Van Air Systems HL-200 - HL2000 - Manual (Page 13)

PAGE 13
PRINCIPLE OF OPERATION SECTION 6
Pneumatic schematic shown above for units equipped with PLC controls
featuring EMCON II. Pneumatic schematic shown above for units equipped with CYCLE
SAVER.
FIGURE 6B PNEUMATIC SCHEMATIC for DRYERS WITH CYCLE SAVER OR EMCON II
6.2 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.
6.1-3 DRYING AND REGENERATION STAGE
During the drying stage, one tower is pressurized with process air.
This tower is in the drying stage. The process air passes through the
desiccant bed, which adsorbs moisture from the air. The
regeneration stage of one tower occurs at the same time as the drying
stage in the opposite 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.
6.1-2 CHANGEOVER/DEPRESSURIZATION STAGE
Tower changeover occurs after the previous regenerating tower is
pressurized. The controller signals the inlet transfer valve to switch.
The tower that was on line and drying the process air will begin to
depressurize.
Pressure in the regenerating tower will approach full line pressure. The
pilot valves SV1 or SV2 will energize. Pilot air will be supplied to one
side of the inlet transfer valve. The inlet transfer valve shuttle will move
to the side that has pilot pressure.
When the inlet transfer valve changes position, the position indicator
will move and actuate the other pneumatic limit switch. This will open
the purge valve on the tower that was drying the process air, causing
the tower to depressurize.
CYCLE SAVER and EMCON II models:
If the dryer is being operated in the AUTO MODE, tower changeover
is delayed until the dew point controller(s) signal the circuit board or
PLC. The dryer will automatically change towers after 4 hours of
ENERGY SAVINGS.
The pilot valves SV1 or SV2 are either energized or de-energized
depending on which tower is on stream (drying). If SV2 is energized, the
LEFT tower is drying and if SV1 is energized, the RIGHT tower is drying.