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Manual Defueling Valve (Fig. 1)
______________________
 A.  The manual defueling valve provides a means of defueling the fuel tanks by using the main tank boost pumps. The valves, one at each fueling station, connect the fuel feed manifold with a pressure fueling receptacle.
 B.  The valve consists of a manually-controlled shutoff element, a valve body, and provisions for attaching the valve to the spar and to the fuel manifold. The valve is located on the front spar between the fueling receptacles. An elbow attaches the forward side of the valve to the fueling receptacle.
Defueling Check Valve (Fig. 1)
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 A.  A defueling check valve is attached to the manual defueling valve inlet to prevent air from entering the fuel feed manifold when the engines are in suction feed, and the manual defueling valve was inadvertently left open.
 B.  The valve consists of a valve body and a hinged flapper which is spring-loaded to the closed position. The valve is installed on the wet side of the front spar opposite the manual defueling valve.
Fueling Receptacle (Fig. 1)
__________________
 A.  The fueling receptacles connect the defueling hoses to the airplane fuel system. When the hose nozzle is coupled to the receptacle adapter, a spring-loaded check valve is lifted to a position that allows the hose nozzle to lock into place. Normally, the check valve is open only during pressure fueling operations when the fuel pressure in the hose nozzle is greater than the fuel pressure in the receptacle manifold. Prior to defueling, the receptacle adapter lever marked LIFT TO DEFUEL must be lifted to hold the check valve open during the defueling operation.
Operation (Fig. 2 and 3)
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 A.  Functional Description
 (1)  
Rapid defueling of the fuel tanks is accomplished by delivering fuel, supplied by fuel system pumps, to the wing fueling stations. Fuel is discharged into a fuel truck or trucks through manual shutoff valves at the fueling receptacles. Either or both fueling stations may be used to defuel the tanks.

 (2)  
Defueling can also be accomplished using truck suction pumps only, drawing fuel into the outboard fueling receptacle through the boost pump bypass valves and fuel crossfeed manifold.

 (3)  
If electrical power is not available, tanks can be defueled by operating airplane pumps with an external power control unit.

 (4)  
Fuel in the tanks which cannot be drawn in by pumps or transferred to other tanks can be removed through the sump drain valves.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

PRESSURE FUELING STATION
SEE A
PRESSURE FUELING STATION
SEE A
FUELING
STATION
DOOR

SEE B SEE B
SEE C
FWD
A
INBD
Defueling - Component LocationFigure 1 (Sheet 1)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400 MAINTENANCE MANUAL
RECEPTACLE ADAPTER LEVER
B
TO FUELING RECEPTACLE MANUAL DEFUELING VALVE
VALVE 
FROM  CONTROL 
FUEL  HANDLE 
CROSSFEED 
MANIFOLD  DEFUELING 
CHECK VALVE 
FRONT 
SPAR 
C 

Defueling Component Location
Figure 1 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

Defueling Flow Diagram (Override/Jettison Pumps Operating)
Figure 2

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