low-pressure (or injector-type) torch is shown in figure 3-55.

Medium-pressure torches are sometimes called balanced-pressure or equal-pressure types, since the acetylene and the oxygen pressure are kept equal. Pressure per square inch may be from 1 to 6 or 8 pounds; ACETYLENE PRESSURE MUST NEVER BE ALLOWED TO EXCEED 15 PSI. A typical equal-pressure general-purpose torch is shown in figure 3-56. The medium-pressure torch is easier to adjust than the low-pressure torch and, since equal gas pressures are used for the medium-pressure torch, you are less likely to get a flashback; the flame is less likely to catch in or behind the mixing chamber. More details on flashback are provided later in this chapter.

Welding TIPS and MIXERS are designed in several ways, depending on the manufacturer. Some makes of torches have a separate mixing head or mixer for each size of tip. Other makes have only one mixer for several tip sizes. Tips come in various types. Some are one-piece, hard copper tips. Others are two-piece tips and include an extension tube to make connection

Figure 3-55. - Mixing head for a low-pressure torch.

Figure 3-56. - Equal-pressure welding torch.