Hale 2CBP - Manual (Page 18)

Sec II- 6 Operating Procedures
Booster Pumps
Warning Signs of Cavitation: Discharge
and Gauges
Discharge Pressure
In a properly functioning pump, an increase in
RPM will increase 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
The operator should 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 accurate near
zero 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 immediate
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:
o
Do not increase the pump speed beyond the
speed at which the pressure ceases to rise.
o
Monitor the water temperature baseline per
NFPA standards is 60° F (16 C). Table 2-1
illustrates the amount of lift loss as
temperatures rise. If there is a marked loss
of suction capacity, the pump may be near
cavitation.
NOTE: When water reaches 95° F( 35 C),
the operator is likely to notice a marked
decrease in lift.
o
Monitor barometric pressure. NFPA
standards sets a baseline of 29.9”Hg. See
Table 2-2.
o Location: The higher the elevation above
sea level, the lower the atmospheric
pressure and less lift. See Table 2-3.
o Open the throttle gradually and watch the
pressure gauge and the tachometer, if
equipped. An increase in engine RPM
without a corresponding increase in
pressure indicates cavitation.
o Use a hard suction hose when pumping from
draft and soft suction hose when pumping
from hydrant.
Preventive Measures:
o Regularly inspect discharge and suction
hoses to check for air leaks: these can also
Barometric Reading
in (mb)
Lift-loss in Head Feet
(meters)
29.9 (1012.53) NFPA Baselines
29.7 (1005.76) .2 (.06)
29.5 (999) .5 (.15)
29.3 (992.21) .7 (.21)
29.1 (985.444) .9 (.27)
28.9 (978.67) 1.1 (.33)
28.7 (971.89) 1.4 (.43)
Table 2-2 : Lift-Loss from Barometric Pressure