Filling a 5lb tank with my 20lb tank

[Rik van den berg]

High pressure stuff always freaks me out for some reason but I have a 20LB tank on my garage kegerator and a 5LB tank in my outdoor kitchen kegerator and I would like to be able to fill the 5lb with the 20lb..

Does anyone do this? If so, please let me know what you are doing!

Thanks

 

[madscientist451]

Never tried it, sounds interesting. The cost to swap the 5 lb tank is only slightly cheaper than the cost of swapping the 20 lb tank, so I suppose you could save a few bucks by transferring some of that gas yourself. If I was going to do it, I'd use the regulator, so how much you can put in there will depend on how high you can crank up the regulator.

 

[pigroaster]

paint ball guys do this all the time. You need a special CO2 tank that draws liquid off the bottom of supply tank and a high pressure valve system. Google it and you will be okay. Perhaps you should stay with your day job and let the experts take the risks. You might be chewing off more that is safe. Find a paint ball person and see if you can swing a deal. Most paint ball fillers work with 50 pound CO2 tanks.

 

[apache_brew]

I haven't done it, but they sell transfer kits that connect both cylinders and have a bleed valve in between. Fill tanks are typically larger and have dip tubes that siphon liquid CO2 into the receiving tank for a more complete fill. I think the way around this is to invert your supply tank and transfer like that. Either way I don't think you can count on a complete full fill with a DIY home system. My solution was a score a couple more 20 lb tanks on Craigslist from growers and swap them at grow stores for half the price then Airgas.

 

[bkboiler]

if you fill slow enough you should be ok (think hours not minutes).
These are high pressures. Don't rush, or it creates a lot of heat. A grad student blew up the thermodynamics lab when I was in undergrad since he forgot about this basic principle.
Commercially they fill "cascading" or in stages and they have pressure regulators and a flow regulator.

 

[day_trippr]

If the 20 pounder lacks a dip tube (ie: it is not a "siphon tank") it will have to be inverted to fill another cylinder.
The transfer line is the same as used with a legit siphon tank - cga320 fittings at both ends and a relief valve in between.
I use one with a 20 pound siphon tank...

Cheers!

 

[Brew_Dude41]

What @day_trippr said with an additional step:
Transfer a very small amount into the #5, close the #20 valve, and then use the purge valve to clear the #5. This will cool the tank to allow for a safer fill, and help to avoid the situation that @bkboiler noted above.

I would also have the tank you are filling on a scale to avoid over filling-don't exceed the tare weight +5.

 

[mabrungard]

I use a twin CGA320 fitting setup to connect the tanks. Regular CO2 tanks don’t have dip tubes, so inverting the 20 pounder does what you want for the transfer.

Connect the fitting fully to the 20 first and loosely to the 5. Then crack the valve on the 20 to flush the fittings and then close the valve and tighten the fitting on the 5. Open the valve on the 5 and then crack the valve on the 20 until you hear flow. You must keep the flow from the 20 at a bleed rate. Do not blast the valve open or you could rupture the 5.

 

[day_trippr]

"rupture the 5" based on what phenomenon? Certainly not from over-filling in that initial scenario.
If anything, it is very difficult to over-fill a CO2 cylinder from another. It's time consuming and wastes a lot of gas to get there...

Cheers!

 

[Rik van den berg]

Thanks everyone for your input! After reading all this I’ve decided to just go get my 5lb filled at my lhbs when it needs to be! I’ll use the 20lb for carbonating all beers and serving the sipping beers in the garage.

 

[Theone964]

My solution was a score a couple more 20 lb tanks on Craigslist from growers and swap them at grow stores for half the price then Airgas.

How do you find grow shops that sell CO2? I'm in Illinois and I can't seem to find any growers that sell CO2 they just have stuff that releases CO2 into the air. My local Airgas wants $34 for a 20lb and $26 for a 5# exchange.

 

[segallis]

Where did all this talk about "heat/rupture/explosion" come from? Could someone please offer a shred of physics theory to substantiate any of these "risks". Feel free to correct anything I am about to say: Pressure in a 20 lb tank is the same as in a 5 lb tank. How can the 20 lb tank "rupture" the 5 lb tank - how can more pressure be created than the 20 lb tanks starts with? And where is the "heat" coming from during a transfer? If any liquid CO2 converts to a gas, things get very COLD. The only heat that can be generated would be heating of the small volume of CO2 gas that remained in the empty 5 lb tank as that gas is compressed to around 850 PSI. I'd have to do some digging to find out how much heat that is, but the mass of that gas is about 1/500th that of the room temperature liquid that will fill the empty tank, so I have to wonder how hot things will get since the liquid will absorb that heat, and with 500X the thermal mass (no to mention the tank itself). Also, you definitely don't want a regulator or anything causing a drop in pressure from the 850 PSI liquid in the 20 lb tank. Dropping the pressure would cause that liquid CO2 to convert to a gas and then you are putting virtually nothing into that 5 lb tank (it will be 850 PSI of gas, which is about 0.2% full). Also, gas regulators don't work on liquids. Using one on an inverted liquid tank will either ruin the regulator worst case, or best case, not regulate anything. Which is why you will see that every transfer hose designed for this, is simply a high pressure hose that connects bottle to bottle (with a purge valve). And no, it does not take hours to accomplish (unless you are trying to get that last few percent just prior to equilibrium). Liquid will flow into the 5 lb tank until the pressure equalizes, going slower for the last little bit until nothing flows since tank pressures will become identical. It would be interesting to weigh the 5 lb tank as you time the fill. I would guess the tank will reach 50% full in a few minutes. Not all that different from filling propane tanks, except the LP tanks are lower pressure and they typicall use a pump to transfer the liquid rather than just gravity (although there are gravity fed transfer hoses to refill small LP bottles too).

 

[day_trippr]

I would guess the tank will reach 50% full in a few minutes.

fwiw, I "fill" my three five pounders from my 20 pound siphon tank and they typically reach equilibrium to a roughly 65% fill much quicker than a few minutes. I don't even try to stuff more in by bleeding/chilling/etc as there's no point in wasting the gas...

Cheers!