TM55-2840-251-23
Section III PRINCIPLES OF OPERATION (Continued)
1-11 FUEL SYSTEM (Cont)
Fuel Control Unit
The fuel control unit, mounted on the fuel pump,
determines the amount of fuel needed by the engine to
meet the pilot's power control lever setting. Engine
power output depends upon compressor turbine speed
(Ng), which is controlled by regulating the amount of fuel
supplied to the fuel manifold assembly nozzles.
Fuel under pressure (P1) is supplied to the metering
valve, which controls the flow of fuel to the engine at
pressure (P2). The bypass valve maintains a steady
P1- P2 differential to enable the metering valve to meet
varying power demands. A minimum pressure valve
insures enough pressure at the fuel nozzles to obtain a
correct spray pattern.
The Ng governor is driven at a speed proportional to Ng,
thus any change in Ng causes the centrifugal weights to
move to open or close valves, changing the pressure
balance of the bellows in the pneumatic section.
Bellows movement is mechanically linked to the
metering valve, thus altering the fuel supply to the fuel
nozzles. Air (Px) to the pneumatic section comes from
the gas generator via the temperature compensator.
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