Can someone please explain how to know how much co2 is left?

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badbrew

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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

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? :eek:

How do I know what's left? Is there a tank weighing rule?
 
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.
 
LOL I'm so dumb! I just googled "how much does 1 lb of co2 weigh":drunk:
 
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.:D
 
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.
 
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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