NOTE: The fuel flow from the bleed valve may continue to flow
____ slowly or stop after the remaining pressure is gone. This depends on the level of fuel in the tank and the height of the bleed valve.
(l) Close the bleed valve.
H. Calculate the Boost Pump Output Pressure
S 975-232
(1) To find the output pressure for one of the boost pumps, subtract the "Pump OFF" pressure from the "Pump ON" pressure that you measured for that pump.
S 975-235
WARNING: REFER TO SB 28-1114 FOR DATA ABOUT FUEL BOOST PUMPS WITH LOW
_______ OUTPUT PRESSURE. LOW BOOST PUMP PRESSURE CAN CAUSE PROBLEMS WITH THE ENGINE IN FLIGHT.
(2) Method 1 - If the pressure was measured at the drain on the fuel filter housing, do these steps:
(a) If the difference between the "Pump ON" pressure and the "Pump OFF" pressure is less than 23 psig, then replace that fuel boost pump (AMM 28-22-41/401).
NOTE: An input pressure at the engine of 23 psi is equal to an
____ output pressure of 36 psi at the pump. A check valve between the pump and the engine opens at 13 psi and reduces the pressure by that quantity at the engine.
1) Refer to SB 28-1114 for more data and for relief.
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737-300/400/500MAINTENANCE MANUAL
(b) If the difference between the "Pump ON" pressure and the "Pump OFF" pressure is more than 23 psig, then the pump is OK.
S 785-260
(3) Method 2 - If the pressure was measured at the forward spar fitting, do these steps:
(a)
If the difference between the "Pump ON" pressure and the "Pump OFF" pressure is less than 36 psig, then replace that fuel boost pump (AMM 28-22-41/401). 1) Refer to SB 28-1114 for more data and for relief.
(b)
If the difference between the "Pump ON" pressure and the "Pump OFF" pressure is more than 36 psig, then the pump is OK.
I. Put the Airplane Back to Its Usual Condition
S 845-258
(1) Method 1 - Do these steps if the pressure was measured at the drain for the fuel filter housing.
(a)
When you have done the test on all four boost pumps for the No. 1 tank and the No. 2 tank, make sure all six fuel pump switches are set to OFF.
(b)
Put the engine start lever back to the CUTOFF position.
(c)
Close the airplane fuel crossfeed valve.
(d)
Open the bleed valve on the pressure gage hose to release the pressure in the fuel line.
(e)
Install a new O-ring with petrolatum lubricant (CP2102) on the drain plug (Fig. 502A) (AMM 73-11-02/401).
(f)
Remove the pressure hose fitting from the engine fuel filter housing.
NOTE:____Fuel will drain from the opening. Make sure that the drain plug is prepared for installation to keep fuel leakage to a minimum.
(g)
Install the drain plug in the engine fuel filter housing and install lockwire (Fig. 502A) (AMM 73-11-02/401).
NOTE: Refer to this procedure for the drain plug torque value.
____
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(h) Do this procedure: "Test No. 3: Leak Check - Idle Power" (AMM 71-00-00/501).
S 845-261
(2) Method 2 - Do these steps if the pressure was measured at the fitting for the low pressure switch.
(a)
When you have done the test on all four boost pumps for the No. 1 tank and the No. 2 tank, make sure all six fuel pump switches are set to OFF.
(b)
Close the removal valve for the applicable fuel boost pump (AMM 28-42-11/401).
(c)
Remove the pressure hose fitting from the forward spar fitting.
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