Welding Gas

The fuel gas lasts a useful amount of time, especially considering that the cylinders are so small, but you can use standard propane or MAPP gas, or even butane if it's warm, instead.

On the other hand, the oxy hardly lasts any time at all - ten minutes at best, and a couple of minutes if you're pushing it.

For oxygen I use a DeVilbiss 4 l/min oxygen concentrator, and normally use butane/propane mix for fuel - if it's a hard job I use MAPP gas instead of butane/propane.

The concentrator cost £240 on fleabay, and it's a permanent source of oxygen at negligible cost, just a bit of lekky. No rental charges, no refill charges, no "transport" charges, no delivery charges. :)

It doesn't produce enough gas to run a full-size torch tip, though it will weld 1/8" steel with MAPP gas, running a #1 tip just fine, and a #2 tip at almost full blast, though it does get a bit sticky then.

I don't use a regulator as the oxygen is only at 5 psi or so. I'm told that with some machines at full flow a regulator or even a thick rubber balloon is useful to minimise the effects of the changing output pressure, which can vary from 5 - 10 psi over 20 seconds or so, but the one I have doesn't seem to have that problem, or at least not badly. It's only even apparent at the highest flow rates, but ymmv.

The output pressure (and flow) is too low to do any cutting however.

For argon I hire cylinders and refill my own from them, though I don't know whether the people I hire them from know that :~) . They don't charge cylinder hire if you only hire them over a weekend, but they only do that deal with 2000 l cylinders. They are BO (and AP iirc) dealers, but I don't think those particular cylinders come from BO or AP.

I speculate that you could usefully use pub CO2 cylinders filled to about 800 psi or so for Argon, but I haven't done it, using purchased empty Argon cylinders (at half pressure or less) instead. This is just speculation, not advice, and I take no responsibility if anyone is injured or killed.

-- Peter Fairbrother

Thank you Peter for your comments.

I didn't know about oxygen concentrators before reading your reply Certainly a route worth considering.

Do you think it would be possible to compress the output of concetrator into say, a calor gas bottle, to give a contolled flow whe welding?

One other question, how do you actually fill a pub CO2 cylinder from big BOC cylinder?

I do have some ideas how to, but never having done it I woul appreciate a pointer.

Thanks.

Joh

-- jlh4

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For welding you don't really need more, unless you are welding above

Note that all tips are not the same, the ones I use seem to be a size or two larger than some others. My #2 will happily weld 1/8" steel, I did just that earlier today to mend the supports on a washing machine. No problems at all, it could probably have done a bit more. I used a butane weedwhacker for preheat, but not a whole lot.

If you want to do cutting then you will need more pressure (and flow) than a concentrator can provide, and you should stick to proper equipment.

Stick to low pressure oxygen - it's still dangerous, but much less so than compressed oxygen. High pressure oxygen is even more dangerous than liquid oxygen!

It is probably possible to compress the output from a concentrator, but oxygen-rated compressors are hard to obtain, and even if you know exactly what you are doing, working with compressed oxygen is *very* dangerous.

Using an ordinary compressor for oxygen would be suicidal.

There are lots of rules for using HP oxygen, and if you don't know them then don't do it, and most especially don't use anything that isn't proper oxygen rated equipment because it WILL blow up in your face, probably sooner rather than later.

No kidding. Even stainless steel burns in high pressure compressed oxygen.

Using a calor gas bottle would also be a good way to get a Darwin award.

I've never done it, and I don't have a clue. Sorry. Sounds bloody dangerous to me, a CO2 cylinder can't take the pressure an argon cylinder can.

Filling a *big* CO2 cylinder from a *small* Argon cylinder sounds a bit less dangerous, as the maximum pressure should be lower. Eg if the big CO2 cylinder is three or four times the capacity of the small Argon cylinder then the maximum possible pressure in the CO2 cylinder should be perhaps 1/4 of the Argon pressure - note I say should, if for instance the CO2 cylinder isn't empty to start with then it could be more.

It still sounds dangerous though.

Sorry to sound so negative, but better safe than sorry, and working with any and all compressed gases is extremely dangerous. Especially compressed oxygen, but even compressed Argon can easily kill you.

That's why compressed gas equipment costs so much and is so highly regulated.

-- Peter Fairbrother

I should clarify this - by capacity I meant the volume of the empty cylinder, not the amount of gas it is rated to contain. CO2 is stored as a liquid, and going by the amount of gas a cylinder is rated to contain would give wrong answers.

I still think this would be dangerous, and do not recommend doing it.

I use empty argon cylinders, not CO2 cylinders, and only at half the rated pressure.

-- Peter Fairbrother

Once again thank you Peter for your comments reminding me of what I'

forgotten.

I was told that many years ago BOC had an oxygen bottle explode at on of their plants because someone had put oil on the threads of th gauges and it was blown inside the during the bottle filling process!

As you say, oxygen is a dangerous gas.

The oxygen concentrator still seems a good bet.

Joh

-- jlh4

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