BENDIX AD-9 Service Data page 2

GOVERNOR COMPRESSOR
FIGURE 2 - AD-9 CHARGE CYCLE
OPERATION OF THE AD-9 AIR DRYER
The AD-9 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, oil vapor and solid contaminants.
Air exits the oil separator and enters the desiccant drying
bed. Air flowing through the column of desiccant becomes
2
CONTROL
ENGINE
TURBO
RESERVOIR
DESICCANT
CARTRIDGE
DESICCANT
BED
OIL
SEPARATOR
PORT
SUPPLY
PORT
PURGE
VALVE
progressively dryer 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
CHECK
ORIFICE
VALVE
SUMP
HEATER
EXHAUST
ELEMENT
PURGE
VOLUME
CHECK
VALVE
ASSEMBLY
DELIVERY
PORT