Desiccant compressed air dryers run the compressed air through a
chamber filled with desiccant, usually activated alumina or silica
gel. The desiccant adsorbs the moisture in its millions of pores,
trapping it. If the air dryer is using a smart controller the
compressed air dryer changes chambers when the dew point downstream
begins to change, indicating the desiccant is wet. Other models
change on a set timer. The wet desiccant is regenerated, or dried,
by the compressed air dryer's hot purge air. The hot air drives off
the moisture preparing the desiccant for its next cycle.