Co2 filling question

I have a full 5lb tank that my LHBS loaned me for the weekend. I was wondering if I could hook the 5lb tank to my 20lb tank would gas from the smaller tank go into the bigger one. And should I turn the small tank upside down.

CO2 tanks are filled with liquid CO2 under high pressure using special fittings and equipment. Don't try this at home kids.

You could but it wouldn't be very practical. You might as well just take your 20lb to get filled.

Essentially the pressures would seek equilibrium. The tank of the higher pressure would donate gas to that of the lower pressure. So depending on what you have in your 20 gallon, maybe. Does it sound safe?...not really.

there will undoubtedly be more pressure in the 20# tank, so no, this won't work. you'll just end up filling the 5# one and if you don't have all the proper relief valves and such, you are just asking for trouble.

The 20lb tank is empty. And it out of date. That's the only reason i was gonna try this.

It works if you have the proper hoses (filling station). The colder you make the 20# tank the more CO2 you'll get in it. And, yes, you'll have to turn the 5 pounder updside down.

https://www.homebrewtalk.com/f35/filling-my-own-5lb-co2-tanks-164074/

The link is to fill small from big, doing the reverse hardly seems worthwhile even as a temporary solution imo but I'd assume the technique would be the same.

android said:

there will undoubtedly be more pressure in the 20# tank, so no, this won't work.

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Why would there be more pressure in the 20# tank?

shtank said:

The 20lb tank is empty. And it out of date. That's the only reason i was gonna try this.

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Well that's a dam good reason not to try it.

What are you trying to do? Steal all the co2 that they loaned you?

bja said:

Why would there be more pressure in the 20# tank?

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i was assuming the volume of gas would be greater in the 20# tank, which would exert more pressure when the valve was opened (seeking equilibrium), but it turns out i was incorrect that any gas existed in the 20# tank.

android said:

i was assuming the volume of gas would be greater in the 20# tank, which would exert more pressure when the valve was opened (seeking equilibrium), but it turns out i was incorrect that any gas existed in the 20# tank.

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Even if there was co2 in the 20# tank, the pressure differential would be minimal. Volume has no effect. Co2 is stored as a liquid so the pressure remains constant (though temperature will affect pressure) until the liquid is depleted. The pressure then begins to drop.

What are you trying to do? Steal all the co2 that they loaned you?[/quote]

No I'm not stealing the gas I paid for the gas so it doesn't matter to them if I bring it back empty. They loaned me the tank.

What are you trying to do? Steal all the co2 that they loaned you?

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No I'm not stealing the gas I paid for the gas so it doesn't matter to them if I bring it back empty. They loaned me the tank.

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I understand now. You didn't say that you paid them for it. Regardless, I wouldn't mess around with that 20# tank until you have it hydro tested.

After hearing so many people say how bad the idea is I'm not going to try it. It just dosent seem that crazy to me I don't understand how a 5lb tank could over pressurize a empty 20 lb tank. But regardless of I'm gonna play it safe thank you all for responding to my post.

shtank said:

After hearing so many people say how bad the idea is I'm not going to try it. It just dosent seem that crazy to me I don't understand how a 5lb tank could over pressurize a empty 20 lb tank. But regardless of I'm gonna play it safe thank you all for responding to my post.

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The idea itself isn't bad, but using an out of date tank is. Get it tested first.

How were you going to transfer it?

I was going to just hook them up with a straight pipe and then slowly crack the valve onthe 5 lb

The real fun would be if any of the fittings comes loose while you have the 5lb tank upside down. Those things can (and will) become missiles if they discharge suddenly. Then you're into the whole F=ma thing...

If you don't have a proper fill station setup, just leave it be.

-chuck

shtank said:

I was going to just hook them up with a straight pipe and then slowly crack the valve onthe 5 lb

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Just remember, you're working with 800-1000 psi of pressure.

bja said:

Even if there was co2 in the 20# tank, the pressure differential would be minimal. Volume has no effect. Co2 is stored as a liquid so the pressure remains constant (though temperature will affect pressure) until the liquid is depleted. The pressure then begins to drop.

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so, if the 20# tank is full and the 5# tank is empty, gas would transfer from the 20# tank to the 5# tank, right? and pressure doesn't have anything to do with it? i'm just trying to understand.

android said:

so, if the 20# tank is full and the 5# tank is empty, gas would transfer from the 20# tank to the 5# tank, right? and pressure doesn't have anything to do with it? i'm just trying to understand.

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It would transfer back and forth as a liquid all day so long as the rexieving vessel is cold. If you are gonna do it, find the proper fill station. A good place to start is a paintball store. I wouldnt be in the same building as this with a jerry-rigged pipe thing.

shtank said:

After hearing so many people say how bad the idea is I'm not going to try it. It just dosent seem that crazy to me I don't understand how a 5lb tank could over pressurize a empty 20 lb tank. But regardless of I'm gonna play it safe thank you all for responding to my post.

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It wouldn't. Co2 is stored as a liquid and if the tank is in a room temp area, it stays at 800-1000 psi and doesn't drop until you've used up all of the co2 in its liquid form and the pressurized tank is all that's left.

The only concern people had was that the tank is old.

Edit.. evidently people got to this before me. Sorry for repeat info.