NAUI Master Scuba Diver 8 Diving Equipment the amount of cylinder expansion in terms of water column displacement. The pressure is increased to five-thirds of the rated pressure of the cylinder. A permanent expansion of 10% or more of the total expansion indicates the cylinder is unsafe and must be removed from service. The cylinder will not be rated for a lower working pressure. Cylinder Care Rules 1. Do handle cylinders carefully. 2. Do fill cylinders slowly, about 20 to 35 bar (300-500 psi) per minute. 3. Do have cylinders visually inspected annually or more frequently if damage is suspected. 4. Do prevent moisture from entering the cylinder. 5. Do remove cylinder boot periodically and inspect for corrosion. 6. Do rinse the outside of the cylinder thoroughly with clean, fresh water after diving. 7. Do store cylinders in a cool, dry place with a small amount of pressure in them. 8. Do not drain a cylinder completely of air except for internal inspections. If it must be drained, do it slowly. 9. Do not exceed the maximum allowable pressure. 10. Do not use a dented, welded, or deeply scarred cylinder. 11. Do not heat cylinders to high temperatures (i.e. by baking, welding, structure fires). 12. Transporting cylinders requires care to assure that they don’t roll around, and that the valve is protected from damage. Cylinder Valve Assemblies and Manifolds A scuba cylinder valve is a simple, manually operated on-off valve that controls the flow of high-pressure gas. Features of all scuba valves include a valve snorkel and a burst disk. The purpose of the valve snorkel, or “dip tube,” is to prevent foreign matter from entering the valve and perhaps blocking the gas flow through it when the cylinder is inverted. Some scuba valves have a safety hole located near FIGURE 1-3. VALVE PARTS (J-VALVE) the top of the valve threads. The purpose of the hole is to indicate there is pressure in a cylinder if someone tries to remove the valve when the cylinder is not empty. Air hisses from the valve and warns the worker. The burst disk is a safety item intended to prevent cylinder pressure from reaching dangerously high levels during filling or under conditions of extreme heat (such as a fire). U.S.-made burst disks are rated at a maximum of five-thirds the working pressure of a cylinder. The rated bursting pressure range of burst disks for 2,250 psi (155 bar) cylinders is from 3,375 to 3,750 psig (230 to 260 bar) and for 3,000 psi (207 bar) cylinders the bursting pressure range is from 4,500 to 5,000 psig (310 to 345 bar). The thin, metal burst disks are color coded and usually also stamped with their maximum pressure rating. When a burst disk ruptures, which can occur under normal circumstances from time to time due to fatigue of the disk, a loud noise and hissing result, but the only danger is to your hearing. The escape of air cannot be stopped, and the burst disk must be replaced by a qualified professional before the cylinder valve may be used again. The standard on-off cylinder valve is known as the K-valve in the USA. A U.S. cylinder valve that incorporates a low-air warning mechanism is known as a J-valve (figure 1-3). The J-valve contains a spring-loaded check valve that begins to close and restrict air flow when cylinder pressure reaches a predetermined pressure (usually 20 or 35 bar 300 to 500 psi). The J-valve permits unrestricted flow of air to the regulator throughout a dive until the valve closing pressure is approached. At the
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