28-22-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
FUEL MANAGEMENT
CONTROL MODULE
SEE A
FUEL CONTROL
SWITCHES
SEE B
FUEL CROSSFEED CENTER WING TANK VALVE POSITION
VALVE SWITCH OVERRIDE/JETTISON DISAGREEMENT LIGHT
(4 PLACES) PUMP SWITCH
INDICATION LIGHT (REFER TO 28-42-00) LOW PRESSURE
INBOARD MAIN TANK OVERRIDE/JETTISON PUMP SWITCH (4 PLACES) A FUEL BOOST PUMP SWITCH (8 PLACES)
FUEL CONTROL SWITCH
B
Engine Fuel Feed System Control Switch Location Figure 2
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
8. Fuel Boost Pump Check Valve (Fig. 1)
___________________________
A. The fuel boost pump check valve closes the boost pump discharge line when the pressure drops below a preset amount, thus preventing reverse fuel flow through the pump.
B. The check valve is located at the discharge port of each boost pump inside the fuel tank. The valve is either a poppet valve or a flapper valve. The check valve housing has three ports: fuel in, fuel out, and a pressure sensing port. The pressure sensing port is located upstream of the check valve. Access to the valves is gained by entering the inboard main tanks.
9. Fuel Boost Pump Inlet Screen (Fig. 1)
____________________________
A. A boost pump inlet screen is installed over the bellmouth assembly of each fuel suction line to prevent foreign material from entering the boost pumps and feed system lines. The screen consists of wire mesh, a ring, and nutplates. The screen is bolted to a flange on the bellmouth.
10. Water Scavenge Ejector Pump (Fig. 1 and 3)
___________________________
A. An ejector pump at the fuel boost pump inlet provides continuous water scavenging whenever the boost pump is operating. The pump consists of a housing and a jet nozzle. The housing has three ports: a motive port, an induced port, and a discharge port. The motive port is connected to the boost pump check valve pressure sensing port. The induced port is connected to an inlet screen which is sealed to the lower surface of the fuel tank. The discharge port is open to the boost pump inlet.
INLET FROMEJECTOR PUMP INLET SCREEN
MOTIVE
PORT
INLET FROM
OUTLETFUEL BOOST PUMP
Ejector Pump
Figure 3
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747-400
MAINTENANCE MANUAL
B. When the fuel boost pump is operating, it pressurizes the motive port of the ejector pump. Flow through the jet nozzle causes fuel and accumulated water to flow from the inlet screen to the induced port and out the discharge port.
11. Fuel Boost Pump Bypass Valve (Fig. 1)
____________________________
A. A boost pump bypass valve is provided for each engine to allow suction feed when the boost pumps fail. The valve consists of a screen and a check valve body with a hinged flapper. The valve is attached to the suction feed line for each engine.
12. Fuel Flow Limiting Valve
________________________
A. A fuel flow equalization valve is installed in the crossfeed manifold in the center tank. The valve consists of two spring loaded flapper check valves oriented in opposite directions. The maximum cracking pressure for each valve is 3.1 psi. The valve permits normal crossfeed operation while restricting uneven fuel distribution from moderate differences in boost pump operating pressure which could result in a lateral fuel imbalance.
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