A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport the high pressure breathing gas required by a scuba set. It may also be used for surface-supplied diving or as decompression gas or an emergency gas supply for surface supplied diving or scuba. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving rebreather.
Diving cylinders are usually manufactured from aluminium or steel alloys, and are normally fitted with one of two common types of cylinder valve for filling and connection to the regulator.
An especially common cylinder provided at tropical dive resorts is the “aluminium-S80” which is an aluminum cylinder design with an internal volume of 0.39 cubic feet (11.0 L) rated to hold a nominal volume of 80 cubic feet (2,300 L) of atmospheric pressure gas at its rated working pressure of 3,000 pounds per square inch (207 bar). Aluminum cylinders are also often used where divers carry many cylinders, such as in technical diving in water which is warm enough that the dive suit does not provide much buoyancy, because the greater buoyancy of aluminum cylinders reduces the amount of extra buoyancy the diver would need to achieve neutral buoyancy. They are also sometimes preferred when carried as “sidemount” or “sling” cylinders as the near neutral buoyancy allows them to hang comfortably along the sides of the diver’s body, without disturbing trim, and they can be handed off to another diver or stage dropped with a minimal effect on buoyancy. Most aluminum cylinders are flat bottomed, allowing then to stand upright on a level surface, but some were manufactured with domed bottoms.
In cold water diving, where a diver wearing a highly buoyant thermally insulating dive suit has a large excess of buoyancy, steel cylinders are often used because they are denser than aluminum cylinders. They also often have a lower mass than aluminum cylinders with the same gas capacity, due to considerably higher material strength, so the use of steel cylinders can result in both a lighter cylinder and less ballast required for the same gas capacity, a two way saving on overall dry weight carried by the diver.
Steel cylinders are more susceptible than aluminum to external corrosion, particularly in seawater, and may be galvanized or coated with corrosion barrier paints to resist corrosion damage. It is not difficult to monitor external corrosion, and repair the paint when damaged, and steel cylinders which are well maintained have a long service life, often longer than aluminum cylinders, as they are not susceptible to fatigue damage when filled within their safe working pressure limits.
Steel cylinders are manufactured with domed (convex) and dished (concave) bottoms. The dished profile allows them to stand upright on a horizontal surface, and is the standard shape for industrial cylinders. The cylinders used for emergency gas supply on diving bells are often this shape, and commonly have a water capacity of about 50 liters (“J”). Domed bottoms give a larger volume for the same cylinder mass, and are the standard for scuba cylinders up to 18 liters water capacity, though some concave bottomed cylinders have been marketed for scuba.
The shoulder of the cylinder carries stamp markings providing required information about the cylinder.
Learn more at :: Wikipedia