Atlas copco desiccant air dryers are used when the compressed air application requires a pressure dew point below 0°. The regenerative atlas copco desiccant air dryers consist of two pressure vessels. Both vessels are filled with desiccant. One vessel is removing moisture from the compressed air.

Wet air passes directly through the desiccant bed which adsorbs the moisture. When this vessel is saturated with moisture the valves will switch and lead the air to the other standby vessel. During adsorption in the other vessel, the first vessel will be regenerated. It's a cyclic process.

The desiccant medium has a finite capacity for adsorbing moisture before it must be dried out, or regenerated. To do this, the tower containing saturated desiccant medium is depressurized and the accumulated water is driven off. How this happens depends on the type of atlas copco desiccant air dryer.