Fuel Feed System: Function

Two methods of Pressure Controlled Fuel Feed
1. High Pressure Pumps
  1. Also called override and jettison pumps
  2. Deliver twice as much pressure as standard boost pumps
    1. Forces discharge check valves on standard pumps to close
      1. Prevents fuel flow from standard pumps
2. Sequence Valves
  1. Installed at the pump outlets of standard boost pumps
    1. Reduce output pressure
      1. Allows some fuel back into the tank
Electrical Fuel Feed Management
1. Performed automatically
2. Controlled in accordance with flight phases
3. Taxiing phase, centre tank feeds engines
  1. Other pumps on standby
4. Take-off phase
  1. Occurs when flaps are extended for take-off
  2. Engines supplied individually
    1. Two boost pumps from each main tanks 2 and 3 (engines 2 and 3 respectively)
    2. Double capacity centre tank boost pumps for engines 1 and 4
5. Cruise phase
  1. After take-off when flaps have been retracted
  2. Centre tanks and stabilizer tank are emptied first
  3. Inner main tanks used next
  4. All engines now supplied by double capacity override and jettison pumps in main tanks 2 and 3
Fuel Scavange
1. Reduces amount of non-usable fuel in the tanks
2. Most commonly used method uses jet pumps
3. Boost pumps supply jet pumps with pressure they need for operation
4. Scavenged fuel is pumped to the main inner tank
5. Another method uses electrically driven scavenge pump
  1. Controlled automatically as fuel level drops below certain threshold
  2. Pump fuel into a main tank
Fuel Recirculation
1. Ensures proper cooling of engine oil and integrated drive generator oil
2. Fuel from tank is pumped through engine oil cooler which heats the fuel and cools the engine oil
3. Fuel then passes through the high pressure gear driven engine pump to the burners on the engine
4. Some fuel is diverted and passes through a bypass valve
  1. Proceeds to the Integrated Drive Generator (IDG) cooler
    1. Fuel is heated further and then recirculated and mixed with new fuel ready to repeat the process
5. Works well until engine runs at lower speed and there is a high electrical load on the IDG
  1. As engine runs slower, the cooling becomes critical as there may not be enough fuel for cooling
6. Solenoid activates on the fuel return valve
  1. Return valve opens and returns fuel to the tank
    1. Cool fuel is mixed to cool down the hot fuel
Fuel Boost Pumps
1. Generally impeller type
2. Impeller forces fuel from the inlet to the pump outlet by centrifugal force
3. Boost pump can be removed from canister without draining fuel
  1. Special removal valve shuts off the fuel inlet as the pump is pulled out

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Fuel Feed System: Function

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	Created by Kenzie Evans over 6 years ago