A gas train consists of filters, slam-shut off valve, pressure regulator, safety relief valve and 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. In case the outlet pressure of the regulator exceeds the permissible limits, the slam shut off valve senses it through the impulse line and instantly shuts off the supply to the downstream system. The safety relief valve is provided for additional safety. It is to be set at higher pressure than the slam shut off valve pressure so that the safety relief valve will operate only when slam shut off valve fails to operate. The outlet of the safety relief valve is vented well above the roof.