I’ve always been a little embarrassed to ask, but when I have, say, a propane torch, how come the flame doesn’t go back through the line and blow up the can?
In: Engineering
It can with other gasses, like acetylene. Propane is kept at a fairly high pressure before being reduced at the regulator. This pretty much prevents a flashback. Not having the right mix helps as well. Acetylene, on the other hand, is never at very high pressure (it can self combust). Ace also requires much less oxygen to combust. On torches using ace there are safety valves called flashback arrestors, they hopefully close in the event of a flashback.
your direct question has been answered.
Another question is “how do gas lines not explode”, there are time when air get into gas lines to houses, and even more-so, the gas burners on your hob are fed with a fuel-air mix that is combustable – AND YET the flame never travels up the pipe to the source of the air/fuel mix.
Fire requires three things, Fuel, Air and Heat
Butane requires 400 degrees to light, in a flame this is trivial to get, but to remove this heat all you need is a small orifice made of heat sinking material (like metal). The flame cannot go “up the pipe” because the nozzle and pipe is made from material that will rob the flame of the heat it requires to stay alight
The gas inside the tank moves to a lower pressure area from a higher pressure area, and a low pressure area wouldnt be able to move into a higher pressure area since there is high pressure gas coming out, theres also no oxygen for it to light.
It can! It’s called flashback.
To prevent it from happening you put a device called a flashback arrestor in between the tank and the torch. It’s a legal requirement on the job in most places.
…But only for an oxy-propane torch. Because the oxygen is also under pressure and can push its way through the propane line and into the tank. If you’re just using a standard propane torch with no compressed air or oxygen hooked up then there is not really a need because no air would be able to overcome the pressure of the propane and create the required flammable air-fuel mixture inside the hose and tank.
Propane only burns if the volume of propane gas in the air is between 2.1% and 9.5%. In the tank it’s higher than that. Unless you introduce oxygen.
Although it could theoretically happen if you ran the tank empty and it was really really windy
Believe it or not, it can happen if your equipment is set up incorrectly or not maintained properly. It’s called a flashback: [https://www.weldingandwelder.com/help-and-advice/preventing-flashbacks-in-welding-understanding-flashback-arrestors-and-safety-tips/](https://www.weldingandwelder.com/help-and-advice/preventing-flashbacks-in-welding-understanding-flashback-arrestors-and-safety-tips/)
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