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

2. Agenda
Units, Pumps, Pressure Relief Valve
Pressure, Flow, Torque and Power in pump/motors
Volumetric and Torque efficiency of pump/motors
Pump implementations

3. Hydraulic Units (SI)
Pascal
Newton
Watt

4. Control can take place in various ways
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. 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. Pump ‘family tree’

7. Video 8: Power units (3:26) Power supply unit Components
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. Mechanical Torque in a pump/motor
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

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. Hydraulic Power in pump/motor ( )

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

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

14. Data sheet Eaton MHT vane pump

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

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

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

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

19. Axial piston pump with swash plate
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

20. Axial piston pump with swash plate
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

21. 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

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

23. External Gear
Fixed Displacement

24. Pump ‘family tree’

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