STORAGE & QUALITY OF CO2 GAS
CO2 gas is supplied in cylinders at a high pressure (140 kg / cm2). When the cylinder is full, nearly 90 % of the volume is filled with CO2 liquid and balance liquid phases are in equilibrium pressure. Two type of CO2 cylinders are available viz. Gas type and syphonic type. In gas type cylinders gaseous CO2 is withdrawn when the cylinder valve is opened. The physical properties of CO2 are such that if the gas is taken off too fast, the CO2 gas in the cylinder will freeze as the temperature and pressure within the cylinder drop rapidly. Where CO2 requirements are in excess of 20 l / min the use of siphon cylinder is recommended. These are fitted with an internal tip tube and CO2 is withdrawn as liquid which must then be passed through a vapouriser unit with sufficient capacity to suit the rate of draw off required. All CO2 cylinders must also be fitted with a heater near the gas regulator to avoid freezing around the regulator.The quality of the CO2 gas used for welding must conform to BS 4105:1967 or IS 307:1966. As per the above standards the moisture in the CO2 gas should be less than 10 ppm.