is usually supplied in a high-pressure cylinder with a pressure of 2,000 to 2,600 psi (pounds per square inch). This high pressure must be reduced to less than 15 psi for welding the typical material thicknesses used in automotive applications.
Connecting an oxygen regulator and adjusting the pressure must be done following the manufacturer’s instructions. Be sure to read and understand the operating and safety precautions. When installing the regulator on a cylinder and opening the cylinder valve, very high oxygen pressure enters the regulator passages. This sudden high-pressure surge can cause a high temperature similar to what occurs in a Diesel engine combustion chamber when air is compressed. Most materials, including stainless steel and copper, burn and melt in the presence of pure oxygen. If not handled properly, the regulator could explode causing serious injury.
The internal design of an oxygen regulator must consider the possibilities of an oxygen fire or explosion. For these regulators to function efficiently, a valvespring is located on the high-pressure side of a diaphragm to regulate the pressure. This valvespring attaches to a valvestem and valvestem guide, which smoothes out the movement of the valvestem, so the regulator does not chatter due to rapid opening and closing of the valve.
Fig. 3.3. An oxygen regulator reduces the approximate 2,600 psi in a high-pressure cylinder to 5 to 15 psi, so it can be safely used for welding. Proper precautions must be followed when installing an oxygen regulator to avoid the possibility of a fire or explosion. Always follow the manufacturer’s instructions.
Here are the steps to avoid an explosion:
1. Before installing a regulator on a cylinder, visually check the cylinder outlet to make sure there is no debris.
2. Crack open the cylinder contents valve to clear any potential contaminants from the opening.
3. A slight opening is all that is needed. Quickly close the valve.
4. The oxygen regulator must have an inlet filter, so carefully check to see that it’s in place. If it is missing or not working, do not use the regulator. Take it to your gas supplier and have one installed or have the existing one repaired.
5. With an inlet filter in place, make sure it is clean, and free of all oil, grease, or contamination. This is particularly important in a location where grease or oil may be in the area where the regulator was placed when changing cylinders. Locate a clean location to place the regulator while swapping cylinders. The workbench needs to be free of grease or oil so you do not contaminate the regulator, and never put the regulator on the floor. Remember that even a small amount of oil or grease located on the regulator inlet can cause a regulator explosion.
6. After the regulator is connected, tighten the nut with no more than a 12-inch-long wrench. The sealing seats on the regulator inlet and cylinder valve are carefully machined metal-to-metal surfaces. Never use thread sealer on any regulator threads because regulator threads are not sealing threads, rather they are only for pulling the seats together. If the seats leak, the threads do not block the flow of gas. With oxygen service, not using thread sealant is even more important because contamination of the inlet occurs.
7. If the seats are clean, they do not need high torque to properly seat. If they do need high torque, either the cylinder or regulator may have a defective seat.
8. If a leak is found after testing, remove the regulator, clean the seat with a clean cloth, and reinstall. If the leak is still present, replace the cylinder or the regulator.
The way a cylinder valve is opened is very important. A valve on any high-pressure cylinder should always be opened very slowly. One reason is the pressure gauge has a small, sealed, curved tube that bends when subjected to pressure. When the tube bends, it actuates levers that move the gauge pointer, and rapidly opening the cylinder stresses the tube.
An explosion is possible if the valve on the oxygen sensors is opened too quickly (I have witnessed many tests of oxygen regulator explosions in a laboratory environment, so this next step is reinforced in my mind). Before opening the oxygen cylinder valve, be sure the regulator pressure adjusting screw is turned out fully. Leaving the pressure adjusting screw turned in to maintain a setting is a very dangerous practice. All regulator manufacturers warn about the need to fully turn the adjusting screw out By leaving the pressure adjusting screw in, even slightly, the high-pressure oxygen gas passes through the open valve seat, exposing the regulator diaphragm and other internal parts.
With the pressure-adjusting screw fully open, very slowly open the cylinder contents valve. One suggestion is to not look at the contents gauges while opening the valve. In fact, take an extra precaution and stand to the side of the regulator. In lab tests, when an explosion occurs, most (but not all) of the flame comes out of the front and sometimes the rear of the regulator. One reason for opening slowly is to avoid a shock to the pressure gauge, but another reason is that a regulator explosion might be caused by high pressure rapidly entering the small gauge tube that bends when pressure is applied.
If even a small amount of hydrocarbon contaminant enters the tube, and the pressure suddenly increases from 14.7 to 2,600 psi of pure oxygen, spontaneous combustion can occur. It is like a Diesel engine combustion chamber. No spark is needed, just fuel and high pressure.
Fig. 3.4. Acetylene regulators only allow pressures up to 15 psi because, beyond that, pressure acetylene gas is unstable. At 29 psi the gas can spontaneously explode. When acetylene is contained in a cylinder, the gas is dissolved in acetone.
A Diesel engine with a high compression ratio of 25:1 has a maximum cylinder pressure of 368 psi of air (25 × 14.7). That is sufficient to ignite Diesel fuel in air. With 2,600 psi of oxygen, it takes little fuel to cause ignition! Once the fire starts, all materials burn in an oxygen environment—the brass regulator body and even a stainless steel diaphragm.
An oxygen regulator burnout is not an everyday occurrence. There are hundreds of thousands of oxygen regulators on cylinders in the United States and just a few burns occur each year. Evidence collected over the years shows that when one does occur the inlet filter was often missing. While filters are necessary for all uses and in all environments, clean filters are especially important in auto body shops, garages, or any place where hydrocarbon products are on benches or floors.
When a full cylinder is being exchanged for an empty cylinder, the oxygen regulator might be placed on a dirty bench or floor. The inlet nipple could pick up some grease or oil and enter the opening. Burnouts have occurred in coal mines where safety precautions are always emphasized and taught to all workers. Could it be the regulators were exposed to coal dust when swapping cylinders?
Most burnouts occur when a new full cylinder is being installed. If the inlet filter is always checked before installing an oxygen regulator, the pressure adjusting screw is backed all the way out, and the cylinder valve is opened very slowly, an oxygen regulator burnout or explosion should never be experienced.
There are also oxygen regulators designed to contain an explosion should one occur. Ask your welding supplier about them.
Acetylene Regulator
Acetylene is potentially unstable at pressures over 15 psi. To increase a cylinder’s capacity, while providing a safe environment, the acetylene is dissolved in acetone and held in a porous media contained in the cylinder. Cylinder pressures of 250 psi can then be used. The acetylene regulator lowers the pressure to the 5 to 8 psi required for welding. Consult the manufacturer’s
