Enter gas, water capacity, pressure and temperature, or the weight for CO₂ and acetylene, and see how much gas there is in cubic feet, pounds and liquid, how long it lasts and how many cylinders the usage needs.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Real and ideal gas versus pressure; for CO₂, vapor pressure versus temperature; for acetylene, maximum withdrawal versus number of cylinders.
Free gas volume at the same water capacity, pressure and temperature.
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In the default example (11.6 gal or 43.8 L water capacity, 2,200 psig, 70 °F), about 248 scf at 70 °F and 1 atm, or about 20.6 lb of oxygen. That is close to the common "K" size rating of about 244 to 251 ft³; the Z factor of about 0.94 adds roughly 7% over the ideal-gas estimate.
It is the internal volume of the cylinder, equal to the water it holds. It is stamped on the shoulder (often as WC in pounds of water) along with the DOT specification, service pressure and hydrostatic test date.
CO₂ is liquid in the cylinder, so the gauge reads vapor pressure (about 830 psig at 70 °F) until the liquid runs out. Acetylene is dissolved in acetone. In both cases, weigh the cylinder and subtract the stamped tare: 50 lb of CO₂ is about 437 scf.
Divide usable contents by flow. An argon cylinder of the same size (11.6 gal water capacity) at 2,200 psig holds about 247 scf; at 30 cfh it lasts about 8.1 hours of arc time after leaving 25 psig residual.
It is the condition at which free gas volume is measured. The same gas takes about 8% more volume at 70 °F than at 32 °F (0 °C). When comparing supplier quotes, confirm each one's reference condition.
OSHA 29 CFR 1910.101 points to CGA P-1: keep cylinders upright and secured, cap them when moved, use the right regulator and no oil on oxygen fittings. Nitrogen, argon, helium and CO₂ are asphyxiants in enclosed spaces; hydrogen and acetylene are flammable (NFPA 55).
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