Hydraulics_Unit-1.pdf

HYDRAULICS &
PNEUMATICS
SUB CODE: ME73 I.A. MARKS: 25
EXAM MARKS: 100
By
M. R. Doddamani

CONTENTS
1. Introduction to Hydraulic power
2. The Source of Hydraulic power
3. Hydraulic Actuators & Motors
4. Control components in Hydraulic systems
5. Hydraulic Circuit Design & Analysis
6. Maintenance of Hydraulic Systems
7. Introduction to Pneumatic control
8. Pneumatic Actuators
9. Directional control valves
10. Simple Pneumatic control
11. Signal processing elements
12. Multi-cylinder applications
13. Electro-Pneumatic control
14. Compressed air

BOOKS
™ Text Books
1. Fluid power with applications by Anthony Espocito
2. Pneumatics & Hydraulics by Andrew Parr
™ Reference Books
1. Oil hydraulic systems by S. R. Majumdar
2. Pneumatics basic level TP 101 by FESTO
3. Fundamentals of pneumatic control engineering by
FESTO
4. Hydraulics basic level TP 501 by FESTO
5. Pneumatic Systems by S. R. Majumdar
6. Power Hydraulics by Ashby
7. Fluid power for Technicians by Donald Newton

INTRODUCTION
• Requirement of Industrial processes
• Device to perform activities
• PRIME MOVER
Prime movers are mechanical devices, which
convert one form of energy into another

• Basic sources (prime movers) of power in Industries
1. Electrical
9 Electrical motors
9 Power transmission through cables
2. Mechanical
9 I.C.Engines
9 Power transmission through gears, shafts etc.
3. FLUID POWER
9 Common source
9 Widely used in modern industries
9 Power transmission through high pressure fluids
(liquid & gases)
SOURCES OF POWER

• It is the technology that deals with the generation, control &
transmission of power using pressurized fluids
• It is used to push, pull, regulate or drives virtually all machines
• F.P. equipment ranges in size from huge presses to miniature digital
components while the fluids may range from superheated steam to
liquid Nitrogen
• Fluid based system using liquids as transmission media are called
Hydraulic systems ( Hydra for water & aulous for a pipe)
• Gas based system are called Pneumatic systems ( Pneumn for wind
or breath)
• Types of Fluid Systems
1. Fluid Transport system
- delivery of fluid (pumping stations, cross country gas lines etc.)
2. Fluid power system
- designed specifically to perform work
WHAT IS FLUID POWER (FP)?

HISTORY OF FLUID POWER
• Use of FP predates the Christian era
• Usage of water to produce power by means of water wheels
• Air was used to turn windmills
• Uses of FP required huge quantity of fluid because of relatively low
pressures provided by nature
• 1650 – discovery of Pascal’s law
• 1750 – Bernoulli’s equation
• 1850 – Industrial revolution in Great Britain
• Late in 19th century – Electricity emerged as dominant technology
• Little development during last 10 years of 19th century
• 1906 – development of hydraulic systems for elevating & controlling
guns on the battleship USS Virginia
• 1926 – Development of packaged Hydraulic systems
• Military requirements in World War – II ( cargo doors, gun drives,
flight control devices, hydraulic actuated landing gear etc.)
• Influence of expanding economy followed by World War - II

ADVANTAGES OF FP
1. Ease & accuracy of control
- Usage of simple levers & push buttons
Hydraulic operation of aircraft landing gear

2. Multiplication of force
ADVANTAGES OF FP
Turntable for handling huge logs

3. Constant force or torque
ADVANTAGES OF FP
FP application in Oceanography

4. Simplicity, Safety & Economy
ADVANTAGES OF FP
Steering control system

5. Removal of heat generated
6. FP devices are highly responsive because of weight to power ratio
ADVANTAGES OF FP

7. FP devices are much easier to install than mechanical system
8. FP devices are readily reversible and may be operated at either
constant or variable torque in either direction
ADVANTAGES OF FP

DISADVANTAGES OF FP
1. Hydraulic fluids are messy
2. Susceptible to damage by dirt or contamination
3. Physical injury from high speed particles
4. Fire or explosion hazard
5. Prolonged exposure to loud noise

DRIVING FORCE
1. No moving parts
2. Force multiplication
3. Flexibility in direction changing

We may summarize by saying that fluid
power is not always best for all
requirements, but it should always be
considered because of its obvious
advantages under certain circumstances

APPLICATIONS
• Overhead tram

• Harvesting corn
APPLICATIONS
Hydraulically driven elevator conveyor

• Industrial lift trucks
APPLICATIONS
Hydraulic lift truck

• Robotic dexterous arm
APPLICATIONS

APPLICATIONS
Use of variable displacement vane pump
Directional control valve is provided for pressure unloading
The pressure relief valve is limiting the maximum pressure
Infinite pressure displacement is achieved with the use of proportional relief
valve
For the speed control of the hydraulic motor a flow control valve is employed

APPLICATIONS
Variable displacement, pressure compensated vane pumps are normally used
for energy saving and smooth control of each machine
heat generation is kept to minimum with variable displacement pumps.

PRINCIPLES OF HYDRAULICS
• Language of physical science for FLUID
• Current focus – Oil as a medium
• Law of Hydrostatics
Potential head

Potential head is independent of shape & size

Potential head is independent of container shape

PRINCIPLES OF HYDRAULICS –
PASCAL’S LAW
Pascal found that when he rammed a cork
down into a jug completely full of wine, the
bottom of the jug broke and fell out
Pressure applied to a confined
fluid is transmitted undiminished
in all directions throughout the
fluid & acts perpendicular to the
surfaces in contact with the fluid

BRAMAH’S PRESS PRINCIPLE (Hydraulic Jack)
Principle of Bramah’s press

P = F1 / A1 (A1 = Π / 4 * D1
2)
F2 = P * A2 (A2 = Π / 4 * D2
2)
P = F2 / A2 P = F1 / A1 = F2 / A2
F2 : F1 = A2 : A1 = D2
2 : D1
2
F2 = F1 * A2 / A1
But as A2 > A1, A2 / A1 is > 1
or F2 is higher than F1
By applying a smaller force F1 on the smaller piston, a bigger force
F2 can be generated in the bigger piston

BRAMAH’S PRESS PRINCIPLE
(Hydraulic Jack)

Assuming Oil to be Incompressible
Cylindrical volume displaced by = Cylindrical volume displaced by
the input piston the output piston
V1 = V2 A1S1 = A2S2
Where S1 = downward movement of piston 1
S2 = downward movement of piston 2
Thus, S2 / S1 = A1 / A2 = F1 / F2
Large output piston does not travel as far as the small input piston
F1 S1 = F2 S2 ( work energy)
Energy input to hydraulic jack equals energy output from the jack

MECHANICAL LEVER
Length of lever arms inversely proportional to the
piston areas
AE/page-102/Ex-3.15&3.16

APPLICATIONS OF PASCAL’S LAW
Hand operated hydraulic jack

APPLICATIONS OF PASCAL’S LAW
Air to hydraulic pressure booster

COMPONENTS OF HYDRAULIC SYSTEM

COMPONENTS – PNEUMATIC SYSTEM

Division of Hydraulic system
I. Signal control section
II. Hydraulic power section
SIGNAL CONTROL SECTION
1. Signal input (sensing)
9 Manually
9 Mechanically
9 Contactlessly
2. Signal processing
9 Operator
9 Electricity
9 Electronics
9 Pneumatics
9 Hydraulics
STRUCTURE OF HYDRULIC SYSTEM

HYDRAULIC POWER SECTION
1. Power supply section (energy conversion & pressure medium
conditioning)
ƒ Components used for energy conversion
- Electric motor
- I. C. engine
- Coupling
- Pump
ƒ Components used for conditioning hydraulic fluid
- Filter
- Cooler
- Heater
- Thermometer
- Pressure gauge

2. Power control section
¾ Directional control valves
¾ Flow control valves
¾ Pressure control valves
¾ Non-return valves
3. Drive section
Executes various working movements of machine or manufacturing
system
Energy contained in the hydraulic fluid is used for the execution of
movements or generation of forces which is achieved using
following components
- cylinders
- motors

POWER CONVERSION IN
HYDRULIC SYSTEM

SOURCE OF
HYDRAULIC POWER
PUMPS

COMPONENTS OF HYDRUALIC SYSTEM

WHAT IS A PUMP?
9 Device for converting mechanical energy into hydraulic energy
9 Heart of the hydraulic system as it generates the force necessary to
move the load
9 Main purpose is to create the flow of oil through the system which in
turn assists transfer of power & motion
9 Does not develop pressure
9 Generally driven at constant speed by 3 phase AC induction motor
9 Mechanical action creates partial vacuum at pump inlet
9 Atmospheric pressure forces the fluid through the inlet line into the
pump
9 Pump pushes the fluid into the hydraulic system

PUMPING THEORY
Pumping action of a simple piston pump
AE/144/Fig. 5-2

PUMP CLASSIFICATION
AP/35/Fig. 2.2

POSITIVE or HYDROSTATIC PUMPS
9 Pumping volume changes from maximum to minimum during each
pumping cycle
9 Used where pressure is the primary consideration
9 Separation between high & low pressure areas or zones
9 Pumping action is caused by varying the physical size of the sealed
pumping chamber
9 Ejects a fixed amount of fluid per rev. of pump shaft rotation
9 Flow enters & leaves the unit at same velocity
9 Capable of overcoming the pressure resulting from the mechanical
loads as well as the resistance to flow due to friction
PUMP CLASSIFICATION

9 Examples include Gear, vane, piston screw pumps
9 Advantages
- High pressure capability
- Small, compact size
- High volumetric efficiency
- Small change of efficiency throughout the pressure range
- Greater flexibility of performance
- Widely used in hydraulic system
9 Variations in design
- Fixed displacement (constant pump flow output)
- Variable displacement (change in pump flow due to change in
displacement output keeping speed constant)
- Variable displacement, pressure compensation capability ( less flow
as the system pressure builds up, no need of pressure relief valve)
PUMP CLASSIFICATION

NONPOSITIVE or HYDRODYNAMIC PUMPS
9 Fluids are displaced & transferred using the inertia of fluid in motion
9 Uses Newton’s 1st law of motion to move the fluid against the system
resistance
9 Used for low pressure (up to 40 bar), high volume flow applications
9 Little use in fluid power field
9 Primarily used for transporting fluids from one location to another
9 Examples include centrifugal (rotational inertia) & axial flow
propeller pumps (transnational inertia)
9 Advantages
- Fewer moving parts - Low initial cost
- Minimum maintenance cost - Quieter operation
- Capable of handling any type of fluid - Simplicity of operation
- High reliability
PUMP CLASSIFICATION

HOME WORK
1. Distinguish between positive & non-positive
displacement pumps
2. Justify the names Hydrodynamic & hydrostatic for
positive & non-positive displacement pumps

CENTRIFUGAL
PUMP
SRM / 92 / Fig. 4.1
AE / 145 / Fig. 5.3

¾ Provides smooth continuous flow
¾ Fluid enters at the center of impeller, picked up by rotating impeller, centrifugal
force causes fluid to move radially outwards
¾ Behaves interestingly in case of no demand of fluid
¾ No positive internal seal against leakage
¾ Highly desirable for pumping stations
¾ Easily handles large change in demand
¾ Reduction in output flow rate with increase in resistance to flow
CENTRIFUGAL PUMP
AE / 147 / Fig. 5-4 (b)
Impeller imparts kinetic energy to
the fluid hence the name
Hydrodynamic or Hydrokinetic
¾ Need of priming

EXTERNAL GEAR PUMP
AP/42/Fig. 2.7

EXTERNAL
GEAR PUMP
Internet source

EXTERNAL
GEAR PUMP
AE/152/Fig. 5-7

¾ One of the gear is connected to drive shaft which in turn is coupled
with prime mover
¾ Second gear gets driven because of meshing (spur gears)
¾ Suction side – teeth unmeshed Discharge side – teeth mesh
¾ Vacuum generation due to evacuation of teeth
¾ Line contact of the gear teeth over one another prevents flow through
the mesh & the close fitting of the housing prevents flow back around
the periphery
¾ Manufacturing range (commercially available)
- Continuous pressure of 200 bar
- Min. pressure range of 10 to 100 bar
- Min. speed of rotation from 400 to 500 rpm
- Max. speed of 3000 to 6000 rpm
- Min. flow rate of 3 to 100 l/min
EXTERNAL GEAR PUMP

GEAR PUMP CHARACTERISTICS
SRM/99/Fig. 4.5

THREE GEAR PUMP
Center gear is connected to motor shaft
Two independent outputs
Short sealing range limits the system
pressure
SRM/99/Fig. 4.6

HELICAL GEAR PUMP
Excessive end thrust

HERINGBONE GEAR PUMP
Thrust elimination
One row of gear right handed while
the other left handed
Develops much higher pressures
Internet

INTERNAL GEAR PUMP
AE/153/Fig. 5-8

INTERNAL GEAR PUMP
AE/153/Fig. 5-9

¾ Consists of an internal gear, a regular spur gear, a crescent shaped seal
& an external housing
¾ Power is applied to either gear
¾ Crescent seal acts as a seal between the suction & discharge ports
¾ Motion of the gear draws fluid from the reservoir & forces it around
both sides of crescent seal
¾ Operates at lower capacities & pressures (up to 70 bar)
INTERNAL GEAR PUMP

GEROTOR PUMP
AP/44/Fig. 2.9 (b)
AE/154/Fig. 5-11

OPERATION PRINCIPLE OF GEROTOR PUMP
Internet

¾ GEROTOR – GENERATED ROTOR
¾ Operates much like the internal gear pump
¾ Inner gear rotor (Gerotor element) is power driven which draws outer
gear rotor
¾ Centers of the gears are offset by approximately one-half the tooth
depth
¾ Inner gear has one tooth less than the outer one
¾ Formation of inlet & discharge pumping chambers between the rotor
blades
¾ Sealing the pumping chamber because of meshing teeth
¾ More compact than the external gear pump
¾ Gears must be made to high precision
¾ Ratings:
- Continuous pressure 125 bar
- Max. speed 2000 to 3600 rpm
- Max. delivery 200 l/min
GEROTOR PUMP

¾ Operates in a fashion similar to that of external gear pump
¾ Both blades are driven externally (one directly by the source of power
& other through timing gears)
¾ Physically blades doesn’t come in contact with each other
¾ Quieter than other types of gear pumps
¾ Greater amount of pulsation in pump output
¾ Used for pumping gas, air, liquid with low pressures with higher flow
rate
LOBE PUMP

SCREW PUMP
2 Element rotary type
SRM/102/Fig. 4.9 (a)
SRM/102/Fig. 4.9 (b)

¾ Axial flow positive displacement unit
¾ Three precision ground screws deliver non pulsating flow quietly &
efficiently
¾ Two symmetrically opposed idler rotors acts as a rotating seals
¾ Idler rotors are in rolling contact with the central power rotor which
are driven by the pressure of the liquid
¾ Operate up to 250 bar pressure at 1000 cm3 per min.
¾ Advantages
1. Most reliable
2. Oil supply is pulsation free, continuous
3. No oil churning, pump turbulence etc.
4. Very quiet in operation
SCREW PUMP

¾ Disadvantages
- Manufacturing of a screw pump poses difficulty in case of close
tolerance requirement
- Viscosity dependant pressure rating
- Decrease in pump efficiency with increase in fluid viscosity
- Overall volumetric & mechanical efficiency is low
SCREW PUMP

VANE PUMP - OPERATION
AE/157/Fig. 5-15

UNBALANCED VANE PUMP
AP/45/Fig. 2.10 (a)

• Axis of the rotor (splined to drive shaft ) positioned eccentric to the
circular cam ring
• Rotor (rotates inside the cam ring) has radial slots containing spring
loaded vanes
• Vane mates with the surface of the cam ring due to centrifugal force
exerted by rotor
• 1st half revolution of rotor – increase in volume between rotor & cam
ring, drop in pressure resulting in suction process
• 2nd half revolution – cam ring pushes vanes back into the slots
resulting in discharge
• The discharge & suction side of the pump are sealed from each other
at any time by at least one vane (track between two ports is slightly
wider than the space between two vanes)
• Pump experiences two different pressures (working pressure at outlet
& pressure at pump inlet)

• One half of the pumping mechanism is less than atmospheric pressure
while the other half is subjected to the full system pressure
• Undesirable side loading on the rotor shaft
• Unbalanced forces reduces pump life cycle considerably
• Seldom used

BALANCED
VANE PUMP
AP/45/Fig. 2.10 (b)

• Circular rotor with vane slots concentrically positioned with the axis
of an elliptical cam ring
• Vanes reciprocates twice during one revolution of rotor giving two
pumping actions per rotor revolution
• Two inlet & two outlet ports are diametrically opposite to each other
(pressure ports are opposite leading to zero net force)
• Forces acting on shafts are fully balanced
• In actual design both inlet & outlet ports are connected together
• Intra-vane principle (pressure oil is fed to the underside of the vane in
such a manner that maximum force occurs on the vane)
• Fixed displacement type pump which operates up to 175 bar pressure
• Relatively quite & of simple construction
• Can not be designed as variable displacement unit
BALANCED VANE PUMP

VARIABLE
DISPLACEMENT
VANE PUMP
AP/47/Fig. 2.11

• In hydraulic system the flow rate of the pump needs to be variable
which can be achieved by varying the rpm of the electric motor
(economically not feasible & hence is not practical)
• Varying the pump displacement can be easily effected
• Displacement of the vane inside the pump & therefore its delivery is
proportional to the eccentricity between rotor axis and cam ring
• When eccentricity (e) is positive, flow (Q) is maximum
• When ‘e’ is zero, ‘Q’ is zero
• When ‘e’ is negative, the direction of the flow gets reversed
VARIABLE DISPLACEMENT VANE PUMP

PRESSURE COMPENSATED VANE PUMP
SRM/112/Fig. 4.19 (c)

• In certain hydraulic systems design, it is desired that when the
predetermined system pressure is reached, the pump should stop
pumping further oil to the system – Pressure compensated vane pump
Consists of an additional spring which is adjusted to offset the cam
ring
As the pressure acting on the inner contour of the ring is more than the
pressure exerted by the spring, the cam ring becomes concentric to the
rotor and pumping action stops
• In some pumps spring is replaced by a piston & pressure control valve
When system pressure reaches the setting of the control valve, it is
applied to the piston centralizing the ring and the rotor, reducing
pump displacement to zero

FLOW-PRESSURE RELATIONSHIP OF
SRM/112/Fig. 4.19 (b)

CHARACTERISTIC OF VANE PUMP
AT CONSTANT SPEED
SRM/112/Fig.
4.19 (b)

OPERATION OF PISTON PUMP
• Consist of finely machined & finished cylinder barrel, plunger
(piston) which moves inside the housing
• Shaft of plunger is connected to prime mover (electric motor)
• Inlet & outlet ports are controlled by ball valves
• Outward motion of plunger – entry of oil
• Inward motion of plunger – discharge of oil
• Continuous cycling of piston results in supply of oil in pulses
Pulsation creates undesirable effects
In order to eliminate & minimize the effect of oil pulsation, to increase
the flow rate capacity in piston pumps a number of cylinders and
pistons are used in parallel

DELIVERY PATTERN
SRM/139/Fig. 4.34 (a)

DELIVERY PATTERN
SRM/139/Fig. 4.34 (b)

DELIVERY PATTERN
SRM/139/Fig. 4.34 (c)

AXIAL PISTON PUMP-IN LINE
Exploded View
SRM/116/Fig. 4.21 (a)

• Pistons are arranged axially parallel to each other around the
circumferential periphery of the cylinder block
• Pistons are driven to & fro inside number of bores of cylinder
• Either a cylinder barrel or a plate (swash plate) is rotated which makes
pistons to have to & fro motion
• Controlled by ball valves, the oil is sucked in or pumped out
AXIAL PISTON PUMP-IN LINE
SRM/116/Fig. 4.21 (b)

SWASH PLATE IN-LINE AXIAL PISTON PUMP
SRM/117/Fig. 4.22 (a)

SWASH PLATE IN-LINE AXIAL PISTON PUMP
SRM/117/Fig. 4.22 (b)

• Different designs of axial piston pumps can be seen in
previous two slides
• Cylinder body containing the axially placed pistons, is
made to rotate against a cam plate (tilting plate or swash
plate)
• Cam plate is kept fixed & positioned at an angle with the
axis of the cylinder block
• Rotating group includes shoe plate, shoes, piston, cylinder
block & drive shaft
• As the cylinder barrel is rotated, the piston shoe follows
the surface of swash plate
• Piston reciprocates inside the cylinder barrel as swash plate
is at an angle resulting in suction & discharge of oil

WOBBLE PLATE IN-LINE
AXIAL PISTON PUMP
SRM/118/Fig. 4.22 (c)

• Swash plate rotates with drive shaft while the cylinder
block is kept fixed
• Swash plate in such pumps are called as wobble plate
• Shoe plate is prevented from rotation
• Swash plate rotating on surface of the shoe plate produces
to & fro motion of piston
WOBBLE PLATE IN-LINE
AXIAL PISTON PUMP

VARIABLE DISPLACEMENT
AXIAL PISTON PUMP
SRM/120/Fig. 4.24

• Stroke length of a piston is determined by the swash plate angle
• Larger the angle larger will be piston stroke consequently smaller the
angle smaller will be piston stroke length
• No displacement for swash plate zero angle
• Piston displacement & volume flow rate in swash plate pump designs
can be varied by by changing the swash plate angle
• Maximum angle is generally limited to 17.5°
VARIABLE DISPLACEMENT
AXIAL PISTON PUMP

PRESSURE
COMPENSATED
PISTON PUMP
SRM/120/Fig. 4.25 (a)
SRM/120/Fig. 4.25 (b)

• Swash plate is connected mechanically to a piston which senses the
system pressure
• Piston is called as compensator piston & is biased against a spring
• Return spring positions (when compensator piston is extremely right
aligned or condition of least system pressure) yoke to full delivery
• As the system pressure increases, the compensator valve spring of the
piston moves to allow the fluid to act against the yoke actuating piston
• The system pressure is dependant on the setting of the compensator
spool spring & adjustment
• When the pressure is high enough to overcome the valve spring, spool
gets displaced and oil enters the yoke piston
• The piston is forced by oil under pressure to decrease or stop the
pump displacement resulting no flow [SRM/120/Fig. 4.25 (b)]
• If the pressure falls off, the spool moves back, oil is discharged from
the piston to the inside of the pump core, and the spring returns to the
yoke to a greater angle
PRESSURE COMPENSATED PISTON PUMP

BENT AXIS PISTON PUMP
AP/49/Fig. 2.15

• Stroking of the pistons is achieved because of the angle between drive
shaft & the rotating cylinder block
• Rotating group consists basically of a cylinder block, pistons,
universal link (keys block to the drive shaft), shaft bearing & drive
shaft
• Cylinder block is supported by the cylinder bearing sub-assembly
which is free to rotate on the bearing
• As the drive shaft rotates it causes rotation of the cylinder block
resulting reciprocation of the pistons
• Pump capacity can be adjusted by altering the drive shaft angle
• SRM/122/Theoretical displacement
BENT AXIS PISTON PUMP

RADIAL PISTON PUMP
AE/170/Fig. 5-29

ROTATING CYLINDER BLOCK
• Design consists of a pintle to direct the fluid in & out of the cylinder,
a cylinder barrel with pistons, and a rotor containing a reaction ring
• Piston remains in constant contact with reaction ring due to the
centrifugal force
• For pumping action reaction ring is moved eccentrically with respect
to the pintle or shaft axis
• As cylinder barrel rotates, the pistons on one side travel outwards
which draws fluid as each piston crosses suction port of the pintle
• When piston passes through point of maximum eccentricity, it is in
turn forced inwards by the reaction ring which forces the fluid to enter
the discharge port
• Displacement can be varied by moving the reaction ring to change the
piston stroke
STATIONARY CYLINDER BLOCK
• Reciprocating motion is imparted to the pistons by a rotating cam
RADIAL PISTON PUMP

PUMP PERFORMANCE CURVES
• Manufacturers specify pump performance characteristics in the form
of graphs
Variable displacement piston pump
AE/176/Fig. 5-32

Variable
displacement
piston pump
AE/176/Fig. 5-32

AE/177/Fig. 5-33
Radial piston pump

PUMP PERFORMANCE
COMPARISION FACTORS
AE/178/Fig. 5-34

GEAR PUMPS
• Least expensive
• Lowest level of performance
• Efficiency is rapidly reduced by wear
• High maintenance cost
• Simple in design
• Widely used in fluid power industry
VANE PUMPS
• Efficiency & cost fall between Gear and Piston pumps
• Have good efficiencies
• Last for longer time
• Leakage losses across the faces of rotor & between the bronze wear
plates and pressure ring
PUMP PERFORMANCE
COMPARISION FACTORS

PISTON PUMPS
• Most expensive
• Provides highest level of overall performance
• Can be driven at high speeds (up to 5000 rpm)
• Produces non pulsating flow
• Operates at the highest pressure levels
• Highest efficiency
• Longer pump life
• Normally can not be repaired in the field because of their
complex design
PUMP PERFORMANCE
COMPARISION FACTORS

• Noise is a sound that people undesirable
• Sound come as a pressure wave through the surrounding air medium.
Pressure waves are generated by a vibrating object (pump. Motor etc.)
Human ear converts sound wave into electrical signals that are
transmitted to brain.Brain translates electrical signal into sensation of
sound.
• Common sound levels (dB) are presented in following slide
• Intensity is defined as the rate at which sound energy is transmitted
through a unit area
• The letter “A” following the symbol dB signifies that the sound level
measuring equipment uses a filtering system that more closely
simulates a human ear.
I (B) = log { I / I (hear. thrsh.)}
I = intensity of sound under consideration (W/m2)
I (hear. thrsh.)= intensity of sound at the threshold of hearing (W/m2)
I (B) = intensity of sound under consideration in units of bels (1 bel=10
dB)
NOISE

COMMON SOUND LEVELS
AE/179/Fig. 5-35

• Generated noise levels vary with
- pump component materials
- pump mountings
- methods applied to eliminate vibration
- rigidity
- manufacturing & fitting accuracies of pump elements
- speed of rotation
- pressure pulsation & other components connected in the circuit
• External gear & the piston pumps are nosiest while screw pumps are
very quiet with vane & internal gear pumps somewhere between
• Any pump which generates noise above 90dB (A) is a loud pump &
those around 60 dB (A) or less are considered quiet
• Noise developed in typical pumps is shown in following slide.
PUMP NOISE

PUMP NOISE
SRM/135/Fig. 4.31 (a)
Noise developed
in typical pumps

• Comparative noise behavior of two pumps with 32 l/min
(PR 32 H) & 20 l/min (PR 20 H) capacity respectively
working at 1500 rpm with oil viscosity of 32 cSt is shown
in the following slide
• The noise level of a pump kept in a noise isolating room is
found to be less by almost 18 dB (A) compared to the
noise level at site for a pump installed on a C.I. Oil
reservoir.
• Pattern of rise of noise level depends on the pump
construction, flow rate, speed, pressure etc.
PUMP NOISE

PUMP NOISE
SRM/136/Fig. 4.31 (b)
Noise intensity in protected room &near pump
installation measured at 1 m away

PUMP NOISE
SRM/137/Fig. 4.32 (a)
Rise of noise level with pressure, flow & RPM

PUMP NOISE
SRM/137/Fig. 4.32 (b)
Rise of noise level with pressure, flow & RPM

WITH REFERENCE TO PREVIOUS SLIDE
• Rise in noise level is considerable influenced by the
rotational speed (n), operating pressure (P) & volume of oil
per revolution of the pump (v)
• Rise in noise level is observed with increase in n, P & v on
case of both the axial piston pump & vane pump [Fig. 4.32
(a) & Fig. 4.32 (b)]
• In comparison to an axial piston pump, a vane pump
produces less noise when n, p and v are increased by same
amount under similar working parameters [Fig. 4.32 (b)]
PUMP NOISE

PUMP NOISE
SRM/137/Fig. 4.33
Dependence of power & noise intensity
Noise level increases with the increase in power rating of pump

Noise vs. Speed, Pressure & Displacement SRM/138/Fig. 4.5

WITH REFERENCE TO PREVIOUS SLIDE
• Rise in noise intercity generated in a positive displacement pump with
an increase in pump speed is higher than with an increase in pressure
or displacement as seen from Table.
• Variable axial piston pump is found to generate more noise level at
higher power rating compared to low power rating
• A fixed displacement pump generates less noise intensity than a
variable displacement pump under similar working parameters & size
• Rise in noise intensity by a positive displacement pump with increase
of pump speed, is higher than that with increase of pressure or
displacement volume.
PUMP NOISE
[SRM/138/Fig. 4.5]

• Make changes to source of noise - noisy pump
- Misaligned pump/motor coupling
- improperly installed pump/motor mounting plates
- pump cavitation
- Excess pump speed or pressure
• Modify components connected to primary source of noise
- clamping of hydraulic piping at specifically located
supports
• Usage of sound absorption materials
Some of the materials are presented in following slide
PUMP NOISE - Control

PUMP NOISE – Barrier Materials
SBM5 MAT SAPT 220
SA25FF/B/6

NOISE IN CENTRIFUGAL PUMP
Things that can cause noise in a centrifugal pump:
• Pump Cavitation
• Pump is experiencing water hammer
• Rubbing of components
• Rubbing of impeller against the volute because of thermal expansion
or improper adjustment.
• Shaft is hitting a thermal bushing in the end of the stuffing box.
• Bearings are bad
• The mechanical seal has come loose from the shaft
• A foreign object has entered into the stuffing box
• The seal faces are running dry
• You have hit a critical speed
• Coupling misalignment
• The noise is coming from the motor or some near by equipment.

PUMP CAVITATION
Cavitation occurs due to entrained air bubbles in the hydraulic fluid or
vaporization of the hydraulic fluid. Occurs when pump suction lift is
excessive & the pump inlet pressure falls below the vapor pressure of
fluid. Air or vapor bubbles which form in the low pressure inlet region
of pump are collapsed when they reach high pressure discharge
region. This produces high fluid velocity & impact forces, which
erodes metallic components subsequently shortening pump life.
Cavitation has been described as:
• A reduction in pump capacity.
- Happens because bubbles take up space and one cannot have
bubbles and liquid in the same place at the same time
- If the bubble gets big enough at the eye of the impeller, the pump
will lose its suction and will require priming
• A reduction in the head of the pump
- Bubbles, unlike liquid, are compressible. It is this compression that
can change the head

PUMP CAVITATION
• Formation of bubbles in a low pressure area of the pump volute.
• A noise that can be heard when the pump is running.
- Any time a fluid moves faster than the speed of sound in the
medium you are pumping, a sonic boom will be heard. (speed of
sound in water is 1480 meters/sec).
• Damage on the pump impeller and volute.
TYPES OF CAVITATION
1. Vaporization cavitation
A fluid vaporizes when its pressure gets too low, or its temperature
too high
2. Air ingestion cavitation
The bubbles collapse as they pass from the eye of the pump to the
higher pressure side of the impeller.
Air ingestion seldom causes damage to the impeller or casing.
The main effect of air ingestion is loss of capacity.

PUMP CAVITATION
3. Internal recirculation cavitation
Fluid recirculates increasing its velocity until it vaporizes and then
collapses in the surrounding higher pressure.
4. Flow turbulence cavitation
5. Vane passing syndrome cavitation
Impeller tip gets damaged due to its passing too close to the pump
cutwater. The velocity of the liquid increases if the clearance is too
small lowering the pressure and causing local vaporization. The
bubbles collapse just beyond the cutwater and there is where you
should look for volute damage

• Increase the suction head
- Raise the liquid level in the tank
- Elevate the supply tank.
- Put the pump in a pit.
- Reduce the piping losses.
- Retrofit the pump with a higher specific speed impeller.
- Install a booster pump or inducer.
- Pressurize the tank.
- Be sure the tank vent is open and not obstructed. Some vents can
freeze in cold weather.
• Lower the fluid inlet temperature
– Injecting a small amount of cooler fluid at the suction is often
practical.
– Insulate the suction piping from the sun's rays.
– Be careful of discharge re-circulation and vent lines re-circulated
to the pump suction; they can heat up the suction fluid.
PUMP CAVITATION CONTROL

• Decrease the fluid velocity
- Remove obstructions in the suction piping
- Do not run the impeller too close to the pump cutwater.
- Reduce the speed of the pump.
- Reduce the capacity of the pump.
- Do not install an elbow too close to the pump suction.
• Reduce the net positive suction head required (NPSHR)
- Use a double suction pump
- Use a lower speed pump.
- Use a pump with a larger impeller eye opening.
- If possible install an inducer
PUMP CAVITATION CONTROL

PUMP
RIPPLE
Small variations of flow
that take place during
pumping are called
ripple

PUMP SELECTION PARAMETERS
1. Maximum operating pressure
Determined by
- power requirements of the circuit - particular application
- availability of components - type of fluid
Higher the operating pressure
- higher component cost - lower choice of components
- reduction in fluid flow rates for a given system power
- smaller pumps, smaller bore pipes & smaller components
2. Maximum delivery
Pump must be capable of delivering maximum flow rate demanded
by the circuit
Constant demand - Fixed displacement pump
Demand at a series of fixed levels - Multi-pump system
Varying demand within narrow band - Variable displacement

3. Type of control
- Manual servo control
- Pressure compensated control
- Constant flow control
- Constant power control
4. Pump drive speed
Fluid delivery rate is proportional to speed of rotation
Higher the pump drive speed, shorter will be its life
5. Type of fluid
Pumps are designed to operate within a particular range of fluid
viscosity
Mineral oils works satisfactorily with most of the pumps
Operating with synthetic or water based fluids reduces the working
life of the pump

6. Pump noise
Noise increases with speed & pressure
7. Size & Weight of pump
Actual size & weight of pump depends upon the particular
manufacturer’s design. In the mobile hydraulic field the trend is to reduce
the weight of the hydraulic system by increasing the operating pressure,
reducing the size of reservoir etc.
8. Efficiency
Efficiency depends upon design, operating pressure, speed & fluid
viscosity pumped.
Pump type
Volumetric
Efficiency
Overall
Efficiency
Piston
plunger in-line <= 99 % <= 95 %
radial > 95 % > 90 %
axial > 95 % > 90 %
Precision gear pump <= 95 % <= 90 %
Vane pump <= 90 % <= 80 %

9. Cost
Initial cost of a pump is usually of secondary importance to running
& maintenance costs.
Lower cost units are gear & vane pumps, the piston types much
dearer, with sealed valve in-line plunger pumps probably being
most expensive
10. Availability & interchangeability
11. Maintenance & spares

Hydraulics_Unit-1.pdf

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