DUAL DRYER SYSTEM
INSTALLATION/SERVICE
MANUAL (L31279)
®
DRYest Function
Charging Phase
Air from the compressor or pre-treatment flows into
the inlet manifold and divides to enter each air dryer.
Once the inlet air pressure is greater than the
TPV
[2.3]
opening pressure, the air enters each
Desiccant
Cartridge [1]
. The air first passes through an aluminum
Inlet Filter [1.1]
in the cartridge, which traps droplets
and solid particles.
The air continues traveling through several sections of
Desiccant [1.2] [1.3] [1.4]
, each section with increasing
sizes of desiccant, to capture contaminants. Once the
air passes through the cartridge the remaining water
and oil molecules will be captured.
As the air exits the cartridge, it passes through an
Outlet Filter [1.5]
, through an
Outlet Check Valve
[2.2]
and finally reaches the outlet manifold where it
combines with the outlet air of the second dryer.
A small portion of air from the cartridge passes to the
purge manifold where it combines with air from the
other dryer and exits the purge manifold to fill an
external purge reservoir.
Unloading Phase
When the air brake system pressure reaches the cut-
out setting of the air governor, the output of the air
governor passes to the air compressor unloader to stop
the air compression and passes to the purge valve of
each dryer via the control manifold. The purge valve
opens to atmosphere and depressurizes the air dryer.
The turbo protection valve (TPV) will close once the
inlet air is below 35 psi. The regeneration cycle will
begin. The outlet check valve will close, preventing the
back flow from the system.
Regeneration Phase
During the unloading phase, a regeneration cycle
(desorption) will remove the contaminants. Since the
cartridge is depressurized, air from the external purge
reservoir will flow back to the dryer, pass through the
purge manifold to the desiccants, collect the captured
contaminants and drain to the atmosphere via the
purge valve and silencing unit. The regeneration
cycle or purge cycle will continue until the purge
reservoir air pressure depletes to 0 psi. This will last
approximately 30 seconds. The purge valve will remain
open until the brake system decreases to the air
governor cut-in setting.
Cut-In
As air is consumed by the brake system, the air pressure
decreases until the air governor cut-in pressure is
achieved. At cut-in pressure the air governor closes,
its output air exhausts to atmosphere, the unloader
valves of the dryer close and the compressor begins to
compress air. A new charging phase begins.
Drying (cont’d)
Page 5
Charging Phase
Unloading Phase
Control Port
Purge Port
Outlet
Port
Inlet
Port
[1.4]
[1.3]
[2.3]
[1]
[1.2]
[1.1]
[1.5]
[2.2]
Purge
Port
