Handbook-Manual Cutting

regulator and torch (unless otherwise stated). The pressure drop in that length of hose, if the nipples used in each

end of the hose have the recommended 1/4-in. (6.3 mm) hole size, will be relatively small (3 psi or 0.2 bars) at an oxygen flow rate of 500 cfh (12 m³/h). The pressure drop in a similar length of 1/4-in. (6 mm) hose will be more than four times as great. Since the oxygen flow required for cutting 150 mm (6 in.) steel is nearly 500 cfh, hose size is extremely significant. Tables showing pressure drops at various flow rates through several hose sizes are given in the Appendix. We urge you to consult these tables whenever you plan to do any heavy cutting, and that you try to avoid using any combination of hose length and size which will cause a pressure drop greater than 10 psi (0.7 bars). (Note: There is one way to be sure you have the correct pressure; that is to measure it at the torch inlet, with the correct size of nozzle in place and the cutting oxygen valve wide open. A simple test gauge adaptor, which can be temporarily inserted between the torch inlet connection and the oxygen hose, is relatively inexpensive.) 4. Don’t expect too much from a small oxygen regulator with a 100 psi (7 bar) delivery-pressure gauge, even though it is rated to deliver pressures as high as 60-75 psi. The pressure drop through the regulator itself may be so great that it cannot deliver 400-500 cfh at 55 psi or more. Almost all standard-size one-stage and two-stage oxygen regulators equipped with 100-psi delivery-pressure gauges, however, will prove more than adequate for the hand cutting of steel 150 mm (6 in.) thick when used on full high-pressure cylinders of oxygen.