Compressed air enters the dryer and is directed to a tower by the inlet valves. It then proceeds up through the tower, gives up its moisture, and then exits through the outlet check valve. A portion of the dry air called â€œpurgeâ€ is metered and expanded to atmospheric pressure through an orifice assembly. The purge air enters a circulation chamber where it is heated and its moisture holding capacity is increased. The purge air also transfers heat to the desiccant bed in addition to the internal heating rods as it enters the tower through the purge check valve. As the desiccant temperature increases it releases the previously adsorbed moisture. The moisture is picked up by the heated purge air and exits to atmosphere through the purge exhaust valve and muffler. The drying and regenerating cycles occur simultaneously for 4 hours. The regeneration cycle begins with 2.5 hours of heating and 1.4 hours of cooling, then the tower repressurizes before the inlet valves invert and the process starts again.