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The Practical Pumping Handbook ...........................

Laws, as the new NPSH Required can usually be read from the same
pump curve.
With these Affinity laws, it becomes quite straightforward to calculate
the change in Performance Conditions which results from a change in
pump speed or impeller diameter. It should be noted that, for any
change greater than 10%, the Affinity Laws should be considered an
approximation. Although an approximation is all that is often required,
if a set of pump performance curves is available at the alternative speed,
these should always be used in preference to the Affinity Laws as they
will be much more accurate.

2.4 Pump performance on special liquids

A number of liquid types will detrimentally affect the performance of a
centrifugal pump, in that they reduce the head with some reduction in
capacity. More importantly, they will lower the efficiency with a
resulting marked increase in the horsepower draw needed to drive the
pump.
The performance curve shown in Figure 2.11 is a general depiction of

Head
B.H.P.
Water

Efficiency

Capacity
Figure 2.11 Effect of special liquids

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