Process Technology Lufran LUF Series Manual page 51

Maintenance Procedures (Continued):
M5: Humidistat Purge Exhaust, Humidistat Switch
There is one humidistat device installed in a heater with 1 or 2 heating columns. Heaters with 3 or 4
heating columns will have two humudistat devices installed. These items are responsible for monitoring
the purge gas exhaust for the presence of moisture. These humidistat devices must be inspected every 6
months.
Procedure M5-1: Humidistat Inspection Procedure:
The inspection part of this procedure must
be repeated for each humidistat device.
Inspect the purge gas exhaust tubing:
1) If the unit is in LOCAL mode, press the
HEATER ON/OFF button to the OFF
position. If the unit is in REMOTE mode
disable the heater from the customer
supplied remote controller. This will also
prevent the heaters from energizing.
2) Open the rear cabinet door.
3) Locate the humidistat device(s) mounted
on each heating column.
4) Locate the ¼-inch tubing connected
between the top of each heating column
and the humidistat. The outlet of the
purge column is labeled EXHAUST.
5) Inspect the tubing for the presence of moisture.
If no moisture is present, then proceed to step 6.
If moisture is present it may be caused by the following:
•
Startup following extended shutdown: If the heater was shut down for an extended period but
was not drained properly, moisture will enter the purge tubing. This heater should be purged
with gas for 12 hours before startup is attempted.
•
Failed heating column: A hole in the heating element or a leaking purge gas fitting will allow
water into the exhaust tube. Contact PROCESS TECHNOLOGY for possible replacement
heating column.
Inspect the adjustment of the humidistat:
6) Using a screwdriver remove the four cover screws and remove the cover from each humidistat
device.
7) Turn the adjustment knob on the humidistat clockwise. The heater will enter alarm mode and the
stack light (if provided) will illuminate the red light.
8) To re-adjust the humidistat, turn knob fully counter-clockwise, then 1/8 turn clockwise.
9) Press the ERROR RESET button on the control display to clear the fault condition.
10) Repeat steps 7-9 for the humidistat on each humidistat device.
If the unit fails to fault when the adjustment knob is turned fully clockwise, or the unit fails to reset the
alarm condition then the humidistat should be replaced. Proceed to the humidistat replacement
procedure on the next page.
11) Replace the black plastic enclosure cover on each of the humidistat devices.
12) Close the rear cabinet door.
M-43-25
Revision - Date 03-01-04-18
Figure 37: Purge Gas Control
50
LUF-Series Lufran Manual
Standard outlet, Standard Interface