NAUI Master Scuba Diver 10 Diving Equipment combined with a periodic coating of a dielectric compound, negate electrolysis in most instances. If the valve plating is worn away however, galvanic corrosion can be a problem and will appear as pits or damaged threads in the cylinder where the valve contact takes place. If this problem develops, it should be corrected by a qualified professional. The valve should also be serviced annually or any time there is air leakage or when the handle becomes difficult to turn. Excessive force should not be used when turning a scuba valve on or off. Valve seat discs, gaskets, and seals will be damaged. Open valves slowly and gently. Open valves slowly and gently. An older practice was to open the valve all the way then back a 1/4 turn. A valve that is closed a 1/4 turn may leave the diver without a gas supply because an inadequately open valve may deliver insufficient gas for the ambient pressure. A small opening that provides sufficient gas flow on the surface may become problematic with increasing depth due to gas density limiting the flow through the restriction. The best practice is to open the valve all the way. A quick predive check and a buddy check should pick up any errors. Look at the submersible pressure gauge (SPG), take a couple of breaths, and if you can breathe and the needle does not move, you are good to go. Always open a valve fully. Some older valves have pipe threads and are tightened with a wrench. They may require considerable force to remove. Having your cylinder valves serviced annually as recommended will help to prevent valve problems. Special Valves, Manifolds, and Cylinder Configurations Special scuba valves are available for specialty applications and multiple cylinder configurations. Most activities requiring the use of such valves are considered advanced specialties requiring special training. A dual valve for a single cylinder, known as a Y-valve or an H-valve (figure 1-5), allows a diver to mount two regulator systems on a single cylinder. This configuration is useful for deep dives or enclosure dives made with a single cylinder, as it allows a totally redundant regulator system for backup use should the primary fail. A high pressure connection between two or more cylinders is called a manifold. This device allows multiple cylinders to be ganged together for specialty activities which mandate a large air supply. There are modular valve system components that allow a variety of configurations, including manifolds, with the ability to isolate individual cylinders as required (figure 1-4). Multiple cylinder configurations such as twin medium sized cylinders or even triple cylinder setups are becoming more common. Smaller pony bottles, which hold 170 to 430 liters (6 to 15 cu ft) or more, can be attached to most cylinders using a simple bracket or band. Another type of valve that is becoming popular is the DIN valve, which is common in many countries outside North America. This allows a thread-on attachment of a regulator to cylinders using higher working pressures. It has a captured o-ring, which lessens the chance of failure at the regulator to valve interface. Some valves have removable inserts to allow valves to be used with both DIN and yoke-equipped regulator first stages. SCUBA REGULATORS A scuba regulator reduces the pressure of air in a scuba cylinder to ambient pressure and delivers the air on demand. It uses the pressure differential created by the respiratory action of your diaphragm to regulate air flow. Scuba regulators automatically adjust to changes in depth and in your respiration rate. High pressure air from your scuba cylinder is reduced in stages (pressure-reduction stops) to ambient pressure. Nearly all scuba regulators are two-stage devices. The first stage (figure 1-6) reduces cylinder pressure to an intermediate pressure (or low pressure) of approximately 6 to 10 bar (90-150 psi). The second stage reduces the low pressure air to ambient (surrounding) pressure. Types of Regulators
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