BENDIX AD-9 Service Data page 3

GOVERNOR COMPRESSOR
RESERVOIR
FIGURE 3 - AD-9 PURGE CYCLE
governor unloader port to the AD-9 end cover control port.
The purge piston moves in response to air pressure causing
the purge valve to open to atmosphere and (partially) closing
off the supply of air from the compressor, this will be further
discussed in the section covering the turbo cut-off feature.
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 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-9 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
DESICCANT
CONTROL
PORT
ENGINE
SUPPLY
TURBO
PORT
TURBO
CUTOFF
PISTON
DESICCANT
CARTRIDGE
BED
OIL
SEPARATOR
PURGE
VALVE
EXHAUST
vapor adhering to it. Generally 15-30 seconds are required
for the entire purge volume of a standard AD-9 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.
TURBO CUT-OFF FEATURE (Refer to Figure 4)
The primary function of the turbo cut-off valve is to prevent
loss of engine turbocharger air pressure through the AD-9 in
systems where the compressor intake is connected to the
engine turbocharger. The turbo cut-off valve also reduces
the “puffing” of air out the open exhaust when a naturally
aspirated, single cylinder compressor equipped with an inlet
check valve is in use.
CHECK
VALVE
ORIFICE
DELIVERY
SUMP
HEATER
ELEMENT
PURGE
VOLUME
CHECK
VALVE
ASSEMBLY
PORT
3