7.1 OPERATION
7.1 PURGE METERING VALVE SETTINGS
● The desiccant dryer uses the adsorption
properties of the desiccant material to
retain the moisture and prevent it from
flowing downstream.
● Cyclic regeneration of the towers
removes the moisture from the
desiccant bed and prepares it for drying
for the next cycle.
● The twin desiccant towers are identical
and are filled with desiccant (Activated
Alumina / Molecular sieve / Silica Gel
etc.). The cycle time is set during the
manufacturing phase (as well as the
regeneration nozzle) according to the
Pressure Dew point (PDP)
- 15 minutes for -4°F-20°C
- 10 minutes for -40°F-40°C
- 6 minutes for -94°F-70°C
7.2 CYCLE DESCRIPTION
PLEASE NOTE: When the dryer is turned ON, both the purge solenoid valves (PVA and PVB) are
closed for approximately 120 seconds. This will pressurize both the towers to line pressure before
the drying process starts and will ensure the proper functioning of the dryer.
Stage 1:
● The right tower inlet valve is opened and it starts to dry the saturated compressed air. The
left purge exhaust valve is opened, depressurizing the left tower.
● As the wet compressed air flows through the right tower, the desiccant bed adsorbs the
H2O molecules and the dry compressed air exits from the right tower and flows
downstream. A small portion of this dry air (termed “Purge Air”) is redirected towards the left
tower (flow controlled by the Repressurization Valve). This compressed purge air expands
to near atmospheric pressure in the left tower, thereby increasing its moisture absorbing
capacity. As this expanded dry air flows through the left tower, it absorbs the moisture from
the desiccant bed and exits the left tower into the atmosphere through the purge solenoid
valve and the purge exhaust muffler. At the end of this stage, the left tower desiccant bed
will have completely regenerated (i.e. completely free of H2O molecules) and is ready for
adsorbing moisture from the incoming wet compressed air.
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