The Kussmaul 12v Auto Pump W/Auto Drain is a small air compressor designed to maintain the air pressure in air brake systems when the vehicle is not in use. A pressure switch senses when the system pressure drops and starts the compressor which then runs until pressure is restored. Normally open solenoid valve drains the moisture from the trap each time the compressor shuts down, but with Auto Drain the filter bowl is always drained. All ball bearing construction, lubricated for life, assures reliable operation and requires no servicing.