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. One new 1" female NPT x 1" male NPT in tank air compressor check valve. This style of check valve is usually screwed directly into the air tank, then the main line coming off of the compressor pump is connected to it. This valve prevents backflow or tank pressure from getting back to the air compressor pump once the compressor is shut off. This valve has a 1/8" female NPT port in the side which usually goes to an unloader valve on your pressure switch or air compressor pump. If you do not use an unloader line in your application, this port can just be plugged. MADE IN USA Specifications: · Valve Inlet Threads: 1" Female NPT (measures about 1-3/16" in diameter) · Outlet Threads / Tank Threads: 1" Male NPT (measures about 1-1/4" in diameter) · Side Port: 1/8" Female NPT (measures about 10/32" in diameter) · Total Lenght: 3-7/8" 450 PSI MAX PRESSURE 400 DEG F. MAX TEMPERATURE 1" FEMALE (NPT) PIPE THREAD TOP INLET X 1" MALE (NPT) PIPE THREAD OUTLET TO TANK 1/8" UNLOADER PORT INCLUDED 60 SCFM FLOW RATE