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 C.  The actuator consists of a dc electric motor, gear train, limit switches, and a manual override handle, which also serves as a position indicator for the valve. The actuator is readily replaceable without disturbing the fuel seals for the valve and without defueling the tank.
 D.  The valve body consists of a valve housing, rotating type valve disk, thermal relief, tubing connections, and a splined universal connector for receiving the adapter shaft from the actuator. Thermal relief is incorporated on each side of the valve disk which relieves line to tank only and not across the element. The valve is designed to allow flow in either direction.
 E.  The adapter assembly consists of an adapter plate, universal joint, shaft, shaft seals, and a shaft support bearing. The adapter plate is attached to the spar web and contains the necessary seals, bearings, and an index plate for the installation of the actuator. The shaft is attached to the adapter plate with a universal joint to provide for misalignment between the actuator and the valve. Both ends of the shaft contain splined indexed slip joints for proper alignment of the actuator with the valve body.
 4.  Fuel Boost Pump_______________(Fig. 1)
 A.  The fuel boost pumps deliver fuel under pressure from the main tanks to the engines. Each pump is a centrifugal-type pump driven by an electric motor, controlled by a separate switch on the fuel management control module. Boost pumps for main tanks No. 2 and No. 3 are mounted through the front and rear spars. Boost pumps for main tanks No. 1 and No. 4 are mounted in dry bay areas on the lower side of the wing, at the outboard end of main tanks No. 2 and No. 3.
 B.  Each pump assembly consists of a motor/impeller unit and a housing that is installed inside the fuel tank. A pump removal valve connected to the end of the housing allows the pump to be removed without draining the tank. The housing also includes a discharge port, a mounting flange, and a pump coolant and vapor discharge port.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 C.  Power for the boost pump motor is 115-volt 3-phase ac. A nonresettable thermal fuse is installed in each phase winding of the motor. The fuse senses overtemperature and is set to actuate before the housing temperature reaches 400°F. Actuation of a fuse will necessitate replacement of the motor. The motor is cooled and lubricated by the circulation of fuel through the motor housing.
 5.  Fuel Boost Pump Removal Check Valve (Fig. 1)
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 A.  The fuel boost pump removal check valve permits removing the pump motor/impeller unit without defueling the tank. The valves are located between the inlet line and the inlet port of each boost pump impeller housing. The valve consists of a housing which includes a mounting flange on the boost pump end and threads for a tubing connector on the opposite end, a spring-loaded poppet valve, and a provision for securing the valve to the wing structure. The poppet valve is spring-loaded to the closed position, but is normally open and held in this position by the motor/impeller unit. The valve will close automatically as the motor/impeller is extracted from the housing during removal.
 6.  Fuel Boost Pump Control Switch (Fig. 2)
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 A.  The fuel boost pump switches control power to the main boost pumps. The switches are located on the fuel management control module on the P5 pilots' overhead panel. The switches provide 28-volt dc power to each of the boost pump relays which enable power to be supplied to the pumps.
 B.  When the switch is operated, the word ON is illuminated on the switch to indicate that the pump has been commanded on. The light is powered by the master dim-and-test circuit. The amber PRESS light on the switch is extinguished when pump fuel pressure increases to normal operating range. For information on the low pressure indicating system, refer to 28-42-00/001.
 7.  Fuel Boost Pump Relay
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 A.  The fuel boost pump relays enable 115-volt, 3-phase ac power to be supplied to the boost pumps. The relays are controlled by 28-volt dc power from the boost pump control switches on the fuel management control module.
 B.  Relays for boost pumps No. 1 main aft, No. 2 main aft, No. 3 main forward, and No. 4 main forward are located in the power distribution center - left (P414). Relays for boost pumps No. 1 main forward, No. 2 main forward, No. 3 main aft, and No. 4 main aft are located in the power distribution center - right (P415).
　
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