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Single-stage oxygen regulator
Equal pressure welding torch

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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Figure 15-26.—Two-stage regulator. working pressure is held constant, and pressure adjustment during welding operations is not required. A two-stage regulator is shown in figure 15-26. The acetylene regulator controls and reduces the acetylene pressure from any standard cylinder that contains pressures up to 500 psi. It is of the same general design as the oxygen regulator, but it will not withstand such high pressures. The high-pressure gauge, on the inlet side of the regulator, is graduated from 0 to 500 psi. The low-pressure gauge, on the outlet side of the regulator, is graduated from 0 to 30 psi. Acetylene should not be used at pressures exceeding 15 psi. ACETYLENE.—Acetylene is a fuel gas made up of carbon and hydrogen. It is manufactured by the chem- ical reaction between calcium carbide, a gray stonelike substance, and water in a generating unit. Acetylene is colorless, but it has a distinctive odor that can be easily detected. Mixtures of acetylene and air that contain from 2 to 80 percent of acetylene by volume will explode when ignited. However, with suitable welding equipment and proper precautions, acetylene can be safely burned with oxygen for welding and cutting purposes. When burned with oxygen, acetylene produces a very hot flame that has a temperature between 5,700°F and 6,300°F. ACETYLENE CYLINDERS.—Acetylene stored in a free state under pressure greater than 15 psi can be made to break down by heat or shock and possibly explode. Under pressure of 29.4 psi, acetylene becomes self-explosive, and a slight shock will cause it to explode spontaneously. However, when dissolved in acetone, it Figure 15-27.—Acetylene cylinder. can be compressed into cylinders at pressures up to 250 psi. The acetylene cylinder (fig. 15-27) is filled with porous materials, such as balsa wood, charcoal, and shredded asbestos, to decrease the size of the open spaces in the cylinder. Acetone, a colorless, flammable liquid, is added until about 40 percent of the porous material is filled. The filler acts as a large sponge to absorb the acetone, which, in turn, absorbs the acetylene. In this process, the volume of the acetone increases as it absorbs the acetylene, while acetylene, being a gas, decreases in volume. The acetylene cylinders are equipped with safety plugs, which have a small hole through the center. This hole is filled with a metal alloy, which melts at approximately 212°F or releases at 500 psi. When a cylinder is overheated, the plug will melt and permit the acetylene to escape before a dangerous pressure can build up. The plug hole is too small to permit a flame to burn back into the cylinder if the escaping acetylene should become ignited. WELDING TORCHES.—The oxyacetylene welding torch is used to mix oxygen and acetylene gas in the proper proportions, and to control the volume of these gases burned at the welding tip. The torch has two needle valves, one for adjusting the flow of acetylene and the other for adjusting the flow of oxygen. In addition, there are two tubes, one for oxygen and the other for acetylene; a mixing head; inlet nipples for the attachment of hoses; a tip; and a handle. The tubes and 15-20







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