supply subsystem, in addition to supplying deice
air, is to control the temperature of that supply.
The high-stage bleed-air regulator valve primarily
maintains a set pressure schedule in the bleed-air
manifold. During deice operations this function
is expanded to maintain a temperature of
500°±25°F (260°±14°C) (or maximum 14th
stage temperature, if less than 500°F).
Pneumatic signals from the bleed-air control
temperature thermostat and anticipator are fed
to the deice temperature control regulator valve
(fig. 1-10), which, in turn, signals the high-stage
bleed-air regulator valve to open, as necessary,
to satisfy either the pressure schedule or the 500°F
requirement, whichever needs the larger amount
of 14th stage bleed air. Both engines are connected
by the cross-bleed manifold, which provides a
flow path for bleed air from either one or both
engines. The total deice system is controlled by
the timing control, which uses pressure regulator
valves and cyclic valves to direct bleed air in the
proper sequence to each of the eight deice
segments. Sequencing minimizes bleed-air con-
sumption. Bleed air is ported from the cross-bleed
manifold to each of the pressure regulator valves.
The pressure regulator valves are energized by
setting the DEICING switch on the environmental
panel on the center console to WING EMP (wing
and empennage). Setting this switch energizes a
solenoid that ports pressure from the bleed-air
supply to open the pressure regulator valve. Duct
pressure is regulated by the pressure regulator
valve to 26 ±2 psi. In the de-energized position,
the pressure regulator valves are pneumatically
Figure 1-10.—Ice protection system.
1-12
