20

82

1.2 (27.2)

0

3

7

14

23

67

185

23

91

1.3 (29.4)

0

3

7

15

24

74

199

26

100

1.4 (31.7)

0

3

8

15

25

81

213

28

109

1.5 (33.9)

0

3

8

16

27

86

226

31

120

1.6 (36.2)

0

3

8

17

28

93

241

33

130

1.7 (38.5)

0

4

9

17

30

98

252

36

140

1.8 (40.7)

0

4

9

18

31

105

264

39

150

1.9 (43)

0

4

10

19

32

111

277

42

161

2.0 (45.2)

0

4

10

20

33

115

287

6

48

183

2.2 (49.8)

0

4

11

21

36

127

312

7

53

205

2.4 (54.3)

1

4

12

22

39

138

337

8

59

225

2.6 (58.8)

1

4

12

23

42

150

360

9

66

245

2.8 (63.3)

1

5

13

24

45

160

380

10

74

265

3.0 (67.9)

1

5

13

25

47

171

401

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

11

81

285

3.2 (72.4)

1

6

14

26

50

183

421

12

87

309

3.4 (76.9)

1

6

15

28

52

194

441

13

95

336

3.6 (81.4)

1

6

15

29

55

205

460

14

102

365

3.8 (86)

1

6

16

30

57

215

479

15

106

390

4.0 (90.5)

1

6

16

31

58

225

500

16

116

410

4.2 (95)

1

7

16

32

61

236

517

18

124

430

4.4 (99.5)

1

7

17

34

63

245

533

5

20

131

448

4.6 (104.1)

2

7

18

35

65

253

549

6

21

139

466

4.8 (108.6)

2

7

19

36

68

263

564

6

22

145

484

5.0 (113.1)

2

7

19

37

72

271

580

7

24

153

504

5.2 (117.6)

2

8

19

38

75

280

597

7

25

163

526

5.4 (122.2)

2

8

20

40

79

289

614

8

26

171

*549

5.6 (126.7)

2

8

20

42

83

298

630

8

27

177

*570

5.8 (131.2)

2

8

21

43

85

306

646

9

29

185

*591

6.0 (135.7)

2

8

21

44

88

314

662

9

30

199

*610

6.2 (140.3)

2

9

22

45

92

323

676

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

(Continued)

ASPE Data Book — Volume 2

134

(Table 5-9 continued) Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

Pipe Size, in. (mm)

2½ (63.5)

10

31

202

*631

6.4 (144.8)

2

9

22

46

95

333

692

10

32

210

*652

6.6 (149.3)

3

9

23

47

97

343

709

11

34

216

*673

6.8 (153.8)

3

9

23

49

101

351

725

11

35

*223

*693

7.0 (158.4)

3

9

23

50

104

359

742

12

37

*231

*713

7.2 (162.9)

3

10

24

51

106

367

758

12

38

*241

*732

7.4 (167.4)

3

10

24

52

109

375

775

13

40

*250

*754

7.6 (171.9)

3

10

24

53

112

385

791

13

41

*259

*774

7.8 (176.4)

3

11

25

54

114

394

808

14

43

*265

*793

8.0 (181)

3

11

25

55

117

401

824

14

44

*273

*811

8.2 (185.5)

3

11

26

56

120

409

840

14

46

*280

*829

8.4 (190)

3

11

26

57

123

416

856

15

47

*286

*848

8.6 (194.5)

3

11

27

57

126

423

872

15

48

*295

*867

8.8 (199.1)

3

11

27

58

128

431

889

16

50

*305

*887

9.0 (203.6)

3

12

27

59

130

437

906

16

51

*314

*908

9.2 (208.1)

3

12

28

60

133

444

925

17

52

*323

*930

9.4 (212.6)

3

12

29

61

136

450

944

17

54

*329

*950

9.6 (217.2)

3

12

29

62

140

455

963

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

18

*56

*336

*970

9.8 (221.7)

3

12

29

64

145

460

982

19

*58

*346

*993

10.0 (226.2)

4

13

30

65

148

467

1003

20

*61

*366

*1022

10.4 (235.3)

4

13

31

67

153

480

1030

21

*63

*374

*1039

10.6 (239.8)

4

13

31

68

155

487

1044

22

*66

*390

*1068

11.0 (248.8)

4

13

32

71

160

500

1072

23

*70

*405

*1089

11.4 (257.9)

4

14

33

74

166

513

1099

24

*72

*414

*1124

11.6 (262.4)

4

14

34

76

169

520

1124

5

25

*76

*430

*1124

12.0 (271.5)

4

14

34

79

175

533

1124

5

*26

*80

*444

*1124

12.4 (280.5)

4

14

35

82

181

545

1124

6

*27

*81

*452

*1124

12.6 (285)

4

15

36

84

184

552

1124

6

*28

*85

*466

*1124

13.0 (294.1)

4

15

37

86

190

564

1124

6

*29

*88

*480

*1124

13.4 (303.1)

4

15

37

89

195

577

1124

6

*30

*90

*488

*1124

13.6 (307.6)

4

15

38

91

199

583

1124

7

*31

*94

*502

*1124

14.0 (316.7)

5

16

40

94

204

595

1124

7

*32

*98

*517

*1124

14.4 (325.7)

5

16

41

98

208

608

1124

8

*33

*99

*526

*1124

14.6 (330.3)

5

16

41

99

210

614

1124

8

*34

*102

*536

*1124

15.0 (339.3)

5

16

42

101

215

622

1124

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

(Continued)

Chapter 5 — Cold-Water Systems

135

(Table 5-9 continued) Pipe Size, in. (mm)

Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

8

*35

*106

*536

*1124

15.5 (350.6)

5

16

43

104

221

622

1124

9

*37

*110

*536

*1124

16.0 (361.9)

5

17

44

107

227

622

1124

9

*39

*114

*536

*1124

16.5 (373.2)

5

17

45

110

233

622

1124

17.0 (384.6)

5

18

*10

*43

*124

*536

*1124

17.5 (395.9)

5

18

47

117

245

622

1124

*11

*44

*129

*536

*1124

18.0 (407.2)

6

19

49

120

250

622

1124

*11

*46

*134

*536

*1124

18.5 (418.5)

6

19

50

123

257

622

1124

19.0 (429.8)

6

19

19.5 (441.1)

6

20

*13

*51

*149

*536

*1124

20 (452.4)

6

20

53

132

276

622

1124

*

*13

*53

*160

*536

*1124

21 (475)

6

21

54

138

286

622

1124

*

*14

*57

*160

*536

*1124

22 (497.7)

6

21

56

145

286

622

1124

*

*15

*61

*160

*536

*1124

23 (520.3)

7

21

58

152

286

622

1124

*

*16

*65

*160

*536

*1124

24 (542.9)

7

22

60

158

286

622

1124

*

*16

*68

*160

*536

*1124

25 (565.5)

7

23

62

164

286

622

1124

*

*19

*71

*160

*536

*1124

26 (588.1)

7

23

65

168

286

622

1124

*

*21

*71

*160

*536

*1124

28 (633.4)

7

24

68

168

286

622

1124

*10

*41

*119

*536

*1124

46

114

239

622

1124

*12

*48

*139

*536

*1124

51

126

263

622

1124

*12

*49

*144

*536

*1124

52

129

270

622

1124

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

*

*

*23

*71

*160

*536

*1124

30 (678.6)

8

26

75

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

32 (723.9)

8

27

81

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

34 (769.1)

8

28

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

36 (814.4)

9

29

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

38 (859.6)

9

31

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

40 (904.8)

9

32

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

42 (950.1)

10

33

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

44 (995.3)

10

34

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

44 (1040.6)

11

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

48 (1085.8)

11

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

50 (1131)

11

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

55 (1244.1)

12

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

60 (1357.2)

13

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

80 (1809.7)

14

35

82

168

286

622

1124

*

*

*26

*71

*160

*536

*1124

100 (2262.1)

14

35

82

168

286

622

1124

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

ASPE Data Book — Volume 2

136

Table 5-10

Water pipe sizing fixture units versus psi/100 ft. (kPa/100 m), Galvanized fairly-rough pipe Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, psi/100 ft (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) (kPa/100 m) Fixture Unitsa

Pipe Size, in. (mm)

2½ (63.5)

8

37

1.0 (22.6)

0

1

4

8

16

42

107

9

42

1.1 (24.9)

0

1

5

9

17

45

115

11

46

1.2 (27.2)

0

1

5

10

19

48

124

12

51

1.3 (29.4)

0

1

6

11

20

51

133

13

55

1.4 (31.7)

0

2

6

11

20

54

143

14

62

1.5 (33.9)

0

2

6

12

21

56

153

15

67

1.6 (36.2)

0

2

6

12

22

58

162

16

74

1.7 (38.5)

0

2

6

12

23

60

171

18

80

1.8 (40.7)

0

2

6

13

23

63

180

20

85

1.9 (43)

0

2

7

13

24

66

189

22

90

2.0 (45.2)

0

3

7

14

25

70

190

25

102

2.2 (49.8)

0

3

7

15

26

77

215

27

112

2.4 (54.3)

0

3

7

15

28

85

231

30

124

2.6 (58.8)

0

3

8

16

30

92

245

33

136

2.8 (63.3)

0

3

8

17

32

99

259

36

148

3.0 (67.9)

0

3

9

18

33

105

275

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, psi/100 ft (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) (kPa/100 m) Fixture Unitsa

2½ (63.5)

40

162

112

288

3.2 (72.4)

0

3

9

19

35 6

43

174

3.4 (76.9)

0

3

10

20

36

118

302

7

46

186

3.6 (81.4)

0

4

10

20

38

123

315

7

49

198

3.8 (86)

0

4

11

21

40

129

329

8

52

210

4.0 (90.5)

1

4

11

21

42

135

343

9

54

221

4.2 (95)

1

4

12

22

43

141

356

10

58

238

4.4 (99.5)

1

5

12

23

45

147

369

10

62

345

4.6 (104.1)

1

5

12

23

46

153

380

10

66

256

4.8 (108.6)

1

5

12

24

48

160

391

11

71

265

5.0 (113.1)

1

5

13

24

49

167

403

12

75

278

5.2 (117.6)

1

6

13

25

51

174

415

13

79

290

5.4 (122.2)

1

6

13

26

52

180

426

13

82

302

5.6 (126.7)

1

6

14

27

54

185

436

14

85

314

5.8 (131.2)

1

6

14

27

55

191

446

14

89

329

6.0 (135.7)

1

6

15

28

56

197

455

15

93

343

6.2 (140.3)

1

6

15

29

57

202

465

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

(Continued)

Chapter 5 — Cold-Water Systems

137

(Table 5-10 continued) Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

Pipe Size, in. (mm)

2½ (63.5)

15

96

358

6.4 (144.8)

1

6

15

29

58

208

474

16

100

372

6.6 (149.3)

1

6

15

30

59

213

484

17

104

384

6.8 (153.8)

1

7

16

31

61

219

495

18

107

395

7.0 (158.4)

1

7

16

32

62

224

505

19

112

407

7.2 (162.9)

1

7

16

32

64

230

515

20

116

420

7.4 (167.4)

1

7

17

33

66

236

525

20

119

432

7.6 (171.9)

1

7

17

33

67

240

535

5

20

123

443

7.8 (176.4)

1

7

17

34

68

244

544

5

22

127

454

8.0 (181)

1

7

18

34

71

249

554

6

23

131

465

8.2 (185.5)

1

7

18

35

73

253

563

6

24

134

475

8.4 (190)

1

7

18

36

75

257

572

6

25

138

487

8.6 (194.5)

1

7

19

37

77

262

582

7

25

142

498

8.8 (199.1)

1

8

19

38

79

267

591

7

26

146

508

9.0 (203.6)

1

8

19

39

81

272

600

7

26

150

519

9.2 (208.1)

1

8

19

39

83

277

609

7

27

154

532

9.4 (212.6)

1

8

20

40

85

281

618

8

28

160

545

9.6 (217.2)

1

8

20

41

86

286

627

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

8

28

164

557

9.8 (221.7)

1

8

20

41

87

291

636

8

29

170

*570

10.0 (226.2)

1

8

20

42

88

297

646

8

31

175

*592

10.4 (235.3)

2

8

20

43

93

304

663

9

31

177

*603

10.6 (239.8)

2

9

21

44

95

307

669

9

33

186

*620

11.0 (248.8)

2

9

21

45

66

315

684

10

34

193

*638

11.4 (257.9)

2

9

22

46

101

323

697

10

35

197

*647

11.6 (262.4)

2

9

22

47

104

327

704

11

37

208

*666

12.0 (271.5)

2

9

23

48

107

334

719

11

39

213

*687

12.4 (280.5)

2

9

23

49

110

348

737

11

40

218

*698

12.6 (285)

3

10

23

50

112

242

746

12

41

*226

*724

13.0 (294.1)

3

10

24

51

114

362

766

12

43

*234

*745

13.4 (303.1)

3

10

24

52

118

370

783

13

44

*239

*754

13.6 (307.6)

3

10

24

53

128

374

791

13

46

*247

*775

14.0 (316.7)

3

10

24

53

122

382

809

13

47

*255

*795

14.4 (325.7)

3

11

25

54

125

290

826

14

48

*258

*805

14.6 (330.3)

3

11

25

55

126

394

834

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

(Continued)

ASPE Data Book — Volume 2

138

(Table 5-10 continued) Pipe Size, in. (mm)

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

Pipe Size, in. (mm)

2½ (63.5)

14

50

*265

*827

15.0 (339.3)

3

11

26

56

129

401

854

14

52

*275

*851

15.5 (350.6)

3

11

26

57

134

411

875

15

53

*284

*875

16.0 (361.9)

3

12

27

58

138

420

896

16

54

*292

*900

16.5 (373.2)

3

12

27

59

142

428

918

16

57

*302

*924

17.0 (384.6)

3

12

28

61

146

436

939

17

*60

*315

*947

17.5 (395.9)

3

13

29

62

150

444

960

18

*62

*325

*969

18.0 (407.2)

3

13

29

64

153

452

981

19

*64

*336

*992

18.5 (418.5)

3

13

30

65

157

460

1002

20

*66

*350

*1015

19.0 (429.8)

3

13

30

66

160

469

1023

21

*69

*362

*1040

19.5 (441.1)

3

13

31

68

166

477

1045

21

*72

*371

*1066

20 (452.4)

4

13

31

69

169

484

1066

23

*76

*390

*1116

21 (475)

4

13

32

74

175

500

1116

22 (497.7)

4

14

34

23 (520.3)

4

14

34

24 (542.9)

4

15

35

25 (565.5)

4

15

37

26 (588.1)

4

15

39

*25

*81

*410

*1165

77

183

517

1165

*26

*85

*430

*1173

82

190

533

1173

*27

*90

*448

*1173

85

198

549

1173

*28

*95

*466

*1173

87

205

564

1173

*30

*99

*484

*1173

91

211

580

1173

Pressure ½ ¾ 1 1¼ 1½ 2 Loss, (12.7) (19.1) (25.4) (31.7) (38.1) (50.8) psi/100 ft (kPa/100 m) Fixture Unitsa

2½ (63.5)

*

*33

*100

*515

*1173

28 (633.4)

4

16

41

98

225

606

1173

*

*35

*118

*521

*1173

30 (678.6)

5

17

43

104

238

611

1173

*

*40

*128

*521

*1173

32 (723.9)

5

17

45

112

250

611

1173

*

*43

*138

*521

*1173

34 (769.1)

5

18

47

117

262

611

1173

*

*

*46

*148

*521

*1173

36 (814.4)

6

19

49

123

275

611

1173

*

*

*49

*159

*521

*1173

38 (859.6)

6

20

51

128

285

611

1173

*

*

*52

*160

*521

*1173

40 (904.8)

6

20

53

134

286

611

1173

*

*

*54

*160

*521

*1173

42 (950.1)

6

21

55

141

286

611

1173

*

*

*59

*160

*521

*1173

44 (995.3)

6

21

56

148

286

611

1173

*

*

*63

*160

*521

*1173

46 (1040.6)

6

22

58

154

286

611

1173

*

*

*

*64

*160

*521

*1173

48 (1085.8)

7

23

60

156

286

611

1173

*

*

*

*64

*160

*521

*1173

50 (1131)

7

23

61

156

286

611

1173

*

*

*

*64

*160

*521

*1173

55 (1244.1)

7

24

66

156

286

611

1173

*

*

*

*64

*160

*521

*1173

60 (1357.2)

7

25

72

156

286

611

1173

*

*

*

*64

*160

*521

*1173

80 (1809.7)

9

31

72

156

286

611

1173

*

*

*

*64

*160

*521

*1173

100 (2262.1)

10

31

72

156

286

611

1173

Note: Velocities at 5 ( ), 6 ( ), 8 ( ), and 10 ( * ) fps. a Numbers in small type are flush-valve fixture units; numbers in large type are flush-tank fixture units.

Chapter 5 — Cold-Water Systems

Figure 5-7

139

Pipe Sizing Data, Smooth Pipe

ASPE Data Book — Volume 2

140

Figure 5-8

Pipe Sizing Data, Fairly Smooth Pipe

Chapter 5 — Cold-Water Systems

Figure 5-9

141

Pipe Sizing Data, Fairly Rough Pipe

ASPE Data Book — Volume 2

142

Figure 5-10

Pipe Sizing Data, Rough Pipe

Chapter 5 — Cold-Water Systems

143

Table 5-11 Required Air Chambers Nominal Pipe Diam., in. (mm)

Pipe Length, ft (m)

½ (12.71)

25 (7.62)

½ (12.71) ¾ (19.1) ¾ (19.1)

Flow Pressure, psig (kPa)

Required Air Chamber

Velocity, fps (m/s)

Volume, in.3 (cm3)

Phys. Size, in. (cm)

30 (0.79)

10 (3.04)

8 (1.3)

¾ × 15 (1.9 × 38.1)

60 (1.57)

10 (3.04)

60 (9.8)

1 × 69½ (2.5 × 176.5)

60 (1.57)

5 (1.52)

13 (2.1)

1 × 5 (2.5 × 12.7)

200 (61.0)

30 (0.79)

10 (3.04)

108 (17.7)

1¼ × 72½ (3.2 × 184.2)

100 (30.5)

60 (1.57)

5 (1.52)

19 (3.1)

1¼ × 127/10 (3.2 × 32.3)

100 (30.5) 50 (15.25)

1

(25.4)

1

(25.4)

50 (15.25)

30 (0.79)

10 (3.04)

40 (6.6)

1¼ × 27 (3.2 × 68.6)

1¼ (31.8)

50 (15.25)

60 (1.57)

10 (3.04)

110 (18.0)

1¼ × 54 (3.2 × 137.2)

30 (0.79)

5 (1.52)

90 (14.8)

2 × 27 (5.1 × 68.6)

60 (1.57)

10 (3.04)

170 (27.9)

2 × 50½ (5.1 × 128.3)

30 (0.79)

10 (3.04)

329 (53.9)

3 × 44½ (7.6 × 113.0)

60 (1.57)

10 (3.04)

150 (24.6)

2½ × 31 (6.4 × 78.7)

60 (1.57)

5 (1.52)

300 (49.2)

3 × 40½ (7.6 × 102.9)

1½ (38.1) 1½ (38.1) 2

(50.8)

2

(50.8)

2

(50.8)

200 (61.0) 50 (15.25) 100 (30.5) 25 (7.62) 200 (61.0)

it retains its initial charge of air. Air-chamber requirements are shown in Table 5-11. The air charge can be depleted during the flow cycle since water is drawn from all directions during flow. Moreover, the entrapped air is also diminished by turbulence. During this process the water absorbs the air, and as the unit becomes waterlogged, it loses its ability to absorb shock.

In most installations where there are several fixtures, usually only one fixture valve will be closed at a time. Occasionally, however, two or more fixture valves may be closed at the same instant. Table 5-12, “Sizing and Selection of Water-Hammer

Water hammer arresters Symbols There are six manufactured sizes of water hammer arrester, each having a different capacity to control shock in piping systems of varied sizes and scopes. The following symbols, recommended by the Plumbing and Drainage Institute (PDI), were devised to denote the range in size of water hammer arrester: A–B–C–D–E–F “A” is the smallest-sized unit and “F” represents the largest. Sizing and placement Sizing is based on fixture units for single and multiple-fixture branch lines and on pipe size.

a

b

c

d

Figure 5-11 Air Chambers: (a, b) Plain Air Chambers, (c) Standpipe Air Chamber, (d) Rechargeable Air Chamber

ASPE Data Book — Volume 2

144

Arresters,” takes into consideration all design factors, including simultaneous usage, pipe size, length, flow, pressure, and velocity.

Table 5-12 Sizing and Selection of Water-Hammer Arresters PDI Units A B Fixture Units 1–11 12–32

C D E F 33–60 61–113 114–154 155–330

In the sizing of cold and hot-water branch lines, it is usual practice to obtain the total number of fixture units on each branch line. This information is then applied to sizing charts to determine the required size of the branch line. The properly sized water-hammer arresters can be selected once the total number of fixture units for a cold or hot-water branch line is known. It is only necessary to apply the fixture units to Table 5-12 and select the appropriate water-hammer arrester. Note the following: •

When water pressure in the line exceeds 65 psig, select the next larger size water-hammer arrester.

•

If the fixture-unit total includes a fraction, it should be rounded up to the next larger whole number. Thus, if the total is 11½ fixture units, the unit should be sized for 12 fixture units.

•

All sizing data in this chapter are based on flow velocities of 10 fps (3 m/s) or less.

It is suggested that the engineer employ PDI symbols for the riser diagrams for sizing waterhammer arresters. This practice will enable manufacturers to furnish the correct units. The location of the water-hammer arresters from the start of the horizontal branch line to the last fixture supply on the branch line should not exceed 20 ft (6.1 m) in length. When the branch lines exceed the 20-ft (6.10-m) length, an additional water-hammer arrester should be used and each should be sized for half the fixture-unit load. It has been established that the preferred location for the water-hammer arrester is at the end of the branch line between the last two fixtures served. Units for branches serving pieces of equipment with quick-closing valves should be placed within a few ft (m) of the equipment isolation valve.

To prevent the harboring of Legionella pneumophila, bellows containing rubber should not be used.

BACKFLOW PREVENTION Theoretically, a well-designed and operated water-supply system should always be under a constant positive pressure, and contamination via backflow or back-siphonage should never be able to enter the distribution mains. Unfortunately, accidents do occur when excessive water demands for fire protection, operation of booster pumps, flushing of water mains, repairs, modifications, and maintenance to the distribution system cause the water pressure to drop. Whenever the pressure in the distribution system becomes low or negative, a condition develops that allows contamination to enter the distribution system through connections with fixtures, equipment, or tanks that contain toxic, unsafe, or unpleasant liquids or gases. These physical connections by which a water supply may be contaminated are known as “cross connections.” There are numerous, well-documented cases where cross connections have been responsible for contaminating drinking water and, as a result, sometimes contributing to the spread of fatal disease. The contamination of a water system through cross connections can be avoided. This section describes the current recommended practice for the detection and elimination of unprotected cross connections.

Types of Cross-Connection Control Device When plumbing fixtures and equipment in water-supply systems are subject to backflow conditions, approved air gaps, backflow preventers, or vacuum breakers should be used. The following methods or devices can be used to protect against backflow or back-siphonage: •

Approved air-gap separation.

•

Barometric loop.

•

Mechanical protection devices.

•

Reduced-pressure-principle backflow devices (RPBD).

•

Double-check valve assemblies (DCVA).

•

Atmospheric vacuum breakers (AVB).

Chapter 5 — Cold-Water Systems

•

Pressure vacuum breakers (PVB).

•

Check valves with vent port (CVB).

The theory of backflow and back-siphonage and the devices for their prevention are described in Volume 4, Chapter 9, of the ASPE Data Book (forthcoming). Refer to local codes and standards before making selections.

Assessment of Hazard The correct application of devices depends on the correct assessment of the degree of hazard, on whether back pressure or back-siphonage will occur, and on knowledge of the operation of various types of approved backflow-prevention device. In applying the recommendations outlined in this section, three degrees of hazard must be considered: severe, moderate, and minor. They are defined as follows: 1. Severe. A cross connection or probable cross connection involving any substance in sufficient concentration to cause death or spread disease or illness or containing any substance that has a high probability of causing such an effect. 2. Moderate. A cross connection or probable cross connection involving any substance that has a low probability of becoming a severe hazard and would constitute a nuisance or be aesthetically objectionable if introduced into the domestic water supply. 3. Minor. An existing connection, or a high probability of a connection being made, between the domestic water pipe and any pipe, equipment, vat, or tank intended for carrying or holding potable water that has a low probability of becoming contaminated with any substance. The application of backflow and back-siphonage prevention devices is related to the probability of contamination as well as the recognition of an existing health hazard. For the assessment of probability, consideration must be given to the possibility of changes being made to piping, improper use of equipment, negligence of the customer, etc. Where a severe hazard exists, an air-gap separation or a reduced-pressure-principle, backflow-prevention device should be used because these two devices offer the highest known degree of protection. An atmospheric or pressure

145

vacuum breaker should be used only to isolate a severe hazard if area isolation is provided. Where a moderate hazard exists, a double-check valve assembly, or pressure or atmospheric vacuum breaker may be used. Where a minor hazard exists, a pressure or atmospheric vacuum breaker or check valves with vent port (no test cocks) may need to be installed. Toxicity and probability of occurrence illustrate the relationship between assessment of hazard and application of devices. Because of the subjective nature of assessing hazard, such illustrations cannot be used as a strict guide, providing a fixed answer for all circumstances. Instead, past experience and local code requirements must also be used as guides. Such past experience was the basis of Tables 5-13 and 5-14. The requirement of protection increases as a function of both an increase in the probability that backflow or back-siphonage will occur and an increase in the toxicity or possible toxicity of a potential source of contamination. Where it is highly probable that backflow or back-siphonage will occur, say from a standpipe in a tall apartment building, the need for a backflow-prevention device is low if the hazard of the potential source of contamination (sinks, water closets, etc.) becoming toxic is very low. The converse is also true, however, where a known health hazard exists, the tendency is to be conservative when selecting a backflow-prevention device (RPBD used in place of DVC). The risk factor for a health hazard is usually of greater concern than the probability of backflow or back-siphonage in the selection of a device.

Premise Isolation In addition to installing backflow-prevention devices at the source of potential contamination, it may be necessary, or required by code, to install a backflow-prevention device on the water-service pipe to isolate an entire area or premise. This additional protection for the purveyor’s water system is warranted if the potential health hazard is severe, or if a high probability exists that piping within a premise will be changed. If inspection on private property is restricted, the only protection for the purveyor’s water system is the installation of a backflow-prevention device on the water-service pipe. Whenever possible, in-plant isolation is preferred over premise isolation because it protects

ASPE Data Book — Volume 2

146

Table 5-13

Guide to the Assessment of Hazard and Application of Devices— Isolation at the Fixture Assessment of Hazard

Recommended Device at Fixture

Recommended Additional Device for Area of Premise Isolation

Aspirator (medical)

Severe

DCAP, AVB or PVB

RPBD

Bed pan washers Autoclaves

Severe Severe

DCAP, AVB or PVB DCAP, AVB or PVB

RPBD RPBD

Specimen tanks Sterilizers

Severe Severe

DCAP, AVB or PVB DCAP, AVB or PVB

RPBD RPBD

Cuspidors Lab bench equipment

Severe Severe

DCAP, AVB or PVB DCAP, AVB or PVB

RPBD RPBD

Autopsy & mortuary equip. Sewage pump

Severe Severe

AVB or PVB RPBD

Sewage ejectors Firefighting system (toxic-foamite)

Severe Severe

RPBD RPBD

Connection to sewer pipe Connection to plating tanks

Severe Severe

AG RPBD

Irrigation system or chemical injectors or pumps

Severe

RPBD

Connection to salt-water cooling system Tank vats or other vessels containing toxic substances

Severe

RPBD

Severe

RPBD

Connection to industrial fluid systems Dye vats or machines

Severe Severe

RPBD RPBD

Cooling towers with chemical additives Trap primer

Severe Severe

RPBD AG

Steam generators Heating equipment

Moderatea Moderatea

DCV DCV

Irrigation systems Swimming pools

Moderatea Moderatea

DCV, AVB or PVB DCV or AG

Vending machines Ornamental fountains

Moderatea Moderatea

DCV or PVB DCV or AVB or PVB

Degreasing equipment Lab bench equipment

Moderatea Minora

DCV AVB, PVB or CVP

Hose bibbs and yard hydrants Trap primers

Minora Minora

AVB AG

Flexible shower heads Steam tables

Minora Minora

AVB AVB

Washing equipment Shampoo basins

Minora Minora

AVB AVB

Kitchen equipment Aspirators

Minora Minora

AVB AVB

Domestic heating boiler

Minora

CVP

Description of Cross Connection

RPBD

aWhere a higher hazard exists (due to toxicity or health hazard), additional area protection with RPBD is required. See Table 5-14 for additional information.

Chapter 5 — Cold-Water Systems

147

in-plant personnel and, in most cases, the device can be sized smaller because in-plant piping is smaller. However, even with in-plant isolation, the purveyor may still require premise isolation.

4. Laboratories.

The choice of devices for in-plant or premise isolation depends on the degree of hazard. Several premises that fall into the severe hazard classification and should be considered for isolation from the purveyor’s system are noted in Tables 5-13 and 5-14 and on the following list.

8. Chemical plants using a water process.

5. Piers, docks, and other waterfront facilities. 6. Sewage-treatment plants. 7. Food and beverage-processing plants. 9. Metal-plating plants. 10. Petroleum-processing or storage plants. 11. Radioactive-material-processing plants and nuclear reactors.

1. Premises with unapproved auxiliary water supplies.

12. Car-washing facilities.

2. Premises where inspection is restricted.

13. Animal-research, care, and processing plants.

3. Hospitals, mortuaries, clinics, etc.

Table 5-14 Guide to the Assessment of Facility Hazard and Application of Devices— Containment of Premise Assessment ot Hazard

Recommended Device on Water-Service Pipe

Hospital building with operating, mortuary, or laboratory facilities

Severe

RPBD

Plants using radioactive material

Severe

RPBD

Petroleum-processing or stage facilities

Severe

RPBD

Premise where inspection is restricted

Severe

RPBD

Sewage-treatment plant

Severe

RPBD

Commercial laundry

Severe

RPBD

Plating or chemical plants

Severe

RPBD

Docks, dockside facilities

Severe

RPBD (if no protection at fixture) DCV (if protection at fixture)

Food & beverage-processing plants

Severe

RPBD

Pleasure boat marina

Severe

RPBD

Tall buildings (protection against excessive head of water)

Moderate

DCV

Steam plants

Moderate

DCV

Fire or sprinkler system to tall building (protection against excessive head of water)

Moderate

DCV

Description of Premise

ASPE Data Book — Volume 2

148

Installation Requirements 1. All backflow devices should be installed in an accessible area to facilitate inspection, semiannual or annual testing, and maintenance. Some municipalities now require licensed inspectors to test and report on each device on an annual basis. Consideration should be given to future changes that may take place in the plumbing system. The devices should be installed so that they will remain accessible regardless of new or future piping. Check the manufacturer’s literature for minimum clearances required for the removal of parts. 2. Adequate drainage should be provided for the discharge from the reduced-pressure-device, relief-valve port. Minimum flow rates and diameters of relief-valve porting are given in Table 5-15 as a guide in the sizing of drain pipes. A. In the case of a reduced-pressure device installed in a hut, the “bore-sighted” daylight drain must be capable of handling the volumes discharged from the relief valve.

Table 5-15

C. A funnel type collector or splash screen should be used to direct the discharge to the drain to prevent objectionable spillage or splashing. 3. Pressure and atmospheric vacuum breakers may also “split” or spill water. Spillage may occur during the testing of devices. Care must be taken in choosing the location of devices so that spillage will not cause damage or be a nuisance. 4. Do not install a reduced-pressure device in a pit below ground unless a drain to the surface is provided. If the atmospheric vent is submerged in groundwater, a cross connection is created that may be more serious than the hazard the device isolates. 5. Before the installion of a backflow-prevention device, pipelines should be thoroughly flushed to remove all foreign material that could foul the operation of the device.

Minimum Flow Rates and Size of Minimum Area of RPBD Minimum Flow Rate Past Relief Valve

Size of Device in.

B. The relief-valve outlet of the reducedpressure device shall not be directly connected to the drain. An air gap of not less than 2 diameters of the relief valve outlet or 1 in. (2.5 cm), whichever is greater, must separate the drain from the outlet.

mm

gpm

½ and s

15 and 17

2.5

¾ and 1

20 and 25

I¼ and 1½

L/s

Minimum Diameter of Relief Valve Porting (IPS) in.

mm

0.19

a

10

4.15

0.31

½

15

32 and 40

8.30

0.63

¾

20

2

50

16.70

1.27

1

25

2½

65

16.70

1.27

1

25

3

80

25.00

1.89

1¼

32

4

100

33.40

2.53

1½

32

6

150

33.40

2.53

1½

32

8

200

50.00

3.79

2

50

10

250

50.00

3.79

2

50

12

300

62.50

4.74

2½

65

14

350

75.00

5.68

3

80

16

400

83.00

6.29

3

80

Chapter 5 — Cold-Water Systems

6. Use of an in-line strainer may be required if the condition is such that foreign material is continually collecting in the line and lodging under seating surfaces. No strainer is to be used in a fire line without the approval of the insurance underwriters or fire marshal. 7. Isolating valves are necessary on reducedpressure backflow devices, double-check valve assemblies, and pressure vacuum breakers to permit replacement, testing, and maintenance. 8. Internally weighted double-check valve assemblies must be installed in the horizontal position. Some brands of spring-loaded, double-check valve devices also must be installed in the horizontal position. Check the list of approved devices issued in each jurisdiction and the manufacturer’s recommendations. 9. All reduced-pressure-principle devices must be installed in the horizontal position, unless it is specifically noted otherwise in the manufacturer’s data. 10. Check with the authority having jurisdiction and the manufacturer before installing any backflow device in hot-water lines. 11. Backflow preventers are not to be installed in corrosive or polluted atmospheres. The surrounding atmosphere can enter the pipeline through the open vent port of atmospheric and pressure vacuum breakers, check valves with vent ports and reducedpressure-principle devices. 12. Reduced-pressure-principle devices, doublecheck valves, and vacuum breakers installed in regions subject to freezing must be protected by the insulation of the units in aboveground, heated structures. Care should be taken to enure that the testing and maintenance of the unit is not hindered by the application of the insulating material. 13. For installations where 24-hour, uninterrupted service is a necessity, a parallel device should be provided to permit annual testing and maintenance. The bypass or parallel device must provide the same degree of protection as the main-line device. 14. For 8-in. (200-mm) and larger units, a method of lifting and installation is required. Existing crane facilities should be taken advantage of when determining a location for a

149

water-service and backflow-prevention device. 15. Adequate support should be provided for devices 6 in. (150 mm) and larger to prevent damage to connected pipe. 16. Backflow-prevention devices should be protected against damage. Units placed in work areas, areas with public access, or areas with vehicular traffic should be protected by fenced enclosures, stanchions, or some other means. 17. The possibility of vandalism and theft should be considered when choosing a location for a backflow-prevention device. 18. For reduced-pressure-principle and doublecheck-valve devices located outside of buildings, consideration should be given to the use of landscaping, etc., to obtain an aesthetically pleasing installation. 19. In a device installed in a deep chamber, the chamber should be self venting. Workers Compensation Board regulations require that the air within a chamber be checked for combustible gas and adequate oxygen content before a workman enters the chamber. 20. A coupling should be installed in the line to allow flexibility for alignment during installation. 21. When installing a double-check-valve, checkvalve-with-vent-port, or reduced-pressureprinciple device on the feed waterline to a pressure vessel, always install the pressurerelief valve between the backflow device and the pressure vessel. 22. If possible, a reduced-pressure-principle or double-check-assembly device should be installed no more than 3 ft (1 m) above the floor to facilitate access.

INADEQUATE WATER PRESSURE When pressure in public water mains is not great enough to satisfy building requirements, there are three ways to boost pressure to an acceptable level: with a hydropneumatic tank, a gravity tank, or a booster pump. These systems can be used singly or in combination.

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Hydropneumatic-Tank System A hydropneumatic tank is not a storage tank. Its sole purpose is to boost inadequate pressure, though it operates between predetermined pressure limits and always contains a minimum amount of water. It was the storage concept that led to the establishment of many wholly incorrect waterair ratios, which are still in use today. Formerly, a 50% tank volume was split into 25% water and 25% air. This resulted in a total of 75% water and 25% air in the tank. Later, this was “refined” to 66Q% water and 333% air. Figure 5-12 illustrates that water remaining in a tank after a given pressure drop cannot be used as a reserve. Assume that a sufficient supply of water is available and that it must be delivered to all water-service outlets at a minimum pressure of 15 psi (103.4 kPa). A 1000-gal (3785L) capacity tank is selected and filled using the rule-of -thumb ratio: q water, 3 air. A minimum tank pressure of 40 psi (275.8 kPa) is required to overcome static head and friction losses if a pressure of 15 psi (103.4 kPa) is required at the highest and farthest outlet. The maximum pressure differential in the tank is limited by how much pressure variation the piping system can tolerate. Usually, a variation of 20 psi (137.9 kPa) is acceptable. On this basis, the tank high pressure is set at 60 psi (413.7 kPa), and the system is ready for operation.

Figure 5-12 Hydropneumatic Pressure System Layout that Determines the Minimum Tank Pressure

ASPE Data Book — Volume 2

Typical installation details for hydropneumatic-tank systems are shown in Figure 5-13. Three factors are considered in the selection of a hydropneumatic tank: water–air ratio, pump capacity, and desired water withdrawal. Assume the system demand is 100 gpm (6.3 L/s) constant, the maximum number of pumping cycles is 6/h (5 min on, 5 min off), and withdrawal of 25% of the total tank capacity is desired. Tank size can be determined by equating ½ of the pump capacity (limited to no more than 6 pumping cycles/h) to the 25% withdrawal capacity. For example, 100 gpm/2 = 50 gpm, and 5 min × 50 gpm = 250 gal. Thus, 250 gal should equal 25% withdrawal. Tank capacity, then, is 100% or 250 × 4 = 1000 gal. Selecting capacity on this basis results in a minimum size tank and maintenance of efficient cycling operation of the pumps.

Gravity-Tank System Basically, a gravity-tank system consists of an elevated tank and a pump or pumps for raising water to fill the tank. Controls in the tank start and stop the pumps to maintain fluid level and

Figure 5-13 Typical Hydropneumatic Supply System

Chapter 5 — Cold-Water Systems

capacity. Water then flows from the tank to the waterlines by gravity action. Three approaches may be used to determine tank capacity for a building: 1. Rule of thumb. An arbitrary tank capacity equal to 30 times pump capacity (gpm) (L/s) is recommended by some authorities. This criterion theoretically provides a building with a 30-min emergency reserve supply of water in case of power failure or disruption of the source of water supply. 2. Empirical. With this method, the quantity of water required for emergency conditions is arbitrarily fixed. Based on this determination, the length of time needed for pumping the water before safe shutdown can be estimated. 3. Cycling of pumps. The capacity of the tank is sized so that cycling of pumps will not occur more than 6 times per hour. This translates to 5 min off, 5 min on. The fewer the cycles per hour, the less the wear and tear on motors and the less maintenance required. Reducing the number of cycles, however, will produce greater fluctuations in tank-water reserve. Selecting a tank that provides a large water surface relative to its capacity makes it possible to withdraw a considerable volume of water without appreciably lowering the liquid level. Main-

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taining the water level in this way ensures a relatively constant water pressure regardless of whether demand is at a low or peak condition. The following piping connections are required at the tank: •

Water supply to the tank.

•

Water supply to the system.

•

Overflow line.

•

Tank drain.

The locations of these connections on the tank are illustrated in Figure 5-14. The system shown is also equipped with fire-standpipe and sprinkler connections to meet local code requirements. The tank connections shown in Figure 5-14 provide the required water supply for each system, with the sprinkler reserve at the bottom, the fire-standpipe reserve at the next level, and the water storage at the top. Piping connections to the standpipe and sprinkler systems should be fitted with bronze strainers within the tank to prevent any debris from entering those systems. Level controls are installed in the tank to start and stop pumps at low and high levels. The level control can be a float switch, pressure switch, electric prober, or any other acceptable device. Tanks should be equipped with both high and low-level alarms. The low-level alarm indicates that the pumps are not keeping up with demand.

Figure 5-14 Piping Connections for a Gravity Water-Storage Tank with Reserve Capacity for Firefighting

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The high-level alarm warns that water has reached the overflow level and is spilling to waste. When storage tanks are used for gravity feed, consideration must be given to the weight of the tank and water so proper support can be provided.

Booster-Pump System There are two ways to make a continuously run system deliver a relatively constant system pressure under varying load conditions. One way is to use a constant-speed pump with a pressureregulating valve in the discharge piping. The other way is to vary the speed of the pump shaft either at the motor or in the coupling. A variety of booster-pump systems are currently in use, with more being introduced all the time. Detailed information on the design criteria and operational characteristics of water-pressure boosting systems is given in the ASPE Pumps and Pump Systems Handbook.

EXCESS WATER PRESSURE One of the main sources of trouble in a waterdistribution system is excessive pressure. Unless a piece of equipment, fixture, or operation requires a specified high pressure, a water system should not exceed a maximum of 80 psi (551.6 kPa) (check local code). To ensure this, a pressure-regulating valve (PRV) should be installed. The purpose of a pressure-regulating valve is to reduce water pressure from higher, supplymain pressures to desirable and adequate flow pressures when water is required at fixtures, appliances, or equipment.

Dead-end service The type of service in which the PRV is required to close bottle-tight when there is no demand on the system. Fall-off The amount that pressure is decreased from set pressure to meet demand. The amount of fall-off depends on the quantity of flow—the greater the flow, the greater the fall-off. A fall-off of 20 psi (137.9 kPa) is considered to be the maximum allowable fall-off. No-flow pressure The pressure maintained in the system when the PRV is shut tight so that high pressure at the inlet of the valve is not permitted to enter the system. Reduced-flow pressure The pressure maintained at the PRV outlet when water is flowing. The no-flow (closed), set-point pressure of a PRV is always higher than the reduced-flow (open) pressure. A PRV that is set to open at 45 psi (310.3 kPa) pressure (no-flow) would deliver a reduced-flow pressure of 30 psi (206.8 kPa) at peak demand if a 15 psi (103.4 kPa) fall-off had been selected. Then the reduced-flow pressure at peak flow would be 30 psi (206.8 kPa). Response The capability of a PRV to respond to change in outlet pressure. Sensitivity The ability of a PRV to sense a change in pressure. If the valve is too sensitive and quick to respond, the results are over-control and a hunting effect. Not enough sensitivity results in operation that is sluggish and great variations in the outlet pressure. Set pressure That pressure, at the outlet of the PRV, at which the valve will start to open. Types of pressure-regulating valve All pressure-regulating valves fall into the following general categories: •

Single-seated—direct-operated or pilot-operated.

•

Double-seated—direct-operated or pilot-operated.

Pressure-Regulating Valves Definitions The following are definitions of terms used in discussing, sizing, and ordering pressure-regulating valves: Accuracy The degree of fall-off in the outlet pressure from the set pressure at full-flow capacity. Also, the capability of producing the same results for repetitive operations with identical conditions of flow.

Single-seated pressure-regulating valves are used for dead-end service and when the flow to be regulated is intermittent. For dead-end service, the valve must be able to shut tight and not permit the passage of any water when there is no demand. Double-seated PRVs are used for continuous-flow conditions. They are not suited for dead-end service and should never be used for this purpose.

Chapter 5 — Cold-Water Systems

Direct-operated PRVs tend to have a reduction of the outlet pressure in direct proportion with the increase of the flow rate. Pilot-operated PRVs will maintain a close fluctuation of the outlet pressure independent of the flow rate assuming that the valve was sized properly. Sizing, selection, and installation Initial cost, maintenance cost, and specific project requirements regarding flow rates and pressure should determine which PRV is recommended for a particular application. Sizing and selection of a pressure-regulating valve can be performed after the following criteria are estimated: inlet pressure, outlet pressure, and capacity (flow rate). “Inlet pressure” is the maximum pressure expected upstream of the regulating valve. “Outlet pressure” is the pressure required downstream of the regulating valve. For large-capacity systems, which may also experience periods of low flow, or when extreme pressure reductions are expected, it is not advisable to have only one regulating valve. A PRV sized to accommodate both small and large flows has, in general, a high noise level during operation. In addition, small flows will produce wire-drawing of the seat and possible chatter. In addition to having economic advantages, the proper application of pressure-regulating valves can greatly influence the overall performance of the system. Under most circumstances, a good application can increase system performance, reduce operating costs, and ensure a longer life expectancy for regulators. For example, where initial pressures exceed 200 psi (1379.0 kPa) or where there is a wide variation between the initial pressure and the reduced pressure, or where the initial pressure varies considerably, “two-stage reduction” is beneficial. Two-stage reduction is the use of two PRVs to reduce high service pressure proportionately and to eliminate an extremely wide variance between the initial and reduced pressure. It is recommended where the initial pressure is 200 lb (1379.0 kPa) or more and where the ratio of initial to reduced pressure is more than 4 to 1 (e.g., 200 to 50 lb [1379.0 to 344.7 kPa]), or where the initial pressure fluctuates greatly. The advantage of this installation is that neither valve is subjected to an excessive range of pressure reductions. This seems to stabilize the final reduced pressure, ensuring close and accurate perfor-

153

mance. Also, this type of installation reduces the velocity of flow (there’s less pressure drop across two regulators than across one), providing longer valve life. Selection of PRVs and pressure settings is fairly simple. The first PRV could reduce from 250 to 150 lb (1723.7 to 1034.2 kPa) and the second from 150 to approximately 50 lb (1034.2 to 344.7 kPa) or there could be some similar division. PRV size can be selected according to the manufacturer’s capacity tables if it is remembered that each PRV should exceed the total capacity of the system. Where there is a wide variation of demand requirements and where it is vital to maintain a continuous water supply as well as provide greater capacity, “parallel installation” is recommended. Parallel installation is the use of two or more smaller size pressure-regulating valves serving a larger size supply-pipe main. This type of installation should be employed wherever there is a wide variation of reduced-pressure requirements and where it is vital to maintain a continuous water supply. It also has the advantage of providing increased capacity beyond that provided by a single valve where needed. Multiple installation improves valve performance for widely variable demands and permits the servicing of an individual valve without the complete shutdown of the line, thus preventing costly shutdowns. For a two-valve parallel installation, the total capacity of the valves should equal or exceed the capacity required by the system. One valve should be set at 10 psi (69.0 kPa) higher delivery pressure than the other. For example, assume that the system requires 400 gpm (25.2 L/s) and the reduced-flow pressure required is 50 psi (344.7 kPa). Select two valves, each rated at 200 gpm (12.6 L/s), with one valve set at 50 psi (344.7 kPa) and the other valve set 10 psi (69.0 kPa) higher at 60 psi (413.7 kPa). Thus, when low volume is required, the higher-set valve operates alone. When a larger volume is demanded, both valves open, delivering full-line capacity. Another possible choice is to install two PRV combinations of different sizes. This is practical on larger installations where supply lines are 2 in. (50 mm) and larger and where there are frequent periods of small demand. The smaller PRV would have the 10-psi (69.0-kPa) higher delivery pressure and thus operate alone to satisfy small demands, such as urinals and drinking foun-

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tains. When a larger volume is demanded, the main PRV would open to satisfy the system demand. For example, take an apartment building requiring 300 gpm (18.9 L/s) at 60 psi (413.7 kPa). The selection might be a 4-in. (100-mm) PRV rated for 240 gpm (15.1 L/s) (80% of total maximum flow rate) and set at 60 psi (413.7 kPa) and a 1½-in. (40-mm) PRV rated for 60 gpm (3.8 L/s) and set at 70 psi (472.7 kPa). Manufacturers have tables indicating recommended capacities and valve sizes for use in parallel installations.

TESTING, CLEANING, AND DISINFECTION OF DOMESTIC, WATER-SUPPLY SYSTEMS Testing Prior to disinfection, connection to faucets and equipment, and installation of pipe insulation, the domestic water system should be hydrostatically tested for leakage. A typical test for interior piping is accomplished by capping all system openings, filling the system with water, and then pumping a static head into the system at a minimum of 1½ times the working pressure (100 psi [689.5 kPa] minimum) for a period of not less than 2 hours. The aforementioned test requirements are acceptable to most inspectors, but note that 80 psi (551.6 kPa) is the maximum pressure allowed by most designs and codes. Under conditions where systems are subject to freezing, and with the approval of the authority having jurisdiction, an air test may be substituted for the water test. This can be accomplished by connecting an air compressor to the system, bringing the system up to 40 psi (275.8 kPa), checking for leaks with liquid soap, repairing any leaks, and then subjecting the system to a minimum of 1½ times the working pressure (100 psi [689.5 kPa] minimum) for a minimum of 2 hours. Any equipment that may be damaged by these tests should be disconnected from the system.

Cleaning and Disinfecting New or repaired potable water systems shall be cleaned and disinfected prior to use whenever required by the administrative authority. The method to be followed should be per AWWA or

ASPE Data Book — Volume 2

as follows (or as required by the administrative authority): 1. Cleaning and disinfection applies to both hot and cold, domestic (potable) water systems and should be performed after all pipes, valves, fixtures, and other components of the systems are installed, tested, and ready for operation. 2. All domestic yard, hot and cold-water piping should be thoroughly flushed with clean, potable water prior to disinfection to remove dirt and other contaminants. Screens of faucets and strainers should be removed before flushing and reinstalled after completion of disinfection. 3. Disinfection should be done using chlorine, either gas or liquid. Calcium or sodium hypochlorite or another approved disinfectant may be used. 4. A service cock should be provided and located at the water-service entrance. The disinfecting agent should be injected into and through the system from this cock only. 5. The disinfecting agent should be injected by a proportioning pump or device through the service cock slowly and continuously at an even rate. During disinfection, flow of the disinfecting agent into the main connected to the public water supply is not permitted. 6. All sectional valves should be opened during disinfection. All outlets should be fully opened at least twice during injection and the residual checked with orthotolidin solution. 7. If chlorine is used, when the chlorine residual concentration, calculated on the volume of water the piping will contain, indicates not less than 50 parts per million (ppm) or milligrams per liter (mg/L) at all outlets, then all valves should be closed and secured. 8. The residual chlorine should be retained in the piping systems for a period of not less than 24 hours. 9. After the retention, the residual should be not less than 5 ppm. If less, then the process should be repeated as described above. 10. If satisfactory, then all fixtures should be flushed with clean, potable water until residual chlorine by orthotolidin test is not greater than that of the incoming water supply (this may be zero).

Chapter 5 — Cold-Water Systems

11. All work and certification of performance should be performed by approved applicators or qualified personnel with chemical and laboratory experience. Certification of performance should indicate:

155

NOTE: It should be understood that local code requirements, if more stringent than above suggested procedures, shall be included in the specifications.

•

Name and location of the job and date when disinfection was performed.

REFERENCES

•

Material used for disinfection.

1.

•

Retention period of disinfectant in piping system.

American Water Works Association (AWWA). AWWA cross connection control manual. New York.

2.

•

Ppm (mg/L) chlorine during retention.

AWWA. AWWA standard for disinfecting water mains, AWWA C601.

•

Ppm (mg/L) chlorine after flushing.

3.

AWWA. AWWA standard for disinfection of water storage facilities, AWWAD105.

•

Statement that disinfection was performed as specified.

4.

AWWA. Standard for hypochlorites, AWWA B300, AWWA M22.

•

Signature and address of company/person performing disinfection.

5.

AWWA. Standard for liquid chlorine, AWWAB301.

6.

Manas, V.T. National plumbing code illustrated handbook. New York: McGraw-Hill.

7.

n.a. 1978. Piping systems fundamentals and application. Plant Engineer Magazine.

8.

US Department of Commerce, National Bureau of Standards. BMS 65, Methods of estimating loads in plumbing systems, by R.B. Hunter. Washington, DC.

9.

US Department of Commerce, National Bureau of Standards. BMS 66, Plumbing manual. Washington, DC.

12. Upon completion of final flushing (after retention period) the contractor should obtain a minimum of one water sample from each hot and cold-water line and submit samples to a state/province and/or local, approved laboratory. Samples should be taken from faucets located at the highest floor and furthest from the meter or main water supply. The laboratory report should show the following: •

Name and address of approved laboratory testing the sample.

•

Name and location of job and date the samples were obtained.

•

The coliform organism count. An acceptable test shall show the absence of coliform organisms. (Some codes require an acceptable test for 2 consecutive days.)

•

Any other tests required by local code authorities.

13. If analysis does not satisfy the above minimum requirements, the disinfection procedure must be repeated. 14. Before acceptance of the systems, the contractor should submit to the architect (engineer) for his review 3 copies of the laboratory report and 3 copies of the certification of performance as specified above. 15. Under no circumstances should the contractor permit the use of any portion of domestic water systems until they are properly disinfected, flushed, and certified.

10. US Department of Commerce, National Bureau of Standards. BMS 79, Water distributing systems for buildings, by R.B. Hunter. Washington, DC. 11. White, George Clifford. 1972. Handbook of chlorination. New York: Van Nostrand Reinhold.

Chapter 6 — Domestic Water Heating Systems

6

157

Domestic WaterHeating Systems

INTRODUCTION

scalding water at fixtures must be prevented in the design stage.

Proper design of the domestic hot-water supply system for any building is extremely important. Careful planning on the basis of all available data will ensure an adequate supply of water at the desired temperature to each fixture at all times. A properly designed system must, of course, conform with all the regulations of the authorities having jurisdiction.

An economic heat source is of prime importance in conserving energy. Various sources include coal, gas, oil, steam, condensate, waste hot water, and solar energy. The availability and cost of any of these sources or combinations of these sources will dictate selection. If an especially economical source is not adequate to satisfy the total demand, then it can be used to preheat the cold-water supply to the heater.

The design objectives for an efficient hotwater distribution system include: 1. Providing adequate amounts of water at the prescribed temperature to all fixtures and equipment at all times. 2. A system that will perform its function safely. 3. The utilization of an economical heat source. 4. A cost-effective and durable installation. 5. An economical operating system with reasonable maintenance. A brief discussion of each of these objectives is warranted. Any well-designed system should deliver the prescribed temperature at the outlet almost instantaneously to avoid the wasteful running of water until the desired temperature is achieved. The hot water should be available at any time of the day or night and during lowdemand periods as well as peak flows. Safety must be built into any hot-water system, and the safety features must operate automatically. The two paramount dangers to be guarded against are excessive pressures and temperatures. Exploding hot-water heaters and

An economical and durable installation can be achieved by judicious selection of the proper materials and equipment. The piping layout also has a marked effect on this objective and will later determine the ease of replacement and repair. Cost-effective operation and maintenance also depend upon the proper pre-selection of materials and equipment. The choice of instantaneous or storage type heaters, the selection of insulation on heaters and piping, the location of piping (avoiding cold, unheated areas), the ease of circulation (the avoidance of drops and rises in piping), bypasses around pumps and tanks, and adequate valving accessibility are all items that affect the operation and maintenance of a system. The design of a domestic water-heating system begins with estimating the facility’s load profile and identifying the peak demand times. To accomplish these steps, the designer must conduct discussions with the users of the space, determine the building type, and learn of any owner requirements. The information thus gath-

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ered will establish the required capacity of the water heating equipment and the general type of system to be used.

BASIC FORMULAE AND UNITS The equations in this chapter are based on the principle of energy conservation. The fundamental formula for this expresses a steady-state heat balance for the heat input and output of the system: Equation 6-1 q = r w c ∆T where q = Time rate of heat transfer, Btu/h (kJ/h) r = Flow rate, gph (L/h) w = Weight of heated water, lb (kg) c = Specific heat of water, Btu/lb/°F (kJ/kg/K)

2.27 m3 4188.32 kJ (333.15−283.15 K) q = ___________ ______________ — ‰ m3/K  ž 9 h = 475 374 kJ/h

Note: The designer should be aware that water heaters installed in high elevations must be derated based on the elevation. The water heaters’ manufacturers’ data should be consulted for information on required modifications.

HEAT RECOVERY—ELECTRIC WATER HEATERS It takes 1 Btu of energy to raise 1 lb of water 1°F. Since 1 kW is equal to 3413 Btu and 1 gal of water weighs 8.33 lb, then it would take 1 kW of electrical power to raise 410 gal (1552.02 L) of water 1°F. This can be expressed in a series of formulae, as follows: Equation 6-3 410 gal = gal of water per kW at ∆T ∆T

∆T = Change in heated water temperature (temperature of leaving water minus temperature of incoming water, represented as Th – Tc, °F [K]) For the purposes of this discussion, the specific heat of water is constant, c = 1 Btu/lb/°F (c = 4.19 kJ/kg/K), and the weight of water is constant at 8.33 lb/gal (999.6 kg/m3).

1552.02 L = L of water per kW at ∆T ‰ ∆T  Equation 6-4 gph × ∆T = kW required 410 gal L/h · ∆T = kW required ‰1552.02 L 

Equation 6-2 q = gph

1 Btu 8.33 lb (∆T) — ‰ lb/°F  ‰ gal  ž

Equation 6-5 gph = kW required gal of water per kW at ∆T

m3 4.188 kJ 999.6 kg q = ____ ____________ ___________ (∆T) 9 ž A h — ‰ kg/K  ‰ m3  Example 6-1 Calculate the heat output rate required to heat 600 gph from 50 to 140°F (2.27 m3/h from 283.15 to 333.15K). Solution From Equation 6-2, q = 600 gph

8.33 Btu (140−50°F) = 449,820 Btu/h — ‰ gal /°F  ž

A

L/h = kW required ‰ L of water per kW at ∆T  where ∆T

= Temperature rise (temperature differential), °F (°C)

gph = Gallons per hour of hot water required

Chapter 6 — Domestic Water Heating Systems

L/h = Liters per hour of hot water required Equation 6-3 can be used to establish a simple table based on the required temperature rise. Temperature Rise, ∆ T, °F (°C)

Gal (L) of Water per kW

159

Table 6-1 Typical Hot-Water Temperatures for Plumbing Fixtures and Equipment Use

Temperature °F (°C)

Lavatory Hand washing

105

(40)

Shaving

115

(45)

Showers and tubs

110

(43)

110 (43)

3.73 (14.12)

100 (38)

4.10 (15.52)

Therapeutic baths

95

(35)

90 (32)

4.55 (17.22)

Surgical scrubbing

110

(43)

80 (27)

5.13 (19.42)

Commercial and institutional laundry

140–180

(60–82)

70 (21)

5.86 (22.18)

Residential dishwashing and laundry

140

(60)

60 (16)

6.83 (25.85)

50 (10)

8.20 (31.04)

Wash

150 min.

(66 min.)

Final rinse

180–195

(82–91)

Wash

160 min.

(71 min.)

Final rinse

180–195

(82–91)

165 min.

(74 min.)

Wash

140

(60)

Rinse

75 min.

(24 min.)

40 (4)

10.25 (38.8)

This table can be used with Equation 6-5 to solve for the kW electric element needed to heat the required recovery volume of water. Example 6-2 An electric water heater must be sized based on the following information: (a) 40 gph (151.42 L/h) of hot water at a temperature of 140°F (43°C) is required. (b) The incoming water supply during winter is 40°F (4°C). Solution Using Equation 6-5 and the above table, we find the following: 40 gph = 9.8 kW required 4.1 gal (100°F) 151.42 L/h = 9.8 kW required — 15.52 L (38°C) ž

HOT-WATER TEMPERATURE The generally accepted minimum hot-water temperatures for various plumbing fixtures and equipment are given in Table 6-1. Both temperature and pressure should be verified with the client and checked against local codes and the manuals of equipment used.

Commercial, spray-type dishwashing (as required by the NSF): Single or multiple-tank hood or rack type:

Single-tank conveyor type:

Single-tank rack or door type: Single-temperature wash and rinse Chemical sanitizing glassware:

Note: Be aware that temperatures, as dictated by codes, owners, equipment manufacturers, or regulatory agencies, will occasionally differ from those shown.

MIXED-WATER TEMPERATURE Mixing water at different temperatures to make a desired mixed-water temperature is the main purpose of domestic hot-water systems. “P” is a hot-water multiplier and can be used to determine the percentage of supply hot water that will blend the hot and cold water to produce a desired mixed-water temperature.

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Equation 6-6 P =

Tm – Tc T h – Tc

where Th

= Supply hot-water temperature

Tc

= Inlet cold-water temperature

Tm

= Desired mixed-water temperature

Values of P for a range of hot and cold water temperatures are given in Table 6-2. Example 6-3 A group of showers requires 25 gpm (1.58 L/s) of 105°F (41°C) mixed-water temperature. Determine how much 140°F (60°C) hot water must be supplied to the showers when the cold-water temperature is 50°F (10°C). Solution P =

105 – 50°F = 0.61 140 – 50°F

41 – 10°C P = = 0.61 ‰  60 – 10°C Therefore, 0.61 (25 gpm) = 15.25 gpm of 140°F water required [0.61 (1.58 L/s) = 0.96 L/s of 60°C water required]. Table 6-2 may also be used to determine P.

WATER HEATERS The most commonly used type of water heater for office buildings, multiple-unit dwellings, and other similar establishments is the “directly heated, automatic storage heater.” Such heaters are simple, inexpensive to install, and very low maintenance. They are generally low-demand heaters, with low Btu input so that the heating of the water is spread over several hours. This reduces the amount of heating medium required. Commonly used heating mediums are electricity, fuel gas, and steam. “Instantaneous” types of water heater must have sufficient capacity to provide the maximum flow rate of hot water at an adequate temperature. The instantaneous heater finds its best application where water-heating demands are constant, such as for swimming pools, certain dishwasher booster requirements, and industrial processes, or where space conditions are a prime

consideration. Because of these high flow rates and the typical on-off operation, the efficiencies of instantaneous heaters are lower than those of storage type heaters. “Booster heaters” are used to raise the temperature of the regular hot-water supply to some higher-than-normal temperature needed to perform special functions. Booster heaters are utilized in applications such as commercial dishwashers where there is a limited use of very hot water. They can be located near their point of intended use and have simple controls, minimal waste, and smooth operation. “Semi-instantaneous heaters” contain between 10 and 20 s of domestic water storage, according to their rated heating capacity. This small quantity of water is adequate to allow the temperature-control system to react to sudden fluctuations in water flow and to maintain the outlet water temperature within ±5°F (2.7°C). The temperature-control system is almost always included with this type of heater as a package.

Controls The purpose for having controls on a hot-water generator is to ensure that a sufficient volume of hot water at the proper temperature for use is provided to a facility. The control components for water heaters differ depending on the type of heater and the manufacturer. Generally, water heater controls should be checked with the equipment manufacturer. Also, the various regulatory and testing agencies have requirements for controls that depend on the size and type of equipment used.

Stratification Because of its lighter density, warm water rises to the top of a storage tank. The result of this rising action, known as “stratification,” occurs in all unrecirculated tanks. It has been found that the amount of usable temperature water in stratified horizontal and vertical tanks is about 65% and 75%, respectively. Stratification during recovery periods can be reduced significantly by mechanical circulation of the water in the tank. During periods of demand, however, it is useful to have good stratification since this increases the availability of water at a usable temperature. If, for example, a tank were equally stratified between

Chapter 6 — Domestic Water Heating Systems

161

Table 6-2 Hot-Water Multiplier, P Th = 110°F Hot-Water System Temperature Tc, CW Temp. (°F)

Tm, Water Temperature at Fixture Outlet (°F) 110

105

100

95

45

1.00

0.92

0.85

0.77

50

1.00

0.92

0.83

0.75

55

1.00

0.91

0.82

0.73

60

1.00

0.90

0.80

0.70

65

1.00

0.89

0.78

0.67

Th = 120°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

120

115

110

105

100

95

45

1.00

0.93

0.87

0.80

0.73

0.67

50

1.00

0.93

0.86

0.79

0.71

0.64

55

1.00

0.92

0.85

0.77

0.69

0.62

60

1.00

0.92

0.83

0.75

0.67

0.58

65

1.00

0.91

0.82

0.73

0.64

0.55

Th = 130°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

130

125

120

115

110

105

100

95

45

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

50

1.00

0.94

0.88

0.81

0.75

0.69

0.63

0.56

55

1.00

0.93

0.87

0.80

0.73

0.67

0.60

0.53

60

1.00

0.93

0.86

0.79

0.71

0.64

0.57

0.50

65

1.00

0.92

0.85

0.77

0.69

0.62

0.54

0.46

Th = 140°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

140

135

130

125

120

115

110

105

100

95

45

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

50

1.00

0.94

0.89

0.83

0.78

0.72

0.67

0.61

0.56

0.50

55

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

0.53

0.47

60

1.00

0.94

0.88

0.81

0.75

0.69

0.63

0.56

0.50

0.44

65

1.00

0.93

0.87

0.80

0.73

0.67

0.60

0.53

0.47

0.40

(Continued)

ASPE Data Book — Volume 2

162

(Table 6-2 continued)

Th = 150°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

150

145

140

135

130

125

120

115

110

105

100

45

1.00

0.95

0.90

0.86

0.81

0.76

0.71

0.67

0.62

0.57

0.52

50

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

55

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

0.47

60

1.00

0.94

0.89

0.83

0.78

0.72

0.67

0.61

0.56

0.50

0.44

65

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

0.53

0.47

0.41

Th = 160°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

160

155

150

145

140

135

130

125

120

115

110

45

1.00

0.96

0.91

0.87

0.83

0.78

0.74

0.70

0.65

0.61

0.57

50

1.00

0.95

0.91

0.86

0.82

0.77

0.73

0.68

0.64

0.59

0.55

55

1.00

0.95

0.90

0.86

0.81

0.76

0.71

0.67

0.62

0.57

0.52

60

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

65

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

0.47

Th = 180°F Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°F)

Tc, CW Temp. (°F)

180

175

170

165

160

155

150

145

140

135

130

45

1.00

0.96

0.93

0.89

0.85

0.81

0.78

0.74

0.70

0.67

0.63

50

1.00

0.96

0.92

0.88

0.85

0.81

0.77

0.73

0.69

0.65

0.62

55

1.00

0.96

0.92

0.88

0.84

0.80

0.76

0.72

0.68

0.64

0.60

60

1.00

0.96

0.92

0.88

0.83

0.79

0.75

0.71

0.67

0.63

0.58

65

1.00

0.96

0.91

0.87

0.83

0.78

0.74

0.70

0.65

0.61

0.57

110

1.00

0.93

0.86

0.79

0.71

0.64

0.57

0.50

0.43

0.36

0.29

120

1.00

0.92

0.83

0.75

0.67

0.58

0.50

0.42

0.33

0.25

0.17

130

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

——

140

1.00

0.88

0.75

0.63

0.50

0.38

0.25

0.13

——

——

——

150

1.00

0.83

0.67

0.50

0.33

0.17

——

——

——

——

——

160

1.00

0.75

0.50

0.25

——

——

——

——

——

——

——

Chapter 6 — Domestic Water Heating Systems

163

Table 6-2 (M) Hot-Water Multiplier, P Th = 43°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

43

41

38

35

7

1.00

0.92

0.85

0.77

10

1.00

0.92

0.83

0.75

13

1.00

0.91

0.82

0.73

16

1.00

0.90

0.80

0.70

18

1.00

0.89

0.78

0.67

Th = 49°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

49

46

43

41

38

35

7

1.00

0.93

0.87

0.80

0.73

0.67

10

1.00

0.93

0.86

0.79

0.71

0.64

13

1.00

0.92

0.85

0.77

0.69

0.62

16

1.00

0.92

0.83

0.75

0.67

0.58

18

1.00

0.91

0.82

0.73

0.64

0.55

Th = 54°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

54

52

49

46

43

41

38

35

7

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

10

1.00

0.94

0.88

0.81

0.75

0.69

0.63

0.56

13

1.00

0.93

0.87

0.80

0.73

0.67

0.60

0.53

16

1.00

0.93

0.86

0.79

0.71

0.64

0.57

0.50

18

1.00

0.92

0.85

0.77

0.69

0.62

0.54

0.46

Th = 60°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

60

58

54

52

49

46

43

41

38

35

7

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

10

1.00

0.94

0.89

0.83

0.78

0.72

0.67

0.61

0.56

0.50

13

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

0.53

0.47

16

1.00

0.94

0.88

0.81

0.75

0.69

0.63

0.56

0.50

0.44

18

1.00

0.93

0.87

0.80

0.73

0.67

0.60

0.53

0.47

0.40

(Continued)

ASPE Data Book — Volume 2

164

(Table 6-2 continued)

Th = 66°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

66

63

60

58

54

52

49

46

43

41

38

7

1.00

0.95

0.90

0.86

0.81

0.76

0.71

0.67

0.62

0.57

0.52

10

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

13

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

0.47

16

1.00

0.94

0.89

0.83

0.78

0.72

0.67

0.61

0.56

0.50

0.44

18

1.00

0.94

0.88

0.82

0.76

0.71

0.65

0.59

0.53

0.47

0.41

Th = 71°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

71

68

66

63

60

58

54

52

49

46

43

7

1.00

0.96

0.91

0.87

0.83

0.78

0.74

0.70

0.65

0.61

0.57

10

1.00

0.95

0.91

0.86

0.82

0.77

0.73

0.68

0.64

0.59

0.55

13

1.00

0.95

0.90

0.86

0.81

0.76

0.71

0.67

0.62

0.57

0.52

16

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

18

1.00

0.95

0.89

0.84

0.79

0.74

0.68

0.63

0.58

0.53

0.47

Th = 82°C Hot-Water System Temperature Tm, Water Temperature at Fixture Outlet (°C)

Tc, CW Temp. (°C)

82

79

77

74

71

68

66

63

60

58

54

7

1.00

0.96

0.93

0.89

0.85

0.81

0.78

0.74

0.70

0.67

0.63

10

1.00

0.96

0.92

0.88

0.85

0.81

0.77

0.73

0.69

0.65

0.62

13

1.00

0.96

0.92

0.88

0.84

0.80

0.76

0.72

0.68

0.64

0.60

16

1.00

0.96

0.92

0.88

0.83

0.79

0.75

0.71

0.67

0.63

0.58

18

1.00

0.96

0.91

0.87

0.83

0.78

0.74

0.70

0.65

0.61

0.57

43

1.00

0.93

0.86

0.79

0.71

0.64

0.57

0.50

0.43

0.36

0.29

49

1.00

0.92

0.83

0.75

0.67

0.58

0.50

0.42

0.33

0.25

0.17

54

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

—

60

1.00

0.88

0.75

0.63

0.50

0.38

0.25

0.13

—

—

—

66

1.00

0.83

0.67

0.50

0.33

0.17

—

—

—

—

—

71

1.00

0.75

0.50

0.25

—

—

—

—

—

—

—

Chapter 6 — Domestic Water Heating Systems

140°F (60°C) at the top and 40°F (4°C) at the bottom, this tank, in theory, could still deliver half its volume at 140°F (60°C). But, if the two layers were completely mixed, the tank temperature would drop to 90°F (32°C), which, in most cases, is an unusable temperature.

HOT-WATER TEMPERATURE MAINTENANCE Hot water of a desired temperature should be readily available at any fixture. Either a hot-water circulation system or an electronically heated system shall be used to achieve this purpose.

Hot-Water Circulation Systems Hot-water supply piping, whether insulated or not, transmits heat to the surrounding lowertemperature air by conduction, convection, and radiation. The user wastes water while waiting for the desired temperature water to warm up the piping system. The sizing of the circulation system includes selection of the pump, sizing the supply and recirculation piping, and selecting the insulation type and thickness. Recirculation systems may not be practical for small systems but may be mandated for systems designed for such places as food establishments. Proper sizing of the hotwater circulating system is essential for the efficient and economical operation of the hot-water system. Oversizing will cause the system to lose additional heat and result in unnecessary expenditures on equipment and installation. Undersizing will seriously hamper circulation and thus starve the fixtures of the desired water temperature. The procedure for sizing the hot-water circulating piping is as follows: 1. Calculate the heat-loss rates of the hot-water supply piping. 2. Calculate the heat-loss rates of the hot-water circulating piping. 3. Calculate the circulation rates for all parts of the circulating piping and the total circulation rate required. 4. Determine the allowable uniform friction-head loss and the total head required to overcome friction losses in the piping when the water is flowing at the required circulation rate.

165

5. Calculate the rates of flow for various pipe sizes that will give the uniform pressure drop established in Step 4, and tabulate the results. 6. Size the system based upon the tabulation set up in Step 5. 7. With the sizes as established in Step 6, repeat Steps 2 through 6 as a check on the assumptions made. As a guide to sizing circulation piping and circulation pumps, the following empirical methods are given but are not recommended in lieu of the more accurate procedures outlined above: 1. An allowance of ½ gpm (0.23 L/min) is assigned for each small hot-water riser (¾–1 in. [1.9–2.54 cm]), 1 gpm (2.2 L/min) for each medium-sized hot-water riser (1¼-1½ in. [3.2–3.8 cm]), and 2 gpm (4.4 L/min) for each large-sized hot-water riser (2 in.[5 cm] and larger). 2. An allowance of 1 gpm (2.2 L/min) is assigned for each group of 20 hot-water-supplied fixtures.

Self-Regulating Heat-Trace Systems A heat-trace system is an economical, energyefficient system for domestic hot-water temperature maintenance. It is a self-regulating heating cable installed on the hot-water supply pipes underneath the standard pipe insulation. The cable adjusts its power output to compensate for variations in water and ambient temperatures. It produces more heat if the temperature drops and less heat if the temperature rises. The heating cable replaces supply-pipe heat losses at the point where heat loss occurs, thereby providing continuous, energy-efficient hot-water temperature maintenance and eliminating the need for a recirculating system. A one-pipe, heat-trace system design eliminates the need for designing complex recirculation systems with their pumps, piping networks, and complicated flow balancing, and special cases, such as retrofits and multiple-pressure zones, are simple to design. The installation of a heat-trace system is simple. The heating cable can be cut to length, spliced, tee-branched, and terminated at the job site, which reduces installation costs. Also, fewer plumbing components are needed; recirculating

ASPE Data Book — Volume 2

166

piping, pumps, and balancing valves are all eliminated. The heat-trace system continuously maintains hot-water temperature at every point along the supply pipe. Unlike conventional recirculation systems, the heat-trace system does not require the overheating of supply water to allow for cooling; there is reduced heat loss from energy supply piping, no heat loss from recirculation piping, and no pump to run. The heat-trace system reduces the energy requirements of typical domestic hot-water systems. Components All heating-cable components shall be UL listed for use as a part of the system to maintain hot-water temperature. Component enclosures shall be rated NEMA 4X to prevent water ingress and corrosion. Installation shall not require the installing contractor to cut into heating cable core to expose the bus wires. Connection systems requiring the installing contractor to strip the bus wires, or that use crimps or terminal blocks shall not be acceptable. All components, except for the power connection, shall be re-enterable for servicing. No component shall use silicone to seal the electrical connectors. Performance 1. Operating temperatures. The system shall maintain a nominal temperature of 105°F (40°C), 115°F (45°C), 125°F (50°C), or 140°F (60°C), at 208VAC. 2. Maintenance temperature. Each hot-water system temperature shall be maintained by specifying only one product. Temperature shall be maintained with heating cable on the pipe. Insulation thickness shall be as follows: Pipe Size, in. (mm)

Fiberglass Insulation Thickness, in. (cm)

½–1 (13–25) 1¼–2 (32–50) 2½–6 (65–150)

1 (2.54) 1½ (3.81) 2 (5.08)

Note: For pipe sizes 1¼ in. and smaller, use ¼-in. larger diameter insulation to allow for installation over cable. 3. Power control self-regulating index. The slope of the power–temperature curve or graph shall be such that the power of the heating cable shall increase as the temperature decreases, at a rate of at least 0.028W/ft-°F (0.16 W/m-°C) from 50–100°F (10–39°C).

4. Long-term thermal stability (as determined by accelerated testing). The power retention of the heating cable shall be at least 90%, after 300 cycles, between 50 and 212°F (10 and 100°C). 5. High-temperature withstand. The heater shall not decrease in resistance, overheat, or burn when powered at 208VAC and exposed to 499°F (205°C) in an oven for 30 min. Selection Variables affecting the performance of the heat-trace system include the system range, time to tap, water wastages, and energy efficiency. The design engineer should consider these factors along with installation and life-cycle costs when selecting the proper hot-water, self-regulating, heat-trace system for a particular building. The heat-trace system is a good system, but it cannot be used in all applications. For more complete design information, refer to the ASPE Domestic Water Heating Design Manual.

RELIEF VALVES Water-heating systems shall be protected from excessive temperatures and pressures by relief valves. Temperature and pressure (T&P) relief valves are available either separately or combined. A combination T&P relief valve is preferred because it offers a more economical and yet effective protective procedure. A relief valve on a water-supply system is exposed to many elements that can affect its performance, such as corrosive water that attacks materials, and deposits of lime, which close up waterways and flow passages. For these reasons, the minimum size of the valve should be ¾ in. (19 mm) for inlet and outlet connections, with the waterways within the valve of an area not less than the area of the inlet connection. Relief valves should be tested on a regular basis to ensure safe and proper operation. All valves should have a discharge pipe connected to its outlet and terminate at a point where the discharge will cause no damage to property or injury to persons. The discharge pipe size shall be at least the size of the valve discharge outlet, shall be as short as possible, and shall run down to its terminal without sags or traps. Typically, T&P relief valves are tested to comply with the standards of the American Society of Mechanical Engineers (ASME), the American Gas Association (AGA), or the National Board of

Chapter 6 — Domestic Water Heating Systems

Boiler and Pressure Vessel Inspectors (NBBPVI) and are so labeled. The designer should verify which agency’s standards are applicable to the water-heating system being designed and follow those standards for the sizes, types, and locations of required relief valves.

Sizing Pressure and Temperature-Relief Valves The following information applies to heaters with more than 200,000 Btu (211 000 kJ) input: Temperature relief valves These shall have the capacity to prevent water temperature from exceeding 210°F (99°C). They shall be water rated on the basis of 1250 Btu (1319 kJ) for each gph of water discharged at 30 lb (13.6 kg) working pressure and a maximum temperature of 210°F (99°C). The temperature rating is the maximum rate of heat input to a heater on which a temperature-relief valve can be installed and is determined as follows: Equation 6-7 gph water heated × 8.33 × ∆T(°F) 0.8

‰

Btu valve = capacity req’d

L/h water heated × 1 kg/L × ∆T(°C) 0.8

kJ valve = capacity req’d

167

THERMAL EXPANSION Water expands as it is heated. This expansion shall be provided for in a domestic hot-water system to avoid damage to the piping. Use of a thermal expansion tank in the cold-water piping to the water heater will accomplish this. It is recommended that the designer contact the manufacturer of the thermal expansion tank for information on installation and sizing. Plumbing codes require some type of thermal expansion compensation—expecially when there is either a backflow-prevention device on the cold-water service to the building or a check valve in the system. Relying only on the T&P relief valve to relieve the pressure is not good practice. Many local codes now require expansion tanks for systems over 4-gal (8.8-L) capacity. The relevant properties of water are shown in Table 6-3. Example 6-4 Using Table 6-3, determine the thermal expansion of a typical residence. Assume the initial heating cycle has incoming water at 40°F (4°C) and a temperature rise of 100°F (38°C). The water heater is 50-gal (189-L) capacity and the piping system volume is 10 gal (38 L). Solution



Specific volume of water @ 40°F = 0.01602 ft3/lb Specific volume of water @ 140°F = 0.01629 ft3/lb

Pressure relief valves These shall have the capacity to prevent a pressure rise in excess of 10% of the set opening pressure. They shall be set at a pressure not exceeding the working pressure of the tank or heater. The pressure rating is the maximum output of a boiler or heater on which a pressure-relief valve can be used and is determined as follows:

Sv 40°F 0.01602 = = 1.66% increase in volume Sv 140°F 0.01629 Total volume = 50-gal tank + 10-gal system = 60 gal 60 gal × 1.66% volume increase = 1-gal expansion 1 gal × 8.33 lb/gal × 0.01628 ft3/lb = 0.1356 ft3 = 19.5 in.3

Equation 6-8

(Specific volume of water @ 4°C = 0.00100 m3/kg

gph water heated × 8.33 × ∆T (°F) = Btu valve capacity req’d

Specific volume of water @ 60°C = 0.00102 m3/kg

[L/h water heated × 1.0 kg/L × ∆T (°C) = kJ valve capacity req’d]

Sv 4°C 0.00100 = = 1.66% increase in volume Sv 60°C 0.00102

Determine the Btu capacity required, then refer to a manufacturer’s catalog for valve size selection.

Total volume = 189-L tank + 38-L system = 227 L 227 L × 1.66% volume increase = 3.79-L expansion 3.79 L × 1 kg/L × 0.0010 m3/kg = 0.0038 m3 = 380 cm3 expansion)

ASPE Data Book — Volume 2

168

Table 6-3 Temperature

Saturation Pressure

Thermal Properties of Water

Specific Volume

Density

m3/kg

lb/ft3

kg/m3

Weight

Specific Heat

°F

°C

psig

kPa

ft3/lb

lb/gal

kg/m3

Btu/lb-°F-h

J/kg-°C-h

32

0.0

29.8

3 019.6

0.01602

0.00100

62.42

999.87

8.345

1001.40

1.0093

4225.74

40

4.4

29.7

3 009.5

0.01602

0.00100

62.42

999.87

8.345

1001.40

1.0048

4206.90

50

10.0

29.6

2 999.4

0.01603

0.00100

62.38

999.23

8.340

1000.80

1.0015

4193.08

60

15.5

29.5

2 989.2

0.01604

0.00100

62.34

998.59

8.334

1000.08

0.9995

4184.71

70

21.1

29.3

2 969.0

0.01606

0.00100

62.27

997.47

8.325

999.00

0.9982

4179.26

80

26.7

28.9

2 928.4

0.01608

0.00100

62.19

996.19

8.314

997.68

0.9975

4176.33

90

32.2

28.6

2 898.0

0.01610

0.00100

62.11

994.91

8.303

996.36

0.9971

4174.66

100

37.8

28.1

2 847.4

0.01613

0.00101

62.00

993.14

8.289

994.68

0.9970

4174.24

110

43.3

27.4

2 776.4

0.01617

0.00101

61.84

990.58

8.267

992.04

0.9971

4174.66

120

48.9

26.6

2 695.4

0.01620

0.00101

61.73

988.82

8.253

990.36

0.9974

4175.91

130

54.4

25.5

2 583.9

0.01625

0.00101

61.54

985.78

8.227

987.24

0.9978

4177.59

140

60.0

24.1

2 442.1

0.01629

0.00102

61.39

983.37

8.207

984.84

0.9984

4180.10

150

65.6

22.4

2 269.8

0.01634

0.00102

61.20

980.33

8.182

981.84

0.9990

4182.61

160

71.1

20.3

2 057.0

0.01639

0.00102

61.01

977.29

8.156

978.72

0.9998

4185.96

170

76.7

17.8

1 803.7

0.01645

0.00103

60.79

973.76

8.127

975.24

1.0007

4189.73

180

82.2

14.7

1 489.6

0.01651

0.00103

60.57

970.24

8.098

971.76

1.0017

4193.92

190

87.8

10.9

1 104.5

0.01657

0.00103

60.35

966.71

8.068

968.16

1.0028

4198.52

200

93.3

6.5

658.6

0.01663

0.00104

60.13

963.19

8.039

964.68

1.0039

4203.13

210

98.9

1.2

121.6

0.01670

0.00104

59.88

959.19

8.005

960.60

1.0052

4208.57

212

100.0

0.0

0.0

0.01672

0.00104

59.81

958.06

7.996

959.52

1.0055

4209.83

220

104.4

2.5

253.3

0.01677

0.00105

59.63

955.18

7.972

956.64

1.0068

4215.27

240

115.6

10.3

1 043.7

0.01692

0.00106

59.10

946.69

7.901

948.12

1.0104

4230.34

260

126.7

20.7

2 097.5

0.01709

0.00107

58.51

937.24

7.822

938.64

1.0148

4248.76

280

137.8

34.5

3 495.9

0.01726

0.00108

57.94

928.11

7.746

929.52

1.0200

4270.54

300

148.9

52.3

5 299.6

0.01745

0.00109

57.31

918.02

7.662

919.44

1.0260

4295.66

350

176.7

119.9

12 149.5

0.01799

0.00112

55.59

890.47

7.432

891.84

1.0440

4371.02

400

204.4

232.6

23 569.4

0.01864

0.00116

55.63

891.11

7.172

860.64

1.0670

4467.32

450

232.2

407.9

41 332.5

0.01940

0.00121

51.55

825.75

6.892

827.04

1.0950

4584.55

500

260.0

666.1

67 495.9

0.02040

0.00127

49.02

785.22

6.553

786.36

1.1300

4731.08

550

287.8

1030.5 104 420.6

0.02180

0.00136

45.87

734.77

6.132

735.84

1.2000

5024.16

600

315.6

1528.2 154 852.5

0.02360

0.00147

42.37

678.70

5.664

679.68

1.3620

5702.42

Chapter 6 — Domestic Water Heating Systems

THERMAL EFFICIENCY

169

B = Internal heat loss of the water heater, Btu/h (kJ/h)

a number of American Legionnaires contracted it during a convention. That outbreak was attributed to the water vapor from the building’s cooling tower(s). The bacteria that cause Legionnaires’ disease are widespread in natural sources of water, including rivers, lakes, streams, and ponds. In warm water, the bacteria can grow and multiply to high concentrations. Drinking water containing the Legionella bacteria has no known effects. However, inhalation of the bacteria into the lungs, e.g., while showering, can cause Legionnaires’ disease. Much has been published about this problem, and yet there is still controversy over the exact temperatures that foster the growth of the bacteria. Further research is required, for there is still much to be learned. It is incumbent upon designers to familiarize themselves with the latest information on the subject and to take it into account when designing their systems. Designers also must be familiar with and abide by the rules of all regulating agencies with jurisdiction.

q = Time rate of heat transfer, Btu/h (kJ/h)

Scalding1

When inefficiencies of the water-heating process are considered, the actual input energy is higher than the usable, or output, energy. Direct-fired water heaters (i.e., those that use gas, oil, etc.) lose part of their total energy capability to such things as heated flue gases, inefficiencies of combustion, and radiation at heated surfaces. Their “thermal efficiency,” Et, is defined as the heat actually transferred to the domestic water divided by the total heat input to the water heater. Expressed as a percentage, this is Equation 6-9 Et =

q−B × 100% q

where

Refer to Equations 6-1 and 6-2 to determine q. Many water heaters and boilers provide input and output energy information. Example 6-5 Calculate the heat input rate required for the water heater in Example 6-1 if this is a direct gas-fired water heater with a thermal efficiency of 80%. Solution From Example 6-1, q = 449,820 Btu/h (475 374 kJ/h). Heat input = q 449,820 Btu/h = = 562,275 Btu/h Et 0.80 q 475 374 kJ/h = = 594 217.5 kJ/h 0.80 ‰ Et 

SAFETY AND HEALTH CONCERNS Legionella Pneumophila (Legionnaires’ Disease) Legionnaires’ disease is a potentially fatal respiratory illness. The disease gained notoriety when 1For more information regarding “Scalding,” refer to ASPE Research Foundation, 1989. 2Moritz and Henriques, 1947.

A research project by Moritz and Henriques at Harvard Medical College2 looked at the relationship between time and water temperature necessary to produce a first-degree burn. A firstdegree burn, the least serious type, results in no irreversible damage. The results of the research show that it takes a 3-s exposure to 140°F (60°C) water to produce a first-degree burn. At 130°F (54°C), it takes approximately 20 s, and at 120°F (49°C), it takes 8 min to produce a first-degree burn. The normal threshold of pain is approximately 118°F (48°C). A person exposed to 120°F (49°C) water would immediately experience discomfort; it is unlikely then that the person would be exposed for the 8 min required to produce a first-degree burn. People in some occupancies (e. g., hospitals), as well as those over the age of 65 and under the age of 1, may not sense pain or move quickly enough to avoid a burn once pain is sensed. If such a possibility exists, scalding protection should be considered. It is often required by code. (For more information on skin damage caused by exposure to hot water, see Table 6-4.)

ASPE Data Book — Volume 2

170

Table 6-4 Time/Water Temperature Combinations Producing Skin Damage

specific requirements that must be observed when designing projects and selecting equipment for them.

Water Temperature °F

°C

Time (s)

Over 140

Over 60

Less than 1

140 135

60 58

2.6 5.5

130 125

54 52

15 50

120

49

290

Source: Tom Byrley. 1979. 130 degrees F or 140 degrees F. Contractor Magazine (September). First published in American Journal of Pathology. Note: The above data indicate conditions producing the first evidence of skin damage in adult males.

CODES AND STANDARDS The need to conform to various codes and standards determines many aspects of the design of a domestic hot-water system as well as the selection of components and equipment. Some of the most often used codes and standards are: 1. Regional, state, and local plumbing codes. 2. American Society of Heating, Refrigerating, and Air-Conditioning Engineers ASHRAE/ IES 90.1. 3. American Society of Mechanical Engineers (ASME) code for fired and unfired pressure vessels. 4. ASME and American Gas Association (AGA) codes for relief valves. 5. Underwriters’ Laboratory (UL) listing for electrical components. 6. National Sanitation Foundation (NSF) listing. 7. AGA approval for gas-burning components. 8. National Fire Protection Association (NFPA) standards. 9. National Electrical Code (NEC). 10. Department of Health and Environmental Control (DHEC). In addition, the federal government, the agencies with jurisdiction over public schools and public housing, and many other agencies have

REFERENCES 1.

ASPE Research Foundation. 1989. Temperature limits in service hot water systems. Journal of Environmental Health (June): 38-48.

2.

Moritz, A. R., and F. C. Henriques, Jr. 1947. The relative importance of time and surface temperature in the causation of cutaneous burns. American Journal of Pathology 23: 695-720.

Chapter 7 — Fuel-Gas Piping Systems

7 LOW AND MEDIUM-PRESSURE NATURAL GAS SYSTEMS The composition, specific gravity, and heating value of natural gas vary depending upon the well (or field) from which the gas is gathered. Natural gas is a mixture of gases, most of which are hydrocarbons, and the predominant hydrocarbon is methane. Some natural gases contain significant quantities of nitrogen, carbon dioxide, or sulfur (usually as H2S). Natural gases containing sulfur or carbon dioxide are apt to be corrosive. These corrosive substances are usually eliminated by treatment of the natural gas before it is transmitted to the customers. Readily condensable petroleum gases are also usually extracted before the natural gas is put into the pipeline to prevent condensation during transmission. The specific gravity of natural gas varies from 0.55 to 1.0 and the heating value varies from 900 to 1100 Btu/ft3 (33.9 to 41.5 mJ/m3). Natural gas is nominally rated at 1000 Btu/ft3 (37.7 J/m3), manufactured gas is nominally rated at 520 Btu/ft3 (20 mJ/m3), and mixed gas is nominally rated at 800 Btu/ft3 (30.1 mJ/m3). Liquefied petroleum gases (LPG) are nominally rated at 2500 Btu/ft3 (94.1 mJ/m3). Natural gas is transmitted from the fields to the local marketing and distribution systems at very high pressures, usually in the range of 500 to 1000 psi (3447.4 to 6894.8 kPa). Local distribution systems are at much lower pressures. The plumbing engineer should determine the specific gravity, pressure, and heating value of the gas from the utility company or LPG provider serving the project area.

173

Fuel-Gas Piping Systems

This chapter covers fuel-gas systems on consumers’ premises—that is, upstream and downstream from the gas supplier’s meter set assembly—and includes system design and appliance gas usage, gas train venting, ventilation, and combustion air requirements. Since natural gas is a depletable energy resource, the engineer should design for its efficient use. The direct utilization of natural gas is preferable to the use of electrical energy when electricity is obtained from the combustion of gas or oil. However, in many areas, the gas supplier and/or governmental agencies may impose regulations that restrict the use of natural gas. Refer to the chapter “Energy Conservation in Plumbing Systems,” in Data Book Volume 1, for information on appliance efficiencies and energy conservation recommendations.

Design Considerations The energy available in 1 cubic foot (cubic meter) of natural gas, at atmospheric pressure, is called the “heating (or caloric) value.” The flow of gas, expressed in cubic feet per hour (cfh) or cubic meters per hour (m3/h), in the distribution piping depends on the amount of gas being consumed by the appliances. This quantity of gas depends on the requirements of the appliances. For example, 33,200 Btu/h (35 mJ/h) are required to raise the temperature of 40 gal (151.4 L) of water from 40 to 140°F (4.4 to 60°C) in 1 hour. This value is obtained as follows: Equation 7-1 Q = m × Cp × ∆T

ASPE Data Book — Volume 2

174

Btu/ft3 (J/m3)

where Q = Energy required, Btu/h (J/h) m = Mass flow, gal/h (L/h) Cp = Specific heat of water, 1 Btu/°F (J/°C) ∆T = Temperature rise, °F (°C) Q = (40 gal/h)(8.33 lb/gal)(1 Btu/lb-°F)(100°F) = 33,320 Btu/h [Q = (151 L/h)(1 kg/L)(6.1 kJ/kg-°C)(38°C) = 35 MJ/h] If the water heater in this case is 80% efficient, then 41,650 Btu/h (43.8 mJ/h) of gas will be needed at the appliance’s burner (33,320 Btu/ h/.80). If natural gas with a heating value of 1000 Btu/ft3 (37.7 mJ/m3) serves the appliance, the piping system must supply 41.7 cfh (1.2 m3/h) of gas to the appliance with adequate pressure to allow proper burner operation. The formula for the flow rate of gas is shown below: Equation 7-2 Q =

Output (Eff × HV)

where Q = Gas flow rate, cfh (m3/h) Output = Appliance’s output, Btu/h (J/h) Eff = Appliance’s efficiency, % HV = Heating value of the fuel gas, Btu/ft3 (J/m3) The difference between the input and the output is the heat lost in the burner, the heat exchanger, and the flue gases. Water heating and space heating equipment is usually 75 to 85% efficient, and ratings are given for both input and output. Cooking and laundry equipment is usually 75 to 85% efficient, and ratings are given for both input and output. However, cooking and laundry equipment is usually rated only by its input requirements. When the input required for the appliance is known, Equation 7-2 is expressed as follows: Equation 7-3 Q =

Input HV

where Q = Gas flow rate, cfh (m3/h) Input = Appliance’s input, Btu/h (J/h) HV = Heating value of the fuel gas,

When the exact data on the appliance’s gas usage is unavailable from the equipment manufacturer, Table 7-1 can be used to obtain the approximate requirements for common appliances. The gas pressure in the piping system downstream of the meter is usually 5 to 14 in. (127 to 355.6 mm) of water column (wc). Design practice limits the pressure losses in the piping to 0.5 in. (12.7 mm) wc, or less than 10%, when 5 to 14 in. (127 to 355.6 mm) wc is available at the meter outlet. However, local codes may dictate a more stringent pressure drop maximum; these should be consulted before the system is sized. Most appliances require approximately 5 in. (127mm) wc; however, the designer must be aware that large appliances, such as boilers, may require higher gas pressures to operate properly. Where appliances require higher pressures or where long distribution lines are involved, it may be necessary to use higher pressures at the meter outlet to satisfy the appliance requirements or provide for greater pressure losses in the piping system. If greater pressure at the meter outlet can be attained, a greater pressure drop can be allowed in the piping system. If the greater pressure drop design can be used, a more economical piping system is possible. Systems are often designed with meter outlet pressures of 3 to 5 psi (20.7 to 34.5 kPa) and with pressure regulators to reduce the pressure for appliances as required. The designer has to allow for the venting of such regulators, often to the atmosphere, when they are installed within buildings. When bottled gas is used, the tank can have as much as 150 psi (1044.6 kPa) pressure, to be reduced to the burner design pressure of 11 in. (279.4 mm) wc. The regulator is normally located at the tank for this pressure reduction. To size the gas piping for a distribution system, the designer must determine the following items: 1. The appliance requirements, including the gas consumption, pressure, and pipe size required at the appliance connection (total connected load). Is the appliance provided with a pressure regulator? 2. The piping layout, showing the length of (horizontal and vertical) piping, number of fittings and valves, and number of appliances.

Chapter 7 — Fuel-Gas Piping Systems

Table 7-1

175

Approximate Gas Demand for Common Appliancesa

Appliance

Input, Btu/h

(mJ/h)

Commercial kitchen equipment Small broiler

30,000

(31.7)

Large broiler

60,000

(63.3)

Combination broiler and roaster

66,000

(69.6)

Coffee maker, 3-burner

18,000

(19)

Coffee maker, 4-burner

24,000

(25.3)

Deep fat fryer, 45 lb (20.4 kg) of fat

50,000

(52.8)

Deep fat fryer, 75 lb (34.1 kg) of fat

75,000

(79.1)

Doughnut fryer, 200 lb (90.8 kg) of fat

72,000

(76)

100,000

(105.5)

96,000

(101.3)

Revolving oven, 4 or 5 trays

210,000

(221.6)

Range with hot top and oven

90,000

(95)

Range with hot top

45,000

(47.5)

100,000

(105.5)

Range with fry top

50,000

(52.8)

Coffee urn, single, 5-gal (18.9 L)

28,000

(29.5)

Coffee urn, twin, 10-gal. (37.9 L)

56,000

(59.1)

Coffee urn, twin, 15-gal (56.8 L)

84,000

(88.6)

Stackable convection oven, per section of oven

60,000

(63.3)

Clothes dryer (Type I)

35,000

(36.9)

Range

65,000

(68.6)

Stove-top burners (each)

40,000

(42.2)

Oven

25,000

(26.4)

30-gal (113.6-L) water heater

30,000

(31.7)

40 to 50-gal (151.4 to 189.3-L) water heater

50,000

(52.8)

Log lighter

25,000

(26.4)

Barbecue

50,000

(52.8)

50,000

(52.8)

5,000

(5.3)

Gas engine, per horsepower (745.7 W)

10,000

(10.6)

Steam boiler, per horsepower (745.7 W)

50,000

(52.8)

2-deck baking and roasting oven 3-deck baking oven

Range with fry top and oven

Residential equipment

Miscellaneous equipment Commercial log lighter Bunsen burner

Commercial clothes dryer (Type 2)

See manufacturer’s data.

aThe values given in this table should be used only when the manufacturer’s data are not available.

176

3. The fuel gas to be supplied, where and by whom; also the specific gravity and heating value of the fuel gas and the pressure to be provided at the meter outlet.

ASPE Data Book — Volume 2

Standard engineering methods may be used to determine pipe sizes for a system, or the acceptable capacity/pipe size tables may be used when such tables are available for the specific operating conditions of the system under consideration. The diversity factor is an important item when determining the most practical pipe sizes to be used in occupancies such as multiple-family dwellings. It is dependent on the type and number of gas appliances being installed. Refer to the “pipe sizing” section later in this chapter.

care should be taken so that, in the event of gas leakage, gas will not accumulate in the concealed space. The installation of gas piping in an unventilated space under a building should be avoided. Such conditions have resulted in disastrous explosions. A gas leak anywhere along the length of a buried pipe can flow in the annular space around the pipe and accumulate in a cavity under the building. Ignition of this accumulated gas can result in an explosion. For this reason, it is best to try to locate the gas main above grade at the point of entrance into the building. If this is not feasible, the main can be installed in a ventilated sleeve (containment pipe). The designer should carefully detail this installation so that leaked gas will be harmlessly vented to the atmosphere and not accumulated in the building. Gas piping should be located where it will not be subject to damage by such things as vehicles, forklifts, cranes, machinery, or occupants. Support of piping should be in accordance with codes and as described in the chapter “Hangers and Supports,” in Data Book Volume 4 (forthcoming).

The most common material used for gas piping is black steel; however, many other materials are utilized, including copper, wrought iron, plastic, brass, and aluminum alloy. The proper material to be used depends on the specific installation conditions and local code limitations. Any condition that could be detrimental to the integrity of the piping system must be avoided. Corrosion and physical damage are the most obvious causes of pipe failure. The piping material itself and/or the provisions taken for the protection of the piping material must prevent the possibility of pipe failure. Corrosion can occur because of electrolysis or because a corrosive material is in contact with either the exterior or the interior surface of the piping.

Valves, controls, pressure regulators, and safety devices used in gas systems should be designed and approved for such use. Shut-off valves should be installed in accessible locations and near each appliance, with a union between the valve and the appliance. Shut-off valves should be of the plug or cock type with a lever handle. Larger sizes should be of the lubricated plug type. The quarter-turn lever handle provides visual indication of whether the valve is opened or closed. An approved assembly of semirigid or flexible tubing and fittings, referred to as an “appliance connector,” is sometimes used to connect the piping outlet to the appliance. Appliance connectors are rated by capacity, based on a specified pressure, flow, and pressure drop.

Coatings are commonly applied to buried metallic pipe to prevent corrosion of the exterior surface. The gas supplier should be contacted to determine if the gas contains any corrosive material, such as moisture, hydrogen sulfide (H2S), or carbon dioxide (CO2). Due to the grave consequences of leakage in the gas piping system, the designer must carefully consider the piping material to be used and the means to protect the piping and protect against leaks.

Laboratory Gas

4. The allowable pressure loss from the meter to the appliances. 5. The diversity factor—the number of appliances operating at one time compared to the total number of connected appliances. This should be provided by the owner and/or user.

Gas piping should be installed only in safe locations. Buried piping should be installed deep enough to protect the pipe from physical damage. When piping is installed in concealed spaces,

Natural gas or propane gas is used in laboratories at lab benches for Bunsen burners and other minor users. Typical Bunsen burners consume either 5000 cfh (141.6 m3/h) (small burners) or 10,000 cfh (283.2 m3/h) (large burners). The maximum pressure at the burner should not exceed 14 in. wc (355.6 mm wc). The gas distribution piping should be sized in the manner discussed later in this chapter; however, the following diversities may be applied:

Chapter 7 — Fuel-Gas Piping Systems

Number of Outlets 1–8 9–16 17–29 30–79 80–162 163–325 326–742 743–1570 1571–2900 2901 and up

Use Factor 100 90 80 60 50 45 40 30 25 20

Minimum Flow, cfh (m3/h) 9 (0.26) 15 (0.43) 24 (0.68) 48 (1.36) 82 (2.32) 107 (3.03) 131 (3.71) 260 (7.36) 472 (13.37) 726 (20.56)

Branch piping that serves one or two laboratories should be sized for 100% usage regardless of the number of outlets. Use factors should be modified to suit special conditions and must be used with judgment after consultation with the owner and/or user. Some local codes require that laboratory gas systems, especially those in schools or universities, be supplied with emergency gas shut-off valves on the supply to each laboratory. The valve should be normally closed and opened only when the gas is being used. It should be located inside the laboratory and used in conjunction with shutoff valves at the benches or equipment, which may be required by other codes. The designer should ensure that locations meet local code requirements. Where compressed air is also supplied to the laboratory, aluminum check valves should be provided on the supply to the laboratory to prevent air from being injected back into the gas system. An alternative to aluminum check valves is gas turrets with integral check valves.

Gas Train Vents Guidelines for the use of vents from pressure regulators, also referred to as “gas-train vents,” can be found in the latest editions of NFPA 54 and Factory Mutual (FM) Loss Prevention Data Sheet 6-4, as well as in other publications of industry standards, such as those issued by Industrial Risk Insurers (IRI) and the American Gas Association (AGA). As a practical matter, many boiler manufacturers can provide resource materials, such as gas-train venting schemes, that reference standards organizations. Factors that determine which standard to reference are based upon the input (Btu/h) and the owner’s

177

insurance underwriter. The plumbing designer must be aware of the existence of these standards—especially when designing piping for boilers with input capacities of 2,500,000 Btu/h (732 kW) or more that are not listed by a nationally recognized testing laboratory agency, e.g., equipment that does not bear a UL label or have Factory Mutual Research Corporation (FMRC) approval listing. Industrial-boiler gas trains often require multiple, piped, gas-train vents to the atmosphere. These are usually ¾ in., and the material used should follow the classification as specified in NFPA 54 under the heading “Gas Piping System Design, Materials, and Components.” Where multiple gas-train vents are indicated, each shall run independently to the atmosphere. Care must be exercised in the location of the termination points of these pipes. Vent pipes should terminate with 90° ells turned down vertically and be protected with an insect screen over the outlet. It should be noted that when the pressure regulators activate they can release large amounts of fuel gas. It is not uncommon for a local fire department to be sumoned to investigate an odor of gas caused by a gas-train vent discharge. Every attempt should be made to locate the terminal point of the vents above the line of the roof and away from doors, windows, and fresh-air intakes. It should also be located on a side of the building that is not protected from the wind. Refer to NFPA 54 and local codes for vent locations.

Appliances Most manufacturers of gas appliances rate their equipment by the gas consumption values that are used to determine the maximum gas flow rate in the piping. Table 7-1 shows the approximate gas consumption for some common appliances. The products of combustion from an appliance must be safely exhausted to the outside. This is accomplished with a gas vent system in most cases. Where an appliance has a very low rate of gas consumption (e.g., Bunsen burner or countertop coffee maker) or where an appliance has an exhaust system associated with the appliance (e.g., gas clothes dryer or range), and the room size and ventilation are adequate, a gas vent system may not be required. Current practice usually dictates the use of factory-fabricated and listed

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vents for small to medium-sized appliances. Large appliances and equipment may require specially designed venting or exhaust systems. For proper operation, the gas vent system must satisfy the appliance draft and building safety requirements. To meet these conditions, consideration of combustion and ventilation air supplies, draft hood dilution, startup conditions, flue gas temperatures, oxygen depletion, external wind conditions, and pollution dispersion is required. For example, appliances equipped with draft hoods need excess vent capacity to draw in the draft hood dilution air and prevent draft hood spillage. Inadequate combustion air supply can cause oxygen depletion and inadequate firing. This condition can create a safety hazard because of a combination of draft hood spillage and inadequate flue gas removal. The motive force exhausting flue gases from an appliance can be gravity (a natural draft due to the difference in densities between hot flue gases and ambient air) or mechanical (induced-draft fan or forceddraft fan). The motive force involved affects the size and configurations that may safely be applied to a vent system. The designer is referred to the chapter on gas vent systems of the local mechanical or plumbing code and to the data developed by the manufacturers of gas vents for sizing information. Due to the fact that many codes require that appliances conform to an approved standard, such as the American Gas Association (AGA), a simple approach to the design of vent systems can be as follows: 1. The vent system conforms to the manufacturer’s instructions and the terms of the listing. 2. The gravity vents cannot exceed certain horizontal lengths, must exceed certain minimum slopes upward to their vertical chimneys, and cannot terminate less than 5 ft (1.5 m) above the appliance outlet. 3. The vent size cannot be smaller than the vent connector collar size of the appliance. 4. The size of a single vent that services more than one appliance must not be less than the area of the largest vent connector served plus 50% of the areas of the additional vent connectors. Since vent chimney heights and flue gas temperatures determine the theoretical draft, there are many situations where the above approach will produce oversized vent systems. Whatever

approach is used, a great deal of care must be taken when designing vents that are horizontal. It is recommended that every system be engineered and checked for compliance with codes. A conservative design is warranted in light of the hazards involved. Combustion air is required for the proper operation of gas appliances. In addition to the theoretical amount of air required for combustion, excess air is necessary to assure complete combustion. Approximately 1 ft3 (0.03 m3) of air at standard conditions is needed for each 100 Btu (1055 J) of fuel burned. Air is also required for the dilution of flue gases when draft hoods are provided. Some additional amount of air is also needed for ventilation of the equipment room. This air for combustion, dilution, and ventilation is usually supplied by permanent openings or ducts connected to the outdoors. Two openings should be supplied. One opening should be high (above the draft hood inlet) and the other opening should be low (below the combustion air inlet to the appliance). The size of these openings can be determined by standard engineering methods, based on the air balance in the equipment room and taking into account the energy (natural draft or mechanical) available to draw air into the room; however, these must comply with codes, which usually give more conservative opening sizes, based on the area of the opening required per Btu (J) of gas consumed.

Gas Boosters Definition A “gas booster” is a mechanical piece of equipment that increases the pressure of gas for the purpose of meeting equipment or functional demands. It is used when there is insufficient pressure available from the gas utility or LPG storage device to supply the necessary pressure to the equipment at hand. It is important to note that the gas service must be capable of the volumetric flow rate required at the boosted level. A booster cannot overcome an inadequate volumetric supply. (See “Sizing a Gas Booster” below.) Gas boosters for natural or liquefied petroleum gas Boosters for natural or utility-supplied gas are hermetically sealed and are equipped to deliver a volumetric flow rate (user defined but within the booster’s rated capacity) to an elevated pressure beyond the supply pressure. The outlet pressure usually remains at a constant differential above the supply pressure within a reasonable range. The discharge pressure is the sum of the

Chapter 7 — Fuel-Gas Piping Systems

incoming gas pressure and the booster-added pressure at the chosen flow rate. The incoming gas pressure usually has an upper safety limit as stipulated by the hermetic gas booster manufacturer. Therefore, in the engineering literature from the manufacturer, the engineer may find cautions or warnings about the upper limits of incoming pressure, usually about 5 psi (34.5 kPa). Materials of construction Housing and rotor Boosters used for fuel gas must be UL listed for the specific duty intended and shall be hermetically sealed. Casings on standard boosters are usually constructed of carbon steel, depending on the equipment supplier. Booster casings are also available in stainless steel and aluminum. Inlet and outlet connections are threaded or flanged, depending on the pipe size connection and the manufacturer selected, and the casings are constructed leak tight. Drive impellers are contained within the casing and always manufactured of a sparkresistant material such as aluminum. Discharge type check valves are furnished on the booster inlet and on the booster bypass. It is important that these checks are listed and approved for use on the gas stream at hand. The fan, control panel, valves, piping, and interelectrical connections can be specified as a skid-mounted package at the discretion of the designer. This allows for UL listing of the entire package rather than of individual components. Electrical components Motor housings for gas-booster systems are designed for explosionproof (XP) construction and are rated per NEMA Class 1, Division 1, Group D classification with thermal overload protection. A factory UL listed junction box with a protected, sealed inlet is necessary for wiring connections. Other electrical ancillary equipment Boosters are equipped with low-pressure switches that monitor the incoming gas pressure. The switch is designed to shut down the booster should the utility-supplied pressure fall below a preset limit. The set point is usually about 3 in. (80 mm) water column (wc), but the designer should verify the limit with the local gas provider. The switch must be UL listed for use with the gas service at hand. When the switch opens, it de-energizes the motor control circuit and simultaneously outputs both audible and visual signals, which require manual resetting. The booster can be

179

equipped with an optional hi/low gas-pressure switch. This feature equips the booster to run only when adequate supply pressure is available. The switch shuts the booster down at the maximum discharge set-point pressure at the output line pressure. Minimum gas flow Gas boosters normally require a minimum gas flow that serves as an internal cooling medium. For example, a booster sized at a flow rate of 10,000 cfh (283.2 m3/h) will have an inherent minimum turndown based on the minimum flow required to cool the unit. This rate, in the example, may be, say 2000 cfh (566.3 m3/h) (see Figure 7-2). Should the unit be required to run below this turndown rate, additional supplemental cooling systems must be incorporated into the booster design. The heat exchangers normally rated for this use are water cooled. Intrinsic safety Electrical connections are made through a sealed, explosion-proof conduit to the XP junction box on the booster unit. Control panels are rated NEMA 4 for outdoor use and NEMA 12 for indoor use unless the booster system is to be located in a hazardous area, which may have additional requirements. The panel, as an assembly, must display a UL label specific for its intended use. Gas laws Pressure-volume relationships The gas laws apply to the relationship of the incoming gas supply and the boosted service. The standard law for compressed gas relationships is as follows: Equation 7-4 PV = RT where P

= Pressure, psi or in. wc (kPa or mm wc)

V

= Volume, cfh (m3/h)

R

= Constant for the gas-air mixture used

T

= Temperature, °F (°C)

Usually the temperature of the gas remains relatively constant and can therefore be ignored in the relationship. Therefore, the pressure times the volume is proportional to a constant R. Further, the pressure/volume ratios before and after the booster are proportional, that is:

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180

Equation 7-5

level and a boiler in the penthouse of a 50-story building, it may be necessary to boost the supply to the kitchen but not to the boiler. The gas rises to the penthouse through the piping system because of the density differential, its rising is dependent on this stack effect, which is directly related to the piping system layout.

P1V1 = P2V2 where P1 = Pressure at a point prior to the booster P2 = Pressure at a point after the booster

Design considerations Although a gas booster is a basic mechanical piece of equipment, there are significant design considerations that should be taken into account when applying it:

For almost every case, the volumetric rating of gas-fired equipment is in Btu/h, which can readily be converted to cfh. In the booster application, sizing criteria should be approached from a “standard” cfh (scfh) not an “actual” cfh (acfh) rating.

1. Indoor vs. outdoor location. This may be driven by local code or the end user. An indoor location involves a lower initial cost and lower costs for long-term maintenance. Outdoor locations are inherently safer.

Gas temperatures and density As stated, the temperature of the gas is usually constant. However, in the event that the gas is to be heated or cooled, the above gas laws are affected by temperature. Gas-density changes affect the constant but usually do not affect the relationship since the same mixture is boosted across the fan.

2. Access. The location should be accessible for installation, inspection, and maintenance. The unit should not be so accessible as to create a security issue. Keep the equipment out of traffic patterns and protect it from heavy equipment.

High-rise building issues It should be noted that consideration must be given to the rise effect in available gas pressure as gas rises in the piping through a high-rise building. Therefore, if the gas system supplies a kitchen on the first

3. Minimum and maximum flow rates. Boosters usually have a minumum flow rate that must be maintained so that the booster’s motor is

(A)

Chapter 7 — Fuel-Gas Piping Systems

181

(B)

(C) Figure 7-1 Variations of a Basic Simplex Booster System: (A) Standby Generator Application with Accumulator Tank Having a Limitation on Maximum Pressure, (B) Dual Booster System for Critical Systems Like Those in Hospitals, (C) Heat Exchanger Loop Example—Required for High Flow Range with Low Minimum Flow.

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kept cool. When specifying a booster, always indicate the minimum flow required in addition to other design parameters. Cooling devices and bypass loops may be required if the application requires a turndown in flow (lowest flow expected) that is higher than the booster’s minimum flow. 4. Controls and interlocking. Determine how the application should be controlled and what demands the application will put on the system. The control philosophy, method of electrically interlocking the system to the gasfired equipment, and physical hardware will vary based on the application. For some specific examples, see the schematics in Figure 7-1, which shows variations of a basic simplex booster system for an emergency generator. In Figure 7-1(A), the regulator controls maximum delivered pressure, and a combination high/low pressure switch on the tank cycles the booster to ensure emergency startup pressure within a design deadband for the generator. Oversized piping, in this case, can be substituted for the tank itself. Provide adequate volume so that the generator can fire and deliver standby power back to the booster system to continue operation during main power interrupt. In Figure 7-1(B), a dual booster system, the booster is controlled in a lead/lag control scenario. Should one booster fail, the second is started automatically. Unit operation is rotated automatically via the control panel to share the duty and to keep both units in operating order. The booster with a heat-exchanger loop shown in Figure 7-1(C) has a potential of up to 15 psi (103.4 kPa), and down to 28 in. wc (711.2 mm wc) supply pressure. The system automatically diverts gas around the booster if there is sufficient supply pressure. While these illustrations obviously do not cover all the potential applications, they are provided to give the system designer some guidance. Sizing a gas booster A gas booster’s main purpose is to elevate the pressure of a volume of gas to overcome a supply-pressure deficiency. When sizing a booster, an engineer needs to understand the following terms and issues: Maximum design flow (Qmax) The sum of all gas loads at the maximum capacity rating (MCR) for all equipment downstream of the booster that could possibly be required to operate simultaneously.

Minimum design flow (Qmin) The minimum volumetric flow that could exist while the booster is operating. This flow is not always associated with the smallest Btu/h rated piece of equipment. For example, when evaluating a 75,000,000 Btu/ h (7.5 mmBtu/h) boiler with a 10:1 turndown ratio in comparison to 1.0 mmBtu/h (0.3 mmW) hotwater heater that is on/off in operation, the larger Btu/h (W) rated boiler has the smaller flow of 0.75 mmBtu/h (0.2 mmW) at its minimum firing rate. Turndown (TD) ratio The ratio of the MCR input to the equipment’s minimum or “low-fire” input. For example, a 100 mmBtu/h (29.3 mmW) burner that can fire at a minimum rate of 20 mmBtu/h (5.9 mmW) has a TD ratio of 5:1. Pressure “droop” and peak consumption “Pressure droop” is the inability of a supply system to maintain a steady or consistent inlet pressure as an increase in volumetric flow is demanded. Often, in areas where boosters are applied, the supply pressure in off-peak months when gas is not in such demand can be sufficient to run a system. As the local demand for gas increases, the supply system can no longer provide the gas efficiently and the pressure falls off or droops. It is the booster’s function to overcome the droop (or excessive pressure drop) of the supply system during such times. Flow rate relationships Do your flows for separate pieces of equipment relate to each other? In other words, do the three boilers always operate in unison while another process machine always operates off peak and alone? Relationships among the equipment can significantly affect both maximum and minimum flow rates. Test block A factor of safety added to design criteria. Typically, a minimum of 5% added volume and 10% added static pressure should be applied to the design criteria. When specifying the equipment, ensure that you note both the design and test block conditions. This makes other people working on the system aware and ensures that safety factors are not applied to criteria that already include safety factors. Minimum inlet pressure (PI-min) What is the minimum supply pressure in in. (mm) wc gage? This must be evaluated during peak flow demands both for the equipment and for the local area! Always evaluate during flow, not static, conditions! It is also important to know how high the inlet pressure is expected to rise during off-

Chapter 7 — Fuel-Gas Piping Systems

peak periods. A booster is typically rated to about 5 psi (34.5 kPa). It may be possible to exceed this rating during off-peak demand periods, therefore, a bypass system or other means of protection is required. Often this pressure can be specified by the local gas company as the minimum guaranteed gas pressure from their supply system. Also, the maximum inlet pressure (PI) must be determined. max Maximum outlet pressure (PO-max) List all maximum and required supply pressures for the various pieces of equipment being supplied gas from the booster. Determine the differential between the highest expected gas pressure supply to the booster (e.g., 8 in. wc [203.2 mm wc]) and the lowest maximum supply pressure rating to a piece of equipment (e.g., 18 in. wc [457.2 mm wc]). The booster’s pressure gain should not exceed this differential (for the above example, 18 – 8 = 10 in. wc [457.2 – 203.2 = 254 mm wc]) unless other means of protecting the downstream equipment are provided. Outlet pressure protection There are several ways to protect equipment downstream of a booster should it be necessary due to potential over-pressurization during off-peak periods. If all the equipment being serviced operates at nominally the same pressure, install a regulator on the inlet or outlet of the booster to maintain a controlled maximum outlet pressure. If the equipment being serviced operates at various inlet pressures, it may be best to supply a regulator for each piece of equipment. Most often, packaged equipment is supplied with its own regulator. If this is the case, review the equipment regulator’s maximum inlet pressure. To perform an evaluation of system requirements: 1. Establish design Qmin and Qmax per the above definitions while evaluating TD requirements. 2. Establish PI-min and PI-max per the above definitions. 3. Define maximum inlet pressure requirements to equipment (PI-eq). 4. Define piping pressure losses (PPL) from gas booster location to each piece of equipment. 5. Design flow rate (QD) = Qmin to Qmax, cfh (m3/h) 6. Design pressure boost (∆P) = PI-eq + PPL – PI-min

183

7. Test block flow (QTB) = (1.05 × Qmin) to (1.05 × Qmax) 8. Test block pressure boost: 1.10 × ∆P = PI-eq + PPL – PI-min where PPL = Pressure losses, psi (kPa)

Pipe Sizing A number of formulae can be used to calculate the capacity of natural gas piping based on such variables as delivery pressure, pressure drop through the piping system, pipe size, pipe material, and length of piping. Most of these formulae are referenced in numerous current model codes, as well as in the NFPA standards. The most commonly referenced formula for gas pressures under 1½ psi (10.3 kPa), the NFPA formula listed in the National Fuel Gas Code, NFPA 54, was used as the basis for Tables 7-3 and 7-4. The other commonly referenced equation, the Weymouth formula, was used as the basis for Table 7-5 and Appendix Tables 7-A1 through 7-A6. The Weymouth formula, referenced within these tables, is applicable only for initial gas pressures greater than 1 psi (6.9 kPa). A third formula, the Spitzglass formula, which is shown in Table 7A7, is limited to gas pressures under 1 psi (6.9 kPa). The design of piping systems for gas flow is a basic fluid flow problem and its solution is similar to that for any other pipe sizing problem. The required flow rate can easily be determined, the pressure losses due to friction can be calculated, and the required residual pressure at each appliance is usually known. Using basic engineering formulae, the engineer can tabulate the various quantities, establish the pipe sizes for each section of piping, and demonstrate the pressure and flow rate at any point in the system. The flow of gas in a pipe with pressures not exceeding 1 psi (6.9 kPa) is often computed using the Spitzglass formula, as shown below: Equation 7-6 h

Q = 3550 K

q SL

Q = 3550 K

h ½ ‰ SL

Q = 3550

d5h ½ 3.6 — SL ˆ1 + d + 0.03dž

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184

where

ing the capacities for the various pipe sizes and lengths give solutions that are quickly and easily obtained and generally adequate for most situations. These tables are in many model codes and in National Fire Protection Association (NFPA) Standard 54. The lengths shown are developed lengths (lengths measured along the center line of the piping plus a fitting allowance). The pressure drops include an allowance for a nominal amount of valves and fittings.

3

Q = The gas at standard conditions, cfh (m /h) K = Constant for a given pipe size h = The pressure drop, in. (mm) wc S = Specific gravity of the gas L = Length of pipe, ft (m) The constant for a given pipe size (K) may be calculated by using the following relation:

To determine the size of each section of pipe in a gas-supply system using the gas pipe-sizing tables, the following method should be used:

Equation 7-7 K =

D5

‰

½

1 + 3.6 + 0.03 × D D

1. Measure the length of the pipe from the gas meter location to the most remote outlet on the system. Add a fitting allowance.



where

2. Select the column showing that distance (or the next longer distance, if the table does not give the exact length).

K = Constant for a given pipe size D = Inside diameter of the pipe, in. (mm) The length used in the above formula should be corrected to allow for the added resistance to flow caused by valves and fittings in the piping.

3. Use the vertical column to locate all gas demand figures for this particular system. 4. Starting at the most remote outlet, find in the vertical column the selected gas demand for that outlet. If the exact figure is not shown, choose the next larger figure below in the column.

This corrected length is called the “equivalent length.” Table 7-2 gives the equivalent lengths for various valve and fitting sizes. The designer is cautioned to conform to applicable codes for the project location.

5. Opposite this demand figure, in the first column at the left, the correct size of pipe will be found.

The above method is accurate and gives a solution that has a definite technical basis. However, in actual practice, published tables show-

Table 7-2 Equivalent Lengths for Various Valve and Fitting Sizes Pipe Size, in. (mm) Fitting

¾ (19.1)

1 (25.4)

1½ (38.1)

2 (50.8)

2½ (63.5)

3 (76.2)

4 (101.6)

5 (127)

6 (152.4) 8 (203.2)

Equivalent Lengths, ft (m) 90° elbow

1.00

2.00

2.50

3.00

4.00

5.50

6.50

9.00

(0.3)

(0.61)

(0.76)

(0.91)

(1.22)

(1.68)

(1.98)

0.50

0.75

1.00

1.50

2.00

3.00

(0.15)

(0.23)

(0.46)

(0.61)

2.50

3.50

4.50

5.00

6.00

(0.76)

(1.07)

(1.37)

(1.52)

Gas cock

4.00

5.00

7.50

9.00

(approx.)

(1.22)

(1.52)

(2.29)

(2.74)

Tee (run)

Tee (branch)

(0.3)

12.0

15.0

(2.74)

(3.66)

(4.57)

3.50

4.50

6.00

7.00

(0.91)

(1.07)

(1.37)

(1.83)

(2.13)

11.0

13.0

18.0

24.0

30.0

(1.83)

(3.35)

(3.96)

(5.49)

(7.32)

(9.14)

12.0

17.0

20.0

28.0

37.0

46.0

(3.66)

(5.18)

(6.1)

(8.53)

(11.28)

(14.02)

Note: The pressure drop through valves should be taken from manufacturers’ published data rather than using the equivalent lengths, since the various patterns of gas cocks can vary greatly.

Chapter 7 — Fuel-Gas Piping Systems

185

6. Proceed in a similar manner for each outlet and each section of pipe. For each section of pipe, determine the total gas demand supplied by that section.

1. The distance from the gas meter to outlet “A” is 600 ft (182.9 m). 2. For sizing the pipe from outlet A to the meter, use Table 7-3:

7. To size all branches, other than the branch to the most remote outlet, measure the length of pipe from the outlet to the meter and follow steps 1 through 6 above utilizing the new length. For conditions other than those covered above, the size of each gas piping system may be determined by standard engineering methods acceptable to the authority having jurisdiction. The maximum allowable pressure drop through a system should not exceed 10% of the supply pressure, which must be verified with the locally referenced code and the authority having jurisdiction. Where a gas of a different specific gravity is delivered or where the pressure differs from what the referenced gas tables in the local code show, the size of the piping required must be calculated by means of standard engineering methods acceptable to the authority having jurisdiction. As an example, calculate the following proposed system’s pipe size (see Figure 7-2):

•

Section 1: 400-ft (123-m) length, carrying 150 cfh (1.2 L/s)—using the 400-ft (123 m) column, the size would be 1¼ in. (31.8 mm).

•

Section 2: 550-ft (168-m) length, carrying 600 cfh (4.7 L/s)—using an interpolation between the 500-ft (153.8m) column and the 750-ft (230.7-m) column, the size would be 2½ in. (63.5 mm).

•

Section 3: 600-ft (183-m) length, carrying 2400 cfh (18.9 L/s)—using an interpolation between the 500-ft (153.8m) column and the 750-ft (230.7-m) column, the size would be 4 in. (101.6 mm).

3. For sizing Section 4: from Table 7-3 on the 300-ft (91.4-m) column, carrying 450 cfh (3.5 L/s), size would be 2 in. (50.8 mm) 4. For sizing Section 5: from Table 7-3 on the 100-ft (30.5-m) column, carrying 1800 cfh (14.2 L/s), size would be 2½ in. (63.5 mm)

Figure 7-2

678

413

84,580

41,166

25,423

14,052

6,890

3,897

2,445

1,270

847

58,131

28,293

17,473

9,658

4,735

2,679

1,681

873

582

284

151

72

50

6,638

3,254

1,841

1,155

600

400

195

103

49

100

9,644

5,331

2,613

1,478

928

482

321

157

83

40

150

8,872

4,904

2,404

1,360

853

443

296

144

76

37

175

8,254

4,562

2,237

1,265

794

412

275

134

71

34

7,315

4,043

1,982

1,121

704

365

244

119

63

30

6,628

3,664

1,796

1,016

637

331

221

108

57

27

200 250 300 Capacities (cfh)

9,186

5,673

3,136

1,537

870

546

283

189

92

49

23

400

8,141

5,028

2,779

1,362

771

484

251

168

82

43

21

500

6,538

4,037

2,232

1,094

619

388

202

135

66

35

17

750

5,595

3,456

1,910

936

530

332

173

115

56

30

14

1000

4,959

3,063

1,693

830

469

295

153

102

50

26

13

1250

9,232

4,493

2,775

1,534

752

425

267

139

92

45

24

11

1500

644

364

228

119

79

39

20

10

2000

8,493 7,901

4,134 3,846

2,553 2,375

1,411 1,313

692

391

246

127

85

41

22

11

1750

84,786 72,566 58,273 53,610 49,874 44,202 40,051 34,278 30,380 24,396 20,880 18,506 16,767 15,426 14,351

46,681 39,953 32,084 29,517 27,460 24,337 22,051 18,873 16,727 13,432 11,496 10,189

22,720 19,446 15,615 14,366 13,365 11,845 10,732

14,031 12,009

7,756

3,802

2,151

1,350

701

468

228

121

58

75

1,524

6,345

3,088

1,907

1,054

517

292

183

95

64

31

16

8

3000

399,251 243,199 167,149 134,227 114,881 92,253 84,872 78,957 69,978 63,405 54,267 48,095 38,622 33,056 29,297 26,545 24,421 22,719 18,244

252,192 153,619 105,582

138,852

67,580

41,736

23,070

11,310

6,398

4,014

2,084

1,391

219

105

25

Natural Gas Pipe Sizing Table for Gas Pressure < 1.5 psi

Total Equivalent Length of Longest Run of Piping in System (ft)

Table 7-3

The pressure drop through the system Correction Factor ( = 0.61 if initial pressure < 1.5 psi) The specific gravity of the natural gas

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

11.938

12

6.065

6

7.981

5.047

5

10.02

4.026

4

10

3.068

3

8

2.067

2.469

2½

1.61

1½

2

1.049

1.38

0.824

¾

1¼

172

0.622

½

360

10

h = 0.5 Cr = 0.61 S = 0.6

Given:

Pipe Actual Size I.D.a (in.) (in.)

Q = D = h = Cr = L =

Where:

1

h 0.541 ‰ Cr × L

Flow (ft3/h) Internal pipe diameter (in.) Pressure drop (in. wc) Correction factor of 0.61 Total equivalent length of system piping (ft)

Q = 2313 × D2.623 ×

NFPA Formula:

186 ASPE Data Book — Volume 2

20.9

26.6

35.1

40.9

52.5

62.7

77.9

102.2

128.2

154.1

202.7

254.5

303.2

20

25

35

40

50

65

75

100

125

150

200

250

300

665.64

323.97

200.08

110.59

54.22

30.67

19.24

9.99

6.67

3.25

1.72

0.82

7.6

830.93

457.49

222.67

137.51

76.01

37.27

21.08

13.23

6.87

4.58

2.23

1.19

0.57

15.2

94.51

52.24

25.61

14.49

9.09

4.72

3.15

1.53

0.81

0.39

30.5

75.90

41.95

20.57

11.63

7.30

3.79

2.53

1.23

0.65

0.31

45.7

69.82

38.59

18.92

10.70

6.72

3.49

2.33

1.13

0.60

0.29

53.4

64.96

35.91

17.60

9.96

6.25

3.24

2.17

1.05

0.56

84.46

52.16

28.83

14.14

8.00

5.02

2.61

1.74

0.85

0.45

0.21

72.29

44.64

24.68

12.10

6.84

4.29

2.23

1.49

0.72

0.38

0.18

64.07

39.57

21.87

10.72

6.07

3.81

1.98

1.32

0.64

0.34

0.16

152.4

51.45

31.77

17.56

8.61

4.87

3.06

1.59

1.06

0.52

0.27

0.13

228.6

90.47

44.03

27.19

15.03

7.37

4.17

2.62

1.36

0.91

0.44

0.23

0.11

304.8

80.19

39.03

24.10

13.32

6.53

3.69

2.32

1.20

0.80

0.39

0.21

0.10

381

72.65

35.36

21.84

12.07

5.92

3.35

2.10

1.09

0.73

0.35

0.19

0.09

457.2

66.84

32.53

20.09

11.11

5.44

3.08

1.93

1.00

0.67

0.33

0.17

0.08

533.4

62.18

30.26

18.69

10.33

5.07

2.87

1.80

0.93

0.62

0.30

0.16

0.08

609.6

667.26 571.09 458.61 421.91 392.51 347.87 315.20 269.77 239.09 192.00 164.33 145.64 131.96 121.40 112.94

367.38 314.43 252.50 232.30 216.11 191.53 173.54 148.53 131.64 105.71

93.22

57.57

31.82

15.60

8.83

5.54

2.88

1.92

0.93

0.50

0.24

76.2 91.4 121.9 Capacities (L/s)

0.27

61.0

178.81 153.04 122.89 113.06 105.18

110.43

61.04

29.93

16.93

10.62

5.51

3.68

1.79

0.95

0.46

22.9

90.69

49.93

24.30

15.01

8.30

4.07

2.30

1.44

0.75

0.50

0.24

0.13

0.06

914.4

3142.11 1913.97 1315.46 1056.36 904.11 726.03 667.94 621.39 550.73 499.00 427.08 378.51 303.96 260.15 230.56 208.91 192.19 178.80 143.58

1984.75 1208.98

1092.76

531.86

328.46

181.56

89.01

50.35

31.59

16.40

10.95

5.33

2.83

1.35

3.1

Natural Gas Pipe Sizing Table for Gas Pressure < 10.3 kPa

Total Equivalent Length of Longest Run of Piping in System (m)

Table 7-3(M)

The pressure drop through the system (mm wc) Correction factor ( = 0.61 if initial pressure < 10.3 kPa) The specific gravity of the natural gas

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

15.8

15

Pipe Actual Size I.D.a (mm) (mm)

h = 12.7 Cr = 0.61 S = 0.6

Given:

Flow (L/s) Internal pipe diameter (mm) Pressure drop (kPa or mm wc) Correction factor of 0.61 Total equivalent length of system piping (m)

Q = D = h = Cr = L =

Where:

h 0.541 Q = 0.00787 2313 × D2.623 × ž — ‰ Cr × L 

NFPA Formula:

Chapter 7 — Fuel-Gas Piping Systems 187

h 0.541 ‰ Cr × L 

130

0.622

0.824

1.049

1.38

1.61

2.067

2.469

3.068

4.026

5.047

6.065

7.981

10.02

11.938

½

¾

1

1¼

1½

2

2½

3

4

5

6

8

10

12

64,157

31,226

19,284

10,659

5,226

2,956

1,855

963

643

313

166

79

25

9,109

5,035

2,469

1,396

876

455

304

148

79

38

100

7,315

4,043

1,982

1,121

704

365

244

119

63

30

150

6,730

3,720

1,824

1,032

647

336

224

109

58

28

175

6,261

3,461

1,697

960

602

313

209

102

54

26

8,141

5,028

2,779

1,362

771

484

251

168

82

43

21

6,968

4,303

2,379

1,166

660

414

215

143

70

37

18

400

6,175

3,814

2,108

1,034

585

367

190

127

62

33

16

500

4,959

3,063

1,693

830

469

295

153

102

50

26

13

750

8,720

4,244

2,621

1,449

710

402

252

131

87

43

23

11

1000

7,729

3,762

2,323

1,284

630

356

223

116

77

38

20

10

1250

7,003

3,408

2,105

1,163

570

323

202

105

70

34

18

9

1500

6,442

3,136

1,936

1,070

525

297

186

97

65

31

17

8

1750

800

392

222

139

72

48

23

12

6

3000

5,993 4,813

2,917 2,342

1,801 1,447

996

488

276

173

90

60

29

16

7

2000

64,314 55,044 44,202 40,666 37,832 33,529 30,380 26,001 23,045 18,506 15,838 14,037 12,719 11,701 10,886 8,742

35,410 30,306 24,337 22,390 20,829 18,461 16,727 14,316 12,688 10,189

8,985

5,549

3,067

1,504

851

534

277

185

90

48

23

200 250 300 Capacities (cfh)

17,234 14,750 11,845 10,897 10,138

10,643

5,883

2,884

1,632

1,024

532

355

173

92

44

75

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

302,849 184,476 126,790 101,817 87,142 69,978 64,379 59,892 53,081 48,095 41,163 36,482 29,297 25,074 22,223 20,135 18,524 17,233 13,839

80,088

44,095

21,461

13,254

7,326

3,592

2,032

1,275

662

442

215

114

55

50

Natural Gas Pipe Sizing Table for Gas Pressure < 1.5 psi

Total Equivalent Length of Longest Run of Piping in System (ft)

Table 7-4

The pressure drop through the system Correction factor ( = 0.61 if initial pressure < 1.5 psi) The specific gravity of the natural gas

191,298 116,527

105,325

51,263

31,659

17,499

8,579

4,853

3,045

1,581

1,055

514

273

10

h = 0.3 Cr = 0.61 S = 0.6

Given:

Pipe Actual Size I.D.a (in.) (in.)

Q = D = h = Cr = L =

Where:

Flow (ft3/h) Internal pipe diameter (in.) Pressure drop (in. wc) Correction factor of 0.61 Total equivalent length of system piping (ft)

Q = 2313 × D2.623 ×

NFPA Formula:

188 ASPE Data Book — Volume 2

20.9

26.6

35.1

40.9

52.5

62.7

77.9

102.2

128.2

154.1

202.7

254.5

303.2

20

25

35

40

50

65

75

100

125

150

200

250

300

917.06

504.92

245.75

151.77

83.89

41.13

23.27

14.60

7.58

5.06

2.46

1.31

0.63

7.6

2383.42 1451.83

1505.52

828.91

403.44

249.15

137.72

67.52

38.19

23.96

12.44

8.30

4.04

2.15

1.03

3.1

997.83

630.29

347.03

168.90

104.31

57.66

28.27

15.99

10.03

5.21

3.48

1.69

0.90

0.43

15.2

71.69

39.63

19.43

10.99

6.90

3.58

2.39

1.16

0.62

0.30

30.5

93.22

57.57

31.82

15.60

8.83

5.54

2.88

1.92

0.93

0.50

0.24

45.7

85.76

52.96

29.28

14.35

8.12

5.09

2.65

1.77

0.86

0.46

0.22

53.4

79.78

49.27

27.24

13.35

7.55

4.74

2.46

1.64

0.80

0.42

0.20

70.71

43.67

24.14

11.83

6.69

4.20

2.18

1.46

0.71

0.38

0.18

64.07

39.57

21.87

10.72

6.07

3.81

1.98

1.32

0.64

0.34

0.16

54.84

33.87

18.72

9.18

5.19

3.26

1.69

1.13

0.55

0.29

0.14

61.0 76.2 91.4 121.9 Capacities (L/s)

99.85

48.60

30.01

16.59

8.13

4.60

2.89

1.50

1.00

0.49

0.26

0.12

152.4

80.19

39.03

24.10

13.32

6.53

3.69

2.32

1.20

0.80

0.39

0.21

0.10

228.6

68.63

33.40

20.63

11.40

5.59

3.16

1.98

1.03

0.69

0.33

0.18

0.09

60.82

29.60

18.28

10.11

4.95

2.80

1.76

0.91

0.61

0.30

0.16

0.08

381

55.11

26.82

16.57

9.16

4.49

2.54

1.59

0.83

0.55

0.27

0.14

0.07

457.2

92.09

50.70

24.68

15.24

8.42

4.13

2.34

1.47

0.76

0.51

0.25

0.13

0.06

533.4

85.67

47.17

22.96

14.18

7.84

3.84

2.17

1.36

0.71

0.47

0.23

0.12

0.06

609.6

68.80

37.88

18.44

11.39

6.29

3.09

1.75

1.10

0.57

0.38

0.18

0.10

0.05

914.4

801.30 685.81 550.73 506.66 471.35 417.75 378.51 323.96 287.12 230.56 197.33 174.89 158.47 145.79 135.63 108.91

506.15 433.20 347.87 320.04 297.73 263.88 239.09 204.63 181.36 145.64 124.65 110.47 100.10

278.67 238.51 191.53 176.21 163.93 145.28 131.64 112.67

135.63 116.08

83.76

46.30

22.70

12.84

8.06

4.18

2.79

1.36

0.72

0.35

22.9

304.8

Natural Gas Pipe Sizing Table for Gas Pressure < 10.3 kPa

Total Equivalent Length of Longest Run of Piping in System (m)

Table 7-4(M)

The pressure drop through the system (mm wc) Correction factor ( = 0.61 if initial pressure < 10.3 kPa) The specific gravity of the natural gas

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

15.8

15

Pipe Actual Size I.D.a (mm) (mm)

h = 12.7 Cr = 0.61 S = 0.6

Given:

Flow (L/s) Internal pipe diameter (mm) Pressure drop (kPa or mm wc) Correction factor of 0.61 Total equivalent length of system piping (m)

Q = D = h = Cr = L =

Where:

h 0.541 Q = 0.00787 2313 × D2.623 × ž — ‰ Cr × L 

NFPA Formula:

Chapter 7 — Fuel-Gas Piping Systems 189

406 257 182 148 128 105 97 91 81 74 64 57 52 47 41 36 33 31 29 26 23 20

0.622

Actual

860 544 385 314 272 222 206 192 172 157 136 122 111 99 86 77 70 65 61 54 50 43

0.824

¾

1,637 1,035 732 598 518 423 391 366 327 299 259 232 211 189 164 146 134 124 116 104 95 82

1.049

1

Table 7-5

Given: P1 = 2 P2 = 1 S = 0.6

3,402 2,152 1,521 1,242 1,076 878 813 761 680 621 538 481 439 393 340 304 278 257 241 215 196 170

1.380

1¼

5,132 3,245 2,295 1,874 1,623 1,325 1,227 1,147 1,026 937 811 726 662 593 513 459 419 388 363 325 296 257

1.610

1½

9,991 6,319 4,468 3,648 3,160 2,580 2,388 2,234 1,998 1,824 1,580 1,413 1,290 1,154 999 894 816 755 706 632 577 500

2.067

2

3

16,048 10,150 7,177 5,860 5,075 4,144 3,836 3,589 3,210 2,930 2,537 2,270 2,072 1,853 1,605 1,435 1,310 1,213 1,135 1,015 927 802

28,641 18,114 12,809 10,458 9,057 7,395 6,847 6,404 5,728 5,229 4,529 4,050 3,698 3,307 2,864 2,562 2,339 2,165 2,025 1,811 1,654 1,432

2.469 3.068 Capacities (cfh)

2½

Pipe Size—Inside Diameter (in.)a

59,116 37,388 26,438 21,586 18,694 15,264 14,131 13,219 11,823 10,793 9,347 8,360 7,632 6,826 5,912 5,288 4,827 4,469 4,180 3,739 3,413 2,956

4.026

4

108,010 68,312 48,304 39,440 34,156 27,888 25,819 24,152 21,602 19,720 17,078 15,275 13,944 12,472 10,801 9,661 8,819 8,165 7,637 6,831 6,236 5,401

5.047

5

176,303 111,504 78,845 64,377 55,752 45,521 42,144 39,423 35,261 32,188 27,876 24,933 22,761 20,358 17,630 15,769 14,395 13,327 12,466 11,150 10,179 8,815

6.065

6

366,604 231,860 163,950 133,865 115,930 94,657 87,635 81,975 73,321 66,932 57,965 51,846 47,328 42,332 36,660 32,790 29,933 27,713 25,923 23,186 21,166 18,330

7.981

8

672,498 425,325 300,750 245,562 212,663 173,638 160,758 150,375 134,500 122,781 106,331 95,106 86,819 77,653 67,250 60,150 54,909 50,836 47,553 42,533 38,827 33,625

10.02

10

Initial pressure in system (psi) Final pressure in system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

½

= = = = = =

Nominal

Q D L S P1 P2

(P12 – P22) × D16/3 ½ — ž LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula:

1,072,823 678,513 479,781 391,740 339,256 277,002 256,454 239,890 214,565 195,870 169,628 151,720 138,501 123,879 107,282 95,956 87,596 81,098 75,860 67,851 61,939 53,641

11.94

12

190 ASPE Data Book — Volume 2

3.20 2.02 1.43 1.17 1.01 0.83 0.76 0.71 0.64 0.58 0.51 0.45 0.41 0.37 0.32 0.29 0.26 0.24 0.23 0.20 0.18 0.16

6.77 4.28 3.03 2.47 2.14 1.75 1.62 1.51 1.35 1.24 1.07 0.96 0.87 0.78 0.68 0.61 0.55 0.51 0.48 0.43 0.39 0.34

20

15.8

20.9

12.9 8.15 5.76 4.70 4.07 3.33 3.08 2.88 2.58 2.35 2.04 1.82 1.66 1.49 1.29 1.15 1.05 0.97 0.91 0.81 0.74 0.64

26.6

25

Table 7-5(M)

Given:

35

26.8 16.9 12.0 9.78 8.47 6.91 6.40 5.99 5.35 4.89 4.23 3.79 3.46 3.09 2.68 2.39 2.19 2.02 1.89 1.69 1.55 1.34

35.1

40

40.4 25.5 18.1 14.7 12.8 10.4 9.65 9.03 8.08 7.37 6.39 5.71 5.21 4.66 4.04 3.61 3.30 3.05 2.86 2.55 2.33 2.02

40.9

78.6 49.7 35.2 28.7 24.9 20.3 18.8 17.6 15.7 14.4 12.4 11.1 10.2 9.08 7.86 7.03 6.42 5.94 5.56 4.97 4.54 3.93

52.5

50

75

126.3 79.9 56.5 46.1 39.9 32.6 30.2 28.2 25.3 23.1 20.0 17.9 16.3 14.6 12.6 11.3 10.3 9.55 8.93 7.99 7.29 6.32

225.4 142.6 100.8 82.3 71.3 58.2 53.9 50.4 45.1 41.2 35.6 31.9 29.1 26.0 22.5 20.2 18.4 17.0 15.9 14.3 13.0 11.3

62.7 77.9 Capacities (L/s)

65

465.2 294.2 208.1 169.9 147.1 120.1 111.2 104.0 93.0 84.9 73.6 65.8 60.1 53.7 46.5 41.6 38.0 35.2 32.9 29.4 26.9 23.3

102.2

100

Pipe Size—Inside Diameter (mm)a 125

850.0 537.6 380.2 310.4 268.8 219.5 203.2 190.1 170.0 155.2 134.4 120.2 109.7 98.2 85.0 76.0 69.4 64.3 60.1 53.8 49.1 42.5

128.2

150

1387.5 877.5 620.5 506.6 438.8 358.3 331.7 310.3 277.5 253.3 219.4 196.2 179.1 160.2 138.8 124.1 113.3 104.9 98.1 87.8 80.1 69.4

154.1

2885.2 1824.7 1290.3 1053.5 912.4 744.9 689.7 645.1 577.0 526.8 456.2 408.0 372.5 333.2 288.5 258.1 235.6 218.1 204.0 182.5 166.6 144.3

202.7

200

5292.6 3347.3 2366.9 1932.6 1673.7 1366.5 1265.2 1183.5 1058.5 966.3 836.8 748.5 683.3 611.1 529.3 473.4 432.1 400.1 374.2 334.7 305.6 264.6

254.5

250

P1 = 13.8 Initial pressure of the system (kPa) P2 = 6.89 Final pressure of the system (kPa) S = 0.6 The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

Actual

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula:

300

8443.1 5339.9 3775.9 3083.0 2669.9 2180.0 2018.3 1887.9 1688.6 1541.5 1335.0 1194.0 1090.0 974.9 844.3 755.2 689.4 638.2 597.0 534.0 487.5 422.2

303.2

Chapter 7 — Fuel-Gas Piping Systems 191

ASPE Data Book — Volume 2

192

Enter chart at left, with cubic feet per hour (liters per second), move horizontally to pipe diameter line, drop perpendicularly to length line and move horizontally to read pressure drop at right.

Figure 7-3 Pipe Sizing, Low Pressure System with an Initial Pressure Up to 1 psi (6.9 kPa) Source: Reprinted from data developed by the Pacific Gas and Electric Company.

Chapter 7 — Fuel-Gas Piping Systems

193

Enter chart at left, with cubic feet per hour (liters per second), move horizontally to pipe diameter line, drop perpendicularly to length line and move horizontally to read pressure drop at right.

Figure 7-4 Pipe Sizing, Any System with an Initial Pressure Between 1 and 20 psi (6.9 and 137.8 kPa) Source: Reprinted from data developed by the Pacific Gas and Electric Company.

ASPE Data Book — Volume 2

194

Many codes, including American National Standards Institute (ANSI) Z223.1 and NFPA 54, recommend the same procedures detailed above, except for Step 7. These codes recommend utilizing the same maximum distance column for all branch lines regardless of the exact distance from the meter. Steps 3 and 4 of the example would be, from Table 7-3 on the 750-ft (230.7m) column carrying 450 cfh (3.5 L/s) for Section 4 and 1800 cfh (14.2 L/s) for section 5, pipe sizes of 2½ in. (63.5 mm) and 4 in. (91.2 mm), respectively. The designer should investigate the local code and apply the appropriate sizing procedure. Therefore, for gas pressures less than 1 psi (6.895 kPa), use Appendix Table 7-A7 and for gas pressures less than 1.5 psi (10.3 kPa), use Tables 7-3 or 7-4. For sizing systems with more than 1 psi (6.9 kPa) supply pressure, Tables 7-4 and 7-5 and Appendix Tables 7-A1–A6 may be used. For sizing systems with less than 1 psi (6.9 kPa) pressure, Table 7-A7 may be used. The use of these tables is similar to that described for Table 7-3. Occasionally, it is necessary to size a natural gas distribution system for pressures other than the conventional low and medium pressures already discussed. Figures 7-3 and 7-4 are included for such applications. (Proprietary pipe sizing calculators are available which also solve the applicable equations.) Figure 7-3 is for any low-pressure system with an initial pressure up to 1 psi (6.9 kPa) or 28 in. (711.2 mm) wc, and Figure 7-4 is for any system with an initial pressure between 1 and 20 psi (6.9 and 137.8 kPa). These graphs can be used in two ways: one, to determine the pressure drop, and the other, to determine the pipe size. Essentially, diversity can only be used to determine the gas flow rate for a system when such a system serves laboratories, as previously discussed, or cooking appliances. Diversity cannot be applied to water heating or space heating appliances because these appliances will, at times, simultaneously demand full capacity gas flows. For more than 25 years, however, many codes have recognized that, in multifamily buildings, the demand is always less than the total connected load when gas is used for cooking. Figures 7-5 and 7-6 indicate the percentage of the maximum possible demand (diversity) that can be expected, based on the number of units in the system.

LIQUEFIED PETROLEUM GAS Liquefied petroleum gas (LPG) is a refined natural gas developed mainly for use beyond the utilities’ gas mains, but it has proven to be competitive within the areas not covered by mains in rural areas. It is chiefly a blend of propane and butane with traces of other hydrocarbons remaining from the various production methods. The exact blend is controlled by the LPG distributor to match the climatic conditions of the area served. For this reason, the engineer must confirm the heat value of the supplied gas. Unlike natural gas, LPG has a specific gravity of 1.53 and a rating of 2500 Btu/cf (93 MJ/cm3). The compact storage for relatively large quantities of energy has led to widespread acceptance and usage of LPG in all areas previously served by utilities providing other gas to users, including automotive users.

Storage The LPG storage tanks can be provided by the vendor or the customer and are subject to the regulations of the US Department of Transportation (DOT) and the local authority, as well as NFPA standards, so the plumbing designer has little opportunity to design storage tanks and piping, per se. Normally, the designer starts at the storage supply outlet, and the piping system is generally in the low-pressure, 11 in. (279 mm) wc, range. Piping must be designed so that there is no more than 2 in. (50 mm) wc pressure drop at any outlet in the system. Gas pipes may be sized in accordance with NFPA 54, which is accepted by most jurisdictions. Small tanks (for example, those for residential cooking and heating) are allowed to be located in close proximity to buildings. Large tanks (e.g., for industrial or multiple building use), however, have strict requirements governing their location in relation to buildings, public use areas, and property lines. If large leaks occur, the heavier-than-air gas will hug the ground and form a fog. The potential for a hazardous condition could exist. Proper safety precautions and equipment, as well as good judgment, must be utilized when locating large LPG storage tanks. Note: The following is only a very brief outline and is not intended to be used in lieu of NFPA 54. The designer must use the current accepted edition.

Chapter 7 — Fuel-Gas Piping Systems

Figure 7-5

Typical Diversity Curves for Gas Supply to High-Rise Apartments

Figure 7-6 Diversity Percentage for Multifamily Buildings (Average)

195

196

Material Pipe Wrought iron, modular iron, steel (galvanized, plastic-wrapped, or black), brass, and copper. Aluminum alloy pipe may be used if pressure is not in excess of ½ psi (34 kPa). To qualify, aluminum piping must be factory coated for external, outdoor use. Cast-iron pipe shall not be used. Tubing Copper (K&L), steel, and aluminum alloy with same restrictions as in pipe. NFPA 54, Par. 2.6.3. Plastic pipe and tubing Plastic pipe and tubing may be used outside underground only. NFPA 54, Par. 2.6.4. Fittings Whenever pipe lines are run, joints and fittings are involved. Since these are the weak points in the system where leaks are most likely to occur, their selection and installation should be made with care and NFPA recommendations should be followed. The following listing includes some of the more important points to be considered regarding these connections. Pipe joints For low-pressure piping (½ psi [3.45 kPa] or less) with LPG, the following standards apply: Metallic pipe joints may be threaded, flanged, or welded, and nonferrous metallic pipe may also be soldered or brazed with material having a melting point in excess of 1000ºF (537.8ºC). Corrosion of the piping must be prevented and the pipe must not be in contact with plaster, cement, or damp insulators and may not be used underground. Brazing alloy must not contain phosphorous. Metallic fittings (except valves, strainers, or filters) must be steel, brass, or malleable or ductile iron when used with steel or wrought-iron pipe, and must be copper or brass when used with copper or brass pipe. NFPA 54, Par. 2-6-8(a)-(e). Cast-iron fittings, in pipe sizes normally used in LPG installations serving domestic and commercial users, may be authorized by the authority having jurisdiction for either low or high-pressure piping. (NFPA 54, Par. 2.6.2.) Defective fittings for either pipe or tubing should be replaced and not repaired. It is not good practice to use second-hand or used fittings unless they are cleaned, carefully inspected, and determined to be the equivalent of new before being reused.

ASPE Data Book — Volume 2

Tubing joints For pressures normally encountered in the utilization of LPG, the following requirement is applicable to the methods of joining tubing: Metallic tubing joints must either be made with approved gas tubing fittings or be soldered or brazed with a material having a melting point in excess of 1000ºF (537.8ºC). Metallic, ball sleeve, compression type tubing fittings must not be used for this purpose. NFPA 54, Par. 2.6.8(b). Flared fittings are commonly used in connection with tube working and are generally less expensive to use than those involving high-temperature soldering. While sleeve type fittings are used in some appliances, their use in piping systems is not approved. Flare nuts used out of doors in areas where freezing temperatures are encountered should be of a heavier weight than those used indoors. These are sometimes referred to as “frost proof” and are preferable to the lighter fittings, which are apt to crack and cause a gas leak.

Flexible Gas Hose The practice of connecting hot plates and portable space heaters with flexible hose is no longer considered a safe practice. The current requirement regarding their use covers both indoor and outdoor applications: Indoor Indoor gas hose connectors may be used with laboratory shop or ironing equipment that requires mobility during operation, if listed for this application. A shut-off valve must be installed where the connector is attached to the building piping. The connector must be of minimum length but shall not exceed 6 ft (1.8 m). The connector must not be concealed and must not extend from one room to another nor pass through wall partitions, ceilings, or floors. Outdoor Outdoor gas hose connectors may be used to connect portable outdoor gas-fired appliances, if listed for this application. A shutoff valve or a listed quick-disconnect device must be installed where the connector is attached to the supply piping and in such a manner as to prevent the accumulation of water or foreign matter. This connection must be made only in the outdoor area where the appliance is to be used. NFPA 54, Par. 5.5.2

Chapter 7 — Fuel-Gas Piping Systems

197

Warning

APPENDIX A

The fact that LPG vapors are heavier than air has a practical bearing on several items. For one thing, LPG systems are located in such a manner that the hazard of escaping gas is kept at a minimum.

The following gas pipe sizing tables (Tables 7-A1 through 7-A7) are for varying gas pressures in both inch-pound (IP) and international standard (SI) units.

Since the heavier-than-air gas tends to settle in low places, the vent termination of relief valves must be located at a safe distance from openings into buildings that are below the level of such valves. With many gas systems, for example, both the gas pressure regulator and the fuel containers are installed adjacently to the building they serve. This distance must be a least 3 ft (0.91 m) measured horizontally. However, the required clearances vary according to the tank size and the adjacent activities. The designer should refer to the local code and NFPA 54 for these clearances. The slope of flash tubes used in connection with lighting devices is determined by the specific gravity of the gas. With propane, for example, the tubes are slanted downward from the burner to the ignition source as the heavier-than-air gas tends to flow downward when released. Automatic appliances are normally equipped with safety pilots, which shut off the flow of gas in the event of pilot failure. With lighter-than-air gases, the automatic shut-off valve usually cuts off the gas to the main burner only, leaving the pilot burner unprotected. The small amount of gas that is released is discharged through the vent or otherwise dissipated. With LPG, however, gas escaping from the pilot would tend to collect in a low place and be a hazard. For this reason, LPG appliances are normally equipped with 100% safety pilots, which shut off the gas to both the main burner and the pilot in the event of pilot failure. When LPG piping is installed in crawl spaces or in pipe tunnels, the engineer may consider a “sniffer” system, which automatically shuts down the gas supply, sounds an alarm, and activates an exhaust system to purge the escaping gas from the area.

Leak Test Prior to charging the new piping with LPG, a satisfactory leak test must be conducted. The designer should refer to the applicable local code and NFPA 54 for test requirements.

These tables are based on the use of schedule 40 black steel pipe with threaded joints.

663 420 297 242 210 171 159 148 133 121 105 94 86 77 66 59 54 50 47 42 38 33

0.622

Actual

1,404 888 628 513 444 363 336 314 281 256 222 199 181 162 140 126 115 106 99 89 81 70

0.824

¾

2,674 1,691 1,196 976 845 690 639 598 535 488 423 378 345 309 267 239 218 202 189 169 154 134

1.049

1

Table 7-A1

Given: P1 = 3 P2 = 1 S = 0.6

5,555 3,513 2,484 2,029 1,757 1,434 1,328 1,242 1,111 1,014 878 786 717 641 556 497 454 420 393 351 321 278

1.380

1¼

8,380 5,300 3,748 3,060 2,650 2,164 2,003 1,874 1,676 1,530 1,325 1,185 1,082 968 838 750 684 633 593 530 484 419

1.610

1½

2½

3

26,207 16,575 11,720 9,569 8,287 6,767 6,265 5,860 5,241 4,785 4,144 3,706 3,383 3,026 2,621 2,344 2,140 1,981 1,853 1,657 1,513 1,310

46,771 29,581 20,917 17,078 14,790 12,076 11,180 10,458 9,354 8,539 7,395 6,614 6,038 5,401 4,677 4,183 3,819 3,536 3,307 2,958 2,700 2,339

2.469 3.068 Capacities (cfh)

16,316 10,319 7,297 5,958 5,159 4,213 3,900 3,648 3,263 2,979 2,580 2,307 2,106 1,884 1,632 1,459 1,332 1,233 1,154 1,032 942 816

2.067

2

4

96,537 61,055 43,172 35,250 30,528 24,926 23,077 21,586 19,307 17,625 15,264 13,652 12,463 11,147 9,654 8,634 7,882 7,297 6,826 6,106 5,574 4,827

4.026

Pipe Size—Inside Diameter (in.)a

176,380 111,553 78,880 64,405 55,776 45,541 42,163 39,440 35,276 32,203 27,888 24,944 22,771 20,367 17,638 15,776 14,401 13,333 12,472 11,155 10,183 8,819

5.047

5

287,901 182,085 128,753 105,127 91,042 74,336 68,822 64,377 57,580 52,563 45,521 40,715 37,168 33,244 28,790 25,751 23,507 21,763 20,358 18,208 16,622 14,395

6.065

6

598,661 378,627 267,729 218,600 189,313 154,574 143,107 133,865 119,732 109,300 94,657 84,663 77,287 69,127 59,866 53,546 48,880 45,255 42,332 37,863 34,564 29,933

7.981

8

1,098,185 694,553 491,123 401,000 347,277 283,550 262,516 245,562 219,637 200,500 173,638 155,307 141,775 126,807 109,818 98,225 89,666 83,015 77,653 69,455 63,404 54,909

10.02

10

Initial pressure of the system (psi) Final pressure of the system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

½

= = = = = =

Nominal

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula:

1,751,912 1,108,007 783,479 639,708 554,003 452,342 418,787 391,740 350,382 319,854 277,002 247,758 226,171 202,293 175,191 156,696 143,043 132,432 123,879 110,801 101,147 87,596

11.94

12

198 ASPE Data Book — Volume 2

5.22 3.30 2.34 1.91 1.65 1.35 1.25 1.17 1.04 0.95 0.83 0.74 0.67 0.6 0.52 0.47 0.43 0.39 0.37 0.33 0.30 0.26

11.05 6.99 4.94 4.04 3.50 2.85 2.64 2.47 2.21 2.02 1.75 1.56 1.43 1.28 1.11 0.99 0.90 0.84 0.78 0.70 0.64 0.55

20

15.8

20.9

21.0 13.31 9.41 7.68 6.65 5.43 5.03 4.70 4.21 3.84 3.33 2.98 2.72 2.43 2.10 1.88 1.72 1.59 1.49 1.33 1.21 1.05

26.6

25

Table 7-A1(M)

Given: P1 = 20.69 P2 = 6.89 S = 0.6

35

43.7 27.7 19.6 15.96 13.83 11.29 10.45 9.78 8.74 7.98 6.91 6.18 5.64 5.05 4.37 3.91 3.57 3.30 3.09 2.77 2.52 2.19

35.1

40

65.9 41.7 29.5 24.1 20.9 17.0 15.76 14.75 13.19 12.04 10.43 9.33 8.51 7.62 6.59 5.90 5.38 4.99 4.66 4.17 3.81 3.30

40.9

128.4 81.2 57.4 46.9 40.6 33.2 30.7 28.7 25.7 23.4 20.3 18.2 16.6 14.83 12.84 11.48 10.48 9.71 9.08 8.12 7.41 6.42

52.5

50

75

206.2 130.4 92.2 75.3 65.2 53.3 49.3 46.1 41.2 37.7 32.6 29.2 26.6 23.8 20.6 18.4 16.8 15.59 14.58 13.04 11.91 10.31

368.1 232.8 164.6 134.4 116.4 95.0 88.0 82.3 73.6 67.2 58.2 52.1 47.5 42.5 36.8 32.9 30.1 27.8 26.0 23.3 21.3 18.4

62.7 77.9 Capacities (L/s)

65

759.7 480.5 339.8 277.4 240.3 196.2 181.6 169.9 151.9 138.7 120.1 107.4 98.1 87.7 76.0 68.0 62.0 57.4 53.7 48.1 43.9 38.0

102.2

100

Pipe Size—Inside Diameter (mm)a 125

1388.1 877.9 620.8 506.9 439.0 358.4 331.8 310.4 277.6 253.4 219.5 196.3 179.2 160.3 138.8 124.2 113.3 104.9 98.2 87.8 80.1 69.4

128.2

150

2265.8 1433.0 1013.3 827.3 716.5 585.0 541.6 506.6 453.2 413.7 358.3 320.4 292.5 261.6 226.6 202.7 185.0 171.3 160.2 143.3 130.8 113.3

154.1

4711.5 2979.8 2107.0 1720.4 1489.9 1216.5 1126.3 1053.5 942.3 860.2 744.9 666.3 608.2 544.0 471.1 421.4 384.7 356.2 333.2 298.0 272.0 235.6

202.7

200

8642.7 5466.1 3865.1 3155.9 2733.1 2231.5 2066.0 1932.6 1728.5 1577.9 1366.5 1222.3 1115.8 998.0 864.3 773.0 705.7 653.3 611.1 546.6 499.0 432.1

254.5

250

Initial pressure of the system (kPa) Final pressure of the system (kPa) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

Actual

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula:

300

13 787.6 8 720.0 6 166.0 5 034.5 4 360.0 3 559.9 3 295.9 3 083.0 2 757.5 2 517.3 2 180.0 1 949.9 1 780.0 1 592.0 1 378.8 1 233.2 1 125.7 1 042.2 974.9 872.0 796.0 689.4

303.2

Chapter 7 — Fuel-Gas Piping Systems 199

307 194 137 112 97 79 73 69 61 56 48 43 40 35 31 27 25 23 22 19 18 15

½

0.622

¾

649 411 290 237 205 168 155 145 130 119 103 92 84 75 65 58 53 49 46 41 37 32

0.824

1,236 782 553 451 391 319 295 276 247 226 195 175 160 143 124 111 101 93 87 78 71 62

1.049

1

Table 7-A2

Given: P1 = 3 P2 = 2.7 S = 0.6

1¼

2,568 1,624 1,149 938 812 663 614 574 514 469 406 363 332 297 257 230 210 194 182 162 148 128

1.380

1½

3,874 2,450 1,733 1,415 1,225 1,000 926 866 775 707 613 548 500 447 387 347 316 293 274 245 224 194

1.610

7,543 4,771 3,373 2,754 2,385 1,948 1,803 1,687 1,509 1,377 1,193 1,067 974 871 754 675 616 570 533 477 436 377

2.067

2

3

12,116 7,663 5,419 4,424 3,832 3,128 2,896 2,709 2,423 2,212 1,916 1,714 1,564 1,399 1,212 1,084 989 916 857 766 700 606

21,624 13,676 9,670 7,896 6,838 5,583 5,169 4,835 4,325 3,948 3,419 3,058 2,792 2,497 2,162 1,934 1,766 1,635 1,529 1,368 1,248 1,081

2.469 3.068 Capacities (cfh)

2½

4

44,632 28,228 19,960 16,297 14,114 11,524 10,669 9,980 8,926 8,149 7,057 6,312 5,762 5,154 4,463 3,992 3,644 3,374 3,156 2,823 2,577 2,232

4.026

Pipe Size—Inside Diameter (in.)a 5

81,546 51,574 36,469 29,776 25,787 21,055 19,493 18,234 16,309 14,888 12,894 11,532 10,528 9,416 8,155 7,294 6,658 6,164 5,766 5,157 4,708 4,077

5.047

6

133,106 84,183 59,527 48,603 42,092 34,368 31,818 29,763 26,621 24,302 21,046 18,824 17,184 15,370 13,311 11,905 10,868 10,062 9,412 8,418 7,685 6,655

6.065

276,780 175,051 123,780 101,066 87,525 71,464 66,163 61,890 55,356 50,533 43,763 39,143 35,732 31,960 27,678 24,756 22,599 20,923 19,571 17,505 15,980 13,839

7.981

8

507,725 321,113 227,062 185,395 160,557 131,094 121,369 113,531 101,545 92,697 80,278 71,803 65,547 58,627 50,772 45,412 41,456 38,380 35,902 32,111 29,314 25,386

10.02

10

Initial pressure of the system (psi) Final pressure of the system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

Nominal

= = = = = =

Actual

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula:

12

809,964 512,266 362,227 295,757 256,133 209,132 193,618 181,113 161,993 147,878 128,066 114,546 104,566 93,527 80,996 72,445 66,133 61,227 57,273 51,227 46,763 40,498

11.94

200 ASPE Data Book — Volume 2

2.41 1.53 1.08 0.88 0.76 0.62 0.58 0.54 0.48 0.44 0.38 0.34 0.31 0.28 0.24 0.22 0.20 0.18 0.17 0.15 0.14 0.12

5.11 3.23 2.29 1.87 1.62 1.32 1.22 1.14 1.02 0.93 0.81 0.72 0.66 0.59 0.51 0.46 0.42 0.39 0.36 0.32 0.30 0.26

20.9

15.8

Actual

9.7 6.15 4.35 3.55 3.08 2.51 2.33 2.18 1.95 1.78 1.54 1.38 1.26 1.12 0.97 0.87 0.79 0.74 0.69 0.62 0.56 0.49

26.6

25

Table 7-A2(M)

Given:

20.2 12.8 9.0 7.38 6.39 5.22 4.83 4.52 4.04 3.69 3.2 2.86 2.61 2.33 2.02 1.81 1.65 1.53 1.43 1.28 1.17 1.01

35.1

35

30.5 19.3 13.6 11.1 9.6 7.9 7.29 6.82 6.10 5.57 4.82 4.31 3.94 3.52 3.05 2.73 2.49 2.30 2.16 1.93 1.76 1.52

40.9

40

59.4 37.5 26.5 21.7 18.8 15.3 14.2 13.3 11.9 10.8 9.4 8.4 7.7 6.85 5.94 5.31 4.85 4.49 4.2 3.75 3.43 2.97

52.5

50

75

95.4 60.3 42.6 34.8 30.2 24.6 22.8 21.3 19.1 17.4 15.1 13.5 12.3 11.0 9.5 8.5 7.8 7.21 6.74 6.03 5.51 4.77

170.2 107.6 76.1 62.1 53.8 43.9 40.7 38.1 34.0 31.1 26.9 24.1 22.0 19.7 17.0 15.2 13.9 12.9 12.0 10.8 9.8 8.5

62.7 77.9 Capacities (L/s)

65

351.3 222.2 157.1 128.3 111.1 90.7 84.0 78.5 70.3 64.1 55.5 49.7 45.3 40.6 35.1 31.4 28.7 26.6 24.8 22.2 20.3 17.6

102.2

100

Pipe Size—Inside Diameter (mm)a

641.8 405.9 287.0 234.3 202.9 165.7 153.4 143.5 128.4 117.2 101.5 90.8 82.9 74.1 64.2 57.4 52.4 48.5 45.4 40.6 37.1 32.1

128.2

125

1047.5 662.5 468.5 382.5 331.3 270.5 250.4 234.2 209.5 191.3 165.6 148.1 135.2 121.0 104.8 93.7 85.5 79.2 74.1 66.3 60.5 52.4

154.1

150

2178.3 1377.6 974.1 795.4 688.8 562.4 520.7 487.1 435.7 397.7 344.4 308.1 281.2 251.5 217.8 194.8 177.9 164.7 154.0 137.8 125.8 108.9

202.7

200

3995.8 2527.2 1787.0 1459.1 1263.6 1031.7 955.2 893.5 799.2 729.5 631.8 565.1 515.9 461.4 399.6 357.4 326.3 302.1 282.5 252.7 230.7 199.8

254.5

250

P1 = 20.69 Initial pressure of the system (kPa) P2 = 18.62 Final pressure of the system (kPa) S = 0.6 The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

20

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula:

6374.4 4031.5 2850.7 2327.6 2015.8 1645.9 1523.8 1425.4 1274.9 1163.8 1007.9 901.5 822.9 736.1 637.4 570.1 520.5 481.9 450.7 403.2 368.0 318.7

303.2

300

Chapter 7 — Fuel-Gas Piping Systems 201

1,149 727 514 420 363 297 275 257 230 210 182 163 148 133 115 103 94 87 81 73 66 57

½

0.622

¾

2,433 1,538 1,088 888 769 628 581 544 487 444 385 344 314 281 243 218 199 184 172 154 140 122

0.824

4,631 2,929 2,071 1,691 1,464 1,196 1,107 1,035 926 845 732 655 598 535 463 414 378 350 327 293 267 232

1.049

1

Table 7-A3

Given: P1 = 5 P2 = 1 S = 0.6

1¼

9,622 6,086 4,303 3,513 3,043 2,484 2,300 2,152 1,924 1,757 1,521 1,361 1,242 1,111 962 861 786 727 680 609 556 481

1.380

1½

14,514 9,180 6,491 5,300 4,590 3,748 3,470 3,245 2,903 2,650 2,295 2,053 1,874 1,676 1,451 1,298 1,185 1,097 1,026 918 838 726

1.610

28,259 17,873 12,638 10,319 8,936 7,297 6,755 6,319 5,652 5,159 4,468 3,996 3,648 3,263 2,826 2,528 2,307 2,136 1,998 1,787 1,632 1,413

2.067

2

3

45,392 28,708 20,300 16,575 14,354 11,720 10,851 10,150 9,078 8,287 7,177 6,419 5,860 5,241 4,539 4,060 3,706 3,431 3,210 2,871 2,621 2,270

81,010 51,235 36,229 29,581 25,617 20,917 19,365 18,114 16,202 14,790 12,809 11,456 10,458 9,354 8,101 7,246 6,614 6,124 5,728 5,123 4,677 4,050

2.469 3.068 Capacities (cfh)

2½

4

167,206 105,750 74,777 61,055 52,875 43,172 39,970 37,388 33,441 30,528 26,438 23,647 21,586 19,307 16,721 14,955 13,652 12,640 11,823 10,575 9,654 8,360

4.026

Pipe Size—Inside Diameter (in.)a 5

305,500 193,215 136,624 111,553 96,608 78,880 73,028 68,312 61,100 55,776 48,304 43,204 39,440 35,276 30,550 27,325 24,944 23,094 21,602 19,322 17,638 15,275

5.047

6

498,660 315,380 223,007 182,085 157,690 128,753 119,202 111,504 99,732 91,042 78,845 70,521 64,377 57,580 49,866 44,601 40,715 37,695 35,261 31,538 28,790 24,933

6.065

1,036,911 655,800 463,721 378,627 327,900 267,729 247,869 231,860 207,382 189,313 163,950 146,641 133,865 119,732 103,691 92,744 84,663 78,383 73,321 65,580 59,866 51,846

7.981

8

1,902,112 1,203,001 850,650 694,553 601,501 491,123 454,692 425,325 380,422 347,277 300,750 268,999 245,562 219,637 190,211 170,130 155,307 143,786 134,500 120,300 109,818 95,106

10.02

10

Initial pressure of the system (psi) Final pressure of the system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

Nominal

= = = = = =

Actual

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula:

12

3,034,401 1,919,124 1,357,026 1,108,007 959,562 783,479 725,361 678,513 606,880 554,003 479,781 429,129 391,740 350,382 303,440 271,405 247,758 229,379 214,565 191,912 175,191 151,720

11.94

202 ASPE Data Book — Volume 2

9.04 5.72 4.04 3.30 2.86 2.34 2.16 2.02 1.81 1.65 1.43 1.28 1.17 1.04 0.90 0.81 0.74 0.68 0.64 0.57 0.52 0.45

19.14 12.11 8.56 6.99 6.05 4.94 4.58 4.28 3.83 3.50 3.03 2.71 2.47 2.21 1.91 1.71 1.56 1.45 1.35 1.21 1.11 0.96

20.9

15.8

Actual

36.4 23.05 16.30 13.31 11.52 9.41 8.71 8.15 7.29 6.65 5.76 5.15 4.70 4.21 3.64 3.26 2.98 2.75 2.58 2.30 2.10 1.82

26.6

25

Table 7-A3(M)

Given:

75.7 47.9 33.9 27.65 23.95 19.55 18.10 16.93 15.15 13.83 11.97 10.71 9.78 8.74 7.57 6.77 6.18 5.72 5.35 4.79 4.37 3.79

35.1

35

114.2 72.2 51.1 41.7 36.1 29.5 27.31 25.54 22.85 20.85 18.06 16.15 14.75 13.19 11.42 10.22 9.33 8.63 8.08 7.22 6.59 5.71

40.9

40

222.4 140.7 99.5 81.2 70.3 57.4 53.2 49.7 44.5 40.6 35.2 31.5 28.7 25.68 22.24 19.89 18.16 16.81 15.73 14.07 12.84 11.12

52.5

50

75

357.2 225.9 159.8 130.4 113.0 92.2 85.4 79.9 71.4 65.2 56.5 50.5 46.1 41.2 35.7 32.0 29.2 27.0 25.26 22.59 20.62 17.86

637.5 403.2 285.1 232.8 201.6 164.6 152.4 142.6 127.5 116.4 100.8 90.2 82.3 73.6 63.8 57.0 52.1 48.2 45.1 40.3 36.8 31.9

62.7 77.9 Capacities (L/s)

65

1315.90 832.3 588.5 480.5 416.1 339.8 314.6 294.2 263.2 240.3 208.1 186.1 169.9 151.9 131.6 117.7 107.4 99.5 93.0 83.2 76.0 65.8

102.2

100

Pipe Size—Inside Diameter (mm)a

2404.30 1520.60 1075.20 877.9 760.3 620.8 574.7 537.6 480.9 439.0 380.2 340.0 310.4 277.6 240.4 215.0 196.3 181.7 170.0 152.1 138.8 120.2

128.2

125

3924.50 2482.00 1755.10 1433.00 1241.00 1013.30 938.1 877.5 784.9 716.5 620.5 555.0 506.6 453.2 392.4 351.0 320.4 296.7 277.5 248.2 226.6 196.2

154.1

150

8160.50 5161.10 3649.50 2979.80 2580.60 2107.00 1950.70 1824.70 1632.10 1489.90 1290.30 1154.10 1053.50 942.3 816.0 729.9 666.3 616.9 577.0 516.1 471.1 408.0

202.7

200

14 969.60 9 467.60 6 694.60 5 466.10 4 733.80 3 865.10 3 578.40 3 347.30 2 993.90 2 733.10 2 366.90 2 117.00 1 932.60 1 728.50 1 497.00 1 338.90 1 222.30 1 131.60 1 058.50 946.8 864.3 748.5

254.5

250

P1 = 34.48 Initial pressure of the system (kPa) P2 = 6.89 Final pressure of the system (kPa) S = 0.6 The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

20

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula:

23 880.7 15 103.5 10 679.8 8 720.0 7 551.8 6 166.0 5 708.6 5 339.9 4 776.1 4 360.0 3 775.9 3 377.2 3 083.0 2 757.5 2 388.1 2 136.0 1 949.9 1 805.2 1 688.6 1 510.4 1 378.8 1 194.0

303.2

300

Chapter 7 — Fuel-Gas Piping Systems 203

511 323 229 187 162 132 122 114 102 93 81 72 66 59 51 46 42 39 36 32 30 26

½

0.622

¾

1,082 684 484 395 342 279 259 242 216 198 171 153 140 125 108 97 88 82 77 68 62 54

0.824

2,060 1,303 921 752 651 532 492 461 412 376 326 291 266 238 206 184 168 156 146 130 119 103

1.049

1

Table 7-A4

Given: P1 = 5 P2 = 4.5 S = 0.6

1¼

4,281 2,707 1,914 1,563 1,354 1,105 1,023 957 856 782 677 605 553 494 428 383 350 324 303 271 247 214

1.380

1½

6,457 4,084 2,888 2,358 2,042 1,667 1,544 1,444 1,291 1,179 1,021 913 834 746 646 578 527 488 457 408 373 323

1.610

12,572 7,951 5,622 4,591 3,976 3,246 3,005 2,811 2,514 2,295 1,988 1,778 1,623 1,452 1,257 1,124 1,027 950 889 795 726 629

2.067

2

3

20,194 12,772 9,031 7,374 6,386 5,214 4,827 4,515 4,039 3,687 3,193 2,856 2,607 2,332 2,019 1,806 1,649 1,527 1,428 1,277 1,166 1,010

36,039 22,793 16,117 13,160 11,397 9,305 8,615 8,059 7,208 6,580 5,698 5,097 4,653 4,161 3,604 3,223 2,943 2,724 2,548 2,279 2,081 1,802

2.469 3.068 Capacities (cfh)

2½

4

74,386 47,046 33,267 27,162 23,523 19,206 17,782 16,633 14,877 13,581 11,762 10,520 9,603 8,589 7,439 6,653 6,074 5,623 5,260 4,705 4,295 3,719

4.026

Pipe Size—Inside Diameter (in.)a 5

135,910 85,957 60,781 49,627 42,979 35,092 32,489 30,390 27,182 24,814 21,489 19,221 17,546 15,694 13,591 12,156 11,097 10,274 9,610 8,596 7,847 6,796

5.047

6

221,843 140,306 99,211 81,006 70,153 57,280 53,031 49,606 44,369 40,503 35,076 31,373 28,640 25,616 22,184 19,842 18,113 16,770 15,687 14,031 12,808 11,092

6.065

461,299 291,751 206,299 168,443 145,876 119,107 110,272 103,150 92,260 84,221 72,938 65,238 59,553 53,266 46,130 41,260 37,665 34,871 32,619 29,175 26,633 23,065

7.981

8

846,208 535,189 378,436 308,992 267,595 218,490 202,282 189,218 169,242 154,496 133,797 119,672 109,245 97,712 84,621 75,687 69,093 63,967 59,836 53,519 48,856 42,310

10.02

10

Initial pressure of the system (psi) Final pressure of the system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

Nominal

= = = = = =

Actual

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula:

12

1,349,939 853,776 603,711 492,928 426,888 348,553 322,697 301,856 269,988 246,464 213,444 190,910 174,276 155,878 134,994 120,742 110,222 102,046 95,455 85,378 77,939 67,497

11.94

204 ASPE Data Book — Volume 2

4.02 2.54 1.80 1.47 1.27 1.04 0.96 0.90 0.80 0.73 0.64 0.57 0.52 0.46 0.40 0.36 0.33 0.30 0.28 0.25 0.23 0.20

8.52 5.39 3.81 3.11 2.69 2.2 2.04 1.9 1.7 1.55 1.35 1.2 1.1 0.98 0.85 0.76 0.7 0.64 0.60 0.54 0.49 0.43

20.9

15.8

Actual

16.2 10.25 7.25 5.92 5.13 4.19 3.88 3.63 3.24 2.96 2.56 2.29 2.09 1.87 1.62 1.45 1.32 1.23 1.15 1.03 0.94 0.81

26.6

25

Table 7-A4(M)

Given:

33.7 21.3 15.1 12.3 10.65 8.70 8.05 7.53 6.74 6.15 5.33 4.76 4.35 3.89 3.37 3.01 2.75 2.55 2.38 2.13 1.95 1.68

35.1

35

50.8 32.1 22.7 18.6 16.1 13.1 12.15 11.36 10.16 9.28 8.03 7.19 6.56 5.87 5.08 4.55 4.15 3.84 3.59 3.21 2.93 2.54

40.9

40

98.9 62.6 44.2 36.1 31.3 25.5 23.7 22.1 19.8 18.1 15.6 14.0 12.8 11.42 9.89 8.85 8.08 7.48 7.00 6.26 5.71 4.95

52.5

50

75

158.9 100.5 71.1 58 50.3 41 38 35.5 31.8 29 25.1 22.5 20.5 18.4 15.9 14.2 13.0 12.01 11.24 10.05 9.18 7.95

283.6 179.4 126.8 103.6 89.7 73.2 67.8 63.4 56.7 51.8 44.8 40.1 36.6 32.8 28.4 25.4 23.2 21.4 20.1 17.9 16.4 14.2

62.7 77.9 Capacities (L/s)

65

585.4 370.3 261.8 213.8 185.1 151.2 139.9 130.9 117.1 106.9 92.6 82.8 75.6 67.6 58.5 52.4 47.8 44.3 41.4 37.0 33.8 29.3

102.2

100

Pipe Size—Inside Diameter (mm)a

1069.60 676.5 478.3 390.6 338.2 276.2 255.7 239.2 213.9 195.3 169.1 151.3 138.1 123.5 107.0 95.7 87.3 80.9 75.6 67.6 61.8 53.5

128.2

125

1745.9 1104.2 780.8 637.5 552.1 450.8 417.4 390.4 349.2 318.8 276.1 246.9 225.4 201.6 174.6 156.2 142.6 132 123.5 110.4 100.8 87.3

154.1

150

3630.4 2296.1 1623.6 1325.6 1148.0 937.4 867.8 811.8 726.1 662.8 574.0 513.4 468.7 419.2 363.0 324.7 296.4 274.4 256.7 229.6 209.6 181.5

202.7

200

6659.7 4211.9 2978.3 2431.8 2106.0 1719.5 1592.0 1489.1 1331.9 1215.9 1053.0 941.8 859.8 769.0 666.0 595.7 543.8 503.4 470.9 421.2 384.5 333.0

254.5

250

P1 = 34.48 Initial pressure of the system (kPa) P2 = 31.03 Final pressure of the system (kPa) S = 0.6 The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

20

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula:

10 624.0 6 719.2 4 751.2 3 879.3 3 359.6 2 743.1 2 539.6 2 375.6 2 124.8 1 939.7 1 679.8 1 502.5 1 371.6 1 226.8 1 062.4 950.2 867.4 803.1 751.2 671.9 613.4 531.2

303.2

300

Chapter 7 — Fuel-Gas Piping Systems 205

2,334 1,476 1,044 852 738 603 558 522 467 426 369 330 301 269 233 209 191 176 165 148 135 117

½

0.622

¾

4,941 3,125 2,209 1,804 1,562 1,276 1,181 1,105 988 902 781 699 638 570 494 442 403 373 349 312 285 247

0.824

9,405 5,948 4,206 3,434 2,974 2,428 2,248 2,103 1,881 1,717 1,487 1,330 1,214 1,086 941 841 768 711 665 595 543 470

1.049

1

Table 7-A5

Given: P1 = 10 P2 = 1 S = 0.6

1¼

19,542 12,360 8,740 7,136 6,180 5,046 4,672 4,370 3,908 3,568 3,090 2,764 2,523 2,257 1,954 1,748 1,596 1,477 1,382 1,236 1,128 977

1.380

1½

29,478 18,644 13,183 10,764 9,322 7,611 7,047 6,592 5,896 5,382 4,661 4,169 3,806 3,404 2,948 2,637 2,407 2,228 2,084 1,864 1,702 1,474

1.610

57,395 36,300 25,668 20,958 18,150 14,819 13,720 12,834 11,479 10,479 9,075 8,117 7,410 6,627 5,740 5,134 4,686 4,339 4,058 3,630 3,314 2,870

2.067

2

3

92,191 58,307 41,229 33,664 29,153 23,804 22,038 20,615 18,438 16,832 14,577 13,038 11,902 10,645 9,219 8,246 7,527 6,969 6,519 5,831 5,323 4,610

164,531 104,059 73,581 60,078 52,029 42,482 39,330 36,790 32,906 30,039 26,015 23,268 21,241 18,998 16,453 14,716 13,434 12,437 11,634 10,406 9,499 8,227

2.469 3.068 Capacities (cfh)

2½

4

339,597 214,780 151,873 124,003 107,390 87,684 81,179 75,936 67,919 62,002 53,695 48,026 43,842 39,213 33,960 30,375 27,728 25,671 24,013 21,478 19,607 16,980

4.026

Pipe Size—Inside Diameter (in.)a 5

620,473 392,422 277,484 226,565 196,211 160,205 148,321 138,742 124,095 113,282 98,105 87,748 80,103 71,646 62,047 55,497 50,661 46,903 43,874 39,242 35,823 31,024

5.047

6

1,012,783 640,540 452,930 369,816 320,270 261,499 242,101 226,465 202,557 184,908 160,135 143,229 130,750 116,946 101,278 90,586 82,693 76,559 71,615 64,054 58,473 50,639

6.065

2,105,977 1,331,937 941,822 768,994 665,968 543,761 503,425 470,911 421,195 384,497 332,984 297,830 271,880 243,177 210,598 188,364 171,952 159,197 148,915 133,194 121,589 105,299

7.981

8

3,863,208 2,443,307 1,727,679 1,410,644 1,221,654 997,476 923,483 863,839 772,642 705,322 610,827 546,340 498,738 446,085 386,321 345,536 315,430 292,031 273,170 244,331 223,042 193,160

10.02

10

Initial pressure of the system (psi) Final pressure of the system (psi) The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 1 psi

Gas flow (cfh) Internal pipe diameter (in.) Total equivalent length, longest run of pipe (ft) Specific gravity of the gas Initial pressure in the system (psi) Final pressure of the system (psi)

Nominal

= = = = = =

Actual

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

10 25 50 75 100 150 175 200 250 300 400 500 600 750 1000 1250 1500 1750 2000 2500 3000 4000

Total Equivalent Length (ft)

Where:

Q = 2038.1

Weymouth Formula

12

6,162,898 3,897,759 2,756,132 2,250,372 1,948,880 1,591,253 1,473,214 1,378,066 1,232,580 1,125,186 974,440 871,565 795,627 711,630 616,290 551,226 503,199 465,871 435,783 389,776 355,815 308,145

11.94

206 ASPE Data Book — Volume 2

18.37 11.62 8.21 6.71 5.81 4.74 4.39 4.11 3.67 3.35 2.90 2.60 2.37 2.12 1.84 1.64 1.50 1.39 1.30 1.16 1.06 0.92

38.88 24.59 17.39 14.20 12.30 10.04 9.29 8.69 7.78 7.10 6.15 5.50 5.02 4.49 3.89 3.48 3.17 2.94 2.75 2.46 2.24 1.94

20.9

15.8

Actual

74.0 46.81 33.10 27.03 23.41 19.11 17.69 16.55 14.80 13.51 11.70 10.47 9.56 8.55 7.40 6.62 6.04 5.60 5.23 4.68 4.27 3.70

26.6

25

Table 7-A5(M)

Given:

153.8 97.3 68.8 56.16 48.64 39.71 36.76 34.39 30.76 28.08 24.32 21.75 19.86 17.76 15.38 13.76 12.56 11.63 10.88 9.73 8.88 7.69

35.1

35

232 146.7 103.8 84.7 73.40 59.90 55.46 51.88 46.40 42.36 36.68 32.81 29.95 26.79 23.20 20.75 18.94 17.54 16.40 14.67 13.39 11.60

40.9

40

451.7 285.7 202.0 164.9 142.8 116.6 108.0 101.0 90.3 82.5 71.4 63.9 58.3 52.16 45.17 40.4 36.88 34.15 31.94 28.57 26.08 22.59

52.5

50

75

725.5 458.9 324.5 264.9 229.4 187.3 173.4 162.2 145.1 132.5 114.7 102.6 93.7 83.8 72.6 64.9 59.2 54.85 51.3 45.89 41.89 36.28

1294.90 818.9 579.1 472.8 409.5 334.3 309.5 289.5 259 236.4 204.7 183.1 167.2 149.5 129.5 115.8 105.7 97.9 91.6 81.9 74.8 64.7

62.7 77.9 Capacities (L/s)

65

2672.6 1690.3 1195.2 975.9 845.2 690.1 638.9 597.6 534.5 488.0 422.6 378 345 308.6 267.3 239.0 218.2 202.0 189.0 169.0 154.3 133.6

102.2

100

Pipe Size—Inside Diameter (mm)a

4883.1 3088.4 2183.8 1783.1 1544.2 1260.8 1167.3 1091.9 976.6 891.5 772.1 690.6 630.4 563.9 488.3 436.8 398.7 369.1 345.3 308.8 281.9 244.2

128.2

125

7970.6 5041.0 3564.6 2910.5 2520.5 2058.0 1905.3 1782.3 1594.1 1455.2 1260.3 1127.2 1029.0 920.4 797.1 712.9 650.8 602.5 563.6 504.1 460.2 398.5

154.1

150

16 574.0 10 482.3 7 412.1 6 052.0 5 241.2 4 279.4 3 962.0 3 706.1 3 314.8 3 026.0 2 620.6 2 343.9 2 139.7 1 913.8 1 657.4 1 482.4 1 353.3 1 252.9 1 172.0 1 048.2 956.9 828.7

202.7

200

30 403.4 19 228.8 13 596.8 11 101.8 9 614.4 7 850.1 7 267.8 6 798.4 6 080.7 5 550.9 4 807.2 4 299.7 3 925.1 3 510.7 3 040.3 2 719.4 2 482.4 2 298.3 2 149.8 1 922.9 1 755.3 1 520.2

254.5

250

P1 = 68.95 Initial pressure of the system (kPa) P2 = 6.89 Final pressure of the system (kPa) S = 0.6 The specific gravity of the natural gas

Natural Gas Pipe Sizing Table for Gas Pressure > 6.895 kPa

Gas flow (L3/s) Internal pipe diameter (mm) Total equivalent length, longest run of piping (m) Specific gravity of the gas Initial pressure in system (kPa) Final pressure in system (kPa)

20

= = = = = =

Nominal 15

Q D L S P1 P2

(P12 – P22) × D16/3 ½ ž — LS

Source: Reprinted, with permission, from data developed by the Boston chapter of ASPE. a I.D. (internal diameter) based on schedule 40 steel pipe.

3.1 7.6 15.2 22.9 30.5 45.7 53.4 61.0 76.2 91.4 121.9 152.4 182.9 228.6 304.8 381.0 457.2 533.4 609.6 762.0 914.4 1219.2

Total Equivalent Length (m)

Where:

Q = 16.04

Weymouth Formula

48 502.0 30 675.4 21 690.8 17 710.4 15 337.7 12 523.2 11 594.2 10 845.4 9 700.4 8 855.2 7 668.8 6 859.2 6 261.6 5 600.5 4 850.2 4 338.2 3 960.2 3 666.4 3 429.6 3 067.5 2 800.3 2 425.1

303.2

300

Chapter 7 — Fuel-Gas Piping Systems 207