28-31-00
ALL ú ú 01 Page 6 ú Oct 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
C. During pressure defuel, fuel transfer or in-flight jettison, the low pressure light for the override/jettison pumps can show. No maintenance action is necessary. The illumination of the low pressure light during defueling, fuel transfer or in-flight jettison is acceptable and expected because the pressure switch is installed to monitor engine feed performance.
8. Fuel Override/Jettison Pump Relay (Fig. 1)
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A. The fuel override/jettison pump relays enable three-phase ac electrical power to be supplied to the override/jettison pumps. The relays are controlled by override/jettison pump switches on the fuel management control module through fault current detectors. The left pump relay is found in the left power distribution center (P414) and the right pump relay is found in the right power distribution center (P415).
9. Override/Jettison Pump Fault Current Detector (Fig. 1 and 2)
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A. Fault current detectors supply protection against short circuit ground faults which may occur in the motor/impeller units of the override/jettison pumps. The fault current detectors detect abnormal current resulting from ground faults either internal or external to the override/jettison pump.
B. The fault current detector has a transformer, printed circuit board, and electrical connector, housed within a case assembly.
C. Wiring to each override/jettison pump is routed through a single-hole current transformer which extends below the detector case. During normal operation, the vector sum of the currents in the three phases is zero, therefore the transformer does not develop a voltage, and the detector does not trigger. If the RMS value of the sum of the 400Hz ac currents sensed by the transformer exceeds 1.5 |0.5 amps, a voltage is developed in the transformer. The detector triggers, energizing a relay that opens the circuit for the override/jettison pump control relay. The control relay de-energizes, and power is removed from the override/jettison pump.
D. OVERRIDE/JETTISON PUMPS IN THE NO. 2 AND 3 MAIN TANKS; If the fault current detector has operated (removed the power to the applicable override/jettison pump) you must open and close the 28 VDC power circuit breaker on the power distribution panel, P180, to set the fault current detection system again (SSM 28-31-04).
E. OVERRIDE/JETTISON PUMPS IN THE CENTER WING TANK; If the fault current detector has operated (removed the power to the applicable override/jettison pump) the fault current detection system is set again when the flight compartment switch for the applicable override/jettison pump is pushed off and then pushed to the ON position or the pump-on command from the fuel system management card or fuel jettison control card is removed (SSM 28-31-02).
10. Fuel Jettison Transfer Valve (Fig. 1)
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A. Fuel jettison transfer valves direct the flow of fuel from the override/jettison pumps to the fuel jettison manifold. The fuel jettison transfer valves are in the inboard landing gear wheel well, installed through the rear spar of the center wing tank and each inboard main tank. Each fuel jettison transfer valve has two separate subassemblies, a valve and an electric actuator.
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28-31-00
ALL ú ú 01 Page 7 ú Oct 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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