Hale Q Series Muscle - Manual (Page 193)

193 MUSCLE (Midship) Pumps Installation, Operation, and Maintenance Manual
p/n: 029-0020-63-0
Cavitation 
Appendix G: Cavitation
(See Figure G-1: “Sample, Cavitation Regions.”)
Cavitation can occur while pumping from draft, in relay, or from a hydrant (although it
is more likely from draft conditions). The operator must be aware of the warning signs
and immediately correct the situation.
Cavitation can damage the impeller and other
sensitive components, impair pump performance,
and reduce flow capacity. The damage done dur-
ing any one period of cavitation is not great, but
the effects are cumulative. Implosions occurring
during cavitation break away or erode tiny pieces
of metal from the internal parts and the pump cas-
ing. When enough metal has been chipped away,
the impeller becomes unbalanced causing a
strain and vibration on bearings, bushings and
shafts.
G.1 PROCESS OF CAVITATION
Cavitation occurs when a centrifugal pump attempts to discharge more water than it is
receiving. Bubbles are created under the vacuum, formed near the eye of the impeller.
Cavitation is often referred to as “the pump running away from the fluid supply.” This
means you are trying to pump more water out of the pump than is going into the
pump.
The formation of bubbles in the low pressure regions of the impeller cause the impel-
ler to “slip” in the water, since the impeller is designed to move liquid not the air in the
bubbles. (See Figure G-1: “Sample, Cavitation Regions.”)
When increased discharge flow exceeds the intake, bubbles form in the low-pressure
region at the eye of the impeller. The pressure of the water in the pump drops as it
flows from the suction flange through the suction nozzle and into the impeller.
As flow from the pump increases, the vacuum at the impeller increases. As vacuum
increases, water near the impeller eye begins to boil and vaporizes.
Figure G-1: Sample, Cavitation
Regions