questions about flashback

whats the different between the small cigar shaped flashback arrestors and the larger ones (at four times the price) with a grenade like reset pin? how do the small ones do without the pin?

i found a video clip (its an advert) showing a flashback at the tip of a torch.

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what i am unsure of is what is an in-torch flashback or in-hose one like?how do you know it is happening? do you feel the tourch warm or smell burning? what does it sound like? also what does a backfire sound like?

thanks again Sam

PS i found this navy facilities safety presentation which other beginners might find interesting

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Reply to
Sam
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Don't know about the big flashback arresters you are asking about. Most flashback arresters have a sintered metal filter that will quench a flame that reaches it. Note that flashback arresters are not the same as check valves. Check valves just prevent the flow of gas from one cylinder to the other, another dangerous situation. A flashback will go right through a check valve if it isn't also designed as a flashback arrester.

Some manufacturers' torches have one or both in the handle. You still need them at the bottles.

A flashback is nothing more than the flame burning inside the torch or hose. The occurence of a flashback is easy to identify. The flame at the tip of your torch is gone and you hear a high pitched squeal indicating the flame is burning inside your torch. Under some circumstances it can progress back to the bottles. But, generally, no significant damage will occur if you shut down promptly.

With a backfire, the flame burns back inside the tip, detonates and goes out. Under some circumstances it can damage the torch, send the tip flying, etc. But, generally, you just have to relight.

Reply to
Footy

They both have a sintered block inside that acts as a flame arrestor. The big sort with the pin also have a sprung loaded plunger that stops shock waves.

If you have a slow-burning combustion of mixed gas, the sintered block is enough to stop it getting past for long enough to allow you to shut off the gas manually. If you have an explosion though, the shock wave can still pass through it. The plunger type attempts to stop this - with a degree of success depending on just how much of an explosive mixture you've got into the hoses.

You shouldn't ever need flashback arrestors. Your real safety comes from good operating practice and the one way check valves on the torch end of the hoses that stop mixed gas getting into the hoses in the first place. But if you ever _do_ need arrestors, you'll be wanting the big sort.

If you ever fire the arrestor, you should let it all cool down (a good time to change your trousers) and then inspect for damage, wear and lack of cleanliness before recommencing work. Chances are your torch mixer was filthy anyway.

Reply to
Andy Dingley

thanks for your answer

i also found a video clip (also an advert) of flashback good for newbies like me. it has a nice scene of a ruptured acetylene tank (looks like a banana peel).

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what puzzled me in the video is the claim that flashbacks travel at supersonic speeds so there is no time to turn off the cylinder valve.

how do people without arrestors survive flashback?

Reply to
Sam

The speed the flame front moves at depends on how lean the mixture is. The leaner it is, the faster it burns back. If it gets too lean, it will just go out.

People without flashback arresters typically survive because they recognize the situation and quickly shut down, don't recognize the situation but still quickly shut down to restart the flame that seems to have gone out, or shut down because the torch starts to melt. You have to be pumping oxygen into the acetylene line for it to burn back to the tank quickly.

I have seen flashbacks where the torch was shut down before any damage (if the guy with the torch didn't do it I was going to). And I know people who have melted torches. I don t know anyone who has had a flashback burn all the way back to the tank. I think the hose will burn through before that happens in all but exceptional cases. Welders and burners survived for many years before flashback arresters became common apparently with only a few catastrophic problems.

FWIW you should see the video of the full acetylene tank placed on a bon fire!

Reply to
Footy

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