BENDIX AD-9 AIR DRYER User Manual

ORIFICE

PURGE

VOLUME

DELIVERY

PORT

HEATER

ELEMENT

SUMP

EXHAUST

PURGE

VALVE

RESERVOIR

SUPPLY

PORT

COMPRESSOR

GOVERNOR

ENGINE

TURBO

CONTROL

PORT

OIL

SEPARATOR

DESICCANT

BED

DESICCANT
CARTRIDGE

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CHECK

VALVE

OPERATION OF THE AD-9

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AIR DRYER

The AD-9

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air dryer alternates between two operational

modes or “cycles” during operation: the charge cycle and
the purge cycle. The following description of operation is
separated into these “cycles” of operation.

CHARGE CYCLE (refer to Figure 2)

When the compressor is loaded (compressing air)
compressed air, along with oil, oil vapor, water and water
vapor flows through the compressor discharge line to the
supply port of the air dryer end cover. As air travels through
the end cover assembly, its direction of flow changes several
times, reducing the temperature, causing contaminants to
condense and drop to the bottom or sump of the air dryer
end cover.

After exiting the end cover, the air flows into the desiccant
cartridge. Once in the desiccant cartridge air first flows
through an oil separator which removes water in liquid form
as well as oil and solid contaminants.

Air exits the oil separator and enters the desiccant drying
bed. Air flowing through the column of desiccant becomes

FIGURE 2 - AD-9

™

AIR DRYER CHARGE CYCLE

progressively drier as water vapor adheres to the desiccant
material in a process known as “adsorption”. The desiccant
cartridge using the adsorption process typically removes
95% of the water vapor from the pressurized air.

The majority of dry air exits the desiccant cartridge through
its integral single check valve to fill the purge volume between
the desiccant cartridge and outer shell. Some air will also
exit the desiccant cartridge through the purge orifice adjacent
to the check valve.

Dry air flows out of the purge volume through the single
check valve assembly and out the delivery port to the first
(supply) reservoir of the air system.

The air dryer will remain in the charge cycle until air brake
system pressure builds to the governor cutout setting.

PURGE CYCLE (refer to Figure 3)

When air brake system pressure reaches the cutout setting
of the governor, the compressor unloads (air compression
stopped) and the purge cycle of the air dryer begins. When
the governor unloads the compressor, it pressurizes the
compressor unloader mechanism and line connecting the

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CHECK

VALVE

ASSEMBLY

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