This document discusses hydraulic pumps, including: - Pumps are not continuous flow devices and have discrete chambers that collect and discharge flow through valve plates. The design of these components affects pressure variation. - Actual pump flow is determined by displacement, speed, efficiency terms accounting for volumetric (leakage) efficiency and mechanical (friction loss) efficiency. - Volumetric efficiency depends on manufacturing tolerances while mechanical efficiency depends on bearing friction and fluid turbulence. - Formulas are provided to calculate theoretical flow, actual flow accounting for efficiencies, torque required to drive the pump, and power delivered versus power input accounting for overall efficiency. - Factors like fluid properties, speed, foreign particles,

1. Hydraulic Pumps
>>Performance and Characteristics

2. General Issues
 Pumps are not strictly continuous
flow devices. Discrete chambers are
involved.
 Flow is collected for discharge
through valve plates
 Design of the valve plate and the
pump mechanism affects pressure
pulses and variation (ripple) of torque
and pressure

3. General Issues
 Our theoretical displacements can be used
to determine theoretical pump flow
 Qth =Displacement (cc/rev) * Speed (rpm)
 Actual flow is a linear function of pump
displacement, speed, a units constant, and
an efficiency term
 Two kinds of inefficiencies to account for
losses:
 Volumetric efficiency (slip)
 Mechanical efficiency (Friction losses)

4. Volumetric efficiency
This indicates the amount of leakage, which takes place
within the pump and involves considerations such as
manufacturing tolerances and flexing of the pump
casing.

5. Actual Pump Output, Q
 QA = (VD np ηV) /1000 where:
Q: L/min
VD : cm3
/rev
ηV: Volumetric efficiency (decimal)
 OR… QA = (VD np ηV) /231 where:
Q: GPM
VD: in3
/rev
ηV: same as above (no units)

6. Mechanical efficiency
 This indicates the amount of energy lost by
friction in bearing and other moving parts and Energy losses
due to fluid turbulence.
 mech eff =

7. Mechanical efficiency
 Mechanical efficiency can also be
computed in terms of torque, and
called torque efficency:

8. overall efficiency
The ratio of power output to power input to the pump
Or the Product of both volumetric and mechanical
efficiencies is known as the overall efficiency

9. Torque to Drive a Pump
 TA = (ΔP VD)/(2π ηm)
where:
TA : Newton meters torque required
ΔP : pressure rise across the pump in MPa
VD : Pump displacement in cm3
/rev
ηm: Pump mechanical (torque) efficiency – a decimal
 OR…

10. Torque to Drive a Pump
English Units
 TA = (ΔP VD)/(2π ηm)
where:
TA : is torque required
ΔP : pressure rise across the pump in PSI
VD : Pump displacement in inches3
/rev
ηm: Pump torque efficiency – a decimal

11. Power to Drive the Pump
 The hydraulic (theoretical) power
delivered by the pump is
QActualΔP/600 or QactualΔP/1714
for SI English units
(note this is actual pump flow, not theoretical)
 Shaft power to drive the pump is
given by Psp = Phydr / ηo where:
 η o = ηv ηm which is total pump efficiency

12. What Determines ηv & ηm ?
 ηv is a function of clearance spaces, system
pressure, viscosity and pump speed
 Leakage flow at a given pressure is relatively
fixed regardless of pump speed
 It is also affected by fluid viscosity as lower
viscosity fluid will result in higher leakage and
lower volumetric efficiency

13. What about Torque (mechanical)
Efficiency?
 Torque efficiency is a function of
speed and fluid viscosity
 Higher pump speeds will result in
lower efficiency as viscous friction is
speed dependent
 Lower viscosity fluid can reduce
viscous losses but acts negatively on
volumetric efficiency

14. Typical Performance curves for pumps

15. Other Factors affecting pump
performance
• Presence of foreign particles
cause damage to the internal surfaces of a pump.
• Foams and bubbles
Generate noise and causes cavitation
• Overheating of oil
poor lubricant and increases the internal leakage,
reducing pump capacity
• Wrong selection of oil.
select the oil in accordance with the ambient
temperature and follow the instructions of pump
manufacturer

16. Comparative analysis of
pumps

17. Cavitation
 Pump cavitation can occur due to entrained air
bubbles in the hydraulic fluid or vaporization of
the hydraulic fluid
 To control cavitation keep the suction pressure
above saturation pressure of fluid by:
 Keeping suction line velocities below 4 ft/sec
(~1m/s) and pump inlet lines as short as possible
 Minimize inlet line fittings; mount pump close to
reservoir; use low-pressure drop filters on inlet, and
use proper oil

18. Catalogue example

19. Double pumps

20. Sizing Pumps
 Component sizing begins with the LOAD
 Load and actuator will determine
 Flow requirement for this circuit
 Pressure range required by the circuit
(We’ll do this with cylinders and motors… soon)
 Total and simultaneous flow requirements
 Select for the maximum load pressure
 Add pressure drops that will occur in valves,
lines and fittings

21. Pump Sizing
 With pump outlet pressure and flow known
we will consider speed.
 Industrial apps will use synchonous speed of
electric motors. Generally 1750 rpm, or possibly
1100. ($ decides)
 Small diesel apps such as skid loaders can
operate directly from engine crankshaft and will
have engine speed. (2000-3000 rpm).
 Larger diesel apps – pump splitter with gear
reductions possible to optimize speed

22. Pump Sizing
 Determine appropriate speed for your app
 Use the equation for pump flow, solved for
displacement
 VD = 1000Q/p (np ηV)
 What shall we use for ηV ??
 This is a function of speed, pressure, and
fluid viscosity
 Look for vendor data or curves and adjust…

23. Pumps Selection
• Flow rate requirement
• Operating speed
• Pressure rating
• Performance
• Reliability
• Maintenance
• Cost and
• Noise.

24. Pump Symbols
 Any fixed displacement
pump
 Variable displacement
pump
 Variable displacement –
Pressure Compensated