Editing Scuba set (section)

==Diving cylinders==
{{Main|Diving cylinder}}

[[Gas cylinder]]s used for scuba diving come in various sizes and materials and are typically designated by material&nbsp;– usually [[aluminium]] or [[steel]], and size. In the U.S. the size is designated by their [[Diving cylinder#Nominal volume of gas stored|nominal capacity]], the volume of the gas they contain when expanded to normal atmospheric pressure. Common sizes include 80, 100, 120 cubic feet, etc., with the most common being the "Aluminum 80". In most of the rest of the world the size is given as the actual internal volume of the cylinder, sometimes referred to as water capacity, as that is how it is measured and marked (WC) on the cylinder (10 liter, 12 liter, etc.).<ref name="SANS 10019:2008" />

Cylinder working pressure will vary according to the standard of manufacture, generally ranging from {{convert|200|bar|psi|abbr=on}} up to {{convert|300|bar|psi|abbr=on}}.

An aluminium cylinder is thicker and bulkier than a steel cylinder of the same capacity and working pressure, as suitable aluminium alloys have lower tensile strength than steel, and is more buoyant although actually heavier out of the water, which means the diver would need to carry more ballast weight. Steel is also more often used for high pressure cylinders, which carry more air for the same internal volume.<ref name="Dive Gear Express"/>

The common [[Gas blending#Blending nitrox|method of blending nitrox by partial pressure]] requires that the cylinder is in "oxygen service", which means that the cylinder and cylinder valve have had any non-oxygen-compatible components replaced and any contamination by combustible materials removed by cleaning.<ref name=RRR6310 />
Diving cylinders are sometimes colloquially called "tanks" "scuba tanks", "bottles" or "flasks", and some of these may be equivalent to the correct term in other languages although the proper technical term for them is "cylinder" or "scuba cylinder".<ref name="Denny" /><!--not a very reliable source as it contains several errors-->

Rebreather divers and some open-circuit scuba divers carry extra [[diving cylinder]]s for bailout in case the main breathing gas supply is used up or malfunctions. If the bailout cylinder is small, they may be called "[[pony cylinders]]". They have their own [[diving regulator|demand regulators]] and mouthpieces, and are technically distinct extra scuba sets. In [[technical diving]], the diver may carry different equipment for different phases of the dive. Some [[breathing gas]] mixes, such as trimix, may only be used at depth, and others, such as pure [[oxygen]], may only be used during [[decompression stop]]s in shallow water. The heaviest cylinders are generally carried on the back supported by a [[backplate and wing|backplate]] while others are side slung from strong points on the harness.{{citation needed|date=December 2016}}