Pg. -6-
AIRTEK 4087 WALDEN AVENUE, LANCASTER, NY 14086 Tel: (716) 685-4040 Fax: (716) 685-1010
IMPORTANT: Just as the dryer is designed to remove only
water vapor, the moisture being purged from the saturated
regenerating bed will also be exhausted in VAPOR form. At
no time should you see liquid water being ejected from the
dryer! The only water you might see is a small amount of
condensate forming at the exhaust due to the Joule-
Thomson cooling effect created by the depressing air.
Prior to switching a freshly regenerated bed on-line to
become the drying bed, it must be slowly pressurized from
atmospheric pressure to line pressure. This step is called
repressurization. Repressurization prevents bed fluidization
(lifting) and associated dusting.
Following repressurization, the beds switch functions with
the fresh bed now drying and the saturated bed being
regenerated.
Note that one bed is always on-line drying. Also note that
purge air is always being consumed except during
repressurization.
This cycle will continue automatically unless the dryer is
shut down, operated in the CycleLoc mode, or equipped
with a demand cycle controller (PowerLoc).
6.
A.
SEQUENCE OF OPERATION:
The above sequence is controlled by a Solid State Timing
and Relay circuit (Sequence Annunciator) which in turn
controls a 4-way solenoid valve (S1: inlet switching valve)
and a 2-way NC solenoid valve (S2: purge stop/exhaust
valve).
STEP 1: LEFT DRYING, RIGHT REGENERATING
The inlet switching valve (S1) is in its default non-
energized position, directing all the wet inlet air to the left
tower. The air is dried as it passes through he desiccant bed
at system pressure, typically 100 PSIG. As the air exits the
tower fully dried, the bulk of the air is directed downstream
via the outlet check valves.
Approximately 15% of the dried air is directed to the right
tower via the purge controls. This purge or regeneration air
is reduced to atmospheric pressure (0 PSIG) by the time it
enters the right tower. This super dry, low pressure purge
air flows down through the desiccant bed, stripping accu-
mulated moisture. It is directed via the inlet-switching valve
through the purge stop solenoid (S2), which is energized
and open. The moisture laden purge air exists to atmo-
sphere through the exhaust muffler.
On TW10 & TW15 models the purge controls consist solely
of a bi-directional flow needle valve connecting the outlet of
each tower. The needle valve is adjusted to obtain the
required purge flow.
On TW25, TW40, & TW55 models the purge control
system consists of a purge filter, needle valve, pressure
gauge, orifice, and two purge check valves. The needle
valve is adjusted to obtain the specified purge pressure,
which equates to the proper purge flow.
STEP 2: LEFT DRYING, RIGHT REPRESSURIZING
The purge stop solenoid (S2) is de-energized and returns to
its normally closed position. This prevents the purge air
from exhausting to atmosphere, resulting in the right tower
and the purge system being pressurized to system pres-
sure.
STEP 3: LEFT REGENERATING, RIGHT DRYING
Simultaneously the inlet switching valve (S1) and the purge
stop solenoid (S2) are energized. Energizing S1 shifts the
inlet switching valve to direct the inlet flow to the right tower
where it is dried as it passes over the freshly regenerated
desiccant bed. S2 opens as it is energized “blowing down”
the left tower. Purge air now flows over the left tower,
stripping the moisture from the desiccant that was adsorbed
when the left tower was on-line drying.
STEP 4: LEFT REPRESSURIZING, RIGHT DRYING:
The purge stop solenoid (S2) is de-energized and returns to
its normally closed position. This prevents the purge air
from exhausting to atmosphere, resulting in the left tower
and the purge system being pressurized to system pres-
sure.
NOTE: The Purge Gauge (middle gauge TW25, 40, 55)
should read purge pressure, except during repressurization.
Purge flow is calculated by the Purge Formula in this
manual and checking the proper chart. Purge pressure for
standard inlet design conditions is listed on the specifica-
tions page. For other than standard or design conditions
use the purge formula and charts for purge flow/pressure
calculation, or consult the factory.
6.
B.
OPERATIONAL NOTES:
A desiccant dryer should never be suddenly pressurized or
depressurized. This will cause fluidizing and dusting.
After start-up, some dusting may occur. This will diminish
with time. Some dusting may occur with normal operation.
The Exhaust Muffler should be cleaned regularly and an
Afterfilter should be used.
Flow direction is Upflow Drying – Downflow Purge.
Switching Failure alarm is optional and the Dryer must be
operating over 70 PSI for proper function of the alarm.
During a power loss situation, the exhaust valve will close
preventing purge air loss and allowing the system to remain
pressurized. Inlet air is able to flow through one tower and
downstream.
The standard AIRTEK dryer has a design pressure of 150
PSIG. In good practice the normal working pressure should
be below 150 PSIG to prevent the safety valve from blowing
off.
