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 Home Brew Forums > Can someone please explain how to know how much co2 is left?

01-13-2012, 12:50 AM   #1
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 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

Quote:
 A gas tank that is properly filled should read about 750 PSIG when the cylinder is at a 72°F temperature. CO2 gas pressure increases when it is exposed to heat, so if the gas tank temperature is above 72°F, the pressure will read higher than 750 PSIG. If the gas tank temperature is colder then 72°F, 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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01-13-2012, 12:54 AM   #2
JohnnyO
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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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01-13-2012, 01:01 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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01-13-2012, 01:16 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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01-13-2012, 01:45 AM   #5
JonnyJumpUp
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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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01-13-2012, 01:48 AM   #6
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Quote:
 Originally Posted by JonnyJumpUp 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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01-13-2012, 01:51 AM   #7
JonnyJumpUp
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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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01-13-2012, 08:02 AM   #8
tektonjp
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Quote:
 Originally Posted by badbrew 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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