Page 379 - The Tribology Handbook

Selection of oil pumps c2 1

Table 21.3 Pump performance factors affecting choice of pump type

Positive displacement Centrifugal
Rate of delivery at given speed substantially unaffected by changes in Rate of delivery affected by change in delivery pressure.
delivery pressure Therefore flow demand and temperature which influence
pressure must be accurately controlled
Rate of delivery varies nearly directly with speed
Because wide variation in output results from change of
Delivery pressure may be increased within material strength limitation
of the pump, by increasing dri,ve power pressure, pump is well suited for installations requiring
large flows and subject to occasional transient surge
Very high delivery pressures can be produced by pumps designed to conditions, e.g. turbine hydraulic controls
reduce internal leakages

INTERNAL THEORETICAL DELIVERY
LEAKAGE /' w
a CENTRIFUGAL PUMP
2
(HIGH VISCOSITY) v)
cn
a
, ACTUAL DELIVERY w POSITIVE DISPLACEMENT
a
(LOW VISCOSITY)
PUMP
I
SPEED FLOW
Figure 21.2 Glelivery against speed and viscosity for Figure 21.3 Pressure against delivery for positive
a positive displacement pump displacement and centrifugal pumps

Table 21.4 Selection by suction characteristics
i Maximum suction lift, m
Self-Priming

Yes if wet
epends on speed
and viscosity

Depends on viscosity

C21.3