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OCECO: Sizing Pressure Vacuum Relief Valves

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http://catalog.oceco.com/products/sizingPR.aspx

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THE SAFETY SPECIALISTS TANK VENTING SIZING PRESSURE - VACUUM RELIEF VALVES In order to determine the number and size of OCECO Vent Valves, Flame Arrestors, or Vent Units needed for a given tank, it is necessary to ascertain first the amount of breathing the tank will experience. This is comprised principally of:

Pumping breathing resulting from: 1. Pumping stock into a tank (i.e., pressure). 2. Pumping stock out of a tank (i.e., vacuum).

Thermal breathing resulting from: 1. An increase in temperature (i.e., pressure). 2. A decrease in temperature (i.e., vacuum). In addition to filling and emptying rates and temperature variations - the tank capacity and a number of other variables, including the characteristics of the product stored, the specific gravity of the vapor, etc. affect the volume of tank breathing TABLE 1: Thermal Venting Requirements (Expressed in cu. Ft. per hour of air at standard conditions) Tank Capacity (42-Gallon Barrels)

Vacuum Venting All Stocks

Pressure Venting-Stocks with Flash Point Above 100° F

Pressure Venting - Stock with Flash Point Below 100° F

1,000

1,000

600

1,000

2,000

2,000

1,200

2,000

3,000

3,000

1,800

3,000

4,000

4,000

2,400

4,000

5,000

5,000

3,000

5,000

10,000

10,000

6,000

10,000

15,000

15,000

9,000

15,000

20,000

20,000

12,000

20,000

25,000

24,000

15,000

24,000

30,000

28,000

17,000

28,000

35,000

31,000

19,000

31,000

40,000

34,000

21,000

34,000

45,000

37,000

23,000

37,000

50,000

40,000

24,000

40,000

60,000

70,000

48,000

29,000

70,000

48,000

29,000

48,000

80,000

52,000

31,000

52,000

90,000

56,000

34,000

56,000

100,000

60,000

36,000

60,000

120,000

68,000

41,000

68,000

140,000

75,000

45,000

75,000

160,000

82,000

50,000

82,000

180,000

90,000

54,000

90,000

PETROLEUM AND PETROLEUM PRODUCTS Pumping Venting Requirements Recognizing the industry's need for a simple guide, for general application, the American Petroleum Institute has set up a standard for determining venting requirements, expressed in terms of cubic feet per hour, of air, at standard conditions (i.e., 60° F and 14.7 lbs. per square inch absolute). This standard, which applies to all vapor-tight aboveground tanks storing petroleum and petroleum products that are liquids at atmospheric temperatures and pressures, is as follows:

Tanks containing petroleum products with a flash point above 100° F Breathing requirement is 6 cu. ft. per hour of air for each barrel per hour of maximum tank filling rate, plus the thermal outbreathing requirement shown in Table 1 (Pressure Venting); also 5.6 cu. ft. per hour of air per barrel of maximum tank emptying rate, plus the thermal inbreathing requirement shown in Table 1 (Vacuum Venting). standards, because the flow capacities of these units are also expressed in terms of air at standard conditions.

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OCECO: Sizing Pressure Vacuum Relief Valves

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http://catalog.oceco.com/products/sizingPR.aspx

Tanks containing petroleum products with a flash point below 100° F Breathing requirement is 12 cu. ft. per hour of air for each barrel per hour of maximum tank filling rate plus the thermal outbreathing requirement shown in Table 1 (Pressure Venting); also 5.6 cu. ft. per hour of air per barrel of maximum tank emptying rate, plus the thermal inbreathing requirement shown in Table 1 (Vacuum Venting). The number and size of OCECO Vent Valves, Free Vent Units or Conservation Units needed for a given tank can be selected easily (see following example) when tank breathing capacities are computed from these standards, because the flow capacities of these units are also expressed in terms of air at standard conditions.

EXAMPLE: To determine the size and number of OCECO V-130 Conservation Vent Valves or Conservation Vent Units needed for the following conditions: Tank Capacity 20,000 Barrels Flash Point Below 100° F. Pumping Rate - In 1,000 bbls. per hour Pumping Rate - Out 1,200 bbls. per hour Allowable Working Pressure 2 inches of Water Allowable Working Vacuum 1 oz. per sq. inch

SOLUTION: Pressure (Cu. Ft./ Hr.)

Vacuum ( Cu. Ft./Hr.)

Pumping Requirement (From preceding Paragraph titled "Tanks containing petroleum products with a flash point below 100° F"

(12 x 1000) = 12,000

(5.6 x 1200) = 6,720

Thermal Requirement (From Table 1-20,000 Bbl. Tank Capacity

+20,000

+20,000

Total Breathing Requirement

32,000

26,720

Then turning to the capacity charts or tables with the bulletins describing the OCECO V-130 Conservation Vent Valves and OCECO Conservation Vent Units we find that a 6" V-130 Vent Valve or and 8" Conservation Vent Unit will be needed to meet the pressure and vacuum requirements.

VENTING REQUIREMENTS FOR OTHER THAN PETROLEUM PRODUCTS In order to determine the number and size of OCECO Conservation Valves, Free Vent Units or Conservation Vent Units needed for a given tank, when the tank is storing something other than petroleum or its products, it is necessary to know the pressure and vacuum information listed below:

Pressure or outbreathing information 1. 2. 3. 4.

Quantity of vapor or free gas to be vented (cu. ft. per hour) Maximum temperature of vapor or gas to be vented. Specific gravity of gas or vapor at standard conditions. Maximum allowable working pressure.

Vacuum or inbreathing information 1. Quantity of free air required (cu. ft. per hour). 2. Maximum temperature of air. 3. Maximum allowable working vacuum. After the above information has been determined, the values can be converted into equivalent values for air. Use the temperature correction factors in Table II, the specific gravity correction factors in Table III and the formula given below. The selection of the proper number and size of OCECO Valves or Conservation Vent Units can be made directly from the capacity tables or charts which also show values based on standard air.

FOR PRESSURE RELIEF

Formula No. 1 Required std. air capacity = Required vapor of free gas capacity x Ks.g. x Kt x 1.05

Definitions: 1. 2. 3. 4.

Free gas = Gas at atmospheric pressure Free air = Air at atmospheric pressure Standard conditions = 60°F. and 14.7 lbs./in.2 absolute Standard air = Air at standard conditions &nbps; = Air at 0.0764 lbs./ft.3 density 5. Specific gravity of gas = Ratio of unit wt. of gas at standard conditions to unit wt. of air at standard conditions = molecular wt. / 29

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OCECO: Sizing Pressure Vacuum Relief Valves

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6. Ks.g = Square root of the Specific Gravity (see Table No. III) 7. Kt = Square root of (T+46) / -520 (see Table No. II) 8. T = Gas Temperature in degrees Fahrenheit TABLE II Temperature Correction Factors Temp. Degrees F. Kt Correction Factor Temp. Degrees F. Kt Correction Factor 0

0.940

110

1.047

10

0.951

120

1.056

20

0.961

130

1.065

30

0.971

140

1.074

40

0.981

150

1.083

50

0.990

160

1.092

60

1.000

170

1.102

70

1.010

180

1.110

80

1.019

190

1.118

90

1.028

200

1.127

100

1.038 TABLE III Specific Gravity Correction Factors

Specific Gravity Ks.g. Correction Factor Specific Gravity Ks.g. Correction Factor Specific Gravity Ks.g. Correction Factor 0.20

0.447

0.95

0.975

1.80

1.342

0.30

0.548

1.00

1.000

1.90

1.378

0.40

0.632

1.05

1.025

2.00

1.414

0.50

0.707

1.10

1.049

2.50

1.590

0.55

0.742

1.15

1.072

3.00

1.732

0.60

0.773

1.20

1.095

3.50

1.871

0.70

0.837

1.30

1.140

4.50

2.121

0.75

0.866

1.40

1.183

5.00

2.236

0.80

0.894

1.50

1.225

5.50

2.345

0.85

0.922

1.60

1.265

6.00

2.449

0.90

0.949

1.70

1.304

EXAMPLE: To determine the size and number of OCECO V-130 Conservation Vent Valves or Conservation Vent Units needed for the following conditions: 1. Quantity of vapor to be vented = 24,000 cu. ft. per hr. 2. Maximum temperature of vapor to be vented = 160° F. 3. Specific gravity of vapor at 60° F. = 1.5 4. Allowable working pressure = 2" of water 1. Quantity of air required = 25,700 cu. ft. per hr. 2. Maximum air temperature = 120° F 3. Allowable working vacuum = 1 oz. per sq. inch

SOLUTION:

Outbreathing, i.e., pressure side Using formula: Formula No. 2 Required std. air capacity: = Required vapor or free gas capacity x Ks.g. x Kt x 1.05 or = 24,000 x 1.225 x 1.092 x 1.05 or = 33,800 cu. ft. per hour i.e., outbreathing requirement is 33,800 cu. ft. per hour.

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OCECO: Sizing Pressure Vacuum Relief Valves

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http://catalog.oceco.com/products/sizingPR.aspx

Inbreathing or vacuum side Using the formula: Required std. air capacity = (Required air capacity) x Kt or = 25,700 x 1.056 or = 27,200 cu. ft. per hour i.e., inbreathing requirement is 27,200 cu. ft. per hour. Then, turning to the capacity charts with the bulletins describing the OCECO V-130 Conservation Vent Valves and the OCECO Conservation Vent Units, we find that a 6" V-130 Vent Valve or an 8" Conservation Vent Unit will be needed to meet the pressure and vacuum requirements.

Converting Gas Weight to Volume Whenever calculating venting requirements for products where the gas is given in weight instead of volume. The equivalent volume can be found as follows: V = 379.5 x (W / M) where: V = volume in cu. ft. at std. cond. (60° F and 14.7 PSI), W = weight product in lbs., and M = molecular wt.

Example: Find the volume at standard conditions of 5 lbs. hydrogen (H2). Volume = 379.5 * 5 / 2.16 = 878 cu. ft. Copyright © 2008 OCECO. Terms of Use

7/23/2014 16:06