- Look for external signs of damage. If it has any dents, deep scratches, rust then it is unlikely to pass it's next test. In fact a visual inspection is the first thing a test cylinder will perform on your cylinder when it is put in for a test. Make sure you remove the boot if fitted and inspect for damage.
- Check the valve has no signs of damage. They are made of brass (covered with chrome) which is quite a soft metal so any impact will be easily noticeable. A dropped cylinder is unlikely to pass it's next test.
- Cylinders stored with some air pressure inside are less likely to have internal problem you cannot see. When a cylinder is filled the air is purified and the moisture removed. If a cylinder is stored without pressure then fresh air with moisture in it will fill the inside of the tank. This is a real problem with a steel cylinder as air with moisture will promote rust.
- Make sure the valve opens smoothly. If it is stiff this may indicate it will need a service, costing around £20. If it will not open then be wary. Firstly you can't tell if it has been stored pressurised (see point above). Secondly the valve may need replacement, costing currently up to £50.
What to look for when buying a used cylinder
Buying a used diving cylinder is a bit like buying a used car, you never quite now what you are buying. Just like buying a used car buying dive tank can be a bargain, saving you a considerable amount off a new one or a complete waste of money. The first thing to keep in mind is that buying a cylinder out of test (in the UK currently two and half years since it's last date stamp) is much like buying a car without a MOT, it's a greater risk and you cannot use it until it passes again. Here are a few tips if you considering buying a used dive cylinder: