The bottle

Before choosing the bottle(s), a number of factors must be taken into consideration:

• Type of material - Steel bottles are more resistant to mechanical stress than aluminum bottles. Aluminum bottles are more resistant to corrosion than steel bottles.

• Size and working pressure - The size of the cylinder (capacity) and its working pressure determine the volume (liters) of gas that can be stored, a determining factor in choosing cylinders based on the type of exposure (time, depth) and use of the cylinder.

• Required valves - The type of valve and the number of outlets should be chosen according to the configuration and the desired level of redundancy.

Type and Size

• The most commonly used bottles for cold water are steel bottles, while aluminum bottles are preferred for tropical waters or as decompression bottles, due to their apparent weight. Typical sizes of aluminum and steel bottles can be found in the figures to the side.

Work Pressure

• Aluminum cylinders typically have a working pressure of 200 to 207 bar, while steel cylinders can be purchased with working pressures of 200, 230-232, or 300 bar. The most commonly used steel cylinders are those with a pressure of 232 bar.

Valves

• DIN valves allow for a better fit of regulators, making them safer valves. DIN valves are available in 232 bar and 300 bar versions.

• In most bottles, single or double outlet valves can be adapted if two first stages are desired for redundancy.

• Valves with rubber knobs instead of plastic knobs withstand impacts without breaking and are preferred over plastic knobs.

Security

• Installing valves adapted to the operating pressure of the bottle (232 or 300 bar) and the bottle thread (M25 or US) prevents potential accidents during filling.

• Use the correct valves on the cylinder depending on the type of gas used to avoid potential accidents. There are specific valves for inert gases or for gases with oxygen concentrations above 40%.