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Buoyancy compensator (diving)

The meaning of «buoyancy compensator (diving)»

A buoyancy compensator, also called a buoyancy control device, BC, BCD, stabilizer, stabilisor, stab jacket, wing or ABLJ depending on design, is a piece of diving equipment with an inflatable bladder which is worn by divers to establish neutral buoyancy underwater and positive buoyancy at the surface, when needed. The buoyancy is controlled by adjusting the volume of air in the bladder. The bladder is filled with ambient pressure gas from the diver's primary breathing gas cylinder via a low-pressure hose from the regulator first stage, directly from a small cylinder dedicated to this purpose, or from the diver's mouth through the oral inflation valve.

They can be broadly classified as having the buoyancy primarily in front, surrounding the torso and behind the diver. This affects the ergonomics and to a lesser degree, the safety of the unit. They can also be broadly classified as having the buoyancy bladder as an integral part of the construction, or as a replaceable component supported inside the structural body.

The buoyancy compensator is one of the items of diving equipment most requiring skill and attention during operation, as control is entirely manual, and adjustment is required throughout the dive as weight reduces due to gas consumption, and buoyancy of the diving suit and BCD varies with depth. Fine buoyancy adjustment can be done by breath control on open circuit, reducing the amount of actual BCD volume adjustment needed, and a skilled diver will develop the ability to adjust volume to maintain neutral buoyancy while remaining aware of the surroundings and performing other tasks. The buoyancy compensator is both an important safety device when used correctly, and a significant hazard when misused.

The ability to control trim effectively is dependent on both appropriate buoyancy distribution and ballast weight distribution. This too is a skill acquired by practice, and is facilitated by minimising the required gas volume by correct weighting.

The function of the buoyancy compensator is to allow the diver to adjust buoyancy underwater or at the surface within the range of slightly negative to slightly positive, to allow neutral buoyancy to be maintained throughout the depth range of the planned dive, and to compensate for changes in weight due to breathing gas consumption during the dive. Where staged cylinders are used, it may also be used to compensate for weight changes when dropping and retrieving these cylinders. Variations in the buoyancy of wetsuits depend on the volume and density of the suit and the ambient pressure, but for thick suits can be in the order of 10 kg.

All buoyancy compensators will have some components in common:

In addition some BCs may include other features:

There are three main types of BC based on buoyancy distribution:

An adjustable buoyancy life jacket (ABLJ) is fitted around the neck and over the chest, secured by straps around the waist and usually between the legs. They are sometimes referred to as "horse collars" because of their resemblance, and are historically derived from the inflatable underwater demolition team (UDT) vest or Mae West life jacket issued to World War II flyers and divers.

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