1. 1 TSM363 Fluid Power Systems Pumps and Actuators Tony Grift Dept. of Agricultural & Biological Engineering University of Illinois

2. 2 Agenda Units, Pumps, Pressure Relief Valve Cylinders Double acting/ Single acting Single rod, Double rod Cylinder construction Pressure, Flow, Work and Power in cylinders Pressure, Flow, Torque and Power in pump/motors Volumetric and Torque efficiency of pump/motors Pump implementations

3. 3 Hydraulic Units (SI) Pascal Newton Watt

4. 4 Control can take place in various ways. Power is pressure times flow rate Pressure control Pressure relief valve Pressure reducing valve (regulator) Pressure compensation: Only provide the pressure needed to move the load(s). In idle reduce energy loss by providing a open center condition Pressure compensated pump. Make the pressure independent of the flow required to move the load at a preset speed. Deal with multiple cylinders that need to move simultaneously Flow control Throttle (needle valve, very crude, Orifice equation applies) Pressure compensated Flow Control Valve: Assure a preset flow rate independent of the pressure drop across the valve Pressure and Flow control Load sensing systems: combine pressure and flow control to reduce energy losses

5. 5 Choice of pump depends on these factors Application Max and working Pressure and Flow rate requirements Constant rate / Variable rate Pump efficiency Leakage Noise level Contamination sensitivity Price

6. 6 Pump ‘family tree’

7. 7 Video 8: Power units (3:26) Power supply unit Converts Mechanical energy into hydraulic energy Hydraulic Fluid is conditioned (cooled, cleaned) Components Drive motor Safety valve Oil reservoir Pump External Gear pump function (constant delivery) Where teeth unmesh, volume increases, oil enters Where teeth mesh, volume decreases, oil leaves Pressure only builds when there is a resistance (load) Safety valve needed to prevent failure when cylinder stalls Pressure Relief Valve diverts flow back to tank when cylinders are stalled Reservoir Cools oil Cleans oil from suspended particles, water and air which takes time (Capacity) Filters trap impurities 70% of all malfunctions are due to impurities

8. 8 In case of a motor shaft, the Work can be found by multiplying a force through a distance. Suppose we assume a force at a distance. The total work per radian of the shaft is now equal to Mechanical Torque in a pump/motor

9. 9 Mechanical Power in a pump/motor The power is now equal to this value divided by the time per radian. If the shaft is turning at it takes seconds per radian. Since for Power we have to divide the Work by time, this leads to:

10. 10 Hydraulic Power in pump/motor ( )

11. 11 Pump/Motor flow is proportional to the speed of rotation and the displacement per revolution Pump displacement is a volume per angular displacement (radian). Assuming the volumetric efficiency is 1.0 (no leakage) More realistic, with Volumetric Efficiency (why in numerator?)

12. 12 Torque Required to drive a pump is proportional to Pressure More realistic, with Torque Efficiency (why in the denominator?) (No losses here)

13. 13 Power Efficiency of Pumps From before: And Power Efficiency: Without loss Efficiencies

14. 14 Data sheet Data sheet Eaton MHT vane pump

15. 15 A Pressure Relief Valve (PRV) provides overload protection In the symbol there are Main pressure lines (solid) Sense lines (dashed) Spring return Adjust arrow Direction arrow Pressure and Tank connections

16. 16 Some questions about a PRV Is this valve normal open or normal closed Closed / open, think of a door Where is the pressure sensed, upstream or downstream and why ? What is the pressure at the tank port ? Why is a PRV adjustable ?

17. 17 Cylinders

18. 18 Video 9: Hydraulic actuators (6:58) Cylinders convert hydraulic energy into linear motion Motors generate rotary motion Single acting cylinder: One working port Can do work in only one direction (extension) External force retracts the cylinder No perfect seal, over time oil passes on to unpressurized side: need for drain Good for high load single lift (scissor platform) Return stroke through gravity or spring return Plunger (ram) cylinders: Cap end only, very powerful and stiff Double acting cylinder: Two working ports Pressure advances and retracts the cylinder: push and pull Cylinder retracts faster than it extends due to different areas of cap end and rod end side

19. 19 Video 9: Hydraulic actuators (6:58) cont. Example: ratio of cap and rod end side area is 2:1. Assume During extension rod end pressure =0 During retraction cap end pressure =0

20. 20 Video 9: Hydraulic actuators (6:58) cont. Example: ratio of cap and rod end side area is 2:1. Linear Power:

21. 21 Hydraulic Cylinder

22. 22 Cylinder construction

23. 23 1.Tie rod ( keeps cylinder assembly together ) 2.Rod end head( mounting point ) 3.Rod end port ( fluid entrance/exit point ) 4.Piston seals ( dynamic, seals cap end from rod end pressure) 5.Cap end head ( mounting point) 6.Cap end port ( fluid entrance/exit point ) 7.Rod bearing ( lateral support of the rod ) 8.Rod wiper ( keeps dirt out ) 9.Rod seal (dynamic, seals fluid from environment ) 10.Barrel ( cylinder ) 11.Piston rod ( mechanical force output ) 12.Piston ( pressure to force converter ) 13.Static seal ( seals fluid from environment )

24. 24 Cylinders are perfect for linear motion Single rod (most common) Dual rod (power steering)

25. 25 Telescopic cylinder

26. 26 Basic Circuit with Double Acting CylinderPump Actuator OverloadProtection Reservoir Pressuregage Electric Motor

27. 27 Question: Can the cylinder be moved ? 1)Cylinder: Double acting, differential area 2)Fluid is incompressible 3)Rod and cap end connected Check in FluidSim

28. 28 Hydraulic Work (rod end pressure = 0)

29. 29 Differential area cylinder: Flow and displacement

30. 30 Differential area cylinder: Force equilibrium

31. 31 Differential area cylinder: Work

32. 32 Differential area cylinder: Power

33. 33 Dual rod cylinder: Power

34. 34 Power if (as in motors and pumps)

35. 35 Question: Will the cylinder extend ? Check in FluidSim

36. 36 Video 5: Pressure transmission (0:53) Pressure intensification in hydraulic systems: Differential area cylinders cause this effect Max pressure in the system is NOT PRV setting ! Check in FluidSim

37. 37 Question in ‘Customary Units’ Given PRV Setting 15 MPa pump displacement of 10.54 cm 3 /rev the speed of the pump is 1800 rpm Required Torque needed to drive the pump Power needed to drive the pump Neglect friction

38. 38 Answer in ‘Customary Units’

39. 39 Question in ‘Customary Units’ Given PRV Setting pump displacement of the speed of the pump Required Torque needed to drive the pump Power needed to drive the pump. Neglect friction

40. 40 Answer in SI Units

41. 41 Types of Pumps and Motors External Gear Internal Gear Vane Axial Piston Radial Piston

42. 42 External Gear pump Poorly sealing Low flow rates Low pressures Fixed displacement Low cost

43. 43 Internal Gear pump Poorly sealing Low flow rates Medium pressures Fixed displacement Medium cost

44. 44 Vane pump Medium sealing Higher pressures Inexpensive Fixed or variable flow rate

45. 45 Axial piston pump with swash plate. In this case the swash plate angle is variable, which results in a variable delivery pump Excellent sealing High pressures Relatively simple design Variable flow rate No need for valves Expensive

46. 46 Axial piston pump with swash plate. In this case the swash plate angle is constant, which results in a constant delivery pump Here fixed flow rate

47. 47 Radial piston pump with variable rate through changing eccentricity between shaft and ‘pintle’ Excellent sealing High pressures Relatively expensive Variable flow rate Valves are needed Complex design

48. 48 Radial piston pump with variable rate through changing eccentricity between shaft and ‘pintle’ Excellent sealing High pressures Relatively expensive Variable flow rate

49. 49 External Gear Fixed Displacement

50. 50 Pump ‘family tree’

51. 51 TSM363 Fluid Power Systems TSM363 Fluid Power Systems Pumps and Actuators The End Dept. of Agricultural & Biological Engineering University of Illinois