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![• 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](https://image.slidesharecdn.com/hydraulicsunit-1-221228173136-cc7982ec/85/Hydraulics_Unit-1-pdf-133-320.jpg)
![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](https://image.slidesharecdn.com/hydraulicsunit-1-221228173136-cc7982ec/85/Hydraulics_Unit-1-pdf-155-320.jpg)
![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]](https://image.slidesharecdn.com/hydraulicsunit-1-221228173136-cc7982ec/85/Hydraulics_Unit-1-pdf-158-320.jpg)
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Hydraulics_Unit-1.pdf
- 1. HYDRAULICS & PNEUMATICS SUB CODE:ME73 I.A. MARKS: 25 EXAM MARKS: 100 By M. R. Doddamani
- 2. CONTENTS 1. Introduction toHydraulic 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
- 3. 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
- 4. INTRODUCTION • Requirement ofIndustrial processes • Device to perform activities • PRIME MOVER Prime movers are mechanical devices, which convert one form of energy into another
- 5. • 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
- 6. • It isthe 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)?
- 7. HISTORY OF FLUIDPOWER • 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
- 8. ADVANTAGES OF FP 1.Ease & accuracy of control - Usage of simple levers & push buttons Hydraulic operation of aircraft landing gear
- 9. 2. Multiplication offorce ADVANTAGES OF FP Turntable for handling huge logs
- 10. 3. Constant forceor torque ADVANTAGES OF FP FP application in Oceanography
- 11. 4. Simplicity, Safety& Economy ADVANTAGES OF FP Steering control system
- 12. 5. Removal ofheat generated 6. FP devices are highly responsive because of weight to power ratio ADVANTAGES OF FP
- 13. 7. FP devicesare 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
- 14. 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
- 15. DRIVING FORCE 1. Nomoving parts 2. Force multiplication 3. Flexibility in direction changing
- 16. We may summarizeby 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
- 17.
- 18. • Harvesting corn APPLICATIONS Hydraulicallydriven elevator conveyor
- 19.
- 20. • Industrial lifttrucks APPLICATIONS Hydraulic lift truck
- 21.
- 22. • Robotic dexterousarm APPLICATIONS
- 23. APPLICATIONS Use of variabledisplacement 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
- 24. APPLICATIONS Variable displacement, pressurecompensated vane pumps are normally used for energy saving and smooth control of each machine heat generation is kept to minimum with variable displacement pumps.
- 25.
- 26.
- 27.
- 28. PRINCIPLES OF HYDRAULICS •Language of physical science for FLUID • Current focus – Oil as a medium • Law of Hydrostatics Potential head
- 29. PRINCIPLES OF HYDRAULICS Potentialhead is independent of shape & size
- 30. PRINCIPLES OF HYDRAULICS Potentialhead is independent of container shape
- 31. 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
- 32. BRAMAH’S PRESS PRINCIPLE(Hydraulic Jack) Principle of Bramah’s press
- 33. 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)
- 34.
- 35. Assuming Oil tobe 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 BRAMAH’S PRESS PRINCIPLE (Hydraulic Jack)
- 36. MECHANICAL LEVER Length oflever arms inversely proportional to the piston areas AE/page-102/Ex-3.15&3.16
- 37. APPLICATIONS OF PASCAL’SLAW Hand operated hydraulic jack
- 38. APPLICATIONS OF PASCAL’SLAW Air to hydraulic pressure booster
- 39.
- 40. COMPONENTS OF HYDRAULICSYSTEM
- 41. COMPONENTS – PNEUMATICSYSTEM
- 42.
- 43.
- 44.
- 45.
- 46. STRUCTURE OF HYDRULICSYSTEM
- 47. Division of Hydraulicsystem 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
- 48. 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 STRUCTURE OF HYDRULIC SYSTEM
- 49. 2. Power controlsection 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 STRUCTURE OF HYDRULIC SYSTEM
- 50. BREAKDOWN OF CONTROLCHAIN
- 52.
- 53.
- 54.
- 55. COMPONENTS OF HYDRUALICSYSTEM
- 56.
- 57.
- 58. WHAT IS APUMP? 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
- 59. PUMPING THEORY Pumping actionof a simple piston pump AE/144/Fig. 5-2
- 60.
- 61.
- 62. POSITIVE or HYDROSTATICPUMPS 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
- 63. 9 Examples includeGear, 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
- 64. NONPOSITIVE or HYDRODYNAMICPUMPS 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
- 65. HOME WORK 1. Distinguishbetween positive & non-positive displacement pumps 2. Justify the names Hydrodynamic & hydrostatic for positive & non-positive displacement pumps
- 66.
- 67. CENTRIFUGAL PUMP SRM / 92/ Fig. 4.1 AE / 145 / Fig. 5.3
- 68. ¾ Provides smoothcontinuous 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
- 69.
- 70.
- 71.
- 72.
- 73.
- 75.
- 76. ¾ One ofthe 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
- 78.
- 79.
- 80. THREE GEAR PUMP Centergear is connected to motor shaft Two independent outputs Short sealing range limits the system pressure SRM/99/Fig. 4.6
- 81. HELICAL GEAR PUMP Excessiveend thrust
- 82. HERINGBONE GEAR PUMP Thrustelimination One row of gear right handed while the other left handed Develops much higher pressures Internet
- 83.
- 85.
- 86. ¾ Consists ofan 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
- 87. GEROTOR PUMP AP/44/Fig. 2.9(b) AE/154/Fig. 5-11
- 88. OPERATION PRINCIPLE OFGEROTOR PUMP Internet
- 89.
- 90. 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
- 91.
- 92.
- 94. ¾ Operates ina 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
- 95.
- 96. SCREW PUMP 2 Elementrotary type SRM/102/Fig. 4.9 (a) SRM/102/Fig. 4.9 (b)
- 97.
- 98.
- 99.
- 101. ¾ Axial flowpositive 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
- 102. ¾ Disadvantages - Manufacturingof 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
- 103.
- 104. VANE PUMP -OPERATION AE/157/Fig. 5-15
- 105. UNBALANCED VANE PUMP AP/45/Fig.2.10 (a)
- 106. • Axis ofthe 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
- 107. • One halfof 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
- 108.
- 109. • Circular rotorwith 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
- 110.
- 111. • In hydraulicsystem 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
- 112. PRESSURE COMPENSATED VANEPUMP SRM/112/Fig. 4.19 (c)
- 113. • In certainhydraulic 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 PRESSURE COMPENSATED VANE PUMP
- 114. FLOW-PRESSURE RELATIONSHIP OF PRESSURECOMPENSATED VANE PUMP SRM/112/Fig. 4.19 (b)
- 115. CHARACTERISTIC OF VANEPUMP AT CONSTANT SPEED SRM/112/Fig. 4.19 (b)
- 116.
- 117.
- 118. OPERATION OF PISTONPUMP • 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
- 119.
- 120.
- 121.
- 122.
- 123. AXIAL PISTON PUMP-INLINE Exploded View SRM/116/Fig. 4.21 (a)
- 124. • Pistons arearranged 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)
- 125. SWASH PLATE IN-LINEAXIAL PISTON PUMP SRM/117/Fig. 4.22 (a)
- 126. SWASH PLATE IN-LINEAXIAL PISTON PUMP SRM/117/Fig. 4.22 (b)
- 127. • Different designsof 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
- 128. WOBBLE PLATE IN-LINE AXIALPISTON PUMP SRM/118/Fig. 4.22 (c)
- 129. • Swash platerotates 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
- 130. VARIABLE DISPLACEMENT AXIAL PISTONPUMP SRM/120/Fig. 4.24
- 131. • Stroke lengthof 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
- 132. PRESSURE COMPENSATED PISTON PUMP SRM/120/Fig. 4.25(a) SRM/120/Fig. 4.25 (b)
- 133. • Swash plateis 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
- 134. BENT AXIS PISTONPUMP AP/49/Fig. 2.15
- 135. • Stroking ofthe 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
- 136.
- 137. 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
- 138.
- 139. PUMP PERFORMANCE CURVES •Manufacturers specify pump performance characteristics in the form of graphs Variable displacement piston pump AE/176/Fig. 5-32
- 140.
- 141.
- 142.
- 143.
- 144.
- 145. GEAR PUMPS • Leastexpensive • 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
- 146. PISTON PUMPS • Mostexpensive • 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
- 147. • Noise isa 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
- 148.
- 149. • Generated noiselevels 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
- 150. PUMP NOISE SRM/135/Fig. 4.31(a) Noise developed in typical pumps
- 151. • Comparative noisebehavior 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
- 152. PUMP NOISE SRM/136/Fig. 4.31(b) Noise intensity in protected room &near pump installation measured at 1 m away
- 153. PUMP NOISE SRM/137/Fig. 4.32(a) Rise of noise level with pressure, flow & RPM
- 154. PUMP NOISE SRM/137/Fig. 4.32(b) Rise of noise level with pressure, flow & RPM
- 155. WITH REFERENCE TOPREVIOUS 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
- 156. PUMP NOISE SRM/137/Fig. 4.33 Dependenceof power & noise intensity Noise level increases with the increase in power rating of pump
- 157. Noise vs. Speed,Pressure & Displacement SRM/138/Fig. 4.5
- 158. WITH REFERENCE TOPREVIOUS 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]
- 159. • Make changesto 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
- 160. PUMP NOISE –Barrier Materials SBM5 MAT SAPT 220 SA25FF/B/6
- 161. NOISE IN CENTRIFUGALPUMP 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.
- 162. PUMP CAVITATION Cavitation occursdue 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
- 163. PUMP CAVITATION • Formationof 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.
- 164. PUMP CAVITATION 3. Internalrecirculation 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
- 165. • Increase thesuction 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
- 166. • Decrease thefluid 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
- 167. PUMP RIPPLE Small variations offlow that take place during pumping are called ripple
- 168. 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
- 169. 3. Type ofcontrol - 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 PUMP SELECTION PARAMETERS
- 170. 6. Pump noise Noiseincreases 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 SELECTION PARAMETERS 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 %
- 171. 9. Cost Initial costof 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 PUMP SELECTION PARAMETERS
- 172.