Bendix Commercial Vehicle Systems AD-4 AIR DRYER 10/04 - Manual (Page 3)

3
FIGURE 3 - AD-4 ™ AIR DRYER PURGE CYCLE
CONTROL
GOVERNOR
SUPPLY RESERVOIR
PURGE VOLUME
DESICCANT
BED
OIL SEPARATOR
DESICCANT
CARTRIDGE
DELIVERY
PORT
HEATER
CHECK
VALVE
PURGE
VALVE
COMPRESSOR
CHECK
VALVE
ORIFICE
EXHAUST
PORT
line connecting the governor unloader port to the AD-4 ™ air
dryer end cover control port is pressurized when the governor
unloads the compressor. Air pressure at the AD-4
™ air dryer
end cover control port is also present on the purge valve
piston. The purge piston moves in response to air pressure
causing the purge valve to open to atmosphere.
Contaminants in the end cover sump are expelled
immediately when the purge valve opens. Also, air which
was flowing through the desiccant cartridge changes direction
and begins to flow toward the open purge valve. Oil, water
and solid contaminants collected by the oil separator are
removed by air flowing from the desiccant drying bed to the
open purge valve.
The initial purge and desiccant cartridge decompression lasts
only a few seconds and is evidenced by an audible burst of
air at the AD-4
™ air dryer exhaust.
The actual reactivation of the desiccant drying bed begins
as dry air flows from the purge volume through the desiccant
cartridge purge orifice and into the desiccant drying bed.
Pressurized air from the purge volume expands after passing
through the purge orifice; its pressure is lowered and its
volume increased. The flow of dry air through the drying bed
reactivates the desiccant material by removing the water
vapor adhering to it. Generally 15-30 seconds are required
for the entire purge volume of a standard AD-4
™ air dryer to
flow through the desiccant drying bed.
The end cover single check valve assembly prevents air
pressure in the brake system from returning to the air dryer
during the purge cycle. After the 30 second purge cycle is
complete, the air dryer is ready for the next charge cycle to
begin.
The purge valve will remain open after the purge cycle is
complete and will not close until air brake system pressure
is reduced and the governor signals the compressor to
charge.
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended warranty
may be voided if intrusive maintenance is performed during
this period.
Because no two vehicles operate under identical conditions,
maintenance and maintenance intervals will vary. Experience
is a valuable guide in determining the best maintenance
interval for any one particular operation.