The equipment used for oxyacetylene welding consists of a source of oxygen and a source of acetylene from a portable or stationary outfit. The portable outfit consists of an oxygen cylinder and an acetylene cylinder with attached valves, regulators, gauges, and hoses (fig. 15-23). This equipment may be temporarily secured on the floor or mounted on a two-wheel, welded, steel truck equipped with a platform that will support two large size cylinders. The cylinders are secured by chains attached to the truck frame. A metal toolbox, welded to the frame, provides storage for torches, tips, gloves, fluxes, goggles, and necessary wrenches. Stationary equipment is installed where welding operations are conducted in a fixed location. The acetylene and oxygen are piped to several welding stations from a central supply. Master regulators are used to control the flow of gas and maintain a constant pressure at each station.

OXYGEN. -Oxygen is a colorless, tasteless, odor-less gas that is slightly heavier than air. Oxygen is nonflammable, but it will support combustion when combined with other gases. This means that it aids in burning, and this burning gives off considerable heat and light. In its free state, oxygen is one of the most common elements. The atmosphere is made up of approximately 21 parts of oxygen and 78 parts of nitrogen, with the remainder being rare gases. It is the presence of oxygen in the air that causes rusting of ferrous metals, the discoloration of copper, and corrosion of aluminum. This action is known as oxidation.

Oxygen is obtained commercially either by the liquid air process or by the electrolytic process. In the liquid air process, air is compressed and cooled to a point where the gases become a liquid. As the temperature of the liquid air is raised, nitrogen in a gaseous form is given off first, since its boiling point is lower than that of liquid oxygen. These gases, having been separated, are further purified and compressed into cylinders for use.

In the electrolytic process, water is broken down into hydrogen and oxygen by the passage of an electric current through it. The oxygen collects at the positive terminal and the hydrogen at the negative terminal. Each of the gases is then collected and compressed into cylinders for use.

OXYGEN CYLINDERS. -A typical oxygen cylinder (fig. 15-24) is made of steel and has a capacity of 220 cubic feet at a pressure of 2,000 psi and a temperature of 70F. Each oxygen cylinder has a high-pressure outlet valve located at the top of the cylinder, a removable metal cap for the protection of the outlet valve during shipment or storage, and a low melting point safety fuse plug and disk. All oxygen cylinders are painted green for identification. Technical oxygen cylinders are solid green, while breathing oxygen cylinders are green with a white band around the top.

Oxygen should never be brought in contact with oil or grease. In the presence of pure oxygen, these substances become highly combustible. Oxygen hose and valve fittings should never be oiled or greased or handled with oily or greasy hands. Even grease spots on clothing may flare up or explode if struck by a stream of oxygen.

PRESSURE REGULATORS. -The gases compressed in oxygen and acetylene cylinders are at pressures too high for oxyacetylene welding. Regulators

are necessary to reduce pressure and control the flow of gases from the cylinders. Most regulators in use are either the single-stage or the two-stage type. Single-stage regulators reduce the pressure of the gas in one step; two-stage regulators do the same job in two steps or stages. Generally, less adjustment is necessary when two-stage regulators are used.

Figure 15-25 shows a typical single-stage regulator. The regulator mechanism consists of a nozzle through which the high-pressure gases pass, a valve seat to close off the nozzle, and balancing springs. These are all enclosed in a suitable housing. Pressure gauges are provided to indicate the pressure in the cylinder or pipeline (inlet), as well as the working pressure (outlet). The inlet pressure gauge, used to record cylinder pressures, is a high-pressure gauge and is graduated from 0 to 3,000 psi. The outlet pressure gauge, used to record working pressures, is a low-pressure gauge and is graduated from 0 to 500 psi.

In the oxygen regulator, the oxygen enters through the high-pressure inlet connection and passes through a glass wool filter that removes dust and dirt. Turn the adjusting screw in, to the right, to allow the oxygen to pass from the high-pressure chamber to the low-pressure chamber of the regulator, through the regulator outlet, and through the hose to the torch at the pressure shown on the working pressure gauge. Changes in this pressure may be made at will, simply by adjusting the

Figure 15-25.-Single-stage oxygen regulator.

handle until the desired pressure is registered. Turning the adjusting screw to the right INCREASES the working pressure; turning it to the left DECREASES the working pressure.  The operation of the two-stage regulator is similar in principle to the single-stage regulator. The difference is that the total pressure decrease takes place in two steps instead of one. On the high-pressure side, the pressure is reduced from cylinder pressure to intermediate pressure. On the low-pressure side, the pressure is reduced from intermediate pressure to working pressure.  Because of the two-stage pressure control, the

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 5,700F and 6,300F.