An air ryer is a device that is mounted directly after an air compressor and dries the air. Compressed air is kept in pressure vessels, mostly made out of steel. Wet air will corode the pressure vessels inside and rust in a pressure vessel may contaminate the pneumatic system so that the components do not work properly anymore. Conservation of the vessels inside is in fact impossible (tests with rubber liners have been made) so it is important to make the air as dry as possible. The compressed air is pressed through a cylinder filled with silica-gel. The silica-gel 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 cylinders with silica-gel are used; one for drying the air, the other is reconditioned. In general the changing of the cylinders is done automatically.