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The standby boost pumps are also used for lateral balance of the fuel load by pumping fuel from one wing to the other. If lateral imbalance of fuel loads occur (e.g. after engine failure), fuel can be pumped from wing to wing by means of the standby boost pumps which are interconnected by a transfer valve. The transfer valve is closed in order to isolate left and right engine feed systems from each other except when restoring balance. Transfer is achieved by opening the transfer valve and then switching on the standby boost pump. Fuel will be pumped from the wing through the transfer valve and the in-active standby boost pump into the other wing to restore fuel balance. A secondary means of balancing fuel completely independent of the pumped system is provided by a gravity crossflow system that provides a direct flow path between the wings and is controlled by the opening and closing of a gravity cross-flow shutoff valve. While the gravity transfer shutoff valve is opened, aircraft maneuvering (steady heading sideslip) may be required to achieve transfer of fuel if the initial imbalance is minimal. Aircraft maneuvering is not required when the imbalance between the two tanks is large. Whether performing balancing by means of the standby boost pumps or by gravity, the action is controlled manually by the pilot while visually monitoring the fuel contents and messages on the EICAS. An independent operated fuel shutoff valve for each engine feed is located forward of the engine rotor burst areas. In the event of an engine fire the valves are closed by the activation of L (R) ENG FIRE switches. on the center pedestal. They can be subsequently reopened if required by depressing the switches once more. ENGINE FUEL SHUTOFF VALVE (SOV) The engine fuel shutoff valves are located on the aft spar of the wing box in the main landing gear bay and are controlled by the L (R) ENG FIRE switches on the ENGINE control panel located on the center pedestal. The engine fuel shutoff valves are electrically operated valves that stop the flow of fuel to the engines. FUEL HEATER/OIL COOLER The fuel heater/oil cooler (FHOC) is located in the engine accessory gear box. The engine FHOC purpose is to heat the fuel sufficiently to prevent ice formation in the engine fuel system, while maintaining the engine oil temperature within limits. FUEL FILTER
APU FUEL SHUTOFF VALVE (SOV) |
