Hale RSD - Manual (Page 122)

❑ Cavitation
122 Appendix F: Cavitation
Hale Products, Inc., Nov.2005, Rev-A
This sudden change from vapor to liquid generates a shock effect that damages
the impeller and pump housing. Usually there are thousands of tiny vapor
pockets (or bubbles).
It is the collapsing (or implosion) of these bubbles that causes the characteristic
sound of cavitation that has been described as rocks tumbling in the pump.
Warning Signs of Cavitation (Discharge and Gauges)
Discharge Pressure
In a properly functioning pump, an increase in RPM increases the discharge
pressure and volume. An increase in engine RPM that does not cause an
increase in the pump discharge pressure is the most reliable indication that a
pump is approaching cavitation.
Vacuum Compound Gauge
Do not depend entirely on the vacuum (compound) gauge to indicate when a
pump is nearing cavitation.
The vacuum gauge is usually tapped into the intake chamber several inches
away from the leading edge of the impeller eye where the greatest amount of
vacuum occurs. The vacuum gauge does not take into account ambient tem-
perature nor atmospheric pressure and is not accurate near zero (0) on the
vacuum scale.
To Eliminate Cavitation
To eliminate cavitation, the operator must be aware of the warning signs listed
above. Low barometer, high elevation, and elevated water temperature also
contributes to cavitation.
Pumps are rated at standard temperatures and barometric pressures. When
conditions vary from standard, the maximum capacity of the pump from draft
can be affected.
The most common way to eliminate cavitation is to decrease the amount of
water being discharged by decreasing engine speed or closing discharge
valves. However, this also results in a reduction of flow.
Cavitation is also eliminated by increasing the pump inlet pressure. This is
accomplished with reduced vertical lift, reduced inlet losses, or running from
positive pressure supplies.