Replacement AD-9 style air dryer. Clean, dry air lines help keep you on the road and out of the shop. The air dryer (installed between the compressor and reservoirs) collects and removes solid, liquid and vapor contaminants before they enter the air brake system and jeopardize efficient operation. A new air dryer provides clean, dry air to reservoirs, valves and other components which increases the life of the air brake system and helps to reduce maintenance costs and prevents system freeze up.