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APU Feed
The ELMS supplies power to the APU dc fuel pump and APU fuel shutoff valve. The pump operates automatically when the APU selector is in the ON position and there is no pressure in the left engine feed manifold. When there is pressure in the left engine feed manifold, the pump does not operate.
The ELMS uses crossfeed valve position and pump pressure switch signals to find if there is pressure in the manifold. The ELMS uses the dc pump pressure switch to monitor pump operation.
The APU fuel shutoff valve opens to permit fuel to go to the APU. In normal operation, the ELMS controls the valve through the a relay in the P101 panel. The ELMS opens the APU fuel shutoff valve when the APU selector is in the ON position or when the APU is running. The APU controller tells the ELMS when the APU is running.
The hot battery bus or the engine fuel spar valve battery supplies the power to open or close the APU fuel shutoff valve. The APU fire switch must be down to open the valve.
The APU fire switch and the APU fire shutdown switch close the APU fuel shutoff valve. The APU fire switch has a direct circuit to the valve. The APU fire shutdown switch controls a relay in the P101 panel to close the valve.
Engine Feed
The APU fuel feed system can supply fuel to the left engine in the air when there is no pressure in the left engine feed manifold and the left engine is not operating. The ELMS opens the APU isolation valve and turns on the APU dc fuel pump to permit this.
Fault and Indicating Information
APU fuel feed faults and indication information goes to the AIMS on the systems ARINC 629 buses.
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777 AIRCRAFT MAINTENANCE MANUAL

APU FUEL FEED -GENERAL DESCRIPTION

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APU FUEL FEED -COMPONENT LOCATIONS -FUEL TANKS

General
The APU fuel feed system has these components:
*
APU DC fuel pump

*
APU isolation valve

*
APU fuel shutoff valve

*
APU isolation check valve.

The APU fuel supply line goes through the center tank dry bay, then aft to the APU. The fuel supply line has a shroud around it. The shroud has a drain line that goes to the APU shroud drain mast on the bottom of the airplane.
APU DC Fuel Pump
The APU dc fuel pump is on the rear spar of the left wing, aft of the second fuel tank access door. The pump housing is inside the center tank. The pump inlet is in the left main tank.
APU Fuel Shutoff Valve
The APU fuel shutoff valve body is high in the left side of the center tank, above the APU isolation valve. You get access to the fuel shutoff valve through the second fuel tank access door. The valve actuator is on the rear spar of the left wing, inboard of the dc fuel pump.
APU Isolation Valve
The APU isolation valve body is in the left side of the center tank, below the APU fuel shutoff valve. You get access to the isolation valve through the second fuel tank access door. The valve actuator is on the rear spar of the left wing, inboard of the dc fuel pump.
APU Isolation Check Valve
The APU isolation check valve is in the left side of the center tank, between the APU fuel shutoff valve and isolation valve. You get access to the isolation check valve through the second fuel tank access door.
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APU FUEL FEED -COMPONENT LOCATIONS -FUEL TANKS

EFFECTIVITY BEJ ALL  28-25-00 
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APU FUEL FEED -COMPONENTS

APU DC Fuel Pump
The APU dc fuel pump supplies fuel to the APU and to the engine feed manifold. It uses 28v dc power. It supplies fuel at a pressure of 24 psi and a flow rate of 3150 pounds per hour (1430 kilograms per hour).
The pump has a pressure switch that sends a signal to the ELMS when the pump is operating.
APU Fuel Shutoff Valve
The APU fuel shutoff valve opens to permit fuel to flow to the APU. Fuel comes from the left engine feed manifold, or from the dc pump.
The APU fuel shutoff valve actuator is the same as the other 28v dc motor actuators on other fuel system valves. See the engine fuel feed section for more information about motor actuated fuel valves (SECTION 28-22).
APU Isolation Valve
The APU isolation valve opens to let fuel flow from the APU dc fuel pump to the left engine feed manifold. The isolation valve is normally closed. The valve opens when there is no pressure in the left engine feed manifold and the left engine is not operating.
The APU isolation valve actuator is the same as the other 28v dc motor actuators on other fuel system valves. See the engine fuel feed section for more information about motor actuated fuel valves (SECTION 28-22).
　
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