An Over Pressure Shut-Off (O.P.S.O.) valve is a safety device which monitors the gas supply pressure and compares it to it's pre-set level. It can be fitted in both main and branch lines, between first and second stage regulators and between second stage and any other regulators. In case the regulator before it should fail, the Over Pressure Shut-Off (O.P.S.O.) valve will automatically activate, thereby switching off the gas supply.