The check valve is an important part of any air compressor. The air compressor check valve can be found on almost any compressor out there. The check valve has only one function: to let air flow from one side to the other, while blocking air flow in the opposite direction. Once the compressed air passes the check valve, there is no way it can go back again. MADE IN USA 450 PSI MAX PRESSURE 400 DEG F. MAX TEMPERATURE 1/2" COMPRESSION PIPE THREAD TOP INLET X 3/4" MALE (NPT) PIPE THREAD OUTLET TO TANK 1/8" UNLOADER PORT INCLUDED 20 SCFM FLOW RATE IMPORTANT: DO NOT CALCULATE YOUR MEASUREMENT WITH A TAPE MEASURE OR RULER. CHECK VALVES FOLLOW THE NPT (NATIONAL PIPE THREAD) GUIDELINES AND CANNOT BE MEASURED WITH A LINEAR TOOL. 3/4" NPT MEASURE 1.050 ON A TAPE MEASURE.