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they can be diagnosed incorrectly. However, they are caused by three
separate conditions and, by focusing on these root causes, an accurate
diagnosis can be simplified.
It must be recognized that the harmful effects on the impeller is only
one consequence of these conditions. The bigger problems come from
the subsequent vibration and its detrimental effects on seals and
bearings.

4.8 Priming

Another important suction condition exists when a pump is operating
on a suction lift. When the pump stops, there is a tendency for the
liquid to run out of the suction pipe. If this occurs and the pump has to
restart under this condition, it must be able to handle the air pocket
that's now in the suction line.
The most popular method of dealing with this eventuality is with the
use of a self-priming pump which is capable of freeing itself of entrained
gas and resuming normal pumping without any attention.
These pumps have a suction reservoir cast integrally with the pump
casing to retain a certain volume of liquid even when the suction line is

Figure 4.10: Self-priming pump (Reproduced with permission of Gorman-Rupp Pump
Company)

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