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Engine Fuel System Components

Engine Fuel System Components

Main Fuel Pumps (Engine Driven)

  • Main fuel pumps deliver a continuous supply of fuel at the proper pressure and at all times during operation of the aircraft engine.
  • The engine-driven fuel the pump must be capable of delivering the maximum needed flow at appropriate
  • pressure to obtain satisfactory nozzle spray and accurate fuel regulation.

These engine driven fuel pumps may be divided into two distinct system categories:

1. Constant displacement

2. Nonconstant displacement

  • Their use depends on wherein the engine fuel system they are used. Generally, a nonpositive displacement (centrifugal pump) is used at the inlet of the engine-driven pump to provide positive flow to the second stage of the pump.
  • The output of a centrifugal pump can be varied as needed and is sometimes referred to as a boost stage of the engine-driven pump.
  • The second or main stage of the engine-driven fuel pump for turbine engines is generally a positive displacement type of pump.
  •  The term “positive displacement” means that the gear supplies a fixed quantity of fuel to the engine for
  • every revolution of the pump gears.
  • Gear-type pumps have approximately straight line flow characteristics, whereas fuel requirements fluctuate with flight or ambient air conditions.
  • Hence, a pump of adequate capacity at all engine operating conditions has excess capacity over most of the range of operation.
  • This is the characteristic that requires the use of a pressure relief valve for bypassing excess fuel back to the inlet.
  • A typical two-stage turbine engine driven pump is . The impeller, which is driven at a greater speed than the high pressure elements, increases the fuel pressure depending upon engine speed.

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