| Buoyancy Compensator |
Shopping Buoyancy |
Shopping Compensator |
Information AboutBuoyancy Compensator |
| CATEGORIES ABOUT BUOYANCY COMPENSATOR | |
| diving equipment | |
|
A buoyancy compensator (or '''buoyancy control device''', '''BC''' or '''BCD''') is a piece of Diving Equipment worn by divers to provide:
Some types of buoyancy compensator also built around the diver's Scuba Set or are built into its harness. FEATURES BCs can have the following features:
TYPES There are three main types of BC: Wings ''' Stab jacket Stab jacket, '''stabiliser jacket''', '''stab''', '''waistcoat''', or '''vest''' BCs are inflatable vests worn by the diver around the upper torso, and also act as the cylinder harness. The air bladder may extend from the back around the diver's sides ("wraparound") or may only cover the back ("back inflation.") Wraparound bladders are favored by some divers because they may make it easier to maintain balance, both submerged and on the surface. However, they have the tendency to squeeze the diver's torso when inflated. Back inflation BC's do not have this problem but have a greater tendency to float the diver face-down on the surface, which presents an obvious hazard in an emergency. Jacket-style BC's typically provide up to 25 litres of buoyancy (depending on size) and are fairly comfortable to wear. Jacket-style BC's are the most common type among recreational divers because they can integrate buoyancy control, weights, attachment points for auxiliary gear, and cylinder retention in a single piece of gear. The diver need only attach a cylinder and regulator set in order to have a complete SCUBA set. Some "tech-rec" jacket-style BC's have the ability to carry multiple cylinders. Diver's lifejacket Adjustable Buoyancy Life Jackets, '''ABLJs''' or '''horsecollar''' BCs: are worn around the neck and chest with straps around the waist and usually between the legs. They are cheap, light and small, providing up to 15 litres of buoyancy. They float an unconscious casualty face-up. But they are old-fashioned, uncomfortable with a strap between the legs and provide less buoyancy than the other types. The diver must use a separate cylinder harness as a platform for the Aqualung . NEUTRAL BUOYANCY When underwater, a diver often needs to be neutrally buoyant so that the diver neither sinks nor rises but remains at constant depth. A state of neutral buoyancy exists when the weight of water that the diver displaces equals the total weight of the diver. The Buoyancy Compensator is used to maintain this state by adjusting its volume and therefore its buoyancy, in response to various effects, which alter the diver’s overall volume or weight, primarily:
In practice, the diver doesn't think about all this theory during the dive. To remain neutrally buoyant, gas is injected into the BC when the diver is too heavy, or is sinking, and vented from the BC when the diver is too buoyant, or is rising. A feature of diving is that there isn't any automatically stable equilibrium position for a diver wearing a BC, or even simply for a diver with lungs full of air. Any change in depth from a position of neutrality-- even a small change-- will result in a force toward an even less neutral depth. Thus, maintenance of neutral buoyancy in scuba must be a continuous and active procedure-- the diving equivalent of balance. A feature of scuba which is often non-intuitive to beginning students of diving, is that gas generally needs to be ''added'' to the BC when a diver descends in a controlled manner, and ''valved-off'' (removed) from the BC when the diver ascends in a controlled manner. This gas maintains the volume of the gas bubble in the BC during depth changes; this bubble needs to remain at constant ''volume'' for the diver to remain even approximately neutrally buoyant. When gas is ''not'' added to the BC during a descent, the gas bubble in the BC decreases in volume due to the increasing pressure, resulting in faster and faster descent with depth, until the diver hits the bottom. The same runaway phenomenon can happen during ascent, resulting in uncontrolled ascent, until a diver prematurely surfaces without a safety stop. With experience, divers eventually learn to minimize this problem by minimizing the size of the "constant volume bubble" in their BC's. This requires learning the minimum weighting requirement needed for their system, at the beginning of the dive (see factors above). Somewhat complex automatic reflexes behaviors are also developed by experienced divers, involving breathing control and BC gas management during depth changes, which allow them to remain neutral without having to think much about the issue. Experienced scuba divers may often be identified by the fact that they maintain neutrality without any fin use, as fish do. ORIENTATION IN THE WATER The orientation of the submerged diver is influenced by the BC and by other buoyancy and weight components and contributed to by the diver's body, clothing and equipment. The diver typically wishes to be positioned face-down while under water, to be able to see and swim usefully, but face-up, to be able to breathe, when on the surface. The orientation of a static and stable object in water, such as a diver, is determined by its centre of buoyancy and its centre of mass. At equilibrium, they will be lined up under gravity with the centre of buoyancy vertically above the centre of mass. The diver's overall buoyancy and centre of buoyancy can routinely be adjusted by altering the volume of the gas in the BC, Lungs and Diving Suit . The diver's mass on a typical dive does not generally change by much (see above-- a typical dive-resort "aluminum 80" tank at 200 bar contains about 2.8 kg of air or nitrox, of which about 2.3 kg is typically used in a dive), although a large change is possible if the Weight Belt is jettisoned or a heavy object is picked up; and any air spaces such as in the BC and in diving suits will expand and shrink with depth pressure. Generally, the diver has no control of the position of the buoyancy in the BC, only its quantity. By inflating the BC at the surface the conscious diver can easily float face-up. By deflating the BC underwater, the diver can easily be positioned facedown. Traditionally, weight belts or weight systems are worn with the weights on or close to the waist and are arranged with a quick release mechanism to allow them to be jettisoned to provide extra buoyancy in an emergency. Current systems integrate the weights into the BCD providing substantial comfort and safety advantages. An unconscious diver can be made to float face up on the surface by placing buoyancy and weights so the buoyancy raises the top and front of the diver's body and the weights act on the lower and back of the body. An inflated ABLJ always provides this orientation, but an inflated stab or old styles of wing BC generally floats the diver facedown because the centre of buoyancy is too far from the diver's front. Possible solutions to this problem are: fixed of quick release weights on or close to the diver's cylinder; using twins, large, steel, or high-density cylinders. All solutions move the centre of mass further behind the diver resulting a face-up orientation. Many other factors, such as the number and position and density of Diving Cylinder s, the type of Diving Suit , the position and size of stage cylinders, the size and shape of the diver's body and the wearing of ankle weights influence each diver's orientation in the water. HISTORY The ABLJ was developed by Maurice Fenzy in 1961 . Early versions were inflated by mouth underwater. Later versions had their own air inflation cylinder. Some had Carbon Dioxide inflation cylinders, a development which was abandoned when valves that allowed divers to breathe from the BC's inflation bag were introduced. Since 1969 most modern BCs have used inflation gas from one of the diver's main gas cylinders, in addition to an oral inflation tube which is used at the surface to save gas. In 1971 , Scubapro developed the Stabilizer Jacket, the first jacket-style BC, and in 1972 Watergill developed the Atpac Wing . More recent innovations for jacket BCs include, weight pouches to adjust attitude underwater, putting the weights on the BC rather than on a weightbelt, integrated regulators, heavily reinforced 1050 denier ballistic nylon. Innovations for wings include redundant bladders, stainless steel backplates, light weight soft nylon backplates, and 85lb lift bladders. Dive Rite pioneered the first wing for diving twin cylinders in 1985. Competitors in tech diving include Ocean Management Systems . Other SCUBA manufacturers include Sherwood , Zeagle , scubapro and [http://cressisub.it/index_int.php?lang=us cressisub. OTHER BUOYANCY EQUIPMENT There are other types of equipment worn by divers that affect buoyancy: REFERENCES |
|
|