8
6.7.1 TIMING CYCLE FOR -40°F DEW POINT DRYERS
The standard SST timing cycle switches the Inlet Flow Valve position every five
minutes which alternates the drying tower. At the same time as a tower Inlet Valve
opens, the appropriate tower Purge Valve opens to depressurize the regenerating
tower. Tower regeneration occurs for 4 minutes and 30 seconds, at which time the
Purge Valve closes to initiate repressurization.
6.7.2 TIMING CYCLE FOR AND -80°F and -100°F DEW POINT DRYERS
The SST timing cycle switches the Inlet Flow Valve position every 2 minutes which
alternates the drying tower. At the same time as a tower Inlet Valve opens, the ap-
propriate tower Purge Valve opens to depressurize the regenerating tower. Tower
regeneration occurs for 1 minute and 50 seconds, at which time the Purge Valve
closes to initiate repressurization. The Repressurization Valve opens to assist tower
repressurization for the last 10 seconds prior to Inlet Flow Valve switching.
6.8 MOISTURE INDICATOR (Optional)
The moisture indicator senses a sample of the dried air which is taken from the
dryer outlet. The indicator provides an indication of dew point deterioration at the
outlet of the dryer. Under normal operating conditions, the indicator is blue. In the
event of a dryer malfunction or prolonged dryer shut down, it will turn gray in the
presence of moisture.
6.9 FAILURE TO SHIFT ALARM (Optional)
The Failure to Shift Alarm provides an indication of switching failure in one of the
dryer switching valves. The Fail to Shift Alarm uses a pressure switch to monitor
the pressure in each tower. The SST anticipates the appropriate open and closed
switch position based on its timing sequence. If either switch is in an incorrect
position, the Failure to Shift Alarm light will illuminate.
6.10 HIGH HUMIDITY ALARM (Optional)
The purpose of the High Humidity Alarm is to provide the operator an indication if
the equipment fails to supply air at its designed dew point. This is accomplished by
passing a sample of dried air from the control line across a sensing element. If the
sensing element is exposed to air with dew point of -10°F or higher (for -40°F
dryers), the sensor sends a signal to the humidistat. Power is then supplied to the
red alarm light on the enclosure. This light will remain illuminated until the problem
is corrected and the sensing element has dried out.
6.11 MOISTURE LOAD CONTROL (PURGE SAVER) (Optional)
The Moisture Load Control (MLC) feature is designed to minimize the loss of purge
air during low flow or low water loading conditions. On -40 °F units, a sensor
samples the moisture content from the online tower and provides a signal to a
humidistat. As long as the humidistat finds that the air in each tower is dry, it will not
allow the timer to open the purge valves. Once the moisture content in either tower
is found to reach the threshold point, the humidistat sends a signal to the timer and
initiates the regeneration cycle. For -80°F and -100°F dryers, a digital dew point
monitor is used in place of the humidistat. For dryers equipped with the digital dew
point monitor, refer to the Dew Point Monitor Addendum.
To Next Page
Loading...
