414 Modern Welding Copyright Goodheart-Willcox Co., Inc. To set the oxygen working pressure, open the torch oxygen valve one-half to one full turn. Then, depress the cutting oxygen lever to open the oxygen cutting valve. Adjust the oxygen regulator to give the desired oxy- gen working pressure. See Figure 15-10. If the oxygen pressure is not set with the oxygen cutting valve open, the oxygen pressure will be too low when this valve is opened during the cutting operation. This results in a reduced preheat fl ame, and possibly a poor cut. Close the torch oxygen valve and the oxygen cutting valve. After the outfi t has been purged and the correct work- ing pressures have been set, the cutting torch is ready to light. Before the torch is lit for the fi rst time each day, the process of turning on the outfi t to purge the hoses, regulators, and torches individually should be completed. Hoses must not be purged into con- fi ned spaces or near ignition sources. Also, the oxy- fuel gas cutting outfi t needs to be purged after every cylinder change. A B Goodheart-Willcox Publisher Goodheart-Willcox Publisher Figure 15-10. Regulator settings. A—An acetylene regulator with the working pressure (marked L.P. for “Low Pressure”) set at 5 psi (35 kPa). B—An oxygen regulator with the working pressure (marked L.P.) set at 25 psi (175 kPa). Procedure Lighting and Adjusting an Oxyacetylene Cutting Torch After the cutting outfit has been turned on and the correct working pressures have been set, the torch is ready to be lit. A flint-and-steel spark lighter or a stationary pilot flame must be used to light the torch. Warning Matches, cigarette lighters, or welding arcs must not be used for lighting torches. Severe burns may result. When lighting the cutting torch, hold it so the cutting tip faces downward. Strike a spark while holding the spark lighter approximately 1″ (25 mm) from the tip. Follow this procedure for lighting an oxyacetylene cutting torch: 1. Open the acetylene torch valve 1/16 turn. 2. Light the cutting torch with a spark lighter. All preheating flames should light at the same time. If all the flames do not light, shut down the torch and clean any dirty orifices. 3. Continue opening the acetylene torch valve until the smoking stops. The flame must remain in contact with the end of the tip. Acetylene Burning in Atmosphere Smith Equipment, Division of Tescom 4. Open the torch oxygen finger valve until neutral preheating flames are obtained. The cutting oxygen valve must be closed (not depressed) during this adjustment. Neutral Flame Smith Equipment, Division of Tescom (Continued)