valve. Because the voltage goes through the reversing
Cabin pressurization automatically starts at
transformer, it shifts 180, and the control winding
8,000 feet. The cabin pressure remains at 8,000 feet
voltage leads the fixed-phase voltage by 90. This
until reaching a pressure differential of 5 PSI. The
causes the valve to drive in a direction to decrease
cabin pressure now maintains a pressure differential
cold air and increase hot air to the cockpit. Upon
of 5 PSI.
releasing the switch, the valve remains fixed.
The cabin pressure regulator maintains the
Under any of the previously described
pressure schedule. This valve allows the air passed
conditions--in either the automatic or manual mode--
into the cabin air-conditioning system to exhaust into
failure of electrical power to the cabin and ventilation
the nose compartment. From sea level to 8,000 feet,
suit temperature controller, or to the dual
the exhaust flow is unrestricted. Above 8,000 feet, the
temperature control valve, causes the valve to remain
valve closes down, restricting the exhaust flow until
in the position it was maintaining at the time of
reaching a cabin pressure equivalent to 8,000 feet
electrical failure.
altitude. The cabin remains at this pressure as the
The cabin may be ram air ventilated by placing
aircraft climbs until reaching a cabin-to-ambient
the cockpit switch at RAM AIR. With the canopy
pressure differential of 5 PSI. Beyond this altitude,
closed, this action de-energizes the air-conditioning
the valve regulates the exhaust flow to maintain this
control relay, closes the cabin bleed air shutoff valve,
constant pressure differential throughout the
and drives the dual temperature control valve to the
remaining altitude range.
full hot position. This effectively blocks the flow of
A cabin pressure safety valve provides a
both hot and cold bleed air to the cabin. Either crew
maximum limit to cabin pressure in the event of a
member may control the degree of ram air ventilation
regulator malfunction. This valve limits the cabin-to-
by depressing the MAN/RAM AIR switch to either
ambient pressure differential to 5.5 PSI. The CABIN
HOT OR COLD. The HOT position drives the cabin
DUMP switch permits either crew member to dump
ram air valve toward the closed position, restricting
cabin pressure through the cabin safety valve. Placing
the ram air flow. The COLD position drives the cabin
the CABIN DUMP switch to ON completes a circuit to
ram air valve toward the open position, increasing the
the cabin dump valve, which opens the cabin safety
ram air flow. You can select any position of the cabin
valve.
ram air valve from full open to full closed.
Figure 4-26.--Equipment cooling flow diagram.
