A gas train consist of Filter, Slam-shut off valve, pressure regulator, safety relief valve & flame arrestor. Filter helps to remove the dust/dirt particles in the gas which may damage the regulator parts. The slam-shut off valve normally remains open. Incase the outlet pressure of the regulator exceeds the permissible limits, the slam-shutoff valve senses it through the impulse line and instantly shuts off the supply to the downstream system.