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Selecting an Oxy-Acetylene Welding Rig

Cross filing

Oxy-acetylene welding rigs come in sizes based on the capacity of the oxygen and acetylene cylinders, which hold from 10 to more than 400 cubic feet. Be sure to get regulators, valves, and hoses that match the cylinder sizes you select. Unless you expect to use the equipment a great deal, 20 cubic feet each of oxygen and acetylene—enough to weld for one hour or cut for 20 minutes—is ample. You can buy the equipment at welding-supply stores or rent it from tool-rental agencies, usually listed in directories under “Welding Equipment—Renting.” If you buy the equipment, the tanks may be empty when you get them. Fill them at a welding-supply shop.

When you rent an oxyacetylene rig you can usually obtain welding or cutting tips in a range of sizes for different metal thicknesses. Buying tips individually can be confusing, since each of the dozens of tip manufacturers uses a different numbering system. To buy the correct size, you must consult a size chart for a specific brand. The same chart prescribes the pressure you need to set on the oxygen and acetylene gauges for each size tip.

Anatomy of an Oxyacetylene Rig

Two cylinders—a tall one containing oxygen and a shorter one containing acetylene—stand on a two-wheel hand cart. They’re chained together to keep them from tipping over. You open the acetylene cylinder’s valve with a T-wrench on top, and the oxygen cylinder’s valve with a knob. When not in use, screw the protective cap onto each valve.

At the side of each valve, a dual regulator with two gauges measures the pressure in the cylinder and the working pressure in the hose. The T screw on the front of each regulator adjusts the working pressure. Separate hoses—a red one for acetylene and a green or black one for oxygen—carry the gases to the torch (inset), where an oxygen valve and an acetylene valve control the proportion of each gas at the tip of the torch.

How To Set Up a Rig for Welding

Setting Up a Rig for Welding



Clearing the Valves

Remove the acetylene cylinder’s protective cap, and stand so that the valve outlet nozzle points away from you. Open the valve slightly by turning the T wrench about a quarter turn counterclockwise. After one second, close the valve by turning it clockwise. Wipe out the inside of the valve nozzle to remove dirt from the seat of the regulator.

Remove the protective cap of the oxygen cylinder and repeat the process to clear the oxygen valve. Again, wipe out the inside of the nozzle.

Attaching the regulators




Attaching the Regulators

Turn the adjusting screw of the valve outlet nozzle counterclockwise until you feel no resistance. Put the regulator fitting inside the valve nozzle and tighten the regulator nut, first by hand, then with a wrench, until it is very snug. Attach the oxygen regulator by following the same steps.



Attaching the hoses

Attaching the Hoses

Connect the red hose to the acetylene regulator and the green or black hose to the oxygen regulator. The acetylene fitting on the hose is notched on the hose fitting. Screw it on counterclockwise. Screw on the oxygen hose fitting clockwise.

If the hoses are new, they may be lined with talcum powder, which you should blow out. To do this, grasp the free ends of both hoses in one hand and point them away from you. Slowly open the acetylene cylinder valve, then turn the adjusting screw of the regulator clockwise until the working-pressure gauge of the regulator reads 10 pounds. After about two seconds, close the adjusting screw and the cylinder valve. Blow out the oxygen hose in the same way, opening the cylinder valve and turning the regulator’s adjusting screw on the oxygen cylinder to bring the working-pressure gauge to 10 pounds. Then close the screw and valve.

Assembling the torch and tip



Assembling the Torch and Tip

Select the tip you plan to use and screw it onto the torch end. Connect the red hose to the torch nozzle marked fuel or gas, and the green or black oxygen hose to the nozzle marked oxy. Turn the acetylene hose nut counterclockwise and the oxygen hose nut clockwise. Tighten both of the nuts with a wrench.

Check to see if the tip is clean. If it is not, insert a metal tip cleaner slightly smaller than the hole, guiding it carefully into the hole in a straight line so that you will not damage the opening. Graduate to a tip cleaner the same size as the hole, and repeat the cleaning process.

Checking for leaks

To make sure the torch valves are closed, turn the oxygen and acetylene valves clockwise. Then stand to one side and slowly open the oxygen cylinder valve one half turn (left). Turn the adjusting screw until the oxygen working-pressure gauge reads 20 pounds. Then open the acetylene cylinder valve a quarter turn, and turn the adjusting screw until the acetylene working-pressure gauge reads 5 pounds. Close both cylinder valves, and watch the cylinder-pressure gauges; if they fall, there is a leak. Repeat steps 2 through 4, tightening all the fittings, then repeat the test.

If tightening the fittings does not solve the problem, you can locate the leak by brushing all the fittings and the hoses with a soapy solution. Mix a capful of liquid dishwashing detergent in a gallon of water (right). (Do not use soap containing lanolin or oil.) Bubbles will appear at the leak. If a fitting leaks beyond correction, return it to the supplier for replacement. After a successful leak test, reset the regulators for the correct tip pressure.