Van Air Systems HL-200 - HL2000 - Manual (Page 12)

PAGE 12
PRINCIPLE OF OPERATION SECTION 6
6.1 PRINCIPLE OF OPERATION
HL Series Heatless Regenerative Air Dryers utilize the pressure swing
principle of operation. The desiccant bed in one tower dries the air stream
while the desiccant bed in the other tower is regenerated.
A purge of dry air is used for tower regeneration. It is taken from the outlet
of the dryer.
The dryer is equipped with a purge metering valve to allow the correct
amount of dry air to flow into the regenerating tower. The heat created
during adsorption of moisture in the drying tower is retained in the
desiccant bed and increases the moisture removal capacity of the purge
air.
The timing cycle of the dryer is controlled by two 3-way pilot valves.
A patented shuttle valve system is used to repressurize, changeover, and
depressurize the towers. The inlet transfer valve is controlled by the pilot
valves. The movement of the shuttle in the inlet transfer valve mechanically
actuates the external pneumatic limit switches, which open the purge
valves and depressurize the tower. The shuttle cannot shift until the tower
pressures are nearly equal. The dryer cannot depressurize until the
shuttle has fully seated and the one of the limit switches is engaged.
FIGURE 6A PNEUMATIC SCHEMATIC for DRYERS WITH STANDARD CONTROL
The dryer operation consists of four stages; REPRESSURIZATION,
CHANGEOVER/DEPRESSURIZATION, DRYING and
REGENERATION.
6.1-1 REPRESSURIZATION STAGE
Repessurization occurs in the regenerating tower. Repessurization
must occur before tower changover. This reduces shock to the
desiccant and the possibility of downstream pressure spikes.
The purge valve is closed and the purge air, which was vented to
atomosphere earlier in the cycle, is now used to repressurize the
regenerated tower.
The pilot valves SV1 & SV2 de-energize causing the purge valve on the
regenerating tower to close. The purge air, which was vented to
atmosphere earlier in the cycle, is now used to repressurize the
regenerated tower.
To achieve maximum performance from this dryer, it should be
operated continuously. Operating this dryer for single shift periods may
result in varied outlet dew point performance.