Oxy-acetylene welding manual

by Lorn Campbell

(21) The mixing chambers for the gases may be located in the head; in the middle of the torch, or in the handle. By mixing chambers reference is made to that portion of the torch where the two gases are brought together and mixed. As can be seen with three different types of welding torches and three different locations for the mixing of the gases, the manufacturers can find a large range for producing oxy-acetylene apparatus. Some undoubtedly will fill certain requirements better than others. Much, too, will depend upon the ability of the operator in handling a torch.

(22) Flashbacks are caused by the improper mixture of the gases, which increases the rate of flame propagation to such an extent that the flame will flash back to the mixing chamber. Acetylene in a pure state will burn very much slower than when mixed with equal parts of oxygen. When more oxygen is introduced the flame propagation is much greater, so that when an excess of oxygen is used, there is bound to be considerable trouble from backflashing. When sufficient acetylene is introduced to the mixing chamber, there is absolutely no chance for this lean mixture to occur. If the flame flashes back to the mixing chamber, both gases should be closed off immediately, at the torch, the oxygen first, and then the acetylene gas.

(23) In some torches the heating of the mixing chamber will cause a flashback and with these it is necessary to shut off the acetylene and leave the oxygen valve just cracked and immerse the torch head in water, dipping it slowly, so as not to cause too great a strain. The oxygen will bubble out and prevent the water backing up in the tip. If the flashback deposits enough soot on the inside of the tip and the head to impair the working quality of the torch, the soot should be removed by using a soft wire, preferably of copper, or some other material which will not mar the tip.

Fig. 16.—Cross-section of Regulator.

A, chamber; B, nozzle; C, seat; D, seat arm; E, diaphragm; F, cross-bar, or adjusting screw; G, diaphragm springs; H, gas outlet; I, gas inlet.

(24) It is interesting to note the action of a regulator, used to reduce the cylinder pressure on both gases. The gas from the cylinder, at high pressure, comes directly into the body of the regulator or chamber (A), [Fig. 16], through a fine nozzle (B). A seat of gallilith, casenite, or fiber (C), attached to an arm (D), presses against this nozzle. Arm (D), in turn, is attached to a very sensitive diaphragm (E) and is moved every time there is a pressure exerted on the latter. The movement of this diaphragm is controlled by a handle or a screw, with a “cross-bar” attached to its end as is shown at (F). This screw bears upon the diaphragm through the medium of the springs (G). As this screw is forced inward the springs force the diaphragm in, and thereby move the seat away from the nozzle of the regulator. The gas, entering under high pressure, exerts an equal force on all parts of the chamber and the diaphragm receives its share. Now the chamber walls are made of a solid material, usually a bronze or brass, and cannot be changed, but this diaphragm can be moved and as this pressure is increased, the diaphragm is forced out and the nozzle (B) is automatically closed by having the seat (C) brought in contact with it. When gas is drawn off through the line (H), the pressure within the chamber will naturally drop and as it does so, the springs will force the diaphragm inward, permitting a replacement of the gas drawn off. Although not noticeable, there is a continual movement of this diaphragm whenever the gas is being used. It can be readily seen that the amount of pressure within the regulator can be accurately set by the tension of the spring against the diaphragm which is controlled by the screw carrying the “cross-bar.”

(25) There are two types of regulators manufactured for the reduction of gases under high pressure, depending upon the nature of work to be done. The high-pressure regulator is employed for heavy work where a great deal of gas is used and the regulator must pass it without much effort, to prevent its freezing. This type of regulator is used on cutting or on large welding work. It differs from the low-pressure or ordinary type in four distinct features. Generally it contains a much heavier diaphragm which is smaller in diameter, making it stiffer in every respect. The tension springs which act upon this diaphragm are much heavier. The nozzle which presses against the seat is much larger, to permit the passage of a greater amount of gas. Then, too, a larger working pressure gauge must be used, in order to read this high pressure. In the welding of metals, especially in steel, the adjustment of the flame is a very important matter, and absolutely dependable regulation must be had. This is not possible with a high-pressure regulator and is not intended to be so. The larger the diaphragm, the more sensitive the regulator, and this point should be borne in mind, and no small welding work attempted with the high-pressure regulator. The reverse form of reasoning may be applied to low-pressure regulators which have been used in cutting. They are very likely to be strained and satisfactory results cannot be expected, for they are not made for that purpose. Acetylene regulators are constructed much more sensitively than the oxygen regulators, to take care of the lower pressure of gas and in a sense might be called weaker, insomuch that the larger nozzle which passes the gas is closed or regulated by springs which are not nearly as strong as in the oxygen regulator. For this reason acetylene regulators cannot be interchanged with oxygen regulators for they will not stand the pressure demanded in the first place, and in the second place, were a small quantity of acetylene gas left in the regulator and oxygen introduced, an inflammable mixture would be formed which is not advisable to have present, on account of its explosiveness. In many instances oxygen regulators are put out with the copper diaphragms, whereas another metal must be used on the acetylene regulators, because acetylene gas attacks copper and usually a German silver or rubber diaphragm is used. On account of the lower pressures used in charging the acetylene cylinders, lower pressure gauges are used than on oxygen regulators.

(26) All tension should be removed from the diaphragm springs by screwing out on the “cross-bar” (that is, to the left), before admitting gas under pressure to the regulator to avoid abusing the seat. If a matter of 1800 pounds pressure were admitted suddenly into any regulator that had the seat removed from the nozzle, there would be a sudden exertion upon the diaphragm, which would draw the regulator seat up very violently against the nozzle, and if it did not crack the seat it would undoubtedly groove it to such an extent that it would leak and a trouble known as “creeping regulator” would result. If this occurs, good work cannot be expected because the flame will not remain steady, and it is therefore necessary to take steps to rectify this abuse. If there is a welding company available, the regulator should be sent to it for repairs, but if the operator is in an isolated district when this occurs, and must have some means of continuing work, it will be possible for him to remove the seat by unscrewing the back of the regulator. If the seat has become grooved, and he thinks that this is the trouble, many times the seat can be turned over and the machined surface on the other side used. If the seat is cracked, however, about the quickest way of making an emergency repair is to turn out a new seat from hard rubber or fiber on a lathe.

(27) In acetylene cylinders an absorbent called acetone is generally used, which gives up the gas as required. A full cylinder can be used for some time without any noticeable difference in the gauge reading, and then, as it nears the empty point, the gauge reading will drop very perceptibly. It is therefore impossible to depend upon a high-pressure acetylene gauge as an index to the contents of the cylinder. The only method known to correctly check the amount of acetylene gas on hand is to weigh the cylinder. There are 14¹⁄₂ cubic feet of acetylene gas to the pound, and when the net weight of the cylinder is given the contents can readily be figured. A tag bearing the net weight or figures which will permit its computation is generally found attached to each acetylene cylinder. In the case of oxygen cylinders, there being no absorbent used, the contents of the cylinder is indicated on the high-pressure gauge. On the latest type gauge the contents will be shown by cubic feet, by pounds pressure and by atmospheric pressure, to facilitate the computation of costs by the operator.