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NAUI Master Scuba Diver 24 Diving Equipment All true BCs are equipped with a pressure relief valve (figure 1-26), which prevents overpressurization of the bladder. The valve is held closed by a spring with a tension of approximately 1/8 bar (2 psi). When the internal pressure of the BC exceeds this amount, the spring pressure is overcome and any excess pressure is vented. Some buoyancy compensators are equipped with a dump valve to allow rapid manual deflation of the bladder. A lanyard from a point high on the bladder extends to a location that enables easy operation by the user. The functions of the pressure relief valve and a dump valve are combined by some manufacturers. BCs, particularly older styles, may be equipped with a CO2 cartridge emergency inflator. The intent of this device is to enable rapid inflation of the BC at the surface. The preferred inflation method is by means of a low pressure inflator, on a hose from the regulator first stage, which is standard equipment on today’s BCs. The CO2 cartridge requires a high degree of care and maintenance to ensure reliable operation. As a result, they have lost popularity. Some manufacturers offer CO2 cartridge inflators as an option. If a CO2 inflator is desired or used, it must be properly cared for. Following every dive, the mechanism must be carefully rinsed and dried. The cartridge must then be removed and the threads cleaned and lubricated prior to replacement. Expended cartridges must be promptly replaced or rust will form, which can damage the mechanism and your BC. If a CO2 cartridge is activated to fill a BC, care must be taken to avoid breathing the gas inside the BC. Be sure to thoroughly purge the CO2 gas out and rinse the BC before orally inflating it. A low pressure inflator, which uses low pressure air from your regulator to inflate your BC, is considered standard equipment (figure 1-25). The inflators are available with either balanced or unbalanced valves. A balanced valve is recommended because its operation is easier since it is unaffected by low air pressure (figure 1-28). A type of BC that is available in Europe and in Canada includes a small air cylinder independent from the primary scuba unit for emergency inflation of the bladder. The unit also has a demand mouthpiece that allows air from the bladder to be inhaled, while the Quick Disconnect Low Pressure Air Inlet Low Pressure Air to Vest Valve Seat Oral Inflation Air FIGURE 1-25. UNBALANCED BC LOW PRESSURE INFLATOR Vest Bladder Relief Valve Body and Seat Vent Cap Retaining Nut Valve Spring Outside B.C. Inside B.C. FIGURE 1-26. BC OVERPRESSURE RELIEF VALVE exhausted breath passes into the water just as it does in a scuba regulator. Partially closing the manual inflator valve after inflating the bladder allows rebreathing of exhaled air to prolong the air supply. The use of a BC as a breathing bag is a skill that requires training and which must be reserved for emergency use only. There is also a high risk of fungal infection.


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