Air compressor check valve, 1/2" Compression x 1/2" MPT with 1/8" hole; plug hole if not needed.  https://mastertoolrepair.com/1-8-blk-steel-plug-s-h-100b6e/ If the small unloader (bleeder) valve on or under your pressure switch leaks constantly...

Old Part Numbers: 034-0184Replacement Condor air compressor pressure switch, 125/155 PSI. 240V, 4-Port manifold. Replace the pressure switch if the compressor no longer cuts in or out at the designated pressure (PSI), if the unit doesn't turn on or off,...