C-25 Transfill

We've all experienced the problem: bought or leased the biggest cylinder possible, because of the economics, but wished for something smaller to be a bit more portable. I picked up an 80 cf helium cylinder (empty) from Craig's List- same valve as shielding gas, still in hydro date, locally these are owner bottles. Then stopped by the McMaster Carr site to pick up parts for a transfill hose.

First thing I did was draw a vacuum on the bottle with a venturi vacuum pump. The Harbor Freight model shown in the pictures is for HVAC use but the fittings match typical compressed air fittings- the clear vinyl tube in the picture is collapsed due to the vacuum but the braided hose is not.

Next I attached the transfill hose- tight on the donor side and loose on the fill side, and gently cracked the supply valve to purge air from the hose, to avoid contaminating the shielding gas. Then tightened the nut and gently opened the supply valve. A few minutes to let the pressures equalize, closed both valves, and done.

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Nice. I've been meaning to do the same so I can economically use some real small bottles for portability.

Great idea. Never thought about it, but that would beat out flux core on a low wind day for me (too much trouble to load the big tanks). And I know where there are a bunch of small tanks I can get my hands one so I will grab one.

Thanks for sharing that Dave.

Glad to share, although I admit it was not without some thinking ahead of time. I was concerned about posting anything too specific (such as McMaster part numbers), thinking Everlast might not approve the posting for some liability reason.

Back in the day I was gopher at an LWS- if a customer came in with, say, an empty 20 cf oxygen to swap for a full, if we didn't have any fulls in inventory it was SOP to just connect it to the nearest 330 cf oxygen cylinder and transfill it. I cringe at that now- no idea where the cylinder had been, no idea if the customer had exposed it to oil/grease/gas or if it had sat with an open valve getting rusty inside, no concern for pressure in the donor cylinder versus pressure capacity of the 20 cf bottle, basically an explosion waiting to happen- maybe that's why the gopher got this chore. These days I would NEVER try this with an oxygen bottle- hydrocarbons can/will flash in the presence of pure oxygen, and the pressure inside the donor cylinder should not exceed the pressure capacity of the receiving cylinder.

So to anyone who takes this on, as with all things welding I'll respectfully suggest caution and careful forethought.

WE AT EVERLAST DO NOT RECOMMEND ANYTHING MENTIONED IN THIS THREAD.

I didn't think about it but you're right (I was thinking as ME not Everlast), larger pressures on the one side. And O/A tanks could get brought in to the mix and a problem.

I will leave it up for a bit and see what Mark thinks on this one. I know he will lean hard to the safety side for sure. So if pulled, no offense.

I have a vacuum pump, etc. So it will be something to try. I have lots of 330+ tanks and some smaller not in use. So for me. Portable option is in mind and not paying out the tail for a 150 refill was my though. And I see Rambozo liked the idea as well.

But this could be dangerous if not thought out or done right.

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Originally Posted by everlastsupport

So if pulled, no offense.

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Understood, no worries. Inert / shielding gasses are one thing, oxygen a totally different deal. Couldn't even begin to imagine what an acetylene (liquid under pressure) would look like.

Oxygen is a whole different kettle of fish.
I would only want to do this with inert gasses. But as long as you observe the rated pressures and do the transfer slow enough that you don't get huge temp swings. I saw some neat little 6000 psi rated argon bottles for a thermal imager that would make for a super compact TIG setup. I think they are 10 cuft or smaller. Just not practical to have filled at LWS, but could be real handy for the right little job, even just filled to 2000 psi, or less.

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Originally Posted by Rambozo

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That is one small cylinder. You could strap that onto a 140st or 160sth and make for a really compact welding unit.

I buy tanks from welding supply places who get the small 25CF at 2015psi and do not want them for $10.00 or free I empty them out take the valve off check the insides to see if it is clean and if so get it hydrostatic tested $18.00 buy a valve CGA-580-1/2 NPT they put it in and I fill them with different gases for the road trips. I vacuum them out and fill to 2000psi by the gauge and ready to go. Mark on them what is in them or paint them different colors.

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I recall from a fairly recent post that you have an elaborate and robust transfill system. Those look like medical oxygen cylinders in your last photo- are you re-using the CGA 870 valves, or are those prior to conversion to 580? Your method sounds like a very cost-effective way to get small cylinders going.

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Originally Posted by DaveO

Understood, no worries. Inert / shielding gasses are one thing, oxygen a totally different deal. Couldn't even begin to imagine what an acetylene (liquid under pressure) would look like.

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Yea, and do not forget the pressures too. I would hope the person doing this would research it and have a bit of a clue as well.

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Originally Posted by DaveO

I recall from a fairly recent post that you have an elaborate and robust transfill system. Those look like medical oxygen cylinders in your last photo- are you re-using the CGA 870 valves, or are those prior to conversion to 580? Your method sounds like a very cost-effective way to get small cylinders going.

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The tanks come with many different CGA valve like CGA-702/703/705, or CGA-870/880/890, or CGA-900/910/920/930/940/950/960/965/973 I just thru them out and put in a CGA-580-1/2 NPT valve in them and vacuum them out. Yes I do have a filling station but it is easer to go from tank to tank at first using the GPSI gauge and if the tank has a +(plus) or square box with a 10 inside it, at the end of the hydrostatic date then you can over fill it by 10% at 68F. cools down, so now at full pressure it would be 2015psi plus 10% that makes it 2216.5psi at 68F deg.

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Originally Posted by DaveO

Understood, no worries. Inert / shielding gasses are one thing, oxygen a totally different deal. Couldn't even begin to imagine what an acetylene (liquid under pressure) would look like.

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Acetylene pressure in a full tank is about 250 psi but it is put in a tank that is packed with balsa wood or monolithic material then filled with acetone or dimethylformanide (DMF) this is why the tank is so heavy the acetylene gas is absorbed in to the liquid under pressure. Acetylene gas under pressure at 29.4 psi, acetylene becomes self-explosive, and a slight shock will cause it to explode spontaneously. However, when dissolved in acetone or DMF, it can be compressed into cylinders at pressures up to 250 psi. safely.