hydraulics unit

HYDRAULICS & PNEUMATICS

SUB CODE: ME73 I.A. MARKS: 25EXAM MARKS: 100

By

M. R. Doddamani

CONTENTS1. Introduction to Hydraulic power2. The Source of Hydraulic power3. Hydraulic Actuators & Motors4. Control components in Hydraulic systems5. Hydraulic Circuit Design & Analysis6. Maintenance of Hydraulic Systems7. Introduction to Pneumatic control8. Pneumatic Actuators9. Directional control valves10. Simple Pneumatic control11. Signal processing elements12. Multi-cylinder applications13. Electro-Pneumatic control14. Compressed air

BOOKSText Books

1. Fluid power with applications by Anthony Espocito2. Pneumatics & Hydraulics by Andrew Parr

Reference Books1. Oil hydraulic systems by S. R. Majumdar2. Pneumatics basic level TP 101 by FESTO 3. Fundamentals of pneumatic control engineering by

FESTO4. Hydraulics basic level TP 501 by FESTO 5. Pneumatic Systems by S. R. Majumdar6. Power Hydraulics by Ashby7. Fluid power for Technicians by Donald Newton

INTRODUCTION

• Requirement of Industrial processes

• Device to perform activities

• PRIME MOVERPrime movers are mechanical devices, which

convert one form of energy into another

• Basic sources (prime movers) of power in Industries1. Electrical

Electrical motorsPower transmission through cables

2. MechanicalI.C.EnginesPower transmission through gears, shafts etc.

3. FLUID POWERCommon sourceWidely used in modern industriesPower 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 Systems1. 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 FP1. 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 torqueADVANTAGES OF FP

FP application in Oceanography

4. Simplicity, Safety & Economy

ADVANTAGES OF FP

Steering control system

5. Removal of heat generated6. 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 messy2. Susceptible to damage by dirt or contamination3. Physical injury from high speed particles4. Fire or explosion hazard5. Prolonged exposure to loud noise

DRIVING FORCE

1. No moving parts2. Force multiplication3. 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

• Brush drives

APPLICATIONS

• Industrial lift trucksAPPLICATIONS

Hydraulic lift truck

• ExcavatorsAPPLICATIONS

• Robotic dexterous armAPPLICATIONS

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.

APPLICATIONS

APPLICATIONS

APPLICATIONS

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

Potential head

PRINCIPLES OF HYDRAULICS

Potential head is independent of shape & size

PRINCIPLES OF HYDRAULICS

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 * D12)

F2 = P * A2 (A2 = Π / 4 * D22)

P = F2 / A2 P = F1 / A1 = F2 / A2

F2 : F1 = A2 : A1 = D22 : D1

2

F2 = F1 * A2 / A1

But as A2 > A1, A2 / A1 is > 1or 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)

BRAMAH’S PRESS PRINCIPLE (Hydraulic Jack)

Assuming Oil to be IncompressibleCylindrical volume displaced by = Cylindrical volume displaced by

the input piston the output piston V1 = V2 A1S1 = A2S2

Where S1 = downward movement of piston 1S2 = downward movement of piston 2

Thus, S2 / S1 = A1 / A2 = F1 / F2

Large output piston does not travel as far as the small input pistonF1 S1 = F2 S2 ( work energy)

Energy input to hydraulic jack equals energy output from the jack

BRAMAH’S PRESS PRINCIPLE (Hydraulic 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

BASIC ELECTRICAL SYSTEM

COMPONENTS OF HYDRAULIC SYSTEM

COMPONENTS – PNEUMATIC SYSTEM

COMPARISION

COMPARISION

COMPARISION

COMPARISION

STRUCTURE OF HYDRULIC SYSTEM

Division of Hydraulic systemI. Signal control sectionII. Hydraulic power section

SIGNAL CONTROL SECTION1. Signal input (sensing)

ManuallyMechanically Contactlessly

2. Signal processingOperatorElectricityElectronicsPneumaticsHydraulics

STRUCTURE OF HYDRULIC SYSTEM

HYDRAULIC POWER SECTION1. Power supply section (energy conversion & pressure medium

conditioning)Components used for energy conversion

- Electric motor- I. C. engine- Coupling- Pump

Components used for conditioning hydraulic fluid

- Filter- Cooler- Heater- Thermometer- Pressure gauge

STRUCTURE OF HYDRULIC SYSTEM

2. Power control sectionDirectional control valvesFlow control valvesPressure control valvesNon-return valves

3. Drive sectionExecutes various working movements of machine or manufacturing systemEnergy contained in the hydraulic fluid is used for the execution of movements or generation of forces which is achieved using following components

- cylinders- motors

STRUCTURE OF HYDRULIC SYSTEM

BREAKDOWN OF CONTROL CHAIN

POWER CONVERSION IN HYDRULIC SYSTEM

END OF CHAPTER 1

SOURCE OF HYDRAULIC POWERPUMPS

COMPONENTS OF HYDRUALIC SYSTEM

HYDRAULIC PUMP

HYDRAULIC PUMP

AP/35/FIG. 2.1

WHAT IS A PUMP?

Device for converting mechanical energy into hydraulic energyHeart of the hydraulic system as it generates the force necessary to move the loadMain purpose is to create the flow of oil through the system which in turn assists transfer of power & motionDoes not develop pressureGenerally driven at constant speed by 3 phase AC induction motorMechanical action creates partial vacuum at pump inletAtmospheric pressure forces the fluid through the inlet line into the pumpPump pushes the fluid into the hydraulic system

PUMPING THEORY

Pumping action of a simple piston pumpAE/144/Fig. 5-2

PUMP CLASSIFICATION

PUMP CLASSIFICATION

AP/35/Fig. 2.2

POSITIVE or HYDROSTATIC PUMPSPumping volume changes from maximum to minimum during each pumping cycleUsed where pressure is the primary considerationSeparation between high & low pressure areas or zonesPumping action is caused by varying the physical size of the sealed pumping chamberEjects a fixed amount of fluid per rev. of pump shaft rotationFlow enters & leaves the unit at same velocityCapable of overcoming the pressure resulting from the mechanicalloads as well as the resistance to flow due to friction

PUMP CLASSIFICATION

Examples include Gear, vane, piston screw pumpsAdvantages- 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 systemVariations 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 PUMPSFluids are displaced & transferred using the inertia of fluid in motionUses Newton’s 1st law of motion to move the fluid against the system resistanceUsed for low pressure (up to 40 bar), high volume flow applicationsLittle use in fluid power fieldPrimarily used for transporting fluids from one location to anotherExamples include centrifugal (rotational inertia) & axial flow propeller pumps (transnational inertia)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 PUMPS

CENTRIFUGAL PUMP

SRM / 92 / Fig. 4.1

AE / 145 / Fig. 5.3

Provides smooth continuous flowFluid enters at the center of impeller, picked up by rotating impeller, centrifugal force causes fluid to move radially outwardsBehaves interestingly in case of no demand of fluidNo positive internal seal against leakageHighly desirable for pumping stationsEasily handles large change in demandReduction 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

Need of priming

AXIAL FLOW PUMP

AXIAL FLOW PROPELLER PUMP

GEAR PUMPS

EXTERNAL GEAR PUMP

AP/42/Fig. 2.7

EXTERNAL GEAR PUMP

Internet source

EXTERNAL GEAR PUMP

AE/152/Fig. 5-7

One of the gear is connected to drive shaft which in turn is coupled with prime moverSecond gear gets driven because of meshing (spur gears)Suction side – teeth unmeshed Discharge side – teeth meshVacuum generation due to evacuation of teethLine contact of the gear teeth over one another prevents flow through the mesh & the close fitting of the housing prevents flow back around the peripheryManufacturing 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

AE/150/Fig. 5-6

GEAR PUMP CHARACTERISTICS

SRM/99/Fig. 4.5

THREE GEAR PUMPCenter 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 PUMPThrust 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

Consists of an internal gear, a regular spur gear, a crescent shaped seal & an external housing

Power is applied to either gear

Crescent seal acts as a seal between the suction & discharge ports

Motion of the gear draws fluid from the reservoir & forces it around both sides of crescent seal

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

AE/155/Fig. 5-12

GEROTOR – GENERATED ROTOR Operates much like the internal gear pumpInner gear rotor (Gerotor element) is power driven which draws outer gear rotorCenters of the gears are offset by approximately one-half the tooth depthInner gear has one tooth less than the outer oneFormation of inlet & discharge pumping chambers between the rotor bladesSealing the pumping chamber because of meshing teethMore compact than the external gear pumpGears must be made to high precisionRatings:- Continuous pressure 125 bar- Max. speed 2000 to 3600 rpm- Max. delivery 200 l/min

GEROTOR PUMP

LOBE PUMP

LOBE PUMP

AP/43/Fig. 2.8

Operates in a fashion similar to that of external gear pump

Both blades are driven externally (one directly by the source of power & other through timing gears)

Physically blades doesn’t come in contact with each other

Quieter than other types of gear pumps

Greater amount of pulsation in pump output

Used for pumping gas, air, liquid with low pressures with higher flow rate

LOBE PUMP

SCREW PUMP

SCREW PUMP

2 Element rotary type

SRM/102/Fig. 4.9 (a)

SRM/102/Fig. 4.9 (b)

SRM/103/Fig. 4.10

SCREW PUMP

SCREW PUMP

Axial flow positive displacement unitThree precision ground screws deliver non pulsating flow quietly & efficientlyTwo symmetrically opposed idler rotors acts as a rotating sealsIdler rotors are in rolling contact with the central power rotor which are driven by the pressure of the liquidOperate up to 250 bar pressure at 1000 cm3 per min.Advantages

1. Most reliable2. Oil supply is pulsation free, continuous3. No oil churning, pump turbulence etc.4. Very quiet in operation

SCREW PUMP

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

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)

UNBALANCED VANE PUMP

• 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

UNBALANCED VANE PUMP

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 thepredetermined system pressure is reached, the pump should stop pumping further oil to the system – Pressure compensated vane pumpConsists of an additional spring which is adjusted to offset the cam ringAs 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 valveWhen 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

PRESSURE COMPENSATED VANE PUMP

FLOW-PRESSURE RELATIONSHIP OF PRESSURE COMPENSATED VANE PUMP

SRM/112/Fig. 4.19 (b)

CHARACTERISTIC OF VANE PUMP AT CONSTANT SPEED

SRM/112/Fig. 4.19 (b)

PISTON PUMP

SRM/115/Fig. 4.20 (a)

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

SRM/115/Fig. 4.20 (b)

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 COMPARISION

PUMP PERFORMANCE CURVES• Manufacturers specify pump performance characteristics in the form

of graphs

Variable displacement piston pumpAE/176/Fig. 5-32

Variable displacement piston pump

AE/176/Fig. 5-32

AE/177/Fig. 5-33

Radial piston pump

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

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 industryVANE 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 PUMPThings 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 CAVITATIONCavitation 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, whicherodes 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 CAVITATION1. Vaporization cavitation

A fluid vaporizes when its pressure gets too low, or its temperature too high

2. Air ingestion cavitationThe 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 CAVITATION3. Internal recirculation cavitation

Fluid recirculates increasing its velocity until it vaporizes and then collapses in the surrounding higher pressure.

4. Flow turbulence cavitation5. 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 youshould 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 oftenpractical.

– 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 PARAMETERS1. 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 deliveryPump must be capable of delivering maximum flow rate demanded by the circuitConstant demand - Fixed displacement pumpDemand at a series of fixed levels - Multi-pump systemVarying 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 speedFluid delivery rate is proportional to speed of rotationHigher the pump drive speed, shorter will be its life

5. Type of fluidPumps are designed to operate within a particular range of fluidviscosityMineral oils works satisfactorily with most of the pumpsOperating with synthetic or water based fluids reduces the working life of the pump

PUMP SELECTION PARAMETERS

6. Pump noiseNoise increases with speed & pressure

7. Size & Weight of pumpActual 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. EfficiencyEfficiency depends upon design, operating pressure, speed & fluid viscosity pumped.

PUMP SELECTION PARAMETERS

Pump type Volumetric Efficiency

Overall Efficiency

Pistonplunger in-line <= 99 % <= 95 %

radial > 95 % > 90 %axial > 95 % > 90 %

Precision gear pump <= 95 % <= 90 %Vane pump <= 90 % <= 80 %

9. CostInitial 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 & interchangeability11. Maintenance & spares

PUMP SELECTION PARAMETERS

END OF CHAPTER 2