supply that is controlled by a fluidic control
system or a torque motor and flapper (5),
depending upon whether the solenoid is energized
or de-energized.
During the ram-air augmentation mode (auto-
matic mode), the ram-air shutoff valve regulates
downstream pressure to a fixed differential of
7.5 ± 2 inches of water above cabin pressure. The
automatic mode is selected by energizing the
solenoid. This allows the fluidic control to
establish the differential across the valve actuator
as determined by valve downstream pressure (6)
and cabin pressure (1).
During manual operation (override mode), the
auxiliary vent switch on the environmental panel
is used to place the ram-air shutoff valve in any
position from fully closed to fully open by varying
electrical power to the valve torque motor. In the
override mode, selected by de-energizing the
solenoid, power is applied to the torque motor
to close the pneumatic supply pressure nozzle and
to open the vent nozzle, thereby lessening the ram-
air shutoff valve actuator closing pressure. This
permits the actuator spring to move the butterfly
toward an open position.
RAM-AIR HIGH-AND LOW-TEMPERA-
TURE LIMIT SWITCH.— The ram-air high- and
low-temperature limit switch senses air tem-
perature at the ram-air inlet duct. There are two
circuits in the ram-air high- and low-temperature
limit switch that are normally closed. One circuit
opens with decreasing ram-air temperature, and
the other opens with increasing ram-air tempera-
ture. The ram-air high- and low-temperature limit
switch circuitry is interconnected with the bleed-
air flow control valve, the ram-air shutoff valve,
and the auxiliary vent switch. The ram-air high-
and low-temperature limit switch operation
controls the ram-air shutoff valve position when
the ram-air shutoff valve is operating in the
automatic mode.
GROUND AIR SUPPLY CHECK VALVE
AND GROUND COOLING AIR CONNEC-
TOR.— Support equipment provides low-pressure
conditioned air when it is attached to the ground
cooling air connector. The connector is located
on the right side of the aircraft in the right wheel
well at fuselage station (FS) 465. It is accessible
through a hinged door on the underside of the
sonobuoy deck. The connector consists of a
silicone-impregnated nylon hose and a clamp
supporting the air check valve.
The ground air check valve is a 4-inch
diameter, split-flapper valve spring-loaded to the
closed position. Ground cooling air opens the
check valve and closes the ram and recirculated
air check valves. The ground source low-pressure
air bypasses the refrigeration unit and enters the
cabin area because the air-conditioning system is
not used when low-pressure ground air is
connected. Therefore, the bleed-air flow control
valve will be closed.
ENVIRONMENTAL CONTROL PANEL
The environmental control panel (fig. 4-12) is
located on the center console and is used by the
flight crew to control temperature, pressurization,
and anti-icing functions. The discussion of this
panel is limited to the ram-air valve position
selector, air-conditioning switch, and the cabin
air temperature selector.
Ram-Air Valve Position Selector
When the ram-air valve position selector
(AUX VENT switch) is placed in the OFF
position, the automatic mode is established by
way of the fluidic control system. Clockwise
rotation towards the ON position overrides logic
controls of the air-conditioning system. Control
of the ram-air shutoff valve is determined by the
Figure 4-12.-Environmental control panel.
4-18
