747-400
MAINTENANCE MANUAL

(17,164 U.S. GALLONS) (14,292 IMPERIAL GALLONS) (64,973 LITERS)
TOTAL USABLE FUEL
(53,864 U.S. GALLONS) (44,852 IMPERIAL GALLONS) (203,897 LITERS)
Fuel Tank Arrangement
Figure 1

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MAINTENANCE MANUAL

 C.  The center wing tank access door is installed inside the tank by inserting bolts through the web into nutplates attached to the door. A metal seal ring with a rubber seal on each side is installed between the web and the door to provide a fluid seal. A handle is installed on the outside of the door to facilitate handling in the vertical position.
 D.  Wing surge tank access doors are installed on the outside of the tank, flush with the wing skin. Screws are installed through the door into sealed nutplates on the inside of the tank. An O-ring fitted into a groove in the door provides a fluid seal between the door and the wing skin. A pressure relief valve is installed on each access door. For additional information, refer to 28-13-00/001, Fuel Vent System.
 3.  Rib and Spar Access Openings
____________________________
 A.  Some of the equipment located inside the fuel tanks is not accessible directly through the fuel access doors. To obtain access to this equipment, personnel must enter the tank through the nearest access door and go through rib access opening and/or spar access openings in the midspar.
 4.  Fuel Sump Drain Valves (Fig. 3)
______________________
 A.  Fuel sump drain valves are installed at the low point of each fuel tank for draining accumulated moisture and for draining fuel trapped in the sumps when the tanks are defueled.
 B.  The drain valves for the No. 2 and No. 3 main, No. 2 and No. 3 reserve, center wing, and all surge tanks are located in the bottom of the respective tanks. The drain valves for No. 1 and No. 4 main tanks are located in No. 2 and No. 3 main tanks, respectively. Fuel from the tanks is delivered to the valves through drain tubes that are attached to fittings on top of the valves.
 C.  The valves in the wing tanks, center wing tank, and surge tanks are spring-loaded poppet-type valves consisting of a housing, mounting base, primary and secondary poppets, and a removable seat for the primary poppet. The complete drain valve assembly is installed from inside the tank with a faying surface seal between the base and wing skin panel. It is attached to the wing panel with two taper shank bolts. To drain the fuel sumps, the poppet is manually pushed from its seat, allowing fuel to drain through the drain hole in the center of the valve.
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MAINTENANCE MANUAL

HIGH IMPACT 
RESISTANT 
ACCESS DOOR 
(2 PLACES)  STANDARD
SEE  C  ACCESS DOOR 
(3 PLACES) 
SEE  B 
RIB ACCESS 
HOLE (TYPICAL) 
NO. 2 MAIN TANK 
CENTER WING 
TANK ACCESS DOOR 
SEE  A 

DOOR HANDLE
CENTER WING TANK ACCESS DOOR
FRONT SPAR
A
Fuel Tank Access Doors Figure 2 (Sheet 1)
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MAINTENANCE MANUAL

DOOR RIB NUT CAPTIVE  SEAL RUBBER MOLDED 
B 
STANDARD B  B  B-B BOLTDOOR ACCESS (KNITTED ALUMINUM) GASKET  RING CLAMP  SKIN WING LOWER 

ALUMINUM HONEYCOMB FILLER  NUT CAPTIVE 
C  MOLDED SEAL RUBBER  UP 
C UP HIGH IMPACT RESISTANT  C  SKIN WING LOWER  C-C ALUMINUM) (KNITTED GASKET BOLT  RING CLAMP  HIGH IMPACT DOOR ACCESS FILLER HONEYCOMB ALUMINUM 
　
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