(f)  
As the fuel levels in the inboard main tanks decrease, the float valves open and fuel flows from the center wing tank into the No. 2 or No. 3 main tank. The float valves in the inboard main tanks are uncovered when the fuel quantity indicates approximately 60,000 lbs (27,270 kgs).

 (g)  
During flight the scavenge system will continue to move (scavenge) the fuel from the center wing tank into the inboard main tanks until the center wing tank is empty (approximately four hours) or the until the flight ends and all of the pumps are set to the off position.

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747-400
MAINTENANCE MANUAL

FUEL SCAVENGE SYSTEM SEE A
CENTER WING TANK
(REF) JET PUMP (4 LOCATIONS)
FLOAT VALVE IN THE
NO. 2 MAIN TANK

FLOAT VALVE IN THE NO. 3 MAIN TANK
SEE B SEE B
A A
NO. 2 MAIN TANK
NO. 3 MAIN TANK (REF)
(REF)
AA FUEL STRAINER HOUSING (2 LOCATIONS)
FLOAT VALVE IN THE CENTER WING TANK (2 LOCATIONS)
FWD
FUEL SCAVENGE SYSTEM
OUTBD
A
FLOAT VALVE IN THE CENTER WING TANK
FUEL STRAINER INLET SCREEN HOUSING
TO THE NO. 2 OR JET PUMP
(2 LOCATIONS) JET PUMP (2 LOCATIONS) (2 LOCATIONS)
NO. 3 MAIN TANKS SEE E(2 LOCATIONS)
SEED SEEF SEE C
NO. 2 (REF) SPANWISE BEAM  (REF) CENTER WING TANK MID-SPAR OF THE  NO. 1 (REF) SPANWISE BEAM A-A  (REF) CENTER WING TANK BOTTOM OF THE  (REF) CENTER WING TANK REAR SPAR OF THE 
Fuel Scavenge System Figure 1 (Sheet 1)

 B31076
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747-400 MAINTENANCE MANUAL
NO. 2 MAIN TANK (REF) FLOAT VALVE IN THE NO. 2 AND NO. 3 MAIN TANK
TANK END RIB (REF)
CENTER WING TANK (REF)
FIRST RIB
MAIN TANK
(REF)

FUEL VENT
OUTBD SYSTEM (REF)
FLOAT VALVE IN THE NO. 2 OR NO. 3
TO JET
MAIN TANK PUMPS B
SPANWISE BEAM NO. 2
(REF)

SPANWISE BEAM NO. 1 (REF)DETAIL OF
THE JET PUMP DETAIL OF
SEE D1 THE JET PUMP
SEE D1
BOTTOM OF THE
CENTER WING
BOTTOM OF THE TANK (REF)
CENTER WING TANK (REF) INLET SCREEN
JET PUMP
FUEL INLET SCREEN (REF)
JET PUMP
(REF)
C VENTURI D
TO THE INBOARD
MOTIVE MAIN TANKS
FLOW
NOZZLE
BALL CHECK VALVE
DEATAIL OF THE JET PUMP

D1

Fuel Scavenge System
Figure 1 (Sheet 2)

B31077
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747-400
MAINTENANCE MANUAL

BOTTOM OF THE  FLOAT VALVE IN THE 
CENTER WING  CENTER WING TANK 
TANK (REF) 

FLOAT VALVE IN THE
CENTER WING TANK

E
STEPSEAL
O-RING O-RING O-RING
SPRING
STRAINER HOUSING
OUTLET
(TO THE JET PUMPS)
POPPET
POPPET
GUIDE
O-RING
INBD
FWD
INLET
TO THE JETPUMPS
FUEL STRAINER HOUSING (2 LOCATIONS)
SEE GFROM THE FUEL-FEED TRANSFER LINE
LOCKWIRE
INBD
FUEL STRAINER HOUSING
F
RETAINER AND SPRING RETAINING RING  (REF) REAR SPAR 
SPRING  WASHER 
O-RING  NUT 

POPPET O-RING GUIDE
RETAINING RETAINER
RING
(FROM THE FUEL-FEED TRANSFER LINE)
FUEL STRAINER HOUSING
G
Fuel Scavenge System Figure 1 (Sheet 3)
REAR SPAR OF THE CENTER WING TANK (REF)
WASHER
STRAINER
CAP
FUEL STRAINER
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