Gas blowtorches, even professional ones, are fairly simple constructions. Their basic design has not really changed in the past century. A professional blowtorch usually consists of a cylinder of fuel gas, a cylinder of oxygen, two gas regulators, two hoses, the torch and the tip.
Regulators on the cylinder heads control the pressure and flow of the gas. Adjusting them to the appropriate pressures is essential to preventing explosions. A regulator has two gauges: the high-pressure gauge reads the gas pressure in the tank, and the low-pressure gauge reads the gas pressure for delivery to the hose and torch. Learn more about pressure and how to measure it in How Tire Pressure Gauges Work.
The hoses that connect the steel cylinders to the torch are made of strong, flexible material, usually rubber. To avoid confusion, the hose containing oxygen typically is green, while the fuel-gas hose is red.
The torch head has two needle valves, which are circular knobs that control the flow of either the oxygen or the fuel gas. The tip attaches to the torch head, and people change it according to the task being performed and the gas used. When a blowtorch is used for cutting metal, an oxygen pipe sends an additional stream of oxygen directly to the center of the flame, increasing its intensity. Finally, an igniter, or pilot light, much like the one on a gas stove, actually lights the torch. It’s a bad idea to ignite these torches with a cigarette lighter or a match because of the dangerously high temperature of the flames.
What prevents this thing from blowing up in your face? Well, the following attachable safety devices usually come standard on blowtorches sold today, but can also be sold separately.
Check valves attached to the regulators and the torch head will help to prevent the gas from flowing back through the hose or cylinder. The pressure in the hose should always be greater than the pressure in the torch head. If this changes and the pressure in the torch head surpasses that of the hose, then the check valve closes, shutting off the gas supply.
The flashback arrestor fastens to a regulator and typically consists of both a check valve and a flame barrier, which allows gas through but not flame. These arrestors prevent flashbacks, which we’ll discuss in the Lighting Up section.
Two types of igniters light blowtorches. In the piezo-electric igniter, pulling the trigger launches a hammer against special crystals, which then produces electric voltage and sparks. To find out about more of the various and unexpected uses of piezoelectricity, read about how the lighter in a bbq grill works. A friction igniter, which looks like an oversized safety pin, creates sparks by scratching special crystals when squeezed.
Lighting Up: Using a Blowtorch
After gearing up, a welder follows certain steps to turn a blowtorch on and off. As different torches have different safety procedures, refer to the specific manufacturer instructions before operating a blowtorch. A step-by-step procedure for turning on an oxyacetylene torch goes like this:
- Turn the acetylene regulator screws out to allow gas through and adjust the working pressure of the gas.
- Open the acetylene cylinder slowly, but only a third to a half turn. This allows for the release of acetylene.
- Open the acetylene needle valve on the torch head and adjust the acetylene regulator to the best working pressure (about 5 psi).
- Close the acetylene needle valve. This stops the flow of acetylene so that you can start the oxygen safely.
- Turn oxygen regulator screws out so that oxygen can flow and you can adjust the working pressure.
- Open the oxygen cylinder valve slowly until completely open. This allows for the release of oxygen.
- Open the oxygen needle valve on the torch head. At this point, you can adjust the oxygen regulator to attain the best working pressure (about 5 psi for welding purposes).
- Close the oxygen needle valve so that you stop the flow of oxygen and can later light the gas safely.
- Pause and test for leaks in any of the valves and hoses.
- Open the acetylene needle valve again so that the gas is released and it can light.
- If the blowtorch is not equipped with an internal spark ignition device, light the acetylene with a friction lighter held about one inch from the tip.
- Wait for the black smoke to stop and slowly open oxygen needle valve. Adjusting the oxygen needle valve affects the type of flame you get. A neutral flame is commonly preferred and is made up of equal parts acetylene and oxygen.
- To switch off the torch, close the acetylene needle valve first, which extinguishes the flame.
- Close the oxygen needle valve. This cuts off the flow of oxygen.
- Turn off the acetylene cylinder valve and then turn off the oxygen cylinder valve. This stops the release of the gases from their cylinders.
- Open the acetylene needle valve until gauges read zero pressure and turn out the pressure adjusting screws on acetylene regulator. Close the acetylene needle valve. This drains any remaining acetylene pressure left in the hoses and torch.
- Open the oxygen needle valve until gauges read zero pressure and turn out pressure adjusting screws on oxygen regulator. Close the oxygen needle valve. This drains any remaining oxygen pressure left in the hoses and torch.
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