BENDIX AD-2 AIR DRYER Manual - Página 3

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The desiccant beads are held in place by steel perforated

plates and filter cloths. The top plate is held in place by a

spring, and the bottom plate rests on a shoulder

approximately 1/8" from the bottom of cartridge housing.

The end cover assembly is retained by a lock ring, cap

screws and retainers and houses the purge valve and heater

assembly if so equipped.

The heater and thermostat assembly prevent freeze-up in

the purge drain valve when the dryer is used in severe winter

conditions. The heater and thermostat assembly is standard

in the AD-2

™

air dryer and was optional equipment for the

AD-1

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air dryer. The 12 volt, 60 watt and 24 volt, 60 or 120

watt DC heater and thermostat assembly has an operating

range between 45°F and 85°F .

NOTE: The heater and thermostat assembly provided with

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the AD-2

air dryer has a 3/16" diameter threaded

electrical terminal protected by a boot. The AD-1

air dryer assembly incorporates a #16 gauge lead

wire. Both types are serviceable. The heater and

thermostat assembly should be connected to the

"on" position of the engine control or ignition switch

and protected with the proper size fuse. For details

on installation, please refer to the "Installation"

section.

OPERATION

The operation of the air dryer can best be described by

separating the operation into two cycles; the charge cycle

and the purge cycle.

Charge Cycle (Figure 3) Compressor in Compressing Cycle

- With the compressor in its "loaded" or compressing cycle,

air from the compressor enters the air dryer through the

discharge line. When the air, along with the water and

contaminants, enter the air dryer, the velocity or speed of

the air reduces substantially and much of the entrained liquid

drops to the bottom or sump of the air dryer. The initial air

flow is toward the bottom of the dryer, but air flow direction

changes 180° at the bottom of the air dryer, dropping some

water and oil.

The air now passes through the oil separator filter which

removes oil and foreign material but does not remove water

vapor. At this point, the air remains saturated with water.

The filtered air and vapors penetrate the desiccant drying

bed and the adsorption process begins. Water vapor is

removed from the air by the desiccant.

The unsaturated "dry" air passes through the ball check

valve and purge orifice into the purge volume. From the

purge volume air flows through an outlet check valve, and

into the first reservoir.

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NOTE: The AD-1

outlet check valve. The single check valve in an

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AD-1

air dryer installation would be located in the

line between the AD-1

first reservoir.

Purge Cycle; (Figure 4) When desired system pressure is

reached, the governor cuts out, pressurizing the unloader

cavity of the compressor which unloads the compressor

(non- compressing cycle). The line connecting the governor

unloader port to the end cover purge valve port (bottom of

the air dryer) is also pressurized, opening the exhaust of

the purge valve to atmosphere. With the exhaust of the

purge valve open, contaminants in the discharge line and

dryer sump are purged, or forced past the open exhaust out

to atmosphere.

The reverse air flows across the desiccant and starts the

removal process of moisture from the desiccant surface.

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Dry air flowing from the purge volume through the purge

orifice and across the drying bed further dries the desiccant.

The combination of these reverse flows strips the water

vapor from the desiccant (drying bed). This normally takes

between 15-30 seconds.

The desiccant becomes activated from this cycle and is

now ready for another charge cycle, which occurs when the

compressor returns to the compressing cycle. It is for this

reason the air dryer must be purged for 30 seconds, after

receiving moisture saturated air for a maximum of 90

seconds from a 12 CFM compressor.

WARNING!

This air dryer is intended to remove moisture and other

contaminants normally found in the air brake system. Do

not inject alcohol, anti-freeze, or other de-icing substances

into or upstream of the air dryer. Alcohol is removed by the

dryer, but reduces the effectiveness of the device to dry

air. Use of other substances can damage the air dryer and

may void the warranty.

PREVENTIVE MAINTENANCE AND CHECKING

SERVICEABILITY

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.

Every 900 operating hours or 25,000 miles or every three

(3) months:

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

reservoirs, drain cocks, or valves and checking for

presence of water. If moisture is present, the desiccant

may require replacement; however, the following

conditions can also cause water accumulation and

should be considered before replacing the desiccant:

air dryer does not incorporate an integral

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air dryer outlet port and the