Purge Cycle Refer to Figure | BENDIX SD-08-2412 specs

GOVERNOR

←

CHECK

VALVE

ORIFICE

DESICCANT

←

CARTRIDGE

←

DESICCANT

BED

←

PURGE

←

VOLUME

←

OIL

SEPARATOR

←

CONTROL

←

PORT

←

COMPRESSOR

←

ENGINE

SUPPLY

←

CHECK

TURBO

VALVE

PORT

←

ASSEMBLY

RESERVOIR

←

DELIVERY

TURBO

PURGE

← ←

HEATER

SUMP PORT

CUT-OFF

EXHAUST

PISTON

VALVE

ELEMENT

FIGURE 3 - BENDIX®AD-9®AND AD-9®IPC AIR DRYER PURGE CYCLE

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 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 cut-out setting.

PURGE CYCLE (Refer to Figure 3)

When air brake system pressure reaches the cut-out 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 governor unloader port to the air dryer 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.