(a)
Do a visual check of the EGT bus bars:
1) Make sure the bus bars are not damaged.
2) Make sure no metal parts touch the bus bars.
3) Make sure the bus bars do not touch each other.
(b)
Disengage the support rods for the APU access doors.
(c)
Put the support rods in the clips on the inner side of the APU access doors.
(d)
Make sure the insulation covers attach correctly to the APU compartment firewall.
(e)
Close the APU access doors.
(f)
Close the latches on the access doors for the APU.
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49-27-07
ALL ú ú 01 Page 410 ú Oct 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
APU ENGINE FUEL SYSTEM - DESCRIPTION AND OPERATION
__________________________________________________
1. General_______
A. The APU fuel system supplies fuel from the airplane fuel system to the APU. The basic system, for providing metered fuel, consists of a fuel pump, fuel metering unit (FMU), flow divider and dump valve, and two fuel manifolds with fourteen nozzle adapters. In addition to the basic system, the total fuel system also includes the fuel cooled oil cooler (FCOC) (Ref 49-91-00/001). Also, fuel is used in the APU control system as hydraulic fluid for the Inlet Guide Vane (IGV) actuator control and the diverter valve control.
B. For a complete description and operation of the APU fuel feed system forward of the APU firewall refer to 28-25-00/001, APU Fuel Feed System -Description and Operation.
2. Fuel Pump (Fig. 1)_________
A. The fuel pump is mounted on and driven by the accessory gearbox. Fuel enters the inlet port and is pressurized by the centrifugal boost stage. The pressurized fuel flows through the inlet filter to the high pressure gear stage. During pump operation, the fuel is carried around the outside of the gears to the outlet side of the gear stage. As the gear teeth mesh, the fuel is forced from the spaces between the gear teeth. The high pressure fuel flows via the replaceable output filter to be discharged through the outlet port.
If during pump operation either the inlet screen filter or the outlet filter element becomes clogged, the resulting pressure differential will cause fuel to bypass the clogged filter. In the case of a clogged inlet screen filter assembly, the screen is spring loaded and will unseat as necessary to allow unfiltered fuel to enter the gear stage. Similarly, a clogged outlet filter element will cause the spring loaded filter bypass valve to lift off its seat to allow pump delivery fuel to the outlet port. The fuel filter bypass indicator provides maintenance warning of filter blockage in advance of filter bypass.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
49-31-00
ALL ú ú 01 Page 1 ú Oct 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
FUEL PUMP,317AL, 318AR FUEL METERING UNIT,
FUEL MANIFOLDS,
APU COMPT FUEL METERING ADAPTER
FUEL NOZZLES,
SEE A ADAPTERS, FLOW SEE B DIVIDER AND DUMP VALVE
SEE C
APU COMPT RIGHT SIDE
A
FUEL COOLED
OIL COOLER
FWD
(REF) STARTER
(REF)
FUEL
METERING
FUEL UNIT FUEL FILTER
METERING
FUEL PUMP
ADAPTER BYPASS
SEE D INDICATOR
FUEL PUMP, FUEL METERING UNIT, FUEL METERING UNIT ADAPTER
B
APU Fuel System Components Figure 1 (Sheet 1)
F58305
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
49-31-00
ALL ú ú 02 Page 2 ú Feb 10/96
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