Air Compressor Piloted Unloader Valve with built in check valve.  Most commonly used on Gas Powered Air Compressors.  The pilot valve is set for 100-125 PSI from the factory, but can be adjusted if needed 30-40 PSI higher or lower.  This valve has a 1/2" Female NPT Air Inlet and a 1/2" Male NPT Air outlet.  There is an 1/8" port on the side for a throttle control valve or cable.  Also on the side of this valve, tehre is a 3/8" Female NPT Outlet to release the air once the compressor reaches full pressure.  This also comes with a 3/8" Male NPT Air muffler to help reduce the noise and can be removed if needed.  The pilot valve has a toggle levere on the top that can be put in the upward position for load free engine start or throttle control.