(d)  
Install the fuel feed low pressure switch with a new O-ring (AMM 28-42-11/401).

 NOTE: If you replace one low pressure switch, you should
____ replace all low pressure switches.
 (e)  
Open the removal valve for the applicable fuel boost pump.

 (f)  
Do the task: Fuel Feed Low Pressure Indicating System Test (AMM 28-42-00/501).

 TASK 28-22-00-715-078
 6. Fuel Boost Pump Removal Valve, Vent Valve, and Check Valve and Pressure
_______________________________________________________________________ Fueling Line Outlet Check Valve Test
____________________________________
 A. General
 (1)  
This procedure is a test for the correct operation of these valves:

 (a)  
The removal valve for each of the boost pumps

 (b)  
The discharge check valve for each of the boost pumps

 (c)  
The redundant check valve (if it is installed) for the aft boost pumps.

 (d)  
The forward/center redundant check valves (if installed) for the forward boost pumps in the main tank and the boost pumps in the center tank.

 (e)  
The vent valve for each of the boost pumps in the No. 1 tank and the No. 2 tank.

 (f)  
The check valve for the fueling line outlet on each of the boost pumps in the center tank.

 (2)  
It is frequently not easy to find the valve that does not operate correctly. This is because all these valves let leakage go out of the same drain valve if they have leakage. It is a good procedure to do the test of the discharge check valve for the fuel boost pump first. This is because you can isolate it from the other valves, but you can not isolate it fully. If you find the discharge check valve for the fuel boost pump operates correctly, you must make a decision to replace one of these valves:

 (a)  the removal valve
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A

737-300/400/500
MAINTENANCE MANUAL

SEE A
SEE B
PLUG DRAIN 
HOUSING FILTER FUEL 
A 
PLUG DRAIN  HANDLE 
Fuel Filter Drain Plug Location Figure 502A  B 

G98757
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A 737-300/400/500MAINTENANCE MANUAL
RANGE: 0-50 PSIG RESOLUTION: 1 PSIG ACCURACY: +/-1 PSIG

BUCKET  ENGINE FILTER DRAIN
Fuel Boost Pump Output Pressure Test - Required Equipment
Figure 502B

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G98766
 B.
C.
D.
E.
A
737-300/400/500MAINTENANCE MANUAL
 (b)  
the vent valve

 (c)  
the removal valve and the vent valve.

 (3)  
This decision is not easy. If you find fuel leakage from the two drain valves for the center boost pump, this shows a failure of the check valve for the fueling line outlet.

Equipment

 (1)  
Container - suitable to hold the residual fuel from the fuel boost

 pumps.References

 (1)  
AMM 24-22-00/201, Manual Control

 (2)  
AMM 27-81-00/201, Leading Edge Flap and Slat Control System

 (3)
AMM 57-30-11/401, Boost Pump Access DoorAccess

 (1)  
Location Zones 101 Control Cabin Left 102 Control Cabin Right 303 Left Wing Inboard Leading Edge 403 Right Wing Inboard Leading Edge

 (2)  
Access Panels 7201 Boost Pump Access Door 7203 Boost Pump Access Door 7401 Boost Pump Access Door 7403 Boost Pump Access Door
　
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