icing. (See figure 4-8.) Ice forming on the wire
screen at the water separator discharge duct is
detected by two pneumatic pickups located just
before and after the water separator. These
pickups sense a differential pressure across the
water separator. If differential pressure is sensed
across the water separator, the nonice and low-
limit control valve will remain open until the
temperature of the inlet air to the water separator
is high enough to melt collected ice. When the ice
is melted, the pressure differential returns to
normal. In addition, the refrigeration pack low-
limit control electrically signals the nonice and
low-limit control valve when separator outflow
drops to 0°F.
REFRIGERATION PACK LOW-LIMIT
CONTROL.— The refrigeration pack low-limit
control (fig. 4-6) is located in the ECS
compartment. It is mounted downstream from the
water separator in a 6-inch duct of cooled
discharged bleed air.
The refrigeration pack low-limit control uses
28-volt dc power to energize its circuitry. A
thermistor senses duct air temperature and
compares it with an internally generated reference.
The difference is amplified to modulate a torque
motor in the nonice and low-limit control valve.
(See figure 4-8.) The torque valve controls the
regulated air supply (3) with a flapper valve (1),
which controls the diaphragm pressure in a
butterfly actuating linkage (12). The nonice and
low-limit control valve can be returned to the
differential pressure control mode by opening the
cabin temperature high-limit thermostat (4). This
causes the upper chamber (6) of the switcher valve
(7) to be vented (17) and returned to its primary
position. A check valve (5) is provided to prevent
extraneous signals from affecting the nonice and
low-limit control valve.
REFRIGERATION UNIT CHECK VALVE.—
The refrigeration unit check valve (fig. 4-7, detail
A) is an insert-type check valve with a split flapper
spring-loaded in the closed position. The valve,
which is installed in the refrigeration unit to
prevent hot bleed air from entering directly into
the turbine, is located in a tee arrangement in the
system just downstream of an orifice.
Icing of the water separator will occur only
at low altitudes where mass airflow and tempera-
ture are relatively high. Only a small amount of
high-temperature air is required through the
orifice to melt such a deposit. However, at high
altitude where the mass flow and bleed-air
temperatures are low, the refrigeration pack low-
limit control operates to open the nonice and low-
limit control valve. When the nonice and low-limit
control valve is open, high differential pressure
across the bleed-air orifice permits the refrigera-
tion unit check valve to open. This allows
intermediate-temperature air to bypass the
turbine, and thereby maintain water separator
temperature above 0°F. (See figure 4-6.)
CABIN AIR/WATER SEPARATOR, CO-
ALESCER CONE, AND COALESCER BAG.—
The water separator is a welded cylindrical
aluminum container installed downstream from
the turbine and fan assembly. Its purpose is to
remove a portion of the moisture condensed
during the air-expansion process within the
expansion turbine. (See figure 4-6.) The water
separator container holds a coalescer bag, which
collects the finely dispersed fog-like moisture
discharged from the turbine. The wet air flows
through the coalescer cone and through louvered
swirl vanes to cause the heavier water particles to
be deposited by centrifugal force against the outer
surface of the collector section. Accumulated
water is drained through the sump in the bottom
of the collector section. The partially dried air
then leaves the water separator by way of the air
outlet duct. The coalescer bag may be removed
for cleaning through an access cover secured with
a quick-disconnect band coupling to the water
separator shell.
WATER SEPARATOR ICE SCREEN.— An
ice screen is located in the discharge end of the
water separator to collect ice when moisturized
airflow temperature is below the dew point
temperature, or below 32°F. The condensed ice
crystals gathered across the ice screen cause a
pressure differential, which is sensed by the nonice
and low-limit control valve. The nonice and low-
limit control valve then increases the warm air
supply through the mixing muff, the coalescer
bag, and to the ice screen to melt collected
ice.
WATER SEPARATOR BYPASS VALVE.—
The bypass valve is a spring-loaded valve mounted
in the water separator container. A failure of the
nonice and low-limit control valve could cause ice
particles to build up in the water separator
coalescer bag. This ice would block the cabin air
system. To ensure that air is supplied to the cabin,
the water separator bypass valve allows turbine
air to bypass the coalescer bag.
4-12
