2-4. Operation Under Usual Conditions
(3) Flow rate.
Flow rate increases with
increased throttle control setting. It reaches maximum
at full throttle (maximum governed engine speed of
(1) When the pump is in operation, check for
3600 rpm); and when cavitation occurs at impeller inlet.
normal instrument readings shown in figure 2-1.
(4) Cavitation. Cavitation will occur when
(2) The engine governor is adjusted to limit
there are air leaks in the suction side of the pump,
maximum speed to 3600 revolutions per minute when
suction lift is too high, or the suction end of the line is
not sufficiently submerged to prevent whirlpools. It
(3) The throttle control permits selection of
produces an effect similar to a slipping clutch and a
power settings from idle speed (700-800 rpm) to
noise that sounds like loose pebbles ricocheting inside
maximum governed speed.
of the pump casing.
Start the pump assembly,
Cavitation is harmful to the pump
assembly. Avoid at all times.
(2) Priming cycle. When the pump and hose
c. Performance Characteristics.
system are initially installed the priming charge is in
(1) Engine horsepower required to drive the
pump body; and the engine is started; the throttle should
pump varies with the weight of the liquid being pumped
be adjusted to 3300 rpm. The pump will operate for a
and the capacity or rate of pumping.
short priming cycle period during which the pump is
overloading, adjust throttle control to maintain the
evacuating the air from the suction hose. During this
desired flow rate.
period it will not be pumping liquid.
(2) A composite pump performance curve is
shown in figure 2-4.
After pump has primed and is
a. Pump capacities are shown in
pumping, adjust throttle setting to
gallons per minute. Pump discharge pressures are
1800 rpm until discharge, hose
shown in pounds per square inch and in feet of head of
system has filled.
the liquid pumped.
b. Lines of constant brake horsepower
When suction must be primed and
represent the loading of the engine. The engine will
the discharge lines lie on a grade
give satisfactory life and performance when normal
considerably higher than the pump
operation does not exceed the continuous duty brake
and are full of liquid, follow the
horsepower for the speed at which it is operated.
procedures prescribed in figure 2-1
regarding priming check valve before