The PCR dryer employs Pressure Swing Adsorption (PSA) Technology to remove water vapor from ordinary compressed air . The inlet (lower) shuttle valve directs the wet air into one of the two desiccant chambers where nearly all of the water vapor is removed. The ultra-dry air leaving the desiccant chamber passes through the outlet (upper) shuttle valv e to the application. Both shuttle valves contain a wafer-like disk, which “shuttles “ back and forth in the valve body based on the pressure differential created by the position of the two-way solenoid valves. A precision orifice in the outlet shuttle disk allows a portion of the dry air leaving the desiccant chamber to be redirected back through the off-line tower, purging it of its accumulated moisture. The purge stream exits the unit through the open solenoid valve directly below the chamber being regenerated. A solid-state timer controls the process by opening and closing the solenoid valves.