The duplex nozzle may be represented in many
The primary fuel entry line (manifold) of the
configurations, depending upon the type of
duplex nozzle is smaller than the secondary entry
combustion chamber installation. Therefore, the
line. This feature permits fuel within the primary
nozzle parts will vary between duplex nozzles of
line to reach a comparatively high degree of
various engines. Figure 4-21 shows a duplex
pressure and atomization during starting and
nozzle for use in a can-annular combustion
altitude idling conditions. The secondary fuel
chamber.
entry line also starts supplying fuel when engine
rpm raises fuel pressure to a predetermined
level--usually after engine rpm is stabilized after
FUEL SELECTORS
a start.
Valves covered in this section are designed to
The single manifold of the simplex nozzle
control the flow of fuel in all aircraft fuel
does not have the above-mentioned feature
systems. Construction and flow control are similar
and must supply fuel under all operating
for most valves used in modern aircraft. The
conditions. So duplex nozzles provide better
construction of the selector is basically a ported
low-speed performance then simplex-type noz-
body housing a rotor. Controlling these valves can
zles.
be manual or electrical. Graphite sealing discs are
so arranged on the rotor that the ports are sealed
At sufficient pump outlet pressure, the
or opened in sequence by rotation of the rotor.
pressurizing valve or flow divider allows fuel
The ends of the rotor bores in the body are closed
to enter the main or secondary line. The
by top and bottom caps with O-rings. The rotor
spray orifice will increase its spray angle be-
stem extends through the top cap with an O-ring
cause of the increased fuel flow and pressure.
seal to prevent leakage. This stem is rotated by
Figure 4-20 shows the spray angle of a typical
an electrical actuator assembly or by either a
duplex nozzle.
handle or a yoke for manual actuation. Where
manual actuation is used, the top cap incorporates
a spring-loaded ball and a stop pin to index the
various rotor positions. Figure 4-22 shows a
selector valve.
The motor-operated gate valve provides a
means of controlling the flow of fuel to various
Figure 4-22.-Selector valve.
Figure 4-21.-Duplex nozzle spray pattern.
4-26
