• Author / Uploaded
• AhmedShah

Citation preview

BASICS OF HYDRAULICS

BASICS OF HYDRAULICS 1)

DEFINITIONS 1.1) HYDRAULICS 1.2) CLASSIFICATION 1.2.1) HYDROSTATICS

BASIC DEFINITIONS & FORMULAE

1.2.2) HYDRODYNAMICS 1.3) FORCE , PRESSURE , AREA 1.4) PASCAL’S LAW 2)

MULTIPLICATION OF FORCES 2.1) BRAMAH’S PRESS 2.2) LAW OF CONSERVATION OF ENERGY

3)

HYDRAULIC POWER TRANSMISSION 3.1) LINEAR ACTUATOR 3.2) ROTARY ACTUATOR

USES OF HYDRAULIC S

BASICS OF HYDRAULICS 4)

ADVANTAGES OF HYDRAULICS 4.1) SPEED CONTROL 4.2) DIRECTION CONTROL 4.3) FORCE CONTROL 4.4) OVERLOAD PROTECTION 4.5) COMPACTNESS

5)

HOW PRESSURE IS CREATED

ADVANTAGES OF HYDRAULICS

PRACTICAL DETAILS IN HYDRAULIC S

 HYDRAULICS HYDRO

AULUS

( meaning Water ) ( meaning Pipe ) HYDRAULICS : Work done by fluids in pipes.

H y d r a u lic s is C la s s if e d a s H Y D R O S T A T IC S

H Y D R O D Y N A M IC S

HYDROSTATICS HYDROSTATICS FORCE F1

Eg.:F1 = 1 Kg A1 = 1 Cm2 P = F1 = 1 Kg A1 1 Cm2

AREA A1

= 1 Kg / Cm2 ( Same Pressure P) A2 = 10 Cm2 F2 = P x A2 = 1

x 10

= 10 Kg

FORCE F2

AREA A2

HYDRODYNAMICS LIQUID AT HIGH VELOCITY NOZZLE

TURBINE

PRESSURE •

IN ORDER TO DETERMINE THE TOTAL FORCE EXERTED ON A SURFACE WE NEED TO KNOW THE PRESSURE OR FORCE PER UNIT AREA.

•

PRESSURE = FORCE AREA

P

=

FORCE IN  KILOGRAMS ( Kg ) AREA IN  SQ. CM ( Cm2 ) PRESSURE IN  KILOGRAM / SQ.CM (Kg / Cm2 )

F A

•

FORCE = PRESSURE x AREA

•

THE ATMOSPHERIC AIR EXERTS UNIFORM PRESSURE ALL ROUND. THIS PRESSURE IS APPROX. 1 Kg / Cm2 AND P IS DENOTED AS 1 BAR ( BAROMETER )

F A

PASCAL’S LAW PRESSURE APPLIED ON A CONFINED FLUID IS TRANSMITTED UNDIMINISHED IN ALL DIRECTIONS AND ACTS WITH EQUAL FORCE ON EQUAL AREAS AND AT RIGHT ANGLES TO THEM. •

PRESSURE APPLIED ON A

•

FRENCH SCIENTIST PASCAL DISCOVERED THIS LAW IN THE 17th CENTURY.

•

RELATES TO USE OF CONFINED FLUID IN  TRANSMITTING POWER  MODIFYING MOTION  MULTIPLYING FORCE.

CONFINED FLUID IS TRANSMITTED  UNDIMINISHED  IN ALL DIRECTIONS  ACTS WITH EQUAL FORCE ON EQUAL AREAS AND  AT RIGHT ANGLES TO THEM

PASCAL’S LAW

FORCE F1 SMALL AREA A1

P = F1 A1

PRESSURE P

F2 = P x A 2

LARGE AREA FORCE F2

A2

BRAMAH’S PRESS

HYDRAULIC LEVERAGE

10 kg

10 Kg ON A 1Cm2 AREA

1Cm2

INPUT

100 kg

PRESSURE DEVELOPED THROUGHOUT IS 10 Kg / Cm2

10 Cm2

THE FORCES ARE PROPORTIONAL TO THE PISTON AREAS 100 Kg 10 Kg = 10 Cm2 1 Cm2

OUTPUT

MECHANICAL LEVERAGE 10 Kg

100 Kg

A LOAD OF 10 Kg HERE 1 0

THIS PRESSURE SUPPORTS A WT OF 100 Kg IF AREA IS 10 Cm2

1

WILL BALANCE A LOAD OF 100 Kg HERE

LAW OF CONSERVATION OF ENERGY MOVING THE SMALL PISTON 10 Cm DISPLACES 1 Cm2 x 10 Cm = 10 Cm3 OF LIQUID

10 Cm

1Cm2

100 kg 10 Cm2

1 Cm

Q=Axh

10 kg

10 Cm OF LIQUID WILL MOVE LARGER PISTON ONLY 1Cm. 10 Cm2 x 1 Cm = 10 Cm3

WORK DONE = FORCE x DISTANCE MOVED

W=Fxd

W=Fxd

W=Fxd

= 10 Kg x 10 Cm

= 100 Kg x 1 Cm

= 100 Kg-Cm

= 100 Kg-Cm

 ENERGY CAN NEITHER BE CREATED NOR DESTROYED.  WHAT IS GAINED BY FORCE IS SACRIFICED IN THE DISTANCE MOVED.

HYDRAULIC POWER TRANSMISSION LINEAR ACTUATOR PUMP

LOAD

PISTON & ROD TO RESERVOIR

ROTARY ACTUATOR PUMP

HYDRO MOTOR

ADVANTAGES OF HYDRAULICS  SPEED CONTROL MAXIMUM SPEED (No speed control ) 10 lpm Q = Ax V PUMP

THIS VOL. IS 10 Lts.

PISTON MOVES “X” Cm IN 1 min.

Q  Flow (Cm3/min) A  Area ( Cm2 ) V  Velocity (Cm/ min ) (Speed control )

FLOW CONTROL VALVE

10 lpm PUMP

5 lpm

RELIEF VALVE ACTUATOR GETS ONLY 5 LPM AND TRAVELS “X/2” Cm IN ONE MIN.

ADVANTAGES OF HYDRAULICS  HYDRAULIC DRIVES ARE REVERSIBLE DIRECTION CONTROL PUMP

RELIEF VALVE

DIRECTIONA L

THE CYLINDER ROD EXTENDS

VALVE

PUMP

RELIEF VALVE

DIRECTIONAL VALVE

THE CYLINDER ROD RETRACTS

ADVANTAGES OF HYDRAULICS

 OVER LOAD PROTECTION  RELIEF VALVE PROTECTS THE SYSTEM BY MAINTAINING THE SYSTEM SET PRESSURE.

 ANY INCREASE IN PRESSURE IN SYSTEM IS RELEAVED TO TANK . ( MOMENTARILY DIVERTING FLOW TO THE TANK. )

 THUS OVERLOAD PROTECTION IS ACHIEVED.

PRESSURE HEAD PUMP INLET LOCATIONS OIL LEVEL ABOVE PUMP CHARGES INLET

PRESSURE HERE IS 0.85 x 100 gm / Cm2 = 0.085 Kg / Cm2

100 Cm

PUMP

OIL LEVEL BELOW PUMP REQUIRES VACUUM TO “LIFT “ OIL

100 Cm

INLET

OUTLET

INLET

OUTLET

PUMP

THERE MUST BE A VACUUM EQUIVALENT TO 0.085 Kg / Cm2 TO LIFT THE OIL PUMP MECHANISM CREATES THE LOWER PRESSURE CONDITION.

HOW PRESSURE IS DEVELOPED NO PRESSURE

NO RESTRICTION

PUMP RELIEF VALVE

Set at 100 Kg/Cm2

PRESSURE BUILDS UP

WITH RESTRICTION

PUMP RELIEF VALVE

Set at 100 Kg/Cm2

PRESSURE BUILDS UPTO RELIEF VALVE SETTING (100 Kg / Cm2)

CLOSING

PUMP RELIEF VALVE

Set at 100 Kg/Cm2

PARALLEL FLOW PATHS THE OIL CAN CHOOSE 3 PATHS

10 A PUMP

B

C

OIL TAKES THE PATH OF LEAST RESISTANCE

20

PUMP

10 BAR OPENS VALVE A 20 BAR OPENS VALVE B

30 BAR OPENS VALVE C IF FLOW IS BLOCKED BEYOND “ A”

OIL WILL FLOW THRO “B” WHEN PRESSURE REACHES 20 BAR

SERIES RESISTANCE ADD PRESSURE A 10 BAR

0

P1 = 0

P2 = ( P1 + 10 )

B

10

=

0 + 10

= 10 BAR

20 BAR P3 = ( P2 + 20 )

C

30

= 10 + 20 = 30 BAR

30 BAR

P = ( P3 + 30 ) PUMP

60

= 30 + 30 = 60 BAR

PRINCIPLES OF FLOW  HOW FLOW IS MEASURED ?  VELOCITY  FLOW ( FLOW RATE )  FLOW RATE AND SPEED  FLOW AND PRESSURE DROP  LAMINAR AND TURBULENT FLOW  BERNOULLI’S PRINCIPLE FLOW IS THE ACTION IN THE HYDRAULIC SYSTEM THAT GIVES THE ACTUATOR ITS MOTION. PRESSURE GIVES THE ACTUATOR ITS FORCE , BUT FLOW IS ESSENTIAL TO CAUSE MOVEMENT. FLOW IN THE HYDRAULIC SYSTEM IS CREATED BY THE PUMP PRESSURE INDICATES WORK LOAD.

VELOCITY : IS THE AVERAGE SPEED OF THE FLUID’S PARTICLES PAST A GIVEN POINT OR THE AVERAGE DISTANCE THE PARTICLES TRAVEL PER UNIT OF TIME. Unit :m/Sec or m / min ( Metres / Sec or Metres/min )

FLOW RATE : IS THE VOLUME OF FLUID PASSING A POINT IN A GIVEN TIME. Unit: Cm3 / min or l / min ( cc / minute or litres / min )

SPEED OF AN ACTUATOR DEPENDES ON THE ACTUATOR SIZE AND RATE OF FLOW INTO IT. Q = Ax V FLOW IN Cm3 / min : AREA IN Cm 2

:

VELOCITY IN Cm / min

FLOW AND PRESSURE DROP MAX. PRESSURE HERE BECAUSE OF THE HEAD OF THE FLUID

SUCEEDINGLY LOWER LEVEL OF LIQUID SHOWS PRESSURE IS REDUCED AT POINTS DOWNSTREAM FROM SOURCE.

PRESSURE GRADIENT

FRICTION IN PIPE DROPS PRESSURE

PRESSURE IS ZERO HERE AS THE FLUID FLOWS OUT UNRESTRICTED

DUE TO EFFECT OF FRICTION RECOMMENDED VELOCITY RANGES ARE : 1.) PUMP INLET LINE

 0.6 ~ 1.2 metres / Second

2.) WORKING LINE ( PR. LINES) :

2~6

metres / Second

NOR DOES A GRADUAL CHANGE IN DIRECTION.

LAMINAR FLOW

LOW VELOCITY FLOW IN A STRAIGHT PIPE IS STREAMLINED. THE FLUID PARTICLES MOVE PARALLEL TO FLOW DIRECTION.

TURBULENT FLOW

THE FLOW MAY START OUT STREAMLINED.

AN ABRUPT CHANGE IN CROSSSECTION MAKES IT TURBULENT.

SO DOES AN ABRUPT CHANGE IN DIRECTION.

NON PARALLEL PATHS OF PARTICLES INCREASE RESISTANCE TO FLOW.