Hale Rear Mount - Manual (Page 17)

EXPLANATION OF TERMS
CENTRIFUGAL PUMP
A centrifugal pump consists of an impeller with an intake at the center, so arranged that, when
rotated, it will discharge water by centrifugal force into a casing or volute body which surrounds
the impeller. The water exits from the impeller at high velocity into the diverging passages of
the volute body, where the velocity, energy is converted into pressure.
A centrifugal pump differs from other types of pumps in that its impeller can be rotated
freely even though the discharge is closed, because the pressure developed is entirely
the result of the velocity imparted to the water by the rotating impeller and is not due to
any impact or displacement.
IMPELLER
The working parts of a centrifugal pump consist of two round discs separated by curved
vanes. When rotating, it imparts energy to the water as the vanes force the water
between the discs so that it is thrown outward at increasing velocity by centrifugal force.
PRIMING
Priming evacuates the air from the main pump and suction hose, thus creating a
vacuum. This allows atmospheric pressure on the source of water to push the water
up into the suction hose and pump.
PRIMING PUMP
A positive displacement pump which creates a vacuum to prime the main pump. The
main pump, being a centrifugal pump, is not a positive displacement pump. The priming
pump is driven by an electric motor which is engaged by a switch on the priming valve.
PRIMING VALVE
A pull type shut-off valve located in the priming line between the priming pump and the
main pump. It is normally closed and is open only during priming to allow air to pass from
the main pump to the priming pump.
RELIEF VALVE
An automatic valve, actuated by the relief valve control, which will hold pump pressure and
engine speed steady when the pump discharge is shut off or partially closed. The relief valve
maintains its given pressure by diverting the pump discharge flow into the pump suction.
RELIEF VALVE CONTROL
A hand adjustment valve mounted on the pump control panel which controls the relief valve to
maintain the desired pump discharge pressure.
PRESSURE GOVERNOR
A pressure activated automatic control, with manual adjustment, that maintains constant pump
pressure by regulating the engine throttle.
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