plastic bladder that is inside the BC might hold the air. The amount of air the BC can hold determines its available lift capacity. You use the lift capacity to offset any weight you and your gear might develop in the water. BCs must be equipped with an overpressure relief valve to prevent damage to the BC from too much internal air pressure. The BC must also have an inflator/ deflator hose that is at least 2 centimeters (3/4 inch) in diameter. At the end of the inflator/deflator hose is a power-inflator mechanism and a deflator/oral inflator valve. All BCs are also equipped with a mouthpiece at the end of the inflator/deflator hose that enables you to inflate the BC by blowing air into it (figure 2-32). The power-inflator mechanism is attached to the regulator first stage with a low-pressure inflator hose. The power-inflator mechanism enables you to add air to the BC directly from your cylinder by pushing a button. If your power-inflator mechanism fails or you have no air in your cylinder, you can orally inflate your BC by pressing the deflator/oral inflator valve button and blowing into the mouthpiece at the same time. Stop pressing the Chapter 2- Diving Equipment button before you stop blowing or take your mouth off the mouthpiece, or air will flow out of your BC. On some BCs, you can pull down on your inflator/deflator hose or bleed valve activator to open the overpressure relief valve or dump valve. Some BCs have the dump valve located elsewhere on the BC. Pulling on a knob attached to a cable that hangs from the valve opens this valve. Alternatively, to deflate or bleed air from your BC, you can lift your inflator/ deflator hose over your head and press the deflator/oral inflator valve button. This allows air in your BC to flow up and out the inflator/deflator hose. For Your Information Some older BCs were equipped with carbon dioxide (CO2) cartridge inflator mechanisms. These mechanisms were designed to be used in an emergency only, but the mechanisms could corrode easily if they weren’t maintained properly and they were unreliable. You can still use a BC that is equipped to use a CO2 cartridge inflator mechanism as long as it has been equipped with a plug to avoid air loss. Avoid using the mechanism. Types There are three general types of buoyancy compensators (BCs): back flotation, jackets, and horse collars. Some BCs have integrated weight systems. Some BCs combine features of more than one type. Back Flotation Back-flotation systems are designed so that the entire bladder of the BC is behind you. This leaves your chest and waist uncluttered. Back-flotation systems are popular for underwater photography for this reason. Back-flotation systems provide good trim as you swim under water because the air in the bladder on your back counteracts the weights you wear around your waist. However, on the surface, the back flotation can tend to push you face down in the water unless you actively kick or recline to maintain a face-up position. Diving Equipment 33 FIG 2-32. THE LOW PRESSURE INFLATOR DEVICE (POWER INFLATOR) IS ATTACHED TO YOUR CYLINDER WITH A LOW PRESSURE HOSE.
19116TC
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