Pub. No. OM-A-10E — April 2004
15
Dry Air Sweep
In order to maintain constant dewpoint, the Pneumatech
dryer uses a dry air sweep during the cool down cycle.
At time equal to 3 hr. 50 minutes,
the purge valve
will close, and the flow or purge air repressurizes the right
tower and prepares it for switch-over.
At time equal to 4 hr.,
the right tower inlet valve
opens, and the left tower inlet valve closes, so the flow of
wet air/gas is switched from left chamber to the right
chamber. The above sequence is then repeated on the
opposite towers.
Shutdown Procedure
Externally Heated dryers are typically installed in 24 Hr.
operations. The dryers operate on a standard time cycle
of 8 hours, 4 hours drying and 4 hours regenerating. This
cycle should not be interrupted (except for servicing). If the
dryer needs to be shut down for a certain shift or
weekend; the dryer should be turned off at the end of the
4 hour regenerating cycle, and with both towers at line
pressure. If servicing is required advance the time
sequence so the purge valves close and both towers
pressurize. At this time, the dryer can be turned off.
1.
If the compressed air system has been
piped with a bypass around the dryer, then
the following should be completed:
a. Open the bypass valve to allow process flow to
continue downstream, then close the dryer outlet
isolation valve.
b. Turn the dryer ON/OFF switch to the OFF
position.
c. Close the dryer inlet isolation valve on the dryer
bypass piping. At this time the dryer is isolated
and can be depressurized for servicing.
2.
If the compressed air system has not been
piped with a bypass, then the following
should be completed:
a. Turn the power switch to the OFF position.
b. The tower switching valves are normally open
valves; therefore, with the power off, the inlet
valves to the towers will be open, and the purge
valves will close. This will give you extended
drying time until desiccant chambers are
saturated.
