747-400 AMM 飞机维护手册 燃油 FUEL 3(132)

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 C.  The valve has a housing, a butterfly-type valve disk, and a vacuum relief valve to prevent negative pressure in the fuel jettison manifold. The valve is flange attached to a fitting in the surge tank wall with provisions on the outboard side for connecting the valve to the fuel jettison nozzle.
 5.  Fuel Jettison Nozzle Valve Switch (Fig. 1)
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 A.  The fuel jettison nozzle valve switches control 28-volt dc power to the fuel jettison nozzle valves. The switches are found on the jettison module on the pilots' overhead panel and are identified as L-NOZZLE-R.
 B.  When a fuel jettison nozzle valve switch is operated, the word ON is shown on the switch to indicate that the valve has been commanded open. The VALVE OPEN circuit on the fuel system/EICAS interface card (FSEIC) is energized by the valve position logic card, causing the fuel system synoptic on EICAS to show that the fuel jettison nozzle valve is open.
 C.  If actual fuel jettison nozzle valve position disagrees with the selected valve position, a valve disagreement advisory is shown on the main EICAS screen and a status message is recorded. The status message is shown on the auxiliary EICAS screen when the STAT button is pushed. In addition, the word VALVE shows on the switch. The VALVE light is powered by the master dim-and-test circuit.
 6.  Override/Jettison Pump (Fig. 1)
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 A.  The override/jettison pumps deliver fuel from the center wing tank and inboard main tanks to the fuel jettison manifold through the fuel jettison transfer valves during the fuel jettison operation. The override/jettison pumps are also used during normal operation to deliver fuel to the engines (AMM 28-22-00/001, Engine Fuel Feed System).
 B.  Two override/jettison pumps, consisting of a motor/impeller unit installed in a housing assembly, are installed on the rear spar of the center wing tank and each inboard main tank.
 C.  Override/jettison pumps in the center wing tank are controlled by switches on the fuel management control module. When a pump switch is placed in the ON position, the pump control relay is energized and 115-volt, 3-phase ac power is supplied to the pump.
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 D.  Override/jettison pumps in the inboard main tanks are controlled by either the fuel system management cards (FSMC) or fuel jettison control cards (FJCC). Placing a pump switch on the fuel management control module in the ON position arms the pump control circuit. When the FSMC provides a ground for the circuit, the pump control relay is energized and 115-volt ac power is supplied to the pump. If the fuel jettison control selector switch is put in the A or B position, the jettison/override relay and management/jettison select relay are energized and pump control is transferred to the FJCC.
 E.  The override/jettison pumps can lose their prime when operated dry (pump inlets not covered by fuel). At a nominal ground attitude (wings level
 0.5 degrees nose down) the left override/jettison pump inlet will be uncovered when the fuel quantity in the center wing tank is approximately 7300 pounds (3300 kilograms). The right pump inlet will be uncovered at approximately 3550 pounds (1600 kilograms). The override/jettison pump inlets in the main tanks will be uncovered when the main tank fuel quantity is between 8600 and 10,600 pounds (3900 and 4800 kilograms). During a pressure fueling operation, the override/jettison pumps for the center wing tanks will be reprimed by fuel from reprime lines attached to the discharge tubes of the refuel lines in the center wing tank.
 (1)  
After you replace an override/jettison pump for the No. 2 or 3 main tank, you must make sure there is enough fuel to prime the pump. Fuel quantity graphs and data on how to prime the inboard override/jettison pumps are contained in the removal and installation procedure (AMM 28-31-01/401).

 (2)  
After you replace an override/jettison pump for the center wing tank, you must make sure there is enough fuel to prime the pump or use the wetting system. Fuel quantity graphs and data on how to use the wetting system for the override/jettison pumps in the center wing tank are contained in the removal and installation procedure (AMM 28-31-01/401).

 7.  Override/Jettison Pump Switch (Fig. 1)
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