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TM 55-2915-335-30&P
d. Most of the fuel pushed through the pump flows to the main fuel line. A small amount of fuel flows through the
motor chamber to cool and lubricate moving motor parts. Fuel exits the motor chamber through fluid ports in the
motor cover fuel bleed valves.
e. Vapor is formed when the impeller pumps fuel. The vapor formed is released through a vapor bleed valve, The
bleed valve removes fuel vapor that would otherwise get into the main fuel line.
f. A fuel bypass valve allows fuel to flow directly from the inlet port to the fuel line while the boost pump is turned
OFF. When the boost pump is turned ON, fuel pressure forces the valve ball down to close off the fuel bypass.
Without the bypass valve, turning the boost pump OFF would partly block fuel flow through the pump.
1-12. Electrical Circuit.
a. The pump motor circuit includes two sets of
motor brushes connected in series. Applying 28 volts DC
across the motor terminals drives the pump impeller
counterclockwise when viewed from the impeller drive
end. If the power leads or the permanent field magnets
are reversed, the motor will run backwards.
b. A thermal shutoff opens the motor circuit if the
motor overheats. Once open, the thermal shutoff will not
reset, and must be replaced.
c. An RFI capacitor inhibits radio frequency inter-
ference. A fuse in series with the RFI capacitor protects
motor wiring in case the capacitor shorts out.
1-5/(1-6 blank)
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