Van Air Systems HL-200 - HL2000 - Manual (Page 23)

PAGE 23
MAINTENANCE & TROUBLESHOOTING SECTION 11
11.5-9 CALIBRATING THE HUMISTAT
CYCLE SAVER AND EMCON II MODELS ONLY:
The set point for the humistat is calibrated by a set plug.
Unplug the cable from the sample cell. Plug the set plug into the end
of the humistat cable.
For dryers equipped with the Cycle Saver Control Box turn the
humistat set point adjustment located on the printed circuit board until
the Humidity Indication LED is lit. This will calibrate the dew point
meter. Reference Figure 11E.
For dryers equipped with the Emcon II Control Box turn the potentiom-
eter on the humistat board until you see the LED input light turn on.
This will calibrate the dew point meter. Reference Figure 11D.
If you get no response from the humistat set point adjustment or the
potentiometer with the set plug in, first check the cable connection. If
the cable and set plug are good, replace the printed circut board
(Cycle Saver) or the humistat board (Emcon II).
The sensor can be tested by removing it from the sample cell and
plugging it into the cable. With the sensor in the ambient air, the
humistat should turn on the corresponding LED. Place the sensor
back into the sample cell and allow compressed air to pass over it.
The LED for the humistat should turn off in several minutes if the air is
dry. If you get no response from the LED, replace the dew point
sensor.
CAUTION
NEVER USE AN OHMMETER TO CHECK THE SENSOR. THE
USE OF AN OHMMETER OR ANY ELECTRICAL TESTING
DEVICE WILL CAUSE DAMAGE TO THE SENSOR.
FIGURE 11D HUMISTAT DETAIL FOR EMCON II
NOTE
DRYERS EQUIPPED WITH EMCON II HAVE TWO HUMISTATS AND SAMPLE CELLS.
FIGURE 11F SAMPLE LINE DETAIL
11.5-10 SAMPLE LINE MAINTENANCE
WARNING
DO NOT ATTEMPT TO REMOVE ANY FITTINGS UNTIL ALL AIR
PRESSURE IS OUT OF THE VESSEL. CHECK ALL TOWER
PRESSURE GAUGES, MAKING SURE THAT THEY ARE AT
0 PSIG AND THE DRYER IS ISOLATED.
Take dryer off stream following the SHUTDOWN PROCEDURES IN
SECTION 10.
Disconnect the sample line at the tee fitting.
Unthread the sample line from the tower at the bushing. Carefully pull
the sample line assembly from the tower. Some desiccant will drain
from the tower. Plug the coupling to prevent more desiccant from
draining.
Unthread the sample line filter from the tubing. Clean or replace the
filter. The filter is made of sintered bronze material. To clean it, use
pressurized, clean air.
FIGURE 11E HUMISTAT DETAIL FOR CYCLE SAVER
11.5-7 CHECKING THE PURGE EXHAUST VALVES
The purge exhaust valves are normally closed. They can be checked
by removing the pilot air lines to them. The valves should be closed.
Using an air nozzle and clean air, pressurize the purge exhaust
valves. The valves should open when pressurized. If valve does not
open and close, it should be rebuilt or replaced. See Section 12.11
through 12.15 for valve breakdown and parts listing.
11.5-8 CHECKING THE OUTLET CHECK VALVES
This dryer uses two check valves for outlet air control. If either of the
outlet valves fails, one of the following will occur:
• A large amount of air will purge from one tower
• The outlet air flow will be blocked
If either happens, the faulty check valve must be replaced.
Re-install the filter. Carefully push the assembly back into the tower
and tighten the bushing into the coupling. DO NOT FORCE THE
ASSEMBLY. An application of pipe sealant to the bushing threads
may be necessary. Reconnect the line at the tee fitting.