Hale SMR - Manual (Page 48)

Operating Procedures
3-14 Stainless Max Series Pumps
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 (bubbles) rather than a few large
ones. It is the collapsing (or implosion) of these bubbles that
causes the characteristic sound of cavitation that has been de-
scribed 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 temperature nor atmospheric pressure and is not accu-
rate near zero (0) on the vacuum scale.
How to Prevent Cavitation
A soft sleeve has an advantage over a hard sleeve when pumping
from a hydrant because it will partially collapse providing an immedi-
ate indication to the operator that cavitation is imminent. A hard
sleeve indicates problems only at the intake gauge, which is not the
best or most reliable indicator.
Monitoring current operating conditions, knowing the capabilities of
the equipment, and regular inspection are the best protection
against cavitation.
During Operations
❑ Do not increase the pump speed beyond the speed at which the
pressure ceases to rise.
❑ Monitor that the water temperature baseline per NFPA
standards is 60° F (16° C).