Dive cylinders are commonly made from aluminium or steel. Composite materials can be used but then extra weight is required to be worn by the diver.
Which is right for you?
Steel cylinders have a round bottom and have to wear a boot and have to be painted. In New Zealand they normally have a working pressure of around 230bar and should be paired with an equally rated valve. They do not become buoyant when the air is breathed down, so the diver does not need extra weight.
Aluminium cylinders have a flat bottom and so do not need a boot. They also do not need to be painted. Most are rated at around 204bar, but there are some higher rated cylinders. They become buoyant from around 120bar and so the diver may need around 1kg to 2kg of extra weight when diving.
In New Zealand all scuba cylinders require a LAB or ISO number that is on the WorkSafe cylinders register to be able to be tested and filled. Cylinders need visually testing every year and hydrostatically tested every 2 years.
