If the cylinder passes the visual inspection, a visual cylinder inspection sticker is attached to the cylinder with the month and year of the inspection noted on the sticker (figure 2-15). If the cylinder does not pass the visual inspection, it might need to be cleaned or tumbled to remove oxidation. If the cylinder needs to be tumbled, it automatically needs hydrostatic testing. Hydrostatic Testing In the United States, hydrostatic testing is required every five years or whenever the cylinder must be cleaned by tumbling. Hydrostatic testing tests the cylinder for metal fatigue. During hydrostatic testing, the scuba cylinder is filled with water and placed in a larger sealed cylinder full of water (figure 2-16). The pressure of the water in the scuba cylinder is increased to 5/3 the service pressure of the cylinder and then reduced to the pressure of the surrounding water. If the cylinder’s size increases with the increase of pressure but does not decrease back within set limits when the pressure is relieved, the cylinder can no longer be used. Storage You should store cylinders for any long term with some pressure in the cylinder. In steel tanks, keeping some air in your cylinder ensures that water cannot enter your cylinder and cause corrosion. With aluminum tanks, this is not as much of a concern. Aluminum tanks can be stored empty and with the valves open so that they will not be a hazard in a fire. You should store cylinders upright in a cool, dry, and protected location where they cannot be knocked over. Never leave a cylinder standing by itself when you are not holding it. You should lay your cylinder down to prevent damage to it, the valve, or injury to someone. When transporting a cylinder in a moving vehicle, place the cylinder on its side and secure it to prevent damage to the cylinder, the valve, or the vehicle. Backpacks Backpacks are designed to hold a cylinder securely on a diver’s back. Backpacks are now usually incorporated directly in the buoyancy compensator, but you might still see divers using a backpack and separate buoyancy control device. The backpack must be used NAUI Scuba Diver 24 Diving Equipment FIGURE 2-16. HYDROSTATIC TESTING STARTS BY FILLING THE SCUBA CYLINDER WITH WATER AND PLACING IT IN A LARGER CYLINDER OF WATER. FIGURE 2-15 A VISUAL CYLINDER INSPECTION STICKER IS PLACED ON YOUR CYLINDER WHEN IT HAS PASSED ITS VISUAL INSPECTION.
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