Turbo Cut-Off Feature - BENDIX AD-9 AIR DRYER Manual

GOVERNOR COMPRESSOR
RESERVOIR
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FIGURE 3 - AD-9 AIR DRYER PURGE CYCLE
governor unloader port to the AD-9
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
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air at the AD-9 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
DESICCANT
SEPARATOR
CONTROL
PORT
ENGINE
SUPPLY
TURBO
PORT
TURBO
CUTOFF
PISTON
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air dryer end cover control
CHECK
VALVE
DESICCANT
CARTRIDGE
BED
OIL
PURGE
VALVE
EXHAUST
vapor adhering to it. Generally 15-30 seconds are required
for the entire purge volume of a standard AD-9
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
air dryer 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.
ORIFICE
PURGE
VOLUME
ASSEMBLY
DELIVERY
PORT
SUMP
HEATER
ELEMENT
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air dryer to
CHECK
VALVE
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3