Chapter 14 Oxyfuel Gas Cutting 413 4. Open the acetylene cylinder valve slowly 1/4 to 1/2 turn. Leave the acetylene cylinder valve wrench in place so the cylinder valve can be shut off quickly if necessary. 5. Open the torch oxygen valve one full turn. Next, depress the cutting oxygen lever to open the oxygen cutting valve. Adjust the oxygen regulator to give the desired oxygen working pressure. Figure 14-7 shows a single-stage oxygen pressure regulator. 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. See the table in Figure 14-8 for proper oxygen and acetylene working pressures. 6. Open the acetylene torch valve one turn. Slowly turn in the acetylene regulator adjusting screw until the low-pressure acetylene gauge indicates working pressure corresponding to tip size. Refer to Figure 14-8. Close the torch acetylene valve. Caution: Never use acetylene at a pres- sure above 15 psig (103kPa). 7. After setting the working pressures, check the low-pressure gauge readings to make sure that the pressures are not rising. A rising gauge pressure indicates that the regulator pressure valve is leaking. The outfi t should be shut down immediately or the gauge may rupture. Preheating flame orifice Cutting oxygen orifice Cutting line (axis) Figure 14-6. Correct alignment of the preheating orifi ces on a cutting torch. Two preheating orifi ces should line up with the cutting line. Figure 14-7. A single-stage oxygen regulator. The low-pressure gauge reads up to 200 psig (1400kPa), indicating that it may be used with a cutting torch. (Uniweld Products, Inc.) Metal thickness Cutting orifice diameter Approximate gas pressures Approximate travel speed in mm in Drill size Acetylene psi Oxygen psi in/min mm 1/8 1/4 3/8 1/2 3/4 1 1 1/2 2 0.040 0.040 0.052 0.052 0.052 0.060 0.060 0.073 1.02 1.02 1.32 1.32 1.32 1.52 1.52 1.85 3 3 3 3 4 4 5 5 10 15 20 25 30 35 40 45 18–22 14–18 12–16 10–14 8–12 8–11 6–8 5–7 60 60 55 55 55 53 53 49 3.2 6.4 9.5 12.7 19.1 25.4 38.1 50.8 Oxyacetylene Cutting Parameters for Positive-Pressure Torch Figure 14-8. This table shows the approximate tip sizes and oxygen and acetylene pressures to use for cutting various sizes of steel sheet and plate with a positive-pressure cutting torch. This table is for a torch equipped with a tip that has four preheating orifi ces. For heavier or faster cutting, a larger diameter cutting orifi ce or tips with more than four preheating orifi ces may be used.