Air Dryer type is base on the function and theory. 2. Refrigeration dryers The basic principle of Refrigeration dryer is to condense water from compressed air using heat exchanging technologies. And it’s function has an limitation for highly purifying air and difficult to maintain. 2. Desiccant dryer The other type dryer is the desiccant dryer. The compressed air is pressed through a vessel filled with desiccant material. The desiccant material brings the dewpoint of the water in the air down to stay -40 degrees Celsius. This means that the air is dry as if the air was cooled down to -40 degrees Celsius. In practice two vessel with desiccant material are used; one for drying the air, while one vessel is in use, the other vessel is being regenerated. In general the changing of the cylinders is done automatically. A. Heatless drying which uses part of the dry compressed air coming from the other vessel to dry the desiccant in the vessel being generated. B. Heated dryer, this can use a hot air blower, so there is no loss of compressed air