Pneumatically operated moisture drain valve with 24 volt thermostatically controlled heater. 3/8 inch male pipe thread attaches to air reservoir tank. The 995107 is recommended for the M939 series trucks. Valve should be installed on the wet tank (first tank compressor is connected to), however additional valves on secondary tanks is recommended for a fully automatic moisture drain system. This drain valve expels contaminants from the air tank with a powerful blast of air whenever the compressor reaches cut in or out pressure. Installation requires a section of 1/4 inch nylon air brake tube from this ejector valve to the air governor unloader port (same port that connects to compressor valves). The heater should be connected to the "ignition circuit” or switched auxiliary circuit capable of suppling approximately 2 amps. The 50 watt heater operates automatically only when ambient temperature is cold enough. The heater does not need to be connected for the valve to function in applications that remain above freezing. Valve also has a manual drain control. Installation instructions included. Made in USA.