Water Separator Refrigeration Bypass Valve the air is allowed to expand at the ACM outlet, cooling even  further. The combined energy loss from the air first driving  the turbine and then expanding at the turbine outlet lowers  the system air temperature to near freezing.  [Figure 16-67] The cool air from the air cycle machine can no longer hold  the quantity of water it could when it was warm. A water  separator is used to remove the water from the saturated air  before it is sent to the aircraft cabin. The separator operates  with no moving parts. Foggy air from the ACM enters and is  forced through a fiberglass sock that condenses and coalesces  the mist into larger water drops. The convoluted interior  structure of the separator swirls the air and water. The water  collects on the sides of the separator and drains down and  out of the unit, while the dry air passes through. A bypass  valve is incorporated in case of a blockage.  [Figure 16-68] As mentioned, air exiting the ACM turbine expands and cools.  It becomes so cold, it could freeze the water in the water  All air cycle air conditioning systems use at least one ram  air heat exchanger and an air cycle machine with expansion  turbine to remove heat energy from the bleed air, but variations  exist. An example of a system different from that described  above is found on the McDonnell Douglas DC-10. Bleed air  from the pneumatic manifold is compressed by the air cycle  machine compressor before it flows to a single heat exchanger.  separator, thus inhibiting or blocking airflow. A temperature  sensor in the separator controls a refrigeration bypass valve  designed to keep the air flowing through the water separator  above freezing temperature. The valve is also identified by  other names such as a temperature control valve, 35° valve,  anti-ice valve, and similar. It bypasses warm air around the  ACM when opened. The air is introduced into the expansion  ducting, just upstream of the water separator, where it  heats the air just enough to keep it from freezing. Thus, the  refrigeration bypass valve regulates the temperature of the  ACM discharge air so it does not freeze when passing through  the water separator. This valve is visible in  Figure 16-62  and  is diagrammed in the system in  Figure 16-63 .  16-40 Figure 16-67.  A cutaway diagram of an air cycle machine. The main housing supports the single shaft to which the compressor and  turbine are attached. Oil lubricates and cools the shaft bearings.  Compressor scroll Turbine scroll Compressor impeller Compressor inlet Compressor outlet  to secondary heat exchanger Sump drain Main housing assembly Slinger Turbine inlet from secondary heat exchanger Turbine outlet Turbine wheel Sump