Subsequent dates, usually at five year intervals, indicate when mandatory hydrostatic pressure testing was performed and by whom. See Figures 1–8 and 1–9.
Figure 1–8High-pressure cylinder markings
Figure 1–9Acetylene cylinder markings
What are common oxygen cylinder sizes?
Figure 1–10 shows high-pressure cylinder sizes. Many gases in addition to oxygen, like nitrogen, carbon dioxide, and argon come in high-pressure cylinders.
Figure 1–10Oxygen cylinder sizes
What factors govern the choice of oxygen and acetylene cylinder size?
Smaller cylinders are suitable for refrigeration repairman who must climb ladders with OAW equipment, but they are impractical for most work. For example, a 55 ft3 (1557 liter) oxygen cylinder would last under two hours cutting
What are the common acetylene cylinder sizes?
See Figure 1–11.
Figure 1–11Acetylene cylinder sizes
Why are pressure gauges on acetylene cylinders poor indicators of remaining gas quantity?
Gas pressure remains nearly constant at a given temperature as acetylene gas is withdrawn from solution in acetone until very little gas remains. The best way to determine a cylinder’s remaining contents is to compare its current weight with its empty weight. Note that the weight of the empty cylinder is stamped on its top. There are 14.6 ft3 of acetylene for every pound of cylinder weight over its empty weight, or one liter of acetylene for every 1.1 grams of cylinder weight over the empty weight. Drawing acetylene from cylinders at pressures below 25 psi (1.7 bar) can cause acetone to be withdrawn from the cylinder.
Under what ownership arrangement may compressed gas cylinders be offered to users by welding equipment suppliers?
•Outright sale of the cylinder with the right to exchange it for a filled one of equal size by paying for refill is most economical in the long run. Usually one gas supplier will accept the cylinders you obtained from another at no additional charge. There will be a problem swapping cylinders if an embossed owner’s name appears on the neck ring.
•Cylinders may be rented by the month or year. Excellent when you don’t have a long-term need for them, just an immediate one.
•Some distributors lease cylinders for a year or more; some for 99 years.
•There is a very silly practice that is worth mentioning. Some gas distributors try to sell you a brand new cylinder for more money than one with previous use—an “old” one, but since most cylinders cannot be refilled immediately, chances are that you will exchange your “new” one for an “old” one when you get your first refill. The “old” ones usually cost less. And since cylinders can last well over 30 years and the cylinders due for pressure hydro testing are tested at the gas supplier’s expense, there is little point in paying extra to get your own “new” cylinder.
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
