Regulators
What is the purpose of pressure regulators?
Regulators reduce the pressures of welding gases from the very high cylinder pressures to the low pressures needed by the torch to function properly. Also, as the cylinder pressure falls with gas consumption, the regulator maintains the constant pressure needed by the torch, even though the cylinder supply pressure drops greatly. For example, an oxygen cylinder may contain oxygen at 2250 psi (155 bar) and the torch requires about 6 psi (0.4 bar) to operate. Similarly, a full acetylene tank may contain gas at 225 psi (15.5 bar) and the torch needs fuel gas at 6 psi (0.4 bar).
How does a single-stage pressure regulator work?
There are two designs for single-stage regulators, the stem-type and the nozzle-type. In the stem-type, the balance of forces on each side of the diaphragm and attached stem perform pressure regulation. There are four forces acting on the diaphragm and stem. In Figure 1–12 the combined forces of the large upper spring and atmospheric pressure act to open the regulator valve and admit gas into the regulator and hoses; in the opposite direction the combined forces of the high-pressure gas on the lower side of the diaphragm and the small stem spring act to close the regulator. When the adjusting screw is unscrewed (or in the up position in the diagram), there is little pressure exerted downward on the diaphragm by the large spring and the regulator stays closed. When the adjusting screw is tightened downward to increase regulator pressure, the increased pressure on the attached spring exerts more pressure on the diaphragm and opens the valve, admitting high-pressure gas to the lower chamber and hose. As gas continues to enter this chamber, chamber pressure rises. When it rises above the pressure called for, the high-pressure gas in the lower chamber partially or fully closes the valve to maintain the desired pressure.
Figure 1–12Single-stage stem-type regulator
The nozzle-type regulator is very similar to the stem-type regulator, but instead of the valve being closed by inlet or cylinder pressure as in the stem-type, the inlet pressure works to open the valve. The result is the same: a balance of pressure across the diaphragm accurately controls pressure to the torch.
How does a two-stage regulator work?
A two-stage regulator is basically two single-stage regulators connected in series inside the same housing with the total pressure drop being split across the two regulator stages. The first stage pressure is factory-set; the second stage pressure is user-set. See Figure 1–14.
Figure 1–13Single-stage nozzle-type regulator
What are the advantages and disadvantages of a two-stage pressure regulator over a single-stage one?
The two-stage regulator’s advantage is that a higher volume of gas may be withdrawn from the cylinder with less pressure fluctuation than produced by a single-stage regulator. The combination of two regulators working together in series maintains a very constant torch pressure over wide cylinder pressure changes. Its disadvantage is cost. They are only needed when large gas volumes are needed as with multiple stations or rosebud tips.
Figure 1–14Two-stage regulator
Torches, Tips, and Hoses
What are the major parts of an oxyacetylene torch?
Shown below is the most common oxyacetylene torch design. Other designs are available. Some have very small flames for jewelry and instrument work, while others take no accessories and are much lighter in weight than standard torch designs to reduce operator fatigue.
Figure 1–15Oxyacetylene torch and tip
Besides a selection of tip sizes for different sized jobs, what other devices can be put on the torch handle and what are they used for?
•Cutting heads also called cutting attachments (see Chapter 2).
•Multi-flames for heating metals prior to bending, brazing, or heat-treating.
Figure 1–16Oxyacetylene torch attachments: cutting head (left), welding tips (center) and multi-flame tip (right)
Why are there different size torch tips?
Matching the size of the flame and the resulting volume of gas to the thickness of the metal in the weld is important. Too much flame and the base metal around the weld may be damaged, too little and there is inadequate heat to melt metal for full penetration.
How are torch tip sizes designated?
There is no industry standard; each torch manufacturer has its own numbering system. Cross-reference tables compare each manufacturer’s tip sizes with numbered drill sizes.
The American Welding Society (AWS) has been urging tip manufacturers to stamp tips with the material thickness size to eliminate the confusion of tip size numbers. The AWS C4.5M Uniform Designation System for Oxy-Fuel Nozzles calls for tips to be stamped with the name of the manufacturer, a symbol to identify the fuel gas, the maximum material thickness, and a code or part number to reference the manufacturer’s operating data; many manufacturers are not in compliance. Most companies making welding tips do provide information booklets available to cross reference their tip sizes to tip drill sizes. See Table 1-2 tip drill size to material thickness.
Table 1-2Matching welding tip size to weld material thickness
How can the drill size of a tip be determined?
Using a tip cleaner find the round file which fits into the tip easily but snuggly then check the drill size of that file listed on the body of the tip cleaner cover.
When should the torch tip be cleaned and how is it performed?
When sparks from the weld puddle deposit carbon inside the nozzle and on the tip face. These act as spark plugs and cause premature ignition of the gas mixture. Torch tips should be cleaned at the start of each day’s welding and whenever flashback occurs, the flame splits, or when the sharp inner cone no longer exists. To clean, select the largest torch tip cleaning wire file that fits easily into the nozzle and use the serrated portion to remove any foreign material. Be careful not to bend the tip cleaner file into the tip which can cause the cleaning file to break inside the tip; if the file breaks inside the tip it is nearly impossible to remove. Also be sure not to enlarge the existing hole. Then touch up the face of the tip with a file or emery cloth to remove any adhering dirt. Use compressed air or oxygen to blow out the tip.