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 TM 55-1905-219-14-8
4-7.10. PUMP AND WATER OUTLET VALVE - MAINTENANCE INSTRUCTIONS.
a. General. The fire pump impeller is enclosed within the inner and outer impeller housings, and mounted
on the crankshaft. It is secured in place by a key and nut. Water is forced into the impeller housing when air is
evacuated from the housing and the suction hose by the action of the primer pump. As the water enters, the
fire pump impeller throws the water outward, creating pressure within the impeller housing. This pressure shuts
off the primer pump by disengaging the primer pump clutch. It is also the pump discharge pressure measured
by the pressure gage.
(1) The ball type water outlet valve is located in the discharge opening of the impeller housing. It
consists of a ball with a hole through it. Pressing against the ball is a plastic sleeve, which helps channel water
from the ball to the discharge line, when the ball is in the open position. When the ball is in the closed position,
(turned 90 degrees), the plastic sleeve presses against the ball sealing the discharge passage against the entry
of air and preventing discharge of water.
CAUTION
Always keep the valve either fully open or fully closed. An intermediate position
will allow the water being discharged to erode the sealing surfaces of the valve,
resulting in eventual damage.
(2) This valve should always be closed when starting the pump, to prevent air from entering the
impeller housing during priming. This permits pump pressure to build up properly, thus insuring that the fire
pump is completely primed, and that the primer pump is disengaged. When pump pressure begins to build up,
as indicated on the pressure gage, the valve should be opened slowly and water will be available in the
discharge line. Regulation of water flow should be made at the discharge nozzles. The external handle which
positions the water outlet valve locks in either the open or closed positions.
(3) The discharge hose is connected to the flange at the outlet valve, and the suction hose to the
opening in the intake side of the impeller housing.
(4) If one and one-half inch discharge hoses are desired, the three-way gate valve supplied with the
pump should be connected to the flange at the pump outlet valve.
(5) The manual primer consists of a lever-arm plug arrangement mounted on the primer bowl in the
impeller housing. Its function is to allow water to be poured into the impeller housing to prime the fire pump in
the event of failure of the primer pump, or if the
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