(c)
Close the bleed valve.
(d)
Record the pressure shown on the pressure gage as the "Pump Off" pressure.
(e)
Push the boost pump switch to the ON.
1) To operate any of the fuel boost pumps, you must be in the flight compartment to continuously monitor the fuel quantity and the low pressure indication in the fuel tank.
WARNING: DO NOT OPERATE ANY FUEL BOOST PUMP IF THE LOW PRESSURE LIGHT COMES ON AND STAYS ON. FUEL VAPORS IN THE TANK MAY IGNITE AND CAUSE A FIRE OR EXPLOSION.
a) Immediately put the applicable fuel boost pump switch(es) to OFF if the LOW PRESSURE light comes on and stays on.
NOTE: When defueling or transferring fuel with minimum backpressure to the pumps, it is possible for the low pressure light(s) to be on. In this case, monitor the tank quantity and put the pump switch(es) to OFF if the tank quantity is not changing.
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(f)
Open the bleed valve on the pressure gage hose and drain approximately 0.25 gallon (1 liter) of fuel.
(g)
Close the bleed valve.
(h)
Read the pressure gage 5 to 10 seconds after closing the bleed valve.
(i)
Record the pressure shown on the pressure gage as the "Pump On" pressure.
(j)
Push the boost pump switch to the OFF position.
(k)
Open the bleed valve on the pressure gage hose to release the pressure in the fuel line.
F. Boost Pump Output Pressure Calculation (Alternate 1)
(1) To find the output pressure for one of the boost pumps, subtract the "Pump Off" pressure from the "Pump On" pressure. This gives the input pressure at the engine. If the input pressure at the engine is less than 23 psi, then replace the 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. This is because a check valve between the pump and the engine opens at 13 psi. This reduces the pressure at the engine 13 psi from the output pressure of the pump.
G. Return Airplane to Normal (Alternate 1)
(1) After testing the four fuel boost pumps, do the following:
(a)
Set all six FUEL PUMP switches to the OFF position.
NOTE: Although only four fuel boost pumps were tested all six fuel pumps switches must be set to the OFF position. If they are not all off, pressurize fuel can come out when you disconnect the pressure gage hose from the fuel filter.
(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 to release the pressure in the fuel line.
(e)
Disconnect the pressure gage from the port.
NOTE: Fuel will drain from the opening. Preparing the drain plug for installation will minimize fuel leakage.
(f)
Install the plug with a new O-ring in the port of the engine fuel pump. Tighten the drain plug to 50-75 inch-pounds (5.6 -8.5 Newton meters).
(g)
Do the "Test A -Ground Check at Idle" (AMM 71-00/501).
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H. Test Preparation (Alternative 2)
NOTE: This alternative is recommended only if replacing the pressure switches at the same time of this inspection.
(1) Do the following inspection at each of the four low pressure switches for the main fuel tanks.
NOTE: This test is not needed for the two fuel boost pumps for the center tank.
NOTE: This inspection is NOT applicable to airplanes with only TRW fuel boost pumps for the two main fuel tanks. On airplanes with some GEC/PLESSEY and some TRW boost pumps for the two main fuel tanks, the test is necessary for GEC/PLESSEY fuel boost pumps and optional for TRW fuel boost pumps.
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