Buoyancy compensators: styles, parts and the standard.

What a BCD does

PADI describes the buoyancy compensator, or BCD, as the piece of kit that lets a diver float at the surface, rest on the bottom or hover in mid-water. It also holds the cylinder on the diver's back. How to use it is taught in training, in the water with an instructor, not from a page.

The essential parts

PADI lists three parts every BCD needs:

• A low-pressure inflator with an option to inflate by mouth.
• A deflator to let air out.
• An overpressure relief valve.

PADI's 2013 guide adds optional features: accessory pockets, a cummerbund waistband and quick-dump valves that release air without the diver raising the inflator hose. Some BCDs also carry integrated weight pockets, which SSI says can replace a weight belt and include quick-release mechanisms; these are covered on weights.

The main styles

Backplate and wing in more detail

Wikipedia (secondary) describes the backplate and wing as modular. A rigid plate, usually stainless steel or anodised aluminium, is worn on a webbing harness, often with a crotch strap. A separate wing sits between the plate and the cylinder, and cambands hold the cylinder on. Wings come in low, medium and high volumes. Wikipedia notes that a steel plate adds negative buoyancy that can replace some of the diver's ballast, while aluminium suits divers who need less weight or who are travelling.

Lift capacity

SSI defines lift capacity as the weight a BCD can hold up at the surface. It says cold-water divers in thick suits, and technical divers carrying several cylinders, need more lift than warm-water divers in light gear. Matching lift to a particular set-up is something to work out with an instructor or dive professional.

Choosing and fitting

PADI advises trying a BCD on while wearing the exposure suit that will be used with it, and checking that the inflator hose is compatible with the regulator set-up. DAN, writing about dry suits in 2012, cautions against using a dry suit in place of a BCD.

The European BCD standard

The CEN standard for buoyancy compensators is EN 1809:2014+A1:2016, "Diving equipment, Buoyancy compensators, Functional and safety requirements, test methods". The Estonian standards catalogue lists the consolidated version as valid from 4 April 2016; the base EN 1809:2014 was published on 4 August 2014. National catalogue listings, seen only in a search summary, say the 2014 edition replaced EN 1809:1997.

The standard covers inflatable devices that let a diver control buoyancy and that may also carry the breathing equipment or weights. It specifically excludes life preservers, personal flotation devices and rescue devices, including devices that combine buoyancy control with rescue. So the standard does not treat a BCD as a life jacket. A standard sets minimum requirements and test methods; it is the maker's marking, not this page, that states whether a product claims to meet it.

Care

PADI says to rinse a BCD inside and out with fresh water after each use, dry it away from direct sun and store it partly inflated in a cool, dry place with the weights removed. SSI adds that the maker's service schedule should be followed. See care and storage for more.