discharge air that is bypassed around the air cycle
Ice-Limiting Sensor
cooling system. Valve A controls the amount of warm
The purpose of the ice-limiting sensor is to
air that is bypassed around the bootstrap refrigeration
eliminate ice formation in the water separator. An
unit. Valve B controls the volume of air flowing through
ice-limiting sensor is installed in the inlet of each water
the refrigeration turbine for cooling. The 3 1/2-inch
separator. Electrical signals from the ice-limiting
diameter valves B and C are identical and have the same
sensor are sent to the programming amplifier in the
part number. Valve A has a diameter of 4 1/2 inches.
temperature controller. The programming amplifier
Each valve assembly consists of a butterfly type
directs the signals to valve A servo-amplifier. The
valve, an alternating current (ac) servomotor, a
servo-amplifier directs the signals to the servomotor
planetary gear train, and a follow-up potentiometer.
that drives the valve toward an open position. This
The servomotor, gear train, and potentiometer are
allows warm air to enter the water separator, which
combined into a single unit called the actuator
eliminates ice formation in the water separator. The
assembly, which is mounted on the valve housing. The
ice-limiting sensor is operative in the manual or
actuator assembly receives signals from the
automatic mode.
temperature controller to position the butterfly valve
Ice formation on the water separator coalescer
during temperature control system operation.
causes a pressure drop between the water separator
TEMPERATURE INDICATOR
inlet and outlet, which is sensed by the ice-limiting
sensor. As this pressure drop increases to 2.9 inches of
The selectors, controls, and monitoring equipment
mercury, low-pressure (yellow) relay K3 is actuated.
for temperature control are mounted in the upper
This relay removes voltage to valve A servo-amplifier,
portion of the panel grouping (fig. 6-7). Control of
which allows only an opening signal to be received. If
cabin and flight station temperature is achieved through
ice buildup increases differential pressure to 4.1 inches
modulation of the two air cycle cooling systems.
of mercury, high-pressure (red) relay K5 is actuated.
This relay removes servo-amplifier signals routed to
valve A and supplies a signal to the valve in the open
direction only. This causes the valve to open, allowing
hot air to enter the water separator and circulate, thus
removing ice.
Pressure Ratio Limiter Assembly
The pressure ratio limiter is mounted on the EDC,
and is part of the EDC surge control system. Its function
is to relieve or eliminate that part of the total EDC back
pressure imposed by the turbine refrigeration units and
water separators when the EDC is operating at
maximum capacity or is overloaded. It is intended to
function above 18,000 feet or during climb and descent.
Airflow Control Valves
There are three airflow control valves installed in
each air cycle system. Their function is to control
system air output. The turbine bypass valves (valve A)
are located in the nose wheel well in the primary of each
heat exchanger outlet to turbine bypass duct. The
turbine shutoff valves (valve B) are located in the nose
wheel well in the secondary section of each heat
exchanger outlet to turbine inlet duct. The hot air
bypass valves (valve C) are located in the forward left
and right sides of the APU compartment. Valve C
Figure 6-7.--Air-conditioning, cabin air compressors, and cabin
controls the amount of hot primary compressor
pressurization control panels.
6-9
