*
Charging
*
Testing.
The switch circuit monitors the voltage of the hot battery bus. If the voltage becomes less than 22v, the switch circuit supplies power from the spar valve battery to the valve actuator circuits.
The charge circuit uses power from the right main dc bus to charge the batteries.
The test circuit does automatic tests of the spar valve battery. It also continuously monitors the battery for these faults:
*
Voltage
*
Shorted cell
*
Open cell
*
One battery section has lower voltage than the other battery section.
The test circuit sends a status signal to OPAS that tells the AIMS if the batteries have sufficient capacity. It sends a health signal to OPAS that tells the AIMS if a fault is found. The AIMS shows the EICAS status message FUEL SOV BATTERY when there is a fault.
Training Information Point
There is a airplane maintenance manual (AMM) test of the blocking diode for the fuel shutoff valve bus. The blocking diode is in the P11 panel.
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777 AIRCRAFT MAINTENANCE MANUAL
ENGINE FUEL FEED -SPAR VALVE BATTERY
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -FUEL FLOW
General
The normal procedure for engine fuel feed operation is to supply fuel from the center tank first. When the center tank is empty, you supply fuel from the main tanks.
If you open a crossfeed valve, you can feed an engine from the opposite main tank to correct a fuel imbalance between the main tanks.
The engines can also use suction feed from a main tank.
Center Tank Engine Feed
When the override/jettison pumps are on and there is fuel in the center tank, fuel goes from the center tank into the engine feed manifold. When the spar valves open, fuel goes from the engine feed manifold to the engines.
Main Tank Engine Feed
When the center tank is empty and the boost pumps are on, fuel goes from the main tanks into the engine feed manifold.
Cross Feed
The crossfeed valves isolate the left and right sides of the engine feed manifold. If a crossfeed valve is open, an engine can receive fuel from the fuel pumps on the opposite side.
Suction Feed
Suction (gravity) feed occurs when all the pumps on one side are off and the crossfeed valves are closed. During suction feed, the engine gets fuel through the suction bypass valve. The engines can only suction feed from the main tanks.
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -FUEL FLOW
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT FORWARD BOOST PUMP CONTROL
General
The left forward boost pump receives 115v ac power from two sources: the ground service bus or the left transfer bus.
The boost pump control switch controls power to the pump. A light on the switch shows when there is low pressure at the pump outlet.
Ground Service Bus Power
The usual power source for the boost pump is the ground service bus. Power goes through the boost pump switching and control relays to the pump.
Power from the ground service bus automatically closes the boost pump switching relay.
Left Transfer Bus Power
The left transfer bus is an alternative power source for the left forward boost pump. The left aft boost pump switch must be off for the forward boost pump to receive power from the left transfer bus. This prevents both boost pumps from operating when the backup generator is the power source.
Boost Pump Power Control
The boost pump control switch supplies a ground to close the boost pump control relay.
The ELMS logic can also supply a ground to close the boost pump control relay. It does this when the airplane is on the ground and the APU selector is on or the APU is running. This permits the APU to get fuel when the boost pump switches are off.
Pressure Indication
The pressure light on the boost pump control switch shows low pump pressure. The boost pump pressure switch closes when there is low pressure at the pump outlet. The ELMS electronics unit sends a signal through OPAS to turn on the low pressure light.
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