Hale SMR - Manual (Page 18)

Introduction
2-4 Stainless Max Series Pumps
This means that the
operator is 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
impeller to "slip" in the
water since the impeller
is designed to move
liquid, not the air in the
bubbles.
To eliminate cavitation,
the operator must be aware of the warning signs and immediately
correct the situation or serious damage to the pump and impeller
will occur. The most reliable indication that a pump is approach-
ing cavitation is when an increase in engine RPM does not cause
an increase in pump discharge pressure. A low barometer, high
elevation, or elevated fluid temperature will also contribute to
cavitation.
Pumps are rated at standard temperatures and barometric pres-
sures. When conditions vary from standard, the maximum capac-
ity of the pump from draft can be affected.
The operator must not depend entirely on the vacuum gauge (if
one is installed in the application) 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 most common
way to eliminate cavitation is to decrease the amount of fluid being
discharged. This is accomplished by decreasing engine speed or
closing discharge valves.
This will allow pressure to increase, however this will result in a
reduction of flow.
Cavitation can also be eliminated be increasing the pressure on
the pump inlet. This is accomplished with reduced vertical lift,
reduced inlet losses, or running from positive pressure supplies.
Also see Section 3: “Operating Procedures,” heading CAVITA-
TION, beginning on page 3-13 for additional information on the
dangers of cavitation.
Figure 2-4: Cavitation Regions
Cavitation
Region
Cavitation
Region