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6.0 Operation
6.1 Controls
A solid-state controller controls valve and heater opera-
tion, monitors all critical operating conditions, and indi-
cates operating status on a 2-line LCD display operator
interface. The controller receives input data from pres-
sure switches, temperature sensors and the operator
interface. The operator interface displays information
about the dryer operating status and is used to change
the dryer operating mode.
6.2 Operating Modes
6.2.1 Automatic and Manual Advance
The drying and regeneration cycles are divided into
discrete steps. The operator selects either one of the
automatic advance modes (Energy Management, Dew
Point Control, or Fixed Cycle) or manual advance mode
(Test Cycle) through the operator interface.
Selecting any of the automatic advance modes enables
a timer in the controller to advance the program step-by-
step according to the programmed schedule.
Setting up the controller for manual advance disables the
timer and the operator can advance the program one step
at a time. This mode is used for diagnostic purposes.
6.2.2 Fixed and Demand Cycle Operation
In Fixed Cycle operation, each tower is on-line (drying) for
a fixed time period regardless of the operating conditions.
In demand cycle operation, a tower remains on-line until
the desiccant bed has been fully utilized. For lower than
designed moisture loads, this results in longer drying
cycles, longer time between regenerations and, therefore
lower energy consumption. Demand cycle operation is
an optional feature. The operator interface is used to
select the fixed or demand cycle.
6.3 Operating Sequence Description
6.3.1 Fixed Cycle (Standard)
1. Left Tower Drying – Right Tower Regenerating
(See Figure 4)
At the start of the Left Tower Drying cycle, Left Inlet
Valve
(A)
opens, Right Inlet Valve
(B)
closes to iso-
late the two towers. Wet, compressed air flows up
through the left tower where it is dried. The dry air
exits the dryer through the Left Outlet Check Valve.
Next, the Purge Supply Valve
(E)
is closed and the
Right Tower Depressurization Valve
(C)
is opened.
The right tower is slowly depressurized through an
exhaust muffler.
Next, Purge Supply Valve
(E)
and Right Tower Purge
Exhaust Valve
(D)
are opened, and the Heater is
turned on. The heated purge air flows through the
Right Purge Check Valve, down through the right
tower, and exits through the Right Tower Purge Ex-
haust Valve
(D)
. The Heater is de-energized when
the Right Chamber temperature sensor detects
desiccant bed heating is complete. Purge flow will
continue to cool the right tower desiccant bed while
“recovered” bed heat strips additional moisture from
the desiccant.
Finally, the Right Tower Depressurization Valve
(C)
and the Right Tower Purge Exhaust Valve
(D)
are
closed. The right tower slowly repressurizes to full
line pressure and is ready to go back on-line.
2. Right Tower Drying – Left Tower Regenerating
At the start of the Right Tower Drying cycle, Right
Inlet Valve
(B)
opens, Left Inlet Valve
(A)
closes to
isolate the two towers. Wet, compressed air flows
up through the right tower where it is dried. The dry
air exits the dryer through the Right Outlet Check
Valve.
Next, the Purge Supply Valve
(E)
is closed and the
Left Tower Depressurization Valve
(C)
is opened.
The left tower is slowly depressurized through an
exhaust muffler.
Next, Purge Supply Valve
(E)
and Left Tower Purge
Exhaust Valve
(D)
are opened, and the Heater is
turned on. The heated purge air flows through the
Left Purge Check Valve, down through the left tower,
and exits through the Left Tower Purge Exhaust
Valve
(D)
. The Heater is de-energized when the Left
Chamber temperature sensor detects desiccant bed
heating is complete. Purge flow will continue to cool
the left tower desiccant bed while “recovered” bed
heat strips additional moisture from the desiccant.
Finally, the Left Tower Depressurization Valve
(C)
and the Left Tower Purge Exhaust Valve
(D)
are
closed. The left tower slowly repressurizes to full
line pressure and is ready to go back on-line.
6.3.2 Demand Cycle (optional)
Operation of the demand cycle is identical to the fixed
cycle except the cycle is extended until the desiccant bed
in the on-line tower has been fully utilized. The off-line
tower is regenerated and remains in a stand-by mode
after being repressurized.
1. Left Tower Drying – Right Tower Regenerating
(See Figure 5)
At the start of the Left Tower Drying cycle, Left Inlet
Valve
(A)
opens, Right Inlet Valve
(B)
closes to iso-
late the two towers. Wet, compressed air flows up
through the left tower where it is dried. The dry air
exits the dryer through the Left Outlet Check Valve.
Next, the Purge Supply Valve
(E)
is closed and the
Right Tower Depressurization Valve
(C)
is opened.
The right tower is slowly depressurized through an
exhaust muffler.
