One new 3/4" flare x 3/4" male NPT in tank air compressor check valve with dual side ports. These 1/8" female dual side ports are commonly used for unloaders or relief valves but can be plugged if not needed. 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.