diving cylinder, scuba tank
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 as 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 typically fitted with one of two common types of cylinder valves for filling and connection to the regulator. Other accessories, such as manifolds, cylinder bands, protective nets, boots and carrying handles, may be provided. Various configurations of harnesses may be used to carry the cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres; however, these are often used for inflation of surface marker buoys, drysuits and buoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, a central cylinder and a more miniature “pony” cylinder, carried on the diver’s back or clipped onto the harness at the sides. Paired cylinders may be manifolded together or independent. In some cases, more than two cylinders are needed.
Steel vs Aluminum Scuba Cylinders
Steel Dive Cylinders
Steel dive cylinders can be made in various ways, but one popular manufacturing technique for steel tanks is called deep draw. In this method, high-grade chrome-molybdenum steel blanks are drawn into form by machine punches into a form similar to an aluminium tank’s form; therefore, steel tanks tend to be more robust and more durable while producing them require less raw material, therefore decreasing wastefulness of production materials.
Steel diving tanks have lower total weight and better buoyancy characteristics. What does it mean in practice? Steel tanks shift from negative to neutral buoyancy during a dive, allowing the diver to have more consistent weight and finish the dive better balanced. Moreover, steel dive tanks are the favourite choice for most divers in the UK as the buoyancy characteristic helps diving in dry suits. Steel diving cylinders have working pressures between 232 bar to 300 bar. Scuba diving cylinders rated at 300 bar are heavier as they have thicker walls to be stronger.
Aluminium Dive Cylinders
Aluminium dive tanks are typically manufactured using “backward extrusion.” This process involves driving a metal rod through a mixture of aluminium alloy in a cylindrical mould to form the familiar cylindrical shape. Since aluminium is a soft material, thicker walls may be necessary to contain pressurised gasses effectively. Aluminium scuba diving cylinders differ from their steel counterparts in their buoyancy characteristics – tending to be negatively buoyant at the start of a dive and positively buoyant once empty. Aluminium scuba tanks are widely used by dive centres across North America and the Middle East; in the UK, however, their primary use lies with technical diving applications such as decompression or stage cylinders for technical diving applications. Their typical working pressure ranges between 200 to 230 bar.
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