Brand new 1-1/2" Female NPT in-line air compressor check valve. This check valve features a 1/8" female NPT port in the side to go to an unloader valve if needed. This is a universal inline check valve with female threads on both ends. This valve prevents back flow or tank pressure from getting back to the air compressor pump once the compressor is shut off. The 1/8" unloader port on the side of the valve is used to relieve pressure from the pump once it has shut off. If your compressor does not use an unloader, this port can simply be plugged.