The end cover single check valve assembly prevents air pressure in the brake system from returning to the air dryer during the purge cycle. Generally 15-30 seconds are required for the entire purge volume of a standard AD-9 в„ў air dryer to flow through the desiccant drying bed. The flow of dry air through the drying bed reactivates the desiccant material by removing the water Pressurized air from the purge volume expands after passing through the purge orifice its pressure is lowered and its volume increased. 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. 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 в„ў air dryer exhaust. Oil and solid contaminants collected by the oil separator are removed by air flowing from the desiccant drying bed to the open purge valve. Also, air which was flowing through the desiccant cartridge changes direction and begins to flow toward the open purge valve. Contaminants in the end cover sump are expelled immediately when the purge valve opens. 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. Governor unloader port to theAD-9 в„ў air dryer end cover control port.

When the governor unloads the compressor, it pressurizes the compressor unloader mechanism and line connecting the 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. The air dryer will remain in the charge cycle until air brake system pressure builds to the governor cutout setting. Some air will also exit the desiccant cartridge through the purge orifice adjacent to the check valve.Дry 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 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. The desiccant cartridge using the adsorption process typically removes 95% of the water vapor from the pressurized air. Progressively drier as water vapor adheres to the desiccant material in a process known as вЂњadsorptionвЂќ. Air flowing through the column of desiccant becomes 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.ДЄir exits the oil separator and enters the desiccant drying bed. 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.ДЄfter exiting the end cover, the air flows into the desiccant cartridge. 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.

The following description of operation is separated into these вЂњcyclesвЂќ of operation. The AD-9 в„ў air dryer alternates between two operational modes or вЂњcyclesвЂќ during operation: the charge cycle and the purge cycle.

Bendix air brake troubleshooting guide