BASICS OF HYDRAULICS

1) DEFINITIONS

1.1) HYDRAULICS

1.2) CLASSIFICATION

1.2.1) HYDROSTATICS

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

BASICDEFINITIONS

& FORMULAE

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

ADVANTAGESOF

HYDRAULICS

PRACTICALDETAILS INHYDRAULIC

S

HYDRAULICS

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

H YD R O ST AT IC S H YD R O D Y N AM IC S

H ydraulics is C lassifed as

HYDROSTATICS

FORCEF1

AREAA1

AREAA2

Eg.:-

F1 = 1 Kg

A1 = 1 Cm2

P = F1 = 1 Kg

A1 1 Cm2

= 1 Kg / Cm2

( Same Pressure P )

A2 = 10 Cm2

F2 = P x A2

= 1 x 10

= 10 Kg

HYDROSTATICS

FORCEF2

TURBINE

NOZZLE

LIQUID AT

HIGH VELOCITY

HYDRODYNAMICS

IN ORDER TO DETERMINE THE TOTAL FORCE EXERTED

ON A SURFACE WE NEED TO KNOW THE PRESSURE OR

FORCE PER UNIT AREA.

PRESSURE = FORCE FORCE IN KILOGRAMS ( Kg )

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

P = F

A FORCE = PRESSURE x AREA

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

F

P A

PRESSURE APPLIED ON A

CONFINED FLUID

IS TRANSMITTED

UNDIMINISHED

IN ALL DIRECTIONS

ACTS WITH EQUAL FORCE ON EQUAL AREAS AND

AT RIGHT ANGLES TO THEM

FRENCH SCIENTIST

PASCAL DISCOVERED

THIS LAW IN THE

17th CENTURY.

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.

• RELATES TOUSE OF CONFINED FLUID IN TRANSMITTING

POWER MODIFYING

MOTION MULTIPLYING

FORCE.

PASCAL’S LAW

FORCE F1 SMALL AREA

A1

FORCE F2

LARGE AREA

A2

P = F1

A1

F2 = P x A2

PRESSURE

P

BRAMAH’S PRESS

HYDRAULIC LEVERAGE

MECHANICAL LEVERAGE

10 kg1Cm2 10 Cm2

100 kg

INPUT OUTPUT

10 Kg ON A 1Cm2

AREA PRESSURE DEVELOPED THROUGHOUT IS 10 Kg / Cm2

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

THE FORCES ARE PROPORTIONAL TO THE PISTON AREAS

10 Kg

1 Cm2

= 100 Kg

10 Cm2

A LOAD OF 10 Kg HERE

WILL BALANCE A LOAD OF 100 Kg HERE

10 Kg

100 Kg

10

1

1 C

m

LAW OF CONSERVATION OF ENERGY

1Cm2 10 Cm2

100 kg10 kg

10

Cm

ENERGY CAN NEITHER BE CREATED NOR DESTROYED.

WHAT IS GAINED BY FORCE IS SACRIFICED IN THE DISTANCE MOVED.

WORK DONE = FORCE x DISTANCE MOVED

W = F x dW = F x d

= 10 Kg x 10 Cm

= 100 Kg-Cm

W = F x d

= 100 Kg x 1 Cm

= 100 Kg-Cm

MOVING THE SMALL PISTON10 Cm DISPLACES 1 Cm2 x 10 Cm = 10 Cm3 OF LIQUID

10 Cm OF LIQUID WILLMOVE LARGER PISTONONLY 1Cm.10 Cm2 x 1 Cm = 10 Cm3

Q = A x h

HYDRAULIC POWER TRANSMISSION

LINEAR ACTUATOR

ROTARY ACTUATOR

LOADPUMP

PUMP

PISTON & ROD

TO RESERVOIR

HYDRO MOTOR

ADVANTAGES OF HYDRAULICS

PUMP

10 lpm

10 lpm

PISTON MOVES

“X” Cm IN 1 min.THIS VOL. IS 10 Lts.

MAXIMUM SPEED

(No speed control )

(Speed control )

RELIEF

VALVE

FLOW CONTROL

VALVE

Q = A x V

Q Flow (Cm3/min)

A Area ( Cm2 )

V Velocity (Cm/ min )

5 lpm

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

SPEED CONTROL

PUMP

ADVANTAGES OF HYDRAULICS

PUMP

PUMP

RELIEF

VALVE

RELIEF

VALVE

DIRECTIONAL

VALVE

DIRECTIONAL

VALVE

DIRECTION CONTROL

THE CYLINDER ROD EXTENDS

THE CYLINDER ROD RETRACTS

HYDRAULIC DRIVES ARE REVERSIBLE

ADVANTAGES OF HYDRAULICS

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.

OVER LOAD PROTECTION

PRESSURE HEAD

PUMP INLET LOCATIONS

OIL LEVEL ABOVE PUMP CHARGES INLET 100 Cm

PUMP

PUMPOIL LEVEL BELOW PUMP REQUIRES VACUUM TO “LIFT “ OIL

INLET OUTLET

PRESSURE HERE IS 0.85 x 100 gm / Cm2

= 0.085 Kg / Cm2

THERE MUST BE A VACUUM EQUIVALENT TO0.085 Kg / Cm2 TO LIFT THEOIL

PUMP MECHANISM CREATES THE LOWER PRESSURE CONDITION.

100 Cm

INLET OUTLET

HOW PRESSURE IS DEVELOPED

NO PRESSURE

NO RESTRICTION

WITH RESTRICTION

CLOSING

RELIEFVALVE

RELIEFVALVE

PRESSURE BUILDS UP

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

PUMP

PUMP

Set at 100 Kg/Cm2

Set at 100 Kg/Cm2

RELIEFVALVE

PUMP

Set at 100 Kg/Cm2

A

B

C

10 BAR OPENS VALVE A

20 BAR OPENS VALVE B

30 BAR OPENS VALVE C

PARALLEL FLOW PATHS

10

PUMP

PUMP

THE OIL CAN CHOOSE

3 PATHS

20

IF FLOW IS BLOCKED BEYOND “ A”

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

OIL TAKES THE PATH OF LEAST RESISTANCE

SERIES RESISTANCE ADD PRESSURE

P1 = 0

P2 = ( P1 + 10 )

= 0 + 10

= 10 BAR

P3 = ( P2 +

20 )

= 10 + 20

= 30 BAR

P = ( P3 + 30

)

= 30 + 30

= 60 BAR

A

10 BAR

B

20 BAR

C

30 BAR

PUMP

0

10

30

60

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 = A x V

FLOW IN Cm3 / min : AREA IN Cm 2 : VELOCITY IN Cm / min

FLOW AND PRESSURE DROP FLOW AND PRESSURE DROP

MAX. PRESSURE HERE BECAUSE OF THE HEAD OF THE FLUID

FRICTION IN PIPE DROPS PRESSURE

PRESSURE IS ZERO HERE AS THE FLUID FLOWS OUT UNRESTRICTED

PRESSURE GRADIENT

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

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

LAMINAR FLOWLAMINAR FLOW

TURBULENT FLOWTURBULENT FLOW

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

NOR DOES A GRADUAL CHANGE IN DIRECTION.

THE FLOW MAY START OUT STREAMLINED.

AN ABRUPT CHANGE IN CROSS-SECTION MAKES IT TURBULENT.

SO DOES AN ABRUPT CHANGE IN DIRECTION.

NON PARALLEL PATHS OF PARTICLES INCREASE RESISTANCE TO FLOW.