The Graham White™ Model 413 Series Auto Stop Drain Valve (ASDV) is a “smart” drain valve designed to provide a reliable and efficient way to drain water and contamination from the locomotive main reservoirs. It differs from previous generations of main reservoir drain valves in that the valve can distinguish between water and air. The automatic portion of the valve will remain open when water is present, and closes automatically after the water has been drained. The ASDV conserves air and operates very quietly when compared to previous generations of drain valves.