Experience refilling argon or 75/25 cylinders yourself?

[adirondackmtnman]

Lots of confusing info on here. In a mix gas like C-25, CO2 can be measured/filled in the gas form because it is a small portion of the total mix. It can also be measured in liquid (weighed before the argon is added to get the same C-25 mixture. For a 100% CO2 cylinder, it is always filled as a liquid. Very similar to propane. There's a fancy term for it but the CO2 is basically boiling/vaporizing inside the cylinder and that creates the gas pressure. A dip tube on the valve will allow liquid CO2 to be withdrawn. Again, similar to propane. The pressure of a CO2 cylinder varies depending on the rate of vaporizing but the maximum pressure is about 850 PSI. A full cylinder is usually between 600 and 800 PSI. Not anywhere close to high pressure gasses at 2200 PSI. CO2 is filled by weight not pressure on a scale the same as propane. Cylinders are referred to by their weight, such as 50 or 75 pounds. The easiest way to know this is to take a 200 cu. ft. oxygen cylinder and put it beside a similar sized 50 lb. CO2 cylinder and load both into the back of a truck. The CO2 will be 50 lbs. heavier because it's filled with liquid. A 100 Lb CO2 like used for fire extinguishing is the last cylinder you ever want to have to pick up by hand.

You can get high pressure braided hoses for filling smaller cylinders from large ones but it's not recommended. Just get at least an 80 cu. ft. C-25 and be done with it. A 125 cu. ft. would be better. A 20 cu. ft. cylinder is a waste of time and will only last about 15 or 20 minutes. If I had to fill a cylinder every 20 minutes of welding, I'd throw the MIG out and use stick! ullinghair:Straight CO2 used for welding usually needs a special regulator to prevent freezing from too fast of withdrawal rate.

Just about anyone needing high volumes of gas can get cryogenic tanks with liquid in them. The problem is you can't let them sit around or all the gas created will vent off when the pressure gets too high.

I didn't read this before my previous post. Interesting info Arc Weld. Curious, as a former hazmat tech, it escapes me, are the 100% co2 cylinders placarded as 'liquid?'

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[Gary Fowler]

Never heard of anyone being happy with 20 cu. ft. cylinder. They're tiny. They might last a little longer than 15 minutes but there's always some wasted gas. You lose some even disconnected the line when transfilling too. Anywhere you go to use MIG, you need to be inside anyway. An 80 cu. ft. cylinder isn't hard to move around but why not use stick since your machine does both? Wouldn't it suck to run out of gas in the middle of a job? A 20 cu. ft, cylinder makes no sense unless you need to carry it to the top of a skyscraper.

I guess I learned something new. It has been a few years(well many, as in 40+) since I handled 75/25 cylinders but I still don't recall them feeling as though they had liquid inside like a propane tank. You can feel liquid changing the center of gravity when you hold them horizontal. We used to have to lay them down on their sides and roll them back and forth before use to mix the gases (at least that was the process as some old timer said argon would settle out to the bottom). I was in the early stages of my welding career at the time so much info was word of mouth back then. We rarely used MIG in field construction due to the propensity to have cold lap, porosity etc in the weld and most clients like Shell, Arco, Exxon etc wont let you use it outside of shop environment and then only in SPRAY mode. I don't use it now as I don't use MIG, I prefer stick for my farm repairs. If I were doing a lot of fabrication of implements, MIG would be OK.

 

[yomax4]

Pure co2 is liquid at the bottom. mixed gases are just gas. Most co2 tanks are only filled to 1800 psi and not a good option for trans filling. Gas is measured by psi. Co2 is measured by the pound.ie: 20# co2 has 20# of liquid in the tank. you use the gas off the top and it allows more to turn to gas. The pressure is what keeps it liquid until you use some of it. Most LWS have 2 versions of co2. welding grade that is usually called a 50# co2 = has 50# of liquid in the tank and you use the gas off the top. And what they call a fountain grade that has a dip tube hooked to the valve and it dispenses liquid co2. You do not want the fountain co2 to weld with. Call your LWS and they will agree.

 

[Sodo]

Gary many times I've tried to 'feel' if my 50cf tank (of 75/25) has liquid in it but it's so heavy I can't tell, will try again on the longer 80 as it's new and full. Never heard of 75/25 separating. Yomax I'm trying to digest what you wrote but Argon & 75/25 are the only gases I use.

Never heard of anyone being happy with 20 cu. ft. cylinder. They're tiny. ?.A 20 cu. ft, cylinder makes no sense unless you need to carry it to the top of a skyscraper.

Agreed it's barely worth going to the gas store to fill a 20cf. You're saying it's not worth heading out to a job with a 20cf and on that I disagree. I think this is only interesting for people who put portable welders in their pickups. And want it to be easy. And I have a brand new MultiMatic200!

A 50cf cylinder lasts me a few months. I often put the 50 in my pickup without detaching the regulator. The 80cf is a lot more hassle, I have to remove the regulator and cap it to put it in the truck. Then uncap, put the regulator back on, purge etc. Weld, then remove regulator, uncap, put in truck.

A re-fillable 20 would be so much easier (never removing the regulator) it would be almost a pleasure. Maybe carry the welder with one hand and the 20 with the other hand. When it gets that easy the option to take the welder to the work becomes feasible.

A 20 would be great IF and ONLY IF I could top it off in 5 minutes, in my shop, from a larger cylinder. Hence the topic of this thread.

 

[Gary Fowler]

Never heard of 75/25 separating. Yomax I'm trying to digest what you wrote but Argon & 75/25 are the only gases I use.QUOTE]
I don't know that it separates, that is just what the old timer said. We were having some trouble with the MIG weld and he said just unhook the tank and roll it around, the gas is feeding off the straight CO2 on top of the tank, mix it up since the bottle had sat a long time in the storage rack. We did that and it welded a lot better, normal in fact. I have not idea if that is what fixed the problem of if we had an air encroachment problem, but it did work.

 

[Shield Arc]

I don't know that it separates, that is just what the old timer said.

Now that you mention it, I remember hearing the same thing around the same time frame. Just forgot all about it until reading your post.

 

[Sodo]

I don't know that it separates, that is just what the old timer said.

All welders with bigger tanks (of mix) that are stationary would be having problems, and telling everyone what a pain it is. It would not be just one old timer saying or one distant memory.

The hot advice would be to get a tank no bigger than what you feel like unhooking to roll around. Also it would be widely known how long you can let it sit before you need to shake it up. And the guy at the gas store would tell you. Never heard of it.

Anyway, topic is feasibility of re-filling a smaller cylinder from a bigger cylinder.

 

[Shield Arc]

All welders with bigger tanks (of mix) that are stationary would be having problems, and telling everyone what a pain it is. It would not be just one old timer saying or one distant memory.

Who knows it may be as simple as sending the new kid in the crew for a sky hook, lumber stretcher, bucket of steam, etc, etc. :laughing:

 

[Arc weld]

Usually in a C-25 or lesser CO2 mix, the CO2 is in the gas state, There just isn't enough liquid to keep it all from vaporizing. I suppose if these cylinders sat around for month's on end they may separate but it's not a common problem. Other gas mixes however do separate. When I toured a large fill plant that made specialty gasses, they had a special horizontal roller to lay cylinders on to mix the gasses if they sat around to long.

Something more important needs to be mentioned. It is ILLEGAL to transport cylinders with the regulators attached!:duh: Even on welding trucks where the cylinders are secured. Just because some people get away with it, doesn't make it right. It does not matter what size they are. Just because it's a smaller cylinder, doesn't make it any less dangerous. It could still be holding 2000+ lbs. pressure. A lot of people have been seriously injured and killed trying to do stuff the easy way. Sometimes the rules are there for a reason.

 

[k0ua]

Now that you mention it, I remember hearing the same thing around the same time frame. Just forgot all about it until reading your post.

We used to send them for a box of dialtone