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Home Brew Forums > Home Brewing Beer > Bottling/Kegging > Can someone please explain how to know how much co2 is left?
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Old 01-13-2012, 01:50 AM   #1
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Default Can someone please explain how to know how much co2 is left?

So I have this very old 15 gallon steel CO2 tank that I filled about 15 years ago. I plugged it in and just read about 750 psi. I thought it was nearly empty because as I recall from SCUBA, I would start with 3000 psi and then watch the pressure go down and when it got to 500 psi it was time to come up. So I assumed that CO2 was similar. Then I read here something different:

How Many Kegs Per CO2 Cylinder

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A gas tank that is properly filled should read about 750 PSIG when the cylinder is at a 72F temperature. CO2 gas pressure increases when it is exposed to heat, so if the gas tank temperature is above 72F, the pressure will read higher than 750 PSIG. If the gas tank temperature is colder then 72F, the pressure will read lower then 750 PSIG.

The tank pressure should read 750 PSIG until the liquid CO2 in the cylinder is gone, and the tank is almost empty. A decreasing pressure indicates the cylinder is nearly empty.
So the pressure won't drop because it's liquid right?

How do I know what's left? Is there a tank weighing rule?


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Old 01-13-2012, 01:54 AM   #2
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I believe the tank should be stamped on it how much it weighs empty.

Then math comes in, and, well, I'm not so good with that.


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Old 01-13-2012, 02:01 AM   #3
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LOL I'm so dumb! I just googled "how much does 1 lb of co2 weigh"
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Old 01-13-2012, 02:16 AM   #4
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So the same site says that their 15 lb tanks weigh 22 lbs empty, and this tank with a new regulator gauge setup weighs 34.4 lbs. I am going to guess 22 + 1 + ~11 lbs co2 left = 34 lbs.

Now to find out if CO2 is what's really in there.
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Old 01-13-2012, 02:45 AM   #5
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Just realize that every tanks weight is at least slightly different. A small error in the weight of the tank could lead to a fairly large error on the amount of gas. You will get a close-ish guess anyway.
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Old 01-13-2012, 02:48 AM   #6
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Quote:
Originally Posted by JonnyJumpUp View Post
Just realize that every tanks weight is at least slightly different. A small error in the weight of the tank could lead to a fairly large error on the amount of gas. You will get a close-ish guess anyway.
I just want enough gas for a couple of 5er's until I need to fill again.
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Old 01-13-2012, 02:51 AM   #7
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Even if you are way off you probably still have 5lbs in there, which should be plenty.
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Old 01-13-2012, 09:02 AM   #8
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Quote:
Originally Posted by badbrew View Post
LOL I'm so dumb! I just googled "how much does 1 lb of co2 weigh"
less than one pound of lead!


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