The S300 in-line over pressure slam shut (OPSS) protects gas installations, especially polyethylene pipework, from dangerous overpressure conditions and can be fitted either before or after the first stage regulator (see over the page for installation diagrams). Versions are available with either internal or external impulse. When the pressure increases above a predetermined value the trigger mechanism actuates and the valve shuts off the gas supply. Resetting can only be achieved manually. The S300 can be used with natural, liquefied petroleum and manufactured gases and can be mounted in any orientation.