One new 3/8" male compression x 1/2" 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 the compressor pump is connected to it. This valve prevents back flow 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 a unloader valve on your pressure switch or compressor pump. If you do not use an unloader in your application you can just plug this port.

Specifications:

Valve Inlet Threads: 3/8" Male Compression (measure about 1/2" diameter)

Outlet Threads / Tank Threads: 1/2" Male NPT (measure about 3/4" diameter)

Side Port: 1/8" Female NPT (measures about 10/32" inside diameter)

Total Length: 2-5/8"