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737-300/400/500MAINTENANCE MANUAL
 CENTER TANK FUEL SCAVENGE SYSTEM - DESCRIPTION AND OPERATION
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General
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 A.  A fuel scavenge system (Fig. 1) is installed to decrease the quantity of fuel that you cannot use in the center tank by approximately 15 gallons. A fuel scavenge shutoff valve, a fuel scavenge jet pump and a fuel scavenge flow indicator/check valve (not installed on all airplanes) are installed on the front spar of the No. 1 tank. A fuel scavenge transfer line goes along into the center tank. On airplanes without a fuel scavenge flow indicator/check valve, a flapper check valve is installed on the fuel scavenge transfer line in the center tank.
Fuel Scavenge Shutoff Valve
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 A.  An electrically controlled fuel scavenge shutoff valve controls the flow of fuel from the fuel boost pumps for the No. 1 tank to the fuel scavenge jet pump to drain fuel from the center tank.
Fuel Scavenge Jet Pump
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 A.  The fuel scavenge jet pump causes a low pressure in the fuel scavenge transfer line when the fuel boost pumps for the No. 1 tank puts fuel through the fuel scavenge jet pump. The fuel scavenge jet pump drains fuel from the center tank into the No. 1 tank.
Fuel Scavenge Flow Indicator/Check Valve (Not on all airplanes)
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 A.  The fuel scavenge flow indicator/check valve has a window that you can see from out of the No. 1 tank. The indicator needle in the blue band shows no fuel flow. The indicator needle in the green band shows usual fuel flow. The indicator needle in the red band shows marginal fuel flow. Marginal fuel flow condition will occur when either the center tank fuel level is below the fuel scavenge pickup (air in the fuel scavenge transfer line), or when there is a component failure.
AIRPLANES WITHOUT FUEL SCAVENGE FLOW INDICATOR/CHECK VALVE;
___________________________________________________________ Fuel Scavenge Flapper Check Valve
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 A.  The flapper check valve installed in the fuel scavenge transfer line in the center tank has a flapper gate which prevents the transfer of fuel back into the center tank.
Operation
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 A.  When the two fuel boost pumps in the center tank are turned off, the fuel scavenge shutoff valve is opened, and a 20-minute timer in the M528 engine accessory unit is started.
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A

737-300/400/500MAINTENANCE MANUAL 
FUEL BOOST 
FLOW INDICATOR/ FUEL SCAVENGE  PUMP (REF) 
CHECK VALVE 
SEE  A  1 
FUEL SCAVENGE 
JET PUMP 
FUEL SCAVENGE  SEE  A 
SHUTOFF VALVE 
SEE  B 
ENGINE SHUTOFF 
VALVE (REF) 
CENTER TANK 

FLAPPER
NO. 1 TANK
CHECK VALVE 2
FUEL SCAVENGE
JET PUMP
FUEL SCAVENGE
FLOW INDICATOR/
CHECK VALVE

1
FRONT SPAR
CAP 1
FWD
A
1 NOT INSTALLED ON ALL AIRPLANES
2 NOT INSTALLED ON AIRPLANES WITH FUEL SCAVENGE FLOW INDICATOR/CHECK VALVE
Center Tank Fuel Scavenge System Component Location Figure 1 (Sheet 1)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

FUEL SCAVENGE SHUTOFF VALVE

Center Tank Fuel Scavenge System Component Location
Figure 1 (Sheet 2)

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