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Hard- Surfacing, Building Fusion Welding Carbon Welding Non-Ferrous Metals Heating & Heat Treating Braze Welding Welding Cast Iron Welding Ferrous Metals Brazing & Soldering Equipment Set-Up Operation Equipment For OXY-Acet Structure of Steel Mechanical Properties of Metals Oxygen & Acetylene OXY-Acet Flame Physical Properties of Metals How Steels Are Classified Expansion & Contraction Prep For Welding OXY-Acet Welding & Cutting Safety Practices Manual Cutting Oxygen Cutting By Machine Appendices Testing & Inspecting
18 In an oxygen cylinder there is a precise relationship between cylinder pressure and cylinder contents. A standard oxygen cylinder that contains 244 cf at 2200 psi and 700 (6.5 m3 at 15200 kPa at 200C) will contain 122 cf (3.25 m3) when the pressure has dropped to 1100 psi at 700F (7600 kPa at 200C). In the dissolved acetylene cylinder, the relationship between pressure and remaining acetylene content is less precise. An acetylene cylinder is not precisely half-full when its pressure has dropped to 125 psi (half the pressure of a full cylinder). If the cylinder temperature is 700F (200C), the amount of acetylene remaining in the cylinder is slightly less than half the ”full” content. However, change in temperature affects the pressure in an acetylene cylinder at a much faster rate than it affects the pressure in an oxygen cylinder. Pressure in an oxygen cylinder will go up or down only about 4 percent for each 20-degree change in temperature (F) from 70 deg.  A full acetylene cylinder which has a pressure of 250 psi at 700F (1725 kPa at 20 C) will have a pressure of 315 psi at 900F (2175 kPa at 310C) and a pressure of 190 psi at 500 F (1300 kPa at 90C). You must always take temperature into account when estimating how much acetylene the cylinder contains. Manifolds and Piping Systems While a great deal of oxy-acetylene welding and cutting is done using gases supplied by a single pair of cylinders, there are many situations which require something more. We have noted that a large acetylene cylinder should not be called upon to supply acetylene at a steady rate of more than about 60 cfh (less than 2 m3/hr). Yet there are heating heads, designed for use with standard torches, which will burn up to 250 cfh (9 m3/hr). While the withdrawal rate from oxygen cylinders is not limited, 45 minutes of cutting 3-in. steel will exhaust the contents of a standard oxygen cylinder. In such situations, portable cylinder manifolds, which link from two to five cylinders together to supply a single torch, are frequently used. Many shops have oxygen and acetylene piping systems. Most oxygen piping systems are now supplied from liquid oxygen storage tanks, although permanently-mounted oxygen cylinder manifolds, to which any number of cylinders can be attached, are still used occasionally. Acetylene piping systems may be supplied by an acetylene generator, by a stationary cylinder manifold, or by an acetylene trailer. An acetylene trailer is essentially nothing more than a group of large acetylene cylinders, coupled together on a trailer, which can be hooked up directly to the user’s piping system. Continued on next page...