INSTALLATION, START-UP & MAINTENANCE MANUAL
MODEL NO.: SD-820 / SD-1710
REV 1 – AUGUST 03,.2001
Page 13
SECTION 3
3.2.1 Description of the operation
SD HEATLESS TYPE DRYER (SD-820 – SD-1710)
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SD dryer has a NEMA cycle time of 10 minutes (STD) or 4 minutes
(LDP) depending upon the air quality desired. In a 10 minute cycle, 5 minutes is
dedicated to drying for each chamber (5 minutes half cycle). In a 4 minutes cycle,
the half cycle is then 2 minutes.
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Through the inlet switching valve wet air enters either desiccant chamber at the inlet
(bottom) and is dried as it flows upward through the desiccant bed. Dry air exits
the dryer through the outlet check valve.
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At the outlet of each chamber, a portion of the dry air (purge air) is diverted to the
regenerating chamber. The dry air, at near atmospheric pressure, will remove
previously adsorbed moisture as it flows downward through the desiccant bed
exiting through the purge exhaust muffler.
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The purge air is controlled by a purge adjusting valve and purge orifices located
in the purge line. Purge pressure can be monitored on the purge pressure gauge.
Refer to section on purge adjustment for instructions on setting the purge rate.
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Near the end of each half cycle, the chamber being regenerated will be re-
pressurized. For this to occur, the exhaust valve of the chamber being regenerated
closes while purge air continues to flow. Re-pressurizing the regenerated chamber
to operating pressure before placing it into service minimizes fluidization of the
desiccant and helps prevent desiccant abrasion which causes desiccant dust to
prematurely block pilot and after-filter elements.
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Dryers operating at pressures greater than 120-125 PSIG or in an accelerated
NEMA cycle could be fitted with a re-pressurizing valve. This valve assists the
regenerated chamber to reach dryer operating pressure before chamber
switchover.
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Chamber switchover takes place when both towers are fully pressurized to
minimize desiccant movement.
When switchover is complete, the regenerated tower will be placed into service and the
exhausted tower will begin a depressurization/regeneration cycle.
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