the speed-set cam is also translated by the servo
Fuel-pressurizing Valve
piston by means of a cross-link to the acceleration
cam. Engine steady-state condition is a function
The fuel-pressurizing valve is usually required
of high compressor
speed, compressor inlet
on jet engines. It incorporates a duplex-type
temperature
burner pressure
and
fuel nozzles to divide the flow into primary and
power lever position.
secondary (main) manifolds. At the low fuel flows
In the event that the primary control system
required for starting and altitude idling, all the
malfunctions, the manual system may be engaged
fuel passes through the primary line. As the fuel
by operating a switch in the cockpit. It then
flow increases, the valve begins to open the main
energizes the manual transfer solenoid to close the
line. At maximum flow, the main line is passing
flapper valve. The flapper valve will remain in the
about 90 percent of the fuel.
closed position because of residual magnetism,
Fuel-pressurizing valves will usually, through
regardless of whether or not the solenoid is
incorporation of spring-loaded inlet check valves,
continuously energized. Servo action positions the
trap fuel forward of the manifold, giving a
shuttle valve to direct pump discharge pressure
positive cutoff. This cutoff prevents fuel from
to the spring side of the manual and normal
leaking into the manifold and through the fuel
systems transfer valve. This pressure, combined
nozzles. This eliminates afterfires and carboniza-
with spring pressure, positions the valve to close
tion of the fuel nozzles. Carbonization occurs
off the primary operating system and direct high-
when low combustion chamber temperatures
pressure fuel to the manual system.
cause incomplete burning of the fuel.
An example of this arrangement is the fuel-
FUEL VALVES
pressurizing and dump valve. This valve performs
two major functions, as indicated by its name.
During engine operation, it divides metered fuel
Fuel valves in the engine fuel system aid in
starting, stopping, and as safety factors. Valves
flow into two properly pressurized portions,
may differ slightly from engine to engine, and they
primary and secondary. During engine shutdown,
may be called by different nomenclature, although
it provides a dump system that connects the fuel
they perform identical functions. Some of these
manifolds to an overboard drain. The features of
valves and their functions are discussed in the
the fuel-pressurizing and dump valve are shown
following paragraphs.
in figure 4-17.
Figure 4-17.-Fuel-pressurizing and dump valve.
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