(b)  
Do this task: Fuel Transfer to Remove Air Pockets from the Engine Fuel Feed Line Adjacent to the Defueling Valve (AMM 28-23-00/201).

 TASK 28-22-00-702-085
 4. Check Valve Leakage Troubleshooting (Fig. 203, 204)
___________________________________
 A. General
 (1)  This task does a pressure check to find out if one of the APU fuel-feed check valves has a leak. Leakage in the primary APU fuel-feed check valve, the bypass APU check valve, or the pressure relief valve in the APU fuel-feed line is found and isolated.
 B. Equipment
 (1)  
Pressure Gage, 0-100 psi (0-689 kPa)

 (2)  
Hose

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
NO. 1 FORWARD BOOST PUMP

APU Check Valve Diagram
Figure 203

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
G88664
A 737-300/400/500MAINTENANCE MANUAL
SEE B
SEE A
A 
INLET HOSE FUEL SUPPLY HOSE  BULKHEAD TEE FITTING  UNIT CONTROL FUEL GAGE PRESSURE  INLET HOSE FUEL SUPPLY HOSE  BULKHEAD TEE FITTING  UNIT CONTROL FUEL PRESSURE GAGE 
LOW-PRESSURE FUEL FILTER 
LOW-PRESSURE FUEL FILTER  B  2 
B  1 
2 1  AIRPLANES WITH THE ETC AIRPLANES WITHOUT THE ETC  Figure 204 APU Check Valve Leakage Check 

G88683
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 C.
D.
E.
A
737-300/400/500MAINTENANCE MANUAL
References
 (1)
AMM 24-22-00/201, Manual ControlAccess

 (1)  
Location Zones 101 Control Cabin (Left) 205 Electronic Compartment 703 APU Compartment

 (2)  
Access Panels 1201 Electronic Equipment Access Door 3804 APU Cowl Door

Leak Test for the Primary APU Fuel Check Valve, the Bypass APU Check Valve, and the APU Pressure Relief Valve
 NOTE: This procedure finds out if there is a leak in the main APU
____ check valve, the bypass APU check valve, or the pressure relief valve. If leakage is found in one of these valves, the procedure, "Leak Check of the Bypass Check Valve and the Pressure Relief Valve" is given below to isolate the leak specifically to one of these valves.
 S 862-113
 (1)  
Set the APU master switch, on the P5 forward overhead panel, to the OFF position and attach a DO-NOT-OPERATE tag.

 S 862-114

 (2)  
Set the No. 1 AFT FUEL PUMP switch, on the P5 forward overhead panel, to the OFF position.

 S 862-115

 (3)  
Open this circuit breaker and attach a DO-NOT-CLOSE tag:

 (a)  E3-3 Electrical Shelf, APU Control Unit
 S 012-089
 (4)  Open the APU cowl door:
 (a)  
Open the latches for the APU cowl door.

 (b)  
Open the APU cowl door.

 (c)  
Connect the door support rods.

 S 012-090
 CAUTION:_______BE CAREFUL WHEN YOU MOVE THE LOWER SHROUD. DAMAGE TO THE SHROUD DRAIN LINES CAN OCCUR.
 (5)  Remove the lower shroud:
 (a)  
Hold the lower shroud and open the shroud latches.

 (b)  
Remove the lower shroud.

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