Pneumatech PH Series - Sequence of Operation

Pub. No. OM-A-10H REV. 7 — June 2006
9
OPTIONAL CONTROLS AND ALARMS
1. DEWPOINT DEMAND SEQUENCE CONTROL:
The dewpoint demand mode function will be
operational if there are 5 minutes before the end of
the drying cycle, and the dewpoint is below the
preset level. When in the dewpoint demand mode
all of the timing functions stop. The yellow LED on the
remote I/O module will light up and “DEMAND
CYCLE” will be indicated on the LCD. When the
dewpoint reaches the preset dewpoint level, the
towers will switch and the normal mode cycle will
commence. The dewpoint demand mode function
will be disabled if the dewpoint is above the preset
level.
2. HIGH HUMIDITY: The high humidity alarm
function is indicated by a red LED on the remote I/O
module. The high humidity relay will energize for
remote annunciation. All the normal functions will be
maintained.
3. FAIL TO SHIFT: The fail to shift inhibit will be
energized if the inhibit switch remains closed for 30
minutes beyond the normal cycle. Fail to shift will be
indicated by the red LED on the remote I/O module
and the fail to shift relay will be energized for remote
annunciation. The fail to shift inhibit is an indication
of a malfunction of the tower switching valves or
purge exhaust valves.
Sequence of Operation
The sequence of operation of the Heatless Regenerative
Air Dryer can be readily followed by referring to the flow
schematic on Page 11. The operation is fully automatic,
controlled by a solid-state timer, pneumatic timer or PLC
controller.
During initial start-up with the power switch in the OFF
position, and the towers pressurized with air, both inlet
valves stay in the OPEN position (standard with models
PH-300 and larger) and the purge valves stay in the
CLOSED position. This type of fail safe valve operation
allows the air to dry through both the towers, without any
purge in the event of loss of power to dryer. This will give
you extended drying time until desiccant chambers are
saturated.
The desiccant is designed to handle air saturated with
water vapor only. Any liquids or slugs of water tend to
decrease the efficiency of the desiccant and retard the
regeneration process to provide the designed dewpoint.
With the power switch in the ON position at
time equal to 0.0 minutes, the left tower air inlet
valve is open to allow the air to pass through the left
tower. The right tower inlet valve is closed. The saturated
compressed air/gas passes through the desiccant in the
left tower where the desiccant adsorbs the moisture, and
the dry air at a pressure dewpoint of -40°F or less exits
through the left outlet check valve and goes out into the
plant air system through the afterfilter.
At time equal to 0.1 minutes, the right tower purge
valve opens to fully depressurize the desiccant bed, and
commence the regeneration cycle.
NOTE: As soon as the purge valve has opened, adjust the
purge adjustment valve to the recommended purge control
setting. This adjustment should only be required once, and
then the locking mechanism should be locked in place.
A portion of dry outlet air is diverted and passed through
a series of regulating and flow control valves to meter the
measured quantity of air for regeneration. The pressure of
this purge air is regulated by the purge adjustment valve
at the specified purge pressure on the meter gauge. This
dry purge air at low pressure passes through the right
purge check valve and is introduced into the right tower.
The purge air picks up the moisture from the desiccant and
exhausts into the atmosphere through the purge valve and
purge muffler.
At time equal to 4.3 minutes, the purge valve closes.
The purge air entering the tower starts to repressurize the
chamber.
At time equal to 4.4 minutes, the repressurizing
valve is energized to open and repressurize the tower to
line pressure (standard with models PH-400 and larger).
At time equal to 4.9 minutes, the repressurizing
valve is de-energized to close.
At time equal to 5 minutes, the right tower inlet valve
opens, and the left tower inlet valve closes, so the flow of
wet air/gas is switched from left chamber to the right
chamber.
Frost or ice development on the regenerat-
ing tower is a sign of low inlet air temper-
atures. Due to the expansion of the purge
air, cooling may develop icing in the desic-
cant. Temperature of the purge air is
determined by the temperature of the air
during the drying cycle and should be
greater than +70°F (>+70°F). Adsorption
of moisture by the desiccant results in the
release of heat of adsorption, which is
retained in the bed to assist in desiccant
regeneration.