Van Air Systems FR-1200 - Manual (Page 7)

PAGE 7
OPERATION SECTION 6
FIGURE 6A PNEUMATIC SCHEMATIC
6.2-1 REPRESSURIZATION STAGE
Repessurization occurs in the off-stream (regenerating) tower.
Repessurization must occur before tower changover to reduce shock
to the desiccant and the possibility of downstream pressure spikes.
Pilot valve SV1 or SV2 de-energizes causing the purge valve on the
off-stream (regenerated) tower to close. The purge air, which was
vented to atomosphere earlier in the cycle, is now used to
repressurize the off-stream tower.
6.2-2 CHANGEOVER/DEPRESSURIZATION STAGE
Tower changeover occurs after the off-stream (regenerated) tower is
pressurized. The SmartRelay signals SV1 or SV2 to open causing pilot
air to be supplied to the opposite side of the inlet transfer valve and
cause exhaust valve to open on regenerative tower. The inlet transfer
valve shuttle will move to the side that has pilot pressure placing the
regenerated tower on-stream. The tower that was on line and drying
the process air is now off-stream.
When the inlet transfer valve changes position, the position indicator
will move.
6.2-3 DRYING AND REGENERATION STAGE
One tower is on-stream (pressurized) drying process air. The process air
passes through the desiccant bed, which adsorbs moisture from the air.
The regeneration stage of the off-stream tower occurs at the same time
as the drying stage in the on-stream tower. During the regeneration
stage, a percentage of dry air is directed through the desiccant bed of
the offstream tower. The purge air is vented through the purge valve
to the atmosphere.
If pilot valve SV2 is energized, the LEFT tower is drying and if pilot
valve SV1 is energized, the RIGHT tower is drying.
6.3 MOISTURE INDICATOR
The moisture indicator is in the center of the panel. The moisture
indicator is a clear plastic tube filled with moisture sensing crystals. A
sample of outlet air is directed through the indicator.
The crystals will change colors from PINK (indicating wet air) to
BLUE (indicating dry air) as the dew point of the air changes from
+20 O F to -40 O F.