The check valve is an Copernican of any air compressor. The air compressor check valve can be on almost any compressor outgoing there. The check valve single one function : to let air flow from one aspect to the else, while blocking air flow in the diametric direction. Once the compressed air passes the check valve, there no way it can go backbone again. IN USA 450 PSI MAX PRESSURE 400 DEG F. MAX TEMPERATURE 3/4 '' feminine -LRB- NPT -RRB- PIPE THREAD bout INLET X 3/4 '' masculine -LRB- NPT -RRB- PIPE THEAD OUTLET TO TANK 1/8 '' UNLOADER PORT INCLUDED 30 SCFM FLOW RATE .