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2 Continued on next page... The Welding Torch The gas welding torch is made up of a torch handle and a welding head. For marketing convenience, the handle is often packed separately, and labelled ”torch”, but it can’t be used for welding until you put the welding head on it. The key parts of a complete welding torch, as shown in the simplified sketch (Fig. 5-2), are valves to control the flow of oxygen and acetylene, a mixer through which the gases pass, a mixing chamber into which the gases are allowed to expand and mix after leaving the mixer, and a welding tip. Of these four sections, only the valves are normally in the handle. The mixer, mixing chamber, and tip are in the welding head. The valves (often called throttle valves) must be big enough to pass the volumes of gas required for the flame without too much pressure drop. In an ”all-purpose” handle, where the flow rate for each gas may range from 4 to 200 cfh (0.1 to 5.6 m3/hr), they must be more generously proportioned than in a small handle designed for flows up to about 55 cfh (1.5 m3/hr). Valves must be equipped with leakproof packing, and are normally fitted with packing
nuts which allow the pressure on the packing to be adjusted for the desired ”stiffness” of the valve operation.