PRIMARY MANIFOLD FUEL  SECONDARY FUEL MANIFOLD 
(14 LOCATIONS) ADAPTER FUEL NOZZLE 
AND DUMP VALVE FLOW DIVIDER 
BRACKET CABLE IGNITER 1  WASHER 1  FWD 
PUMP FUEL  FUEL MANIFOLDS, FUEL NOZZLES, ADAPTERS, C FLOW DIVIDER AND DUMP VALVE 
FILTER INLET FUEL PUMP 
FUEL PUMP OUTLET FILTER 
FWD 
FUEL PUMP D  ELECTRICAL (REF) CONNECTOR 
1  NOT INSTALLED ON ALL APUs 

APU Fuel System Components
Figure 1 (Sheet 2)

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 49-31-00
 ALL  ú ú 01 Page 3 ú Oct 10/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 3.  Fuel Metering Unit (Fig. 1)__________________
 A.  The fuel metering unit (FMU) is mounted on the fuel pump via a fuel metering adapter. High pressure fuel enters the FMU and first encounters the high pressure relief valve and the vapor vent valve. The pressure relief valve drains fuel to the pump interstage if the fuel pressure exceeds 1400 psig. The vapor vent valve automatically vents air from the FMU when the system is being primed.
 Dual independent shutoff solenoids provide immediate fuel flow shutoff in response to an APU controller signal. The primary shutoff solenoid provides fuel flow shutoff for normal shutdown, rotor overspeeds and for other protective shutdowns. The secondary shutoff solenoid provides fuel flow shutoff for backup protective shutdowns.
 Metered fuel flow exits the FMU through the minimum pressure valve. This valve ensures a minimum pressure level exists in the FMU for proper operation of the regulating valve. Servo regulated pressure fuel to the inlet guide vane (IGV) actuator control and to the diverter valve control flows through the servo supply regulator. The regulator maintains a constant pressurized fuel supply of 300 psi above fuel pump interstage pressure.
 4.  Fuel Cooled Oil Cooler (Fig. 1)______________________
 A.  For a complete description of the fuel cooled oil cooler (FCOC), refer to 49-91-00/001.
 5.  Flow Divider and Dump Valve (Fig. 1)___________________________
 A.  The flow divider and dump valve assembly is mounted on the fuel inlet manifold adapter located at the 6 o'clock position on the gas generator case. The flow divider schedules the metered fuel from the FMU between the primary and secondary fuel manifolds. During APU start, low pressure fuel from the FMU closes the dump port of the flow divider and dump valve and opens the primary spool valve to permit fuel flow to the primary fuel nozzles for engine lightup. As APU speed increases, the secondary spool valve is opened by increased fuel pressure to operate both the primary and secondary fuel nozzles at power ranges of idle and above.
 The dump valve, contained within the flow divider, shuts off fuel flow to the nozzles during APU shutdown. An operating spring in the flow divider and dump valve overcomes the fuel inlet pressure and moves a piston within the unit body to block the fuel inlet port. The movement of the piston connects both primary and secondary flow ports to the dump valve port and allows residual fuel in the manifolds to drain overboard.
 6.  Fuel Manifold and Nozzles (Fig. 1)_________________________
 A.  Primary and secondary fuel manifolds deliver metered fuel from the flow divider to the nozzle assemblies. The manifolds are continuous flexible lines which encompass the gas generator case and connect to the primary or secondary side of each fuel nozzle. The fourteen duplex fuel nozzles are postiioned around the gas generator case and inject fuel into the combustion chamber for engine start and run respectively.
 7.  Operation (Fig. 2)
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 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
 49-31-00
 ALL  ú ú 01 Page 4 ú Apr 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400
MAINTENANCE MANUAL

SHT 2
SHT 2
SHT 2

APU Fuel System Schematic
Figure 2 (Sheet 1)

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