nonflammable, but it will support combustion whencombined with other gases. This means that it aids inburning, and this burning gives off considerable heat andlight. In its free state, oxygen is one of the most commonelements. The atmosphere is made up of approximately21 parts of oxygen and 78 parts of nitrogen, with theremainder being rare gases. It is the presence of oxygenin the air that causes rusting of ferrous metals, thediscoloration of copper, and corrosion of aluminum.This action is known as oxidation.Oxygen is obtained commercially either by theliquid air process or by the electrolytic process. In theliquid air process, air is compressed and cooled to a pointwhere the gases become a liquid. As the temperature ofthe liquid air is raised, nitrogen in a gaseous form isgiven off first, since its boiling point is lower than thatof liquid oxygen. These gases, having been separated,are further purified and compressed into cylinders foruse.In the electrolytic process, water is broken downinto hydrogen and oxygen by the passage of an electriccurrent through it. The oxygen collects at the positiveterminal and the hydrogen at the negative terminal. Eachof the gases is then collected and compressed intocylinders for use.OXYGEN CYLINDERS.—A typical oxygencylinder (fig. 15-24) is made of steel and has a capacityof 220 cubic feet at a pressure of 2,000 psi and atemperature of 70°F. Each oxygen cylinder has ahigh-pressure outlet valve located at the top of thecylinder, a removable metal cap for the protection of theoutlet valve during shipment or storage, and a lowmelting point safety fuse plug and disk. All oxygencylinders are painted green for identification. Technicaloxygen cylinders are solid green, while breathingoxygen cylinders are green with a white band around thetop.CAUTIONOxygen should never be brought in contactwith oil or grease. In the presence of pureoxygen, these substances become highlycombustible. Oxygen hose and valve fittingsshould never be oiled or greased or handledwith oily or greasy hands. Even grease spotson clothing may flare up or explode if struckby a stream of oxygen.PRESSURE REGULATORS.—The gasescompressed in oxygen and acetylene cylinders are atpressures too high for oxyacetylene welding. RegulatorsFigure 15-24.—Typical oxygen cylinder.are necessary to reduce pressure and control the flow ofgases from the cylinders. Most regulators in use areeither the single-stage or the two-stage type. Single-stage regulators reduce the pressure of the gas in onestep; two-stage regulators do the same job in two stepsor stages. Generally, less adjustment is necessary whentwo-stage regulators are used.Figure 15-25 shows a typical single-stage regulator.The regulator mechanism consists of a nozzle throughwhich the high-pressure gases pass, a valve seat to closeoff the nozzle, and balancing springs. These are allenclosed in a suitable housing. Pressure gauges areprovided to indicate the pressure in the cylinder orpipeline (inlet), as well as the working pressure (outlet).The inlet pressure gauge, used to record cylinderpressures, is a high-pressure gauge and is graduatedfrom 0 to 3,000 psi. The outlet pressure gauge, used torecord working pressures, is a low-pressure gauge andis graduated from 0 to 500 psi.In the oxygen regulator, the oxygen enters throughthe high-pressure inlet connection and passes through aglass wool filter that removes dust and dirt. Turn theadjusting screw in, to the right, to allow the oxygen topass from the high-pressure chamber to the low-pressure chamber of the regulator, through the regulatoroutlet, and through the hose to the torch at the pressureshown on the working pressure gauge. Changes in thispressure may be made at will, simply by adjusting the15-18
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