6
The actual regeneration of the desiccant drying bed begins
as dry air from the purge reservoir then flows through the
purge orifice into the desiccant bed. Pressurized air from
the purge reservoir expands after passing through the
purge orifice; its pressure lowers and its volume increases.
The flow of dry air through the drying bed regenerates the
desiccant material by removing any water vapor adhering to
it.
See Table 2 for the time required for the entire contents
of the purge reservoir of a Bendix
®
AD-IS
®
air dryer &
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 during
the purge cycle. The air dryer remains in the purge mode
until the air system pressure drops below the governor
cut-in pressure thereby placing both the compressor and
the air dryer in the charge mode. After the purge reservoir
pressure is depleted, the air dryer desiccant has been
regenerated and is now ready for the next charge cycle.
TURBO CUT-OFF VALVE
(Refer to Figure 3)
The primary function of the turbo cut-off valve is to prevent
loss of engine turbocharger air pressure through the
AD-IS
air dryer when the dryer is in the purge mode.
At the onset of the purge cycle, the downward travel of the
purge piston is stopped when the turbo cut-off valve (the
tapered portion of the purge piston) contacts its mating
metal seat in the purge valve housing. With the turbo
cut-off valve seated (in the closed position), air in the
compressor discharge line – as well as the AD-IS air dryer
inlet port – cannot enter the air dryer. By completing these
actions, 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.
Bendix
®
AD-IS
®
Air Dryer Purge Reservoir Size and Purge Time
AD-IS Air Dryer Purge
Reservoir Options
Description
Purge Reservoir Size (in
3
)
Approximate Purge Time
(
See Note 2
)
4"
AD-IS air dryer
with standard purge volume
200 in
3
35 seconds
6"
AD-IS air dryer with extended
purge volume
300 in
3
55 seconds
4"
AD-IS air dryer with standard
purge volume and extended purge
volume mounted remotely
200 in
3
(standard purge)
+
288 in
3
(remote purge)
=
488 in
3
total volume
(
See Note 1
)
85 seconds
Note 1: The remote purge reservoir volume can vary based on vehicle manufacturer options. Purge time is directly related to the purge
reservoir volume, the larger the purge volume the longer the time needed to purge.
Note 2: Purge times are approximate and based on a new system with minimal leakage
.
Table 2 - Purge Volume Size and Purge Time
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