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of the contaminants to condense and drop to the bottom of

the air dryer and reservoir system purge valve assembly,

ready to be expelled at the next purge cycle. The air then

flows into the desiccant cartridge, where it flows through an

oil separator which removes liquid oil and solid contaminants.

Air then flows into the desiccant drying bed and becomes

progressively drier as water vapor adheres to the desiccant

material in a process known as "ADSORPTION."

Dry air exits the desiccant cartridge through the center of

the base assembly. The air then flows to the delivery check

valve and also through an orifice into the purge reservoir.

The delivery check valve opens, supplying air to the pressure

protection valves (A) through (D) simultaneously, the safety

valve, and also to the reservoir port of the attached governor.

The purge reservoir fills, storing air that will be used to

reactivate the desiccant during the purge cycle. This air is

available to supply downstream components during the

charge mode.

When the air pressure reaches approximately 106 psi, the

four pressure protection valves will open and air will be

supplied to the primary reservoir, secondary reservoir and

accessories. If the pressure protection valves are preset to

different values the valves will open in order of lowest setting

to highest setting when charging a flat system.

The air dryer and reservoir system will remain in the charge

cycle until the air brake system pressure builds to the

governor cut-out setting of approximately 130 p.s.i.

PURGE CYCLE

(Refer to Figure 3.)

When air brake system pressure reaches the cut-out setting

of the governor, the governor unloads the compressor and

the purge cycle of the air dryer and reservoir system begins.

The governor unloads the compressor by allowing air

pressure to fill the line leading to the compressor unloader

mechanism - causing the delivery of compressed air to

the AD-IS

air dryer and reservoir system to be suspended.

Similarly, the governor also supplies air pressure to the

AD-IS

air dryer and reservoir system purge control channel.

The AD-IS

air dryer and reservoir system purge piston

moves down in response to this air pressure, causing the

purge valve to open to the atmosphere and the turbo cut-off

valve to close off the supply of air from the compressor (this

will be further discussed in the Turbo Cut-off Feature

section). Water and contaminants which have collected in

the purge valve base 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 purge reservoir through the desiccant drying bed

to the open purge valve.

The initial purge and desiccant cartridge decompression

lasts only a few seconds and is evidenced by an audible

burst of air at the AD-IS

exhaust.

The actual reactivation of the desiccant drying bed begins

as dry air from the purge reservoir flows through the purge

orifice into the desiccant bed. Pressurized air from the

purge reservoir expands after passing through the purge

orifice; its pressure is lowered and its volume increased.

The flow of dry air through the drying bed reactivates the

desiccant material by removing the water vapor adhering to

it. Approximately 30 seconds are required for the entire

contents of the purge reservoir of a standard AD-IS

and reservoir system to flow through the desiccant drying

bed.

The delivery check valve assembly prevents air pressure in

the brake system from returning to the air dryer and reservoir

system during the purge cycle. After the purge cycle is

complete, the air dryer and reservoir system is ready for

the next charge cycle to begin.

TURBO CUT-OFF FEATURE

The primary function of the turbo cut-off valve is to prevent

loss of engine turbocharger air pressure through the

AD-IS

air dryer and reservoir system when the dryer is in

the unloaded mode.

At the onset of the purge cycle, the downward travel of the

purge piston is stopped when the turbo cut-off valve (tapered

portion of purge piston) contacts its mating metal seat in

the purge valve housing. With the turbo cut-off valve seated

(closed position), air in the compressor discharge line and

AD-IS

air dryer and reservoir system inlet port cannot enter

the air dryer and reservoir system. In this manner the turbo

cut-off effectively maintains turbo charger boost pressure

to the engine.

PREVENTIVE MAINTENANCE

Important: Review the warranty policy before performing

any intrusive maintenance procedures. An extended

warranty may be voided if intrusive maintenance is performed

during this period. Purge valve maintenance is permissible

during the warranty period only when using a genuine Bendix

purge valve kit.

Because no two vehicles operate under identical conditions,

maintenance and maintenance intervals will vary.

Experience is a valuable guide in determining the best

maintenance interval for any one particular operation.

Every 900 operating hours, or 25,000 miles or three (3)

months:

1. Check for moisture in the air brake system by opening

reservoir drain valves and checking for presence of

water. If moisture is present, the desiccant cartridge

air dryer and reservoir system

(Refer to Figure 3.)

air dryer