How to work out how much gas is left in a cylinder

For a compressed gas — oxygen, argon, nitrogen, compressed air or an argon/CO₂ mix — the gas content is simply the cylinder’s water capacity multiplied by the pressure. A cylinder stamped WC 47 on the neck holds 47 litres of water, and at a filling pressure of 150 bar it contains roughly 7 cubic metres of gas.

Gas content (m³) = water capacity (litres) × pressure (bar) ÷ 1000

That formula also works part-way through a cylinder. If the contents gauge on a 47 litre cylinder reads 60 bar, you have about 2.8 m³ left — 47 × 60 ÷ 1000. Divide the remaining litres by your flow rate in litres per minute to get the running time.

Carbon dioxide and acetylene are different. Both are stored as a liquid or dissolved in a solvent, so the pressure gauge shows the vapour pressure and stays almost constant until the cylinder is nearly finished. A CO₂ cylinder will read around 57 bar at Malaysian ambient temperature whether it is full or a quarter full. The only reliable way to check the contents of a CO₂ or acetylene cylinder is to weigh it and subtract the tare weight (marked TW) stamped on the neck.

Common industrial cylinder sizes and contents

Contents are quoted at 15 °C and one atmosphere. Sizes vary between suppliers, so check the label on the cylinder you actually receive. Bann Edar is an authorised MOX-Linde distributor and can confirm exactly what is available for your account in Perlis and Kedah.

Typical gas flow rates

The acetylene one-seventh rule

Acetylene is not compressed like other gases. The cylinder is packed with a porous mass soaked in acetone, and the acetylene is dissolved in that acetone. If you draw the gas too quickly, acetone comes out with it. That contaminates the flame, ruins the weld or cut, and leaves the cylinder short of the solvent that keeps the acetylene stable.

The limit is one-seventh of the cylinder’s contents per hour. For a 6 kg cylinder holding about 5.5 m³, that is 0.79 m³ per hour, or roughly 13 litres per minute of continuous draw. If your job needs more than that, use a larger cylinder or run two or more cylinders together on a manifold.

Two other acetylene rules that are not negotiable: never set the regulator above 1 bar (15 psi) working pressure, and always fit flashback arrestors at both the regulator and the torch.

Frequently asked questions

How long does a 47 litre argon cylinder last?

A 47 litre cylinder at 150 bar holds about 7,000 litres of argon. At a typical TIG flow of 8 litres per minute that is around 14 hours of continuous welding, and at a MIG flow of 15 litres per minute it is closer to 7 hours. Because a welder is rarely welding more than 30 to 40 per cent of the working day, a cylinder usually lasts three to six working days in general fabrication.

How do I check how much gas is left in a CO₂ cylinder?

Weigh it. Carbon dioxide is stored as a liquid, so the pressure gauge reads roughly the same whether the cylinder is full or nearly empty. Subtract the tare weight stamped on the cylinder neck from the total weight to get the kilograms of CO₂ remaining. One kilogram of CO₂ gives about 0.54 cubic metres of gas.

What does WC mean on a gas cylinder?

WC is the water capacity — the internal volume of the cylinder in litres, stamped on the neck along with the tare weight, the test pressure and the last hydrostatic test date. It is the number you need to calculate gas content, and it is not the same as the amount of gas inside.

Why should I not run a cylinder completely empty?

The last few bar of pressure are what keep air and moisture out. Once the pressure reaches zero, air can be drawn back through the valve, and the moisture that comes with it contaminates the cylinder and the next fill. Stop at around 10 bar, close the valve, and mark the cylinder as empty. Unexplained porosity that appears right after a cylinder exchange often traces back to this.

How much gas will my job need?

Multiply the arc-on hours by the flow rate in litres per minute, then by 60, to get litres of gas. Forty hours of MIG welding at 14 litres per minute needs about 33,600 litres, or 33.6 m³ — roughly five 47 litre cylinders once you allow for a reserve and some contingency for purging and re-runs.

Where can I buy or exchange industrial gas cylinders in Perlis and Kedah?

Bann Edar Sdn. Bhd. is an authorised MOX-Linde distributor supplying oxygen, argon, argon mixtures, carbon dioxide, acetylene, nitrogen and special gases from branches in Kangar, Perlis and Sungai Petani, Kedah. Call 04-976 5570 or message 019-470 9929 on WhatsApp to check current cylinder availability and pricing.

Disclaimer. The figures and recommendations on this page are general guidance for planning and set-up only. They are not a substitute for the manufacturer’s data sheet, an approved welding procedure or the applicable standard, and they cannot account for the conditions of your particular job. You remain responsible for checking every figure before you rely on it. Bann Edar Sdn. Bhd. accepts no liability for any loss, damage or injury arising from the use of this tool.

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