Figure 4.29. Antiicing System Diagram.
The hot air solenoid valve is mounted on top of the compressor
and impeller housing. The solenoidoperated valve controls the flow
of anti icing hot air from the diffuser to the inlet housing. It is
an electrically controlled, pneumatically operated, failsafe valve
and will open in the event of an electrical failure.
During engine operation, the solenoid is generally energized
and the valve remains closed. When antiicing air is needed, the
solenoid is deenergized by activating a switch in the cockpit. This
vents one side of the valve to atmospheric pressure, and the
differential pressure between diffuser pressure and atmospheric
pressure overcomes spring tension and allows antiicing air to flow
to the inlet area. The valve will antiice at gas producer speeds
(N1) above flight autorotation (68% 72% N1).
After leaving the hot air solenoid valve, antiicing air flows
forward through a tube into the port on top of the inlet housing.
This antiicing air is then circulated through five of the six hollow
inlet housing support struts to prevent ice formation in the inlet
housing area. Antiicing air also flows into the rear of the inlet
housing where it passes through the hollow inlet guide vanes to
prevent icing. After passing through the inlet guide vanes, the air
exits in front of the inlet guide vanes and flows into the compressor
area. Hot scavenge oil, draining through the strut at the 6 o'clock
position of the inlet housing prevents ice formation in the bottom of
the inlet housing area.