20# c02 longevity

Hey I was just wondering how long my 20 # c02 tank will last me .. I will be using it for a single tap kegerator with 19 liter keg .. Just wondering from other persons experience what I could expect for service time before it will need to be filled ?

A long time assuming no leaks. I'm on month 7 with 4 taps and carbing off same tank.

My first 20# tank lasted 18 months and 25 kegs. And, I wasted plenty.

Good to know since I just bought one from Micromatic and will be serving 4 kegs at a time via a jockey box for a wedding

Mine also lasted 18 months.

MC

I've had mine for just under 2 years now. I got it almost full, used it until just recently when I had to downsize my kegorator. I would estimate 20-30 kegs in that time, force carbed and served.

A general rule of thumb is one pound of CO2 will carbonate and serve 1-2 five gallon kegs, depending on carb level, how much you use purging, etc. Assuming no leaks and a full 20# tank, you should get 20-40 kegs out of it.

my 20# tanks usually last me about a year.

zman said:

Good to know since I just bought one from Micromatic and will be serving 4 kegs at a time via a jockey box for a wedding

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You will be serving at a much higher pressure through a jockey box. You wont get nearly as many kegs out of that same tank.....

fpweeks said:

You will be serving at a much higher pressure through a jockey box. You wont get nearly as many kegs out of that same tank.....

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It uses the same amount of gas- no matter what the pressure is, the same amount of gas would be used to push the beer. You wouldn't use more gas.

Yooper said:

It uses the same amount of gas- no matter what the pressure is, the same amount of gas would be used to push the beer. You wouldn't use more gas.

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I gotta disagree with this...

To keep it simple and assume that no CO2 is absorbed by the beer (let's say it's previously carbed and you go through the keg quickly):

If you push a keg at 10 psi, when it's kicked you're left with 5 gallons of CO2 at 10 psi. If you push a keg at 20 psi, when it's kicked you're left with 5 gallons of CO2 at 20 psi. You have twice the mass of CO2 in the otherwise empty keg, so you've used twice as much CO2.

That assumes both kegs are at the same temperature, which might not be true for a jockey box. But that's not that big of an effect since a 20 degree F change is only ~3-4% on an absolute scale (Kelvin or Rankine).

JuanMoore said:

A general rule of thumb is one pound of CO2 will carbonate and serve 1-2 five gallon kegs, depending on carb level, how much you use purging, etc. Assuming no leaks and a full 20# tank, you should get 20-40 kegs out of it.

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This

Dumb question... Does burst carbing at 30 PSI for a few days and then 10 PSI for a week use any more CO2 than the set and forget method?
I would think the same amount of CO2 is dissolved when all is said and done, so it should be the same, right?

evandena said:

Dumb question... Does burst carbing at 30 PSI for a few days and then 10 PSI for a week use any more CO2 than the set and forget method?
I would think the same amount of CO2 is dissolved when all is said and done, so it should be the same, right?

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Same amount of gas either way.

Yup, same amount of CO2 if you reach the same carbonation level... as long as you don't overcarb then have to vent it all out!

fpweeks said:

You will be serving at a much higher pressure through a jockey box. You wont get nearly as many kegs out of that same tank.....

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While serving at a higher pressure does use more gas to push the beer, it won't make a huge difference in the number of kegs a 20# tank can carb and serve. If you compare 10-12psi serving pressure to say doubling it for a jockey box, you'd use ~22g more CO2 per keg. So if the 20# tank would have served and pushed 30 kegs at normal serving pressure, it would only carb serve ~28.5 kegs at double the pressure. IMO that's "nearly as many kegs".

And FWIW not all jockey boxes require higher pressure.

Haven't done the math but I know my 5# tank will not push very many kegs through my jockey box.

JuanMoore said:

While serving at a higher pressure does use more gas to push the beer, it won't make a huge difference in the number of kegs a 20# tank can carb and serve. If you compare 10-12psi serving pressure to say doubling it for a jockey box, you'd use ~22g more CO2 per keg. So if the 20# tank would have served and pushed 30 kegs at normal serving pressure, it would only carb serve ~28.5 kegs at double the pressure. IMO that's "nearly as many kegs".

And FWIW not all jockey boxes require higher pressure.

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Not sure how you're calculating this, but I disagree again.

I do agree that the difference is 25 or so grams of CO2 if you go from 10 to 20 psi serving pressure, which is double the consumption if you don't include force carbing. Hopefully we both agree on that.

If you do include force carbing:

Let's assume you're carbing 19 liters of beer to 2.5 vol CO2 = 47.5 liters of CO2 at 20 degrees = 1.94 moles = 85 grams of CO2.

So if you force carb the keg then serve it at 10 psi, you've used 85 grams + 25 grams = 110 grams of CO2.

If you force carb the keg then serve it at 20 psi, you've used 85 grams + 50 grams = 135 grams of CO2.

If you have 20 pounds = 9,072 grams of CO2, that means you'd get 9,072 / 110 = 82.5 kegs if you serve at 10 psi, or 9,072 / 135 = 67.2 kegs. That's a 19% difference, which is very different from the 5% you calculated.

Edit: OK, I realized after the fact that you just took the 1-2 kegs per pound of CO2 rule and assumed an average of 1.5 to get your "30 kegs per 20 lb tank" number. I guess I'm just pointing out that if you want to assume an ideal situation (with no leaks, purging or other inefficiencies) you have to do it across the board. The 1-2 kegs per pound is a very empirical number, so you can't really modify that number with something calculated from the ideal gas law. The ideal gas law tells us that we should be getting 2-4 times more kegs per CO2 tank than we actually do, so obviously there are a lot of things we aren't taking into account. I'm just saying we should acknowledge that when calculating things like this. But my point still stands that in a theoretical (perfect) system, dispensing a keg at 20 psi vs. 10 psi will use significantly more CO2.

I'm a dumb civil engineer and had trouble with thermodynamics.....but I know my co2 tank empties quicker when pushing through the cold plate.....

zachattack said:

The 1-2 kegs per pound is a very empirical number, so you can't really modify that number with something calculated from the ideal gas law.

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Yes, it is a very empirical number, and as such it's much more accurate than any theoretically calculated ones. I understand your point about modifying it using theoretical calculations, but the number already takes into account the initial purging loss and other variables, and the only thing I'm calculating using ideal laws is the difference in gas left in the keg at the end of serving, which I think is relatively accurate. It certainly provides a much more accurate estimate than one made using entirely theoretical numbers and not accounting for what are obviously significant variables.

zachattack said:

But my point still stands that in a theoretical (perfect) system, dispensing a keg at 20 psi vs. 10 psi will use significantly more CO2.

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Quite true, but I never referred to a theoretical system. And FWIW if you want your theoretical numbers to be more accurate you should take the temperature difference into account. It's likely the reason I estimated a 22g difference where you estimated 25g. Serving in a kegerator at serving pressure the keg is typically kept cold (serving temp). Serving through a jockey box the keg is typically kept closer to room temp, and the beer is chilled to serving temp in the jockey box.

JuanMoore said:

Yes, it is a very empirical number, and as such it's much more accurate than any theoretically calculated ones. I understand your point about modifying it using theoretical calculations, but the number already takes into account the initial purging loss and other variables, and the only thing I'm calculating using ideal laws is the difference in gas left in the keg at the end of serving, which I think is relatively accurate. It certainly provides a much more accurate estimate than one made using entirely theoretical numbers and not accounting for what are obviously significant variables.



Quite true, but I never referred to a theoretical system. And FWIW if you want your theoretical numbers to be more accurate you should take the temperature difference into account. It's likely the reason I estimated a 22g difference where you estimated 25g. Serving in a kegerator at serving pressure the keg is typically kept cold (serving temp). Serving through a jockey box the keg is typically kept closer to room temp, and the beer is chilled to serving temp in the jockey box.

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I don't disagree with any of this!

You make a good point about most of the inefficiencies/losses being included in the empirical 1-2 kegs/lb CO2. However, I still think it's reasonable to acknowledge that the calculated and experimental CO2 use seems to be off by quite a bit. Because there's such a big discrepancy, I'm not comfortable modifying the empirical number with something that's purely theoretical without at least giving a disclaimer. That's why I only presented the ideal case. If actual CO2 usage is 4x higher than what we predict (due to purging, leaks etc.) it's not unreasonable to assume you'll use more than 22 or 25 grams during dispensing. So in my opinion (and it's obvious that we disagree here) it's bad practice to compare the two numbers.

I can say with 100% confidence that in the ideal system I presented, given the assumptions I made, CO2 use will increase by about 19% if you double the serving pressure and change nothing else. I can't conclude anything with any confidence for the actual system, which is why I didn't attempt to.

The next step is to secure funding (perhaps a corporate sponsor) and conduct a series of experiments. We're going to need a lot of beer...

shelly_belly said:

My first 20# tank lasted 18 months and 25 kegs. And, I wasted plenty.

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Forget about CO2 tank life, how did you go through 25 kegs in 18 months!!!? I am using you as an example when my wife tells me that I drink too much beer!

ColumbusAmongus said:

Forget about CO2 tank life, how did you go through 25 kegs in 18 months!!!? I am using you as an example when my wife tells me that I drink too much beer!

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That doesn't seen that outlandish. Easy to kick a session keg in a few weeks if sharing a few brews.

ColumbusAmongus said:

Forget about CO2 tank life, how did you go through 25 kegs in 18 months!!!? I am using you as an example when my wife tells me that I drink too much beer!

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My friends drink most of it.

ColumbusAmongus said:

Forget about CO2 tank life, how did you go through 25 kegs in 18 months!!!? I am using you as an example when my wife tells me that I drink too much beer!

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I assume we are talking 5 gal kegs? That's only 1.25/month....so what 2-1/2 cases or a 12 pack a week

Now if we are talking half barrels....I'll have to redo my math.