Author Topic: CO 2 Questions  (Read 1242 times)

Offline pete b

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CO 2 Questions
« on: June 22, 2016, 12:39:59 PM »
I have a couple months kegging under my belt and have a few questions.
How full should a canister be? The first time I got one the needle on the regulator's gage was about as far into the green area as possible. Since then they have all been only about 1/4 into the green. This is all room temperature.
How much do you get out of a 5# canister? Any tricks to conserve it? Should I turn it off once carbed and I'm not pouring? I live in a fairly rural area and getting tanks filled is an hour round trip that I would like to minimize. I have two tanks.
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Offline HoosierBrew

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Re: CO 2 Questions
« Reply #1 on: June 22, 2016, 12:59:13 PM »
I'm sure there'll be a lot of different responses. Since it's all at room temp,it sounds like you're probably not getting complete fills every time. I leave my kegs connected at serving pressure. The biggest trick I have is to use keg lube on the lid ring and post rings every time - with my old kegs it makes a tank last much longer. And at kegging, I seat the lid ring with ~ 30psi for a minute or so, before reducing to carb pressure.
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Offline leejoreilly

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Re: CO 2 Questions
« Reply #2 on: June 22, 2016, 01:24:34 PM »
CO2 is sold by weight, not fill level; e.g., I have a 20 lb canister, which is 20 lbs of (mostly liquid) CO2. All of the canisters I've seen also have a tare weight (weight of the container) stamped into their sides. So you can measure the fill of your can by weighting it and subtracting the tare weight.

My gauge reads in psi, at about 800 psi new and stays steady as the level decreases. When it gets close to empty, it'll drop fairly quickly to maybe 200-300 psi. I keep a second 5 lb can as a back-up, to use until I can get the 20 refilled.

I also keep the gas connected constantly. And I fully agree with HoosierBrew's liberal use of keg lube - cheap insurance - and the 30 psi seat-the-lid process.

Offline narvin

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Re: CO 2 Questions
« Reply #3 on: June 22, 2016, 01:25:12 PM »
CO2 in your tank is liquid, so the pressure will be constant for a given temperature until all of the liquid has evaporated into gas.  At this point, you're almost empty, so the high pressure gauge is not very useful.

At room temperature, if you have any liquid CO2 left you'll read 816 psi.

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Offline pete b

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Re: CO 2 Questions
« Reply #4 on: June 22, 2016, 01:37:07 PM »
I use keg lube but don't always remember. I think I will put it the container on top of my keezer as a reminder. I think maybe I should invest in a 20# tank since my concern is reducing trips to get it filled.
Does a 5# can lasting for two 5 gallon kegs, one with 4.5 gallons of beer and one with 3 gallons? Does putting amounts less than 5 gallons in smaller kegs have a significant impact on gas usage?
Thanks for the chart Narvin.
« Last Edit: June 22, 2016, 08:03:24 PM by pete b »
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Offline Stevie

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Re: CO 2 Questions
« Reply #5 on: June 22, 2016, 01:41:35 PM »
What these guys said. High pressure gauges are awesome, but very misleading. They don't function like a gas gauge and change with temp.

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Offline Phil_M

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Re: CO 2 Questions
« Reply #6 on: June 22, 2016, 01:45:06 PM »
If it takes you a half hour to get to the shop that swaps your tanks, I don't think I'd get a 20# tank. I'd think more 5# tanks would be better, that way if a leak crops up you can just switch to another 5 pounder. It'd suck to come home from work to find that the 20# tank had all leaked out.
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Offline pete b

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Re: CO 2 Questions
« Reply #7 on: June 22, 2016, 01:49:34 PM »
If it takes you a half hour to get to the shop that swaps your tanks, I don't think I'd get a 20# tank. I'd think more 5# tanks would be better, that way if a leak crops up you can just switch to another 5 pounder. It'd suck to come home from work to find that the 20# tank had all leaked out.
Good point. I already have two.
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Offline kramerog

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Re: CO 2 Questions
« Reply #8 on: June 22, 2016, 01:53:04 PM »
I turn off the CO2 in case I have a leak.    I believe that rising stem valves like those used on gas tanks will leak unless fully open or fully closed.

Offline mainebrewer

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Re: CO 2 Questions
« Reply #9 on: June 22, 2016, 06:11:19 PM »
I get 3-4 months out of my 5 pound tanks.
That's pushing 5 kegs at a time and pushing cleaning fluids through the kegs and beer lines.
I also leave my tank on at all times.
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Offline pete b

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Re: CO 2 Questions
« Reply #10 on: June 22, 2016, 08:05:35 PM »
Wow! Do others get that much out of a tank?
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Offline narvin

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Re: CO 2 Questions
« Reply #11 on: June 22, 2016, 08:35:10 PM »
In theory, a 5lb tank should last a while. 

At STP, 1 mole of CO2 (or any gas) is 22.4L.  This equates to 1.96g of CO2 per liter.  2.5 volumes of CO2 is 2.5L of CO2 at stp per L of beer.  Assuming your beer has maybe 1 vol of CO2 before you carbonate to 2.5L, and then you push it out at the same pressure, filling the entire keg with CO2, you'd use 4 L of CO2 per L of beer.  This is around 76 Liters per keg.  5 pounds at 1.96 g/L equates to 1157L, which is 15 kegs at that rate.

I'm sure there are some simplifications (or mistakes  >:() here, but it seems like a good estimate.
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Offline hopfenundmalz

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Re: CO 2 Questions
« Reply #12 on: June 22, 2016, 08:38:07 PM »
CO2 in your tank is liquid, so the pressure will be constant for a given temperature until all of the liquid has evaporated into gas.  At this point, you're almost empty, so the high pressure gauge is not very useful.

At room temperature, if you have any liquid CO2 left you'll read 816 psi.


The CO2 in the tank is gas over liquid, to be more exact. I think you know that from the rest of your post.

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Offline narvin

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Re: CO 2 Questions
« Reply #13 on: June 22, 2016, 08:44:34 PM »
CO2 in your tank is liquid, so the pressure will be constant for a given temperature until all of the liquid has evaporated into gas.  At this point, you're almost empty, so the high pressure gauge is not very useful.

At room temperature, if you have any liquid CO2 left you'll read 816 psi.


The CO2 in the tank is gas over liquid, to be more exact. I think you know that from the rest of your post.

Yes, that's a good thing to point out.  The liquid is evaporating into gas as it is released from the tank, leaving more gas and less liquid.

This is also why tanks that you fill other tanks from have a dip tube.

Until enough liquid has been removed that only gas is left, the temperature and pressure are tied together on the black line between liquid and gas:

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Offline mainebrewer

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Re: CO 2 Questions
« Reply #14 on: June 22, 2016, 10:59:26 PM »
Wow! Do others get that much out of a tank?
I don't know about others, but my experience is based on several years of records.
I'm kind of anal about keeping records.  ;D
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