hydraulics
DESCRIPTION
an overview on fundamentals on hydraulicsTRANSCRIPT
BASICS OF HYDRAULICSBASICS OF HYDRAULICS
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 Y D R O S TA TIC S H Y D R O D Y N A M 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 )
PRESSURE
F
P 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
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.
• 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.