Moisture in pneumatic systems can cause corrosion and reduce component life. Refrigerated dryers reduce system moisture by cooling the air, thus reducing the dew point. Membrane dryers use hollow fiber membranes that enable moisture to easily pass, but block the passage of air, separating the two. Heatless dryers alternate between two desiccant columns and use a small portion of the dry air from the column in service to regenerate the other column.