*
Use ground pumps (suction-defuel).

You must open the defuel valve to move fuel to the refuel station. Refuel hoses transfer fuel to ground tanks or a defuel truck.
You do these things for a tank-to-tank transfer:
*
Open the defuel valve

*
Open the applicable refuel valves

*
Operate the applicable fuel pumps.

You must open a crossfeed valve to remove fuel from the left main tank through the engine feed manifold.
Control and Indication
You use the IRP to open and close the defuel valve and refuel valves. The ELMS supplies power to open and close the valves.
The defuel valve switch controls relays in the ELMS to open and close the defuel valve. The refuel valve switches send valve position signals to the FQPU. The FQPU controls relays in the ELMS to open and close the refuel valves. The FQPU controls the refuel and defuel valve position lights on the IRP.
The FQPU supplies fuel quantity data to the IRP.
You use the fuel panel switches on the P5 panel to operate the fuel pumps.
The refuel section describes the refuel valves. The engine fuel feed section describes the fuel pumps and the crossfeed valves.
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777 AIRCRAFT MAINTENANCE MANUAL

DEFUEL -GENERAL DESCRIPTION

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DEFUEL -COMPONENT LOCATIONS -CENTER FUEL TANK

Purpose
The defuel valve connects the engine feed manifold to the refuel/jettison manifold.
Location
There is one defuel valve. It is in the right side of the center tank. You get access to the defuel valve though the first fuel tank access door in the right wing.
The defuel valve actuator is on the rear spar. It is aft of the first fuel tank access door in the right wing.
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DEFUEL -COMPONENT LOCATIONS -CENTER FUEL TANK

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DEFUEL -DEFUEL VALVE

Purpose
The defuel valve connects the engine feed manifold to the refuel/jettison manifold so you can remove fuel from the fuel tanks.
Description
The defuel valve is a motor-actuated valve. The valve body is in tubing in the right side of the center tank. The tubing connects to the right engine feed manifold and the refuel/jettison manifold. The valve actuator is on the right rear spar. See the engine fuel feed section for more information about motor-actuated fuel valves (SECTION 28-22).
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777 AIRCRAFT MAINTENANCE MANUAL

DEFUEL -DEFUEL VALVE

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DEFUEL -FUNCTIONAL DESCRIPTION -FUEL FLOW

General
You can pressure-defuel the fuel tanks with the engine feed system. You can also suction defuel the main tanks through the bypass valve.
Pressure-Defueling With Engine Feed System
When you use the boost pumps to pressure-defuel the airplane, the pumps put fuel into the engine feed manifold. When you open the defuel valve the fuel goes into the refuel/jettison manifold and out the refuel station adapters. One of the crossfeed valves must be open for fuel from the left side to get to the defuel valve.
Suction-Defueling
You suction-defuel the main tanks through the bypass valves. You must open the defuel valve to get fuel from the engine feed manifold into the refuel/jettison manifold. Suction-defuel will remove fuel until the fuel level is below one of the two bypass valves. Then you must use another method to defuel the tanks.
Tank-to-Tank Transfer
You can also defuel a tank by moving fuel into another tank. In this case, instead of removing fuel through the refuel adapters at the refuel station, you open the refuel valves for the tank in which you want to put the fuel.
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DEFUEL -FUNCTIONAL DESCRIPTION -FUEL FLOW

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DEFUEL -FUNCTIONAL DESCRIPTION -ELECTRICAL

General
The hot battery bus supplies power to the defuel valves. Power goes through the refuel panel door relay and defuel valve control relay in the P310 standby power management panel.
Defuel Valve Control
　
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