B. Each VPLC is a single-board printed circuit assembly installed in a slot in the fuel system card file. The card is retained in the card file by two lever locks and two captive screws that thread into holes in the card file. The card is easily replaced - no special tools are required. Four identical cards are installed in the fuel system card file at file positions 6, 9, 11, and 12. The valves associated with each card is determined by the airplane wiring at the card file connector.
C. A typical VPLC circuit contains two relays, one connected to the shutoff valve close coil and the other connected to the shutoff valve open coil. When power is available at the shutoff valve circuit breaker, either the open or closed relay is energized, depending on the position of the valve. The relay provides a ground for a "valve open" or "valve closed" circuit on the FSEIC, and the FSMC or FJCC, if applicable. Each VPLC can monitor up to seven different shutoff valves, using identical circuitry.
19. Operation
_________
A. Functional Description (Fig. 5 and 6)
(1)
The engine fuel feed system becomes operational when 28-volt dc power is supplied to the valves, pump relays, and fuel system control cards and 115-volt ac power is supplied to the pumps. Prior to flight, the fuel management system is armed by turning on all boost pumps and override/jettison pumps and opening the crossfeed valves.
(2)
When the main tank boost pumps are turned on, the boost pump control relays are energized, supplying power to the boost pumps. The pumps draw fuel from the tanks through screened inlets and pressurize the fuel feed manifold. While the boost pumps are operating, fuel is fed through the ejector pumps. Any water that has accumulated near the ejector pump pick-up is drawn through the pump by suction, discharged at the boost pump inlet, and delivered to the engines.
(3)
If the boost pumps become inoperative, fuel is drawn to the engines, through the boost pump bypass valves, by suction from the engine-driven fuel pumps.
(4)
When the fuel control switches on the aisle stand are placed in RUN position, the engine fuel shutoff valves open, and fuel in the fuel feed manifold is delivered to the engines. The valve positions are monitored by valve position logic cards, which send valve-open or valve-closed signals to EICAS through the FSEIC. Flowbars on the EICAS fuel synoptic illuminate to indicate that the valves are open and fuel is being delivered to the engines.
(a)
If the position of an engine fuel shutoff valve disagrees with its commanded position, a SPAR VLV status message is recorded in EICAS.
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747-400
MAINTENANCE MANUAL
FUEL FLOW LIMITING VALVE
BOOST PUMP CROSSFEEDBYPASS VALVEMANIFOLD
FUEL BOOST PUMP
FUEL CROSSFEED
P
VALVE
ENGINE FUEL SHUTOFF VALVE
FUEL BOOST PUMPS JETTISON TRANSFERFUEL VALVES CROSSFEED VALVE
ENGINE FUEL
SHUTOFF VALVE
P
P
P P P
P
P
OVERRIDE/JETTISON PUMPS
FUEL BOOST
PUMP EJECTOR PUMPS
BOOST PUMP BYPASS VALVE
Engine Fuel Feed System Flow Diagram Figure 5
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A
747-400
MAINTENANCE MANUAL
(5)
When the center wing tank override/jettison pumps are turned on, the pump control relays are energized, supplying power to the pumps. The pumps draw fuel from the center wing tank through screened inlets and pressurize the fuel crossfeed manifold. Symbols on the EICAS fuel synoptic illuminate to indicate that the pumps are operating.
(a)
If the pump output pressure does not increase to the normal operating range when pump is turned on, the PRESS light on the pump control switch illuminates, a FUEL OVRD CTR advisory message is displayed on the EICAS main screen, and a status message is recorded.
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