Aircel AHLD E-Series Installation And Operation Manual page 28

Aircel AHLD E-Series - Models 70 - 750
Aircel Programmable Controller
Step 1: Vessel 2 Depressurizing (0-5 secs)
Vessel 2 (T2) purge exhaust pilot solenoid valve is energized which
supplies control air to the purge exhaust valve (V4) which opens
slowly, depressurizing vessel 2 (T2). Simultaneously the inlet and
outlet APV (Automatic Piston Valve V1 & V2) shift positions
directing the inlet air to vessel 1 (T1) to be drying the air. The air
flows up through the desiccant bed and exits to the outlet APV
valve (V2) to the outlet particulate filter then to the customer
dry process air system.
Step 2: Vessel 2 Regenerating (6-240 secs)
Step 2 is a continuation of step 1 except vessel 2 (T2) will be
regenerating, vessel 2 (T2) purge exhaust valve (V4) is still open,
vessel 1 (T1) is drying the inlet air. A small portion of dry outlet air
from vessel 1 (T1) (15% average based on standard design capacity
of 100 psig, 100°F inlet air, 100°F ambient air and PDP of -40°F) is
taken through a small orifice in the outlet APV valve (V2) and used to regenerate the desiccant bed
in vessel 2 (T2) until 240 seconds has been reached. The screen also shows the relative humidity
reading as well as the (optional) dew point when applicable. The timer on this step counts to 240
seconds (4-minutes). There is a warning sign that will flash in the upper right hand portion of the
screen for any alarm. There is also a red LED alarm light that will flash on the PLC display for any
alarm. The user must scroll to the alarm screen to view the alarms (press the left arrow once from
the main screen to view the alarm screen).
Step 3: Vessel 2 Repressurizing (241-300 secs)
Vessel 2 (T2) purge exhaust pilot solenoid valve will de-energize
causing vessel 2 (T2) purge exhaust valve (V4) to close, this
allows vessel 2 (T2) to repressurize to line pressure, since air
continues flowing though the small orifice in the outlet APV
valve (V2) pressurizing vessel 2 (T2).
Step 4: Extended Drying Vessel 1
A few seconds before the end of repressurization the AHLD
E-SERIES Controller's integrated Energy Management Purge
Reduction System looks at the moisture sensor, if the moisture
load is low enough, vessel 1 (T1) will continue to dry for an
extended drying period until the moisture load has reached a
set high level, the controller will then advance to step 5 and the
vessels will switch. This feature reduces the overall purge consumption saving energy and money.
The extended drying cycle timer will count to 30 minutes unless the EMS relative humidity sensor
is higher than the set point. After 30 minutes, the unit will switch and continue normal operation
until the next extended savings step. At the start of each extended savings step the PLC checks for
faults, EMS relative humidity sensor value and high outlet dewpoint setting (optional) to ensure if
the dryer needs to continue drying and the dryer will go into extended drying. If the dryer needs to
continue to the next step to regenerate, the extended savings step 4 will be skipped.
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