TM 5-3805-263-14&P-3
AIR SYSTEM AND BRAKES WITH
TWO SECTION AIR TANK
PURGE CYCLE
For the unloaded or purge cycle, the air flow through cartridge
(6) of the air dryer is the reverse of the compression cycle.
When the air system gets to the pressure setting (cutout
pressure) of the air compressor governor, the governor
operates the unloader valve(s) in the air compressor. The
unloader valve(s) stop the flow of air from the air compressor.
At this time, air goes to unloader passage (4) of the air dryer.
This air pressure raises purge valve (11) off its seat and causes
a sudden loss of air pressure out of purge passage (13) in the
air dryer. The air from outlet passage (2) moves suddenly
(rushes) down through desiccant (8) and filter (9). Any foreign
material (water, oil, dirt, etc.) in the desiccant, filter and the
bottom of housing (7) goes around purge valve (11) and out
purge passage (13) to the atmosphere. The compressed air,
that has been dried by the desiccant, is very efficient in the
removal of water on its reverse flow through desiccant (8).
The purge valve stays in the open (purge) position until the
pressure in the air system decreases, through usage, to the cut-
in pressure of the air compressor governor. At this point, the
governor moves the unloader valve(s) to permit air flow from the
air compressor to inlet passage (3) and onto the air reservoir.
The flow of air to unloader passage (4) is now stopped and
spring (10) moves purge valve (11) down to the closed position.
The compression cycle now starts again.
A heating element is installed in heater passage (12) to keep
the moisture in housing (7) from freezing.
3-116C
