BENDIX SD-08-2415A manual Purge Piston, Desiccant RE-ACTIVATION Drying the Desiccant

				DESICCANT
	OIL
	COALESCING
	FILTER
	PURGE				REAR
REMOTE	ORIFICE			DELIVERY	RESERVOIR
PURGE	REMOTE			CHECK
RESERVOIR				VALVE
	PURGE
	PORT
	CONTROL
	PORT
PURGE	SUPPLY				FRONT
CONTROL LINE					RESERVOIR
	PORT
GOVERNOR
		TURBO	SAFETY	DELIVERY
	ENGINE CUT-OFF		VALVE	PORT
	TURBO	EXHAUST		PURGE
		PORT		VALVE
COMPRESSOR
FIGURE 5 - BENDIX® AD-RP™AIR DRYER SYSTEM - PURGE CYCLE

TURBO CUT-OFF VALVE (Refer to Figure 5)

The primary function of the turbo cut-off valve is to prevent loss of engine turbocharger air pressure through the Bendix® AD-RP™air dryer in systems where the compressor intake is connected to the engine turbocharger. The turbo cut-off valve also eliminates the “puffi ng” of air out the open air dryer exhaust when a naturally aspirated, single cylinder compressor is equipped with an inlet check valve. Governor unloader pressure causes the turbo cut-off valve piston to move and close. With the turbo cut-off valve piston seated (closed position), air in the discharge line and AD-RP air dryer inlet port is prevented from entering the air dryer.

PURGE PISTON

The Bendix® AD-RP™air dryer purge piston also moves in response to governor unloader pressure, causing the purge valve to open to atmosphere. Contaminants in the body sump are instantly expelled when the purge valve opens. Air — which was fl owing through the desiccant cartridge — immediately changes direction and begins to fl ow back toward the open purge valve. Oil and solid contaminants collected by the oil separator are removed by air fl owing from the desiccant

drying bed to the open purge valve.

DESICCANT RE-ACTIVATION (DRYING THE DESICCANT)

The initial decompression of the air dryer assembly lasts only a few seconds and is evidenced by an audible burst of air at the AD-RP air dryer exhaust. The actual reactivation of the desiccant drying bed begins as dry air fl ows from the purge volume through the purge orifi ce in the body and into the desiccant bed. Pressurized air from the purge volume expands after passing through the purge orifi ce; its pressure is lowered and its volume increased. The fl ow of dry air through the drying bed reactivates the desiccant material by removing the water vapor adhering to it. Generally 30 seconds minimum are required for the entire purge volume of a standard AD-RP air dryer to fl ow through the desiccant drying bed.

The delivery check valve assembly prevents air in the brake system from returning to the air dryer during the purge cycle. After the purge cycle is complete, the desiccant has been reactivated (or dried), and the air dryer is ready for the next charge cycle to begin. However, the purge valve will remain open and will not close until air brake system pressure is reduced and the governor signals the compressor to charge the system.

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