ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT FORWARD BOOST PUMP CONTROL

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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT AFT BOOST PUMP CONTROL

General
This page shows control for the left aft boost pump. Control of the right aft boost pump is almost the same.
The left aft boost pump receives 115v ac power from the left transfer bus.
Left Aft Boost Pump Control
The boost pump control switch closes the boost pump control relay in the left power management panel. This permits power to go from the left transfer bus to the boost pump.
Pressure Indication
The boost pump control switch has a light to show when there is low pressure at the pump outlet. The boost pump pressure switch closes when there is low pressure. The ELMS logic sends a signal through OPAS to turn on the low pressure light in the switch.
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT AFT BOOST PUMP CONTROL

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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT CENTER OVERRIDE/JETTISON PUMP CONTROL

General
The left center override/jettison pump receives 115v ac power from the left main bus. Control of the right center override/ jettison pump is almost the same.
Left Center Override/Jettison Pump Control
The center left fuel pump switch supplies a ground to an electrical load control unit (ELCU) in the left power panel. The ELCU uses a control relay to close an internal contactor. This permits power to go from the left main bus to the pump.
The ELCU receives power from the left main dc bus. When the airplane is on the ground and has only one external power source, the ELMS removes the dc power to the ELCU. The right override/jettison pump operates the same. This inhibits the pump and prevents an electrical power overload. During the inhibit no EICAS message shows.
If the APU generator is the single power source, you can operate the left override/jettison pump. You cannot operate the right override/jettison pump if the APU generator is the only power source.
If an IDG is the single power source, you can operate the related override/jettison pump.
The pump inhibit logic does not operate during these conditions:
*
The air/ground system is set to air mode

*
A refuel panel door is open

*
The fuel jettison arm switch is in the armed position.

Pressure Indication
The pressure light on the switch shows low pump pressure. The override/jettison pump pressure switch closes when there is low pressure at the pump outlet. The EEU sends a signal through the OPAS to turn on the pressure light on the switch. The pressure light will come on only when the pump is commanded on.
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -LEFT CENTER OVERRIDE/JETTISON PUMP CONTROL

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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -ENGINE FUEL SPAR VALVE

General
The engine fuel spar valves get power to operate from the hot battery bus or the spar valve battery. The fuel control switches control relays to operate the spar valves. The engine fire switch must be down to permit the spar valve to open.
Control
Power goes through engine fuel spar valve control relay to the spar valve. The fuel control switch controls the reset/fuel spar relay to move the control relay. When the fuel control switch is in the RUN position, the open coil in the control relay energizes. This sends power to open the spar valve. When the fuel control switch is in the CUTOFF position, the close coil in the control relay energizes. This sends power to close the valve.
Power to operate the valve goes through limit switches to the actuator. The actuator moves the valve to the commanded position. When the valve is in the commanded position, the limit switches remove power from the actuator.
Fault Indications
The OPAS monitors the spar valve control relay position and the spar valve position. If there is a disagreement between the relay position and valve position, the OPAS sends a fault message to the AIMS. The fault messages cause an EICAS status message.
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ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -ENGINE FUEL SPAR VALVE

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