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High pressure on full C02 tanks

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sunblock

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Do you guys know what the high pressure level should be for various full C02 tanks? I have found a cheap place to get mine refilled but they only take it to 1200 PSI, I could be wrong but I thought it was a 50 pound tank. My 5 pounder only goes to about 550-600 so that seems low for a big tank.
 
The size of the tank has nothing to do with the pressure. CO2 is in liquid form, in the tank. It "boils off" in the tank up to a certain pressure at a specific temperature. This is known as "vapor pressure".

So, in a nutshell, the tank can be 5#, or 500# the pressure will be the same, as long as there is liquid in the tank.
 
The size of the tank has nothing to do with the pressure. CO2 is in liquid form, in the tank. It "boils off" in the tank up to a certain pressure at a specific temperature. This is known as "vapor pressure".

So, in a nutshell, the tank can be 5#, or 500# the pressure will be the same, as long as there is liquid in the tank.

This makes some sense, but why then does my smaller tank always have a lower pressure, near the change tank level. The pressure seems to correlate somehow to the volume of gas remaining.
 
The pressure seems to correlate somehow to the volume of gas remaining.

Exactly! Smaller tank, smaller volume of gas. Runs out faster than a tank with larger volume.

Most folks ignore the tank pressure gauge. When it starts to drop, your done, get it refilled.
 
About the only time you'd see a difference is if the bigger tank was over-filled, otherwise CO2 pressure is strictly related to temperature. If there isn't enough head space, the liquid can expand enough to raise the pressure. If you do a bit of searching, you can read about what happens if an over-filled tank is left in a hot car.
 
ok strange then, I have only had my 20 lb tank filled twice, but its always at the 1200 psi mark, or so says my regulator.
 
The difference is probably the fact that your 5 pound tank is sitting in your kegerator in the cold.

CO2 tank pressure is correlated to temperature, no matter what.

How much liquid CO2 they put in your tank is determined by weight, which is why CO2 tanks are rated in POUNDs, not pressure or volume like a scuba tank.

Ponder this chart for a bit:
co2pv.gif
 
The difference is probably the fact that your 5 pound tank is sitting in your kegerator in the cold.

CO2 tank pressure is correlated to temperature, no matter what.

How much liquid CO2 they put in your tank is determined by weight, which is why CO2 tanks are rated in POUNDs, not pressure or volume like a scuba tank.

Ponder this chart for a bit:
co2pv.gif

nope, they both sit outside the fridge, I use the 5 pounder for backup and parties or such.
 
then your regulator gauge is wrong. Science dictates the psi of CO2 WILL be 'x' value at 'y' temperature. Period. And it'll stay that psi until you're down to the last few ounces of liquid CO2.

A CO2 tank with a pound left is still going to be about 1,000 psi at room temperature, as is a full tank at room temperature, even if one is 5lbs total and the other is 50lbs.
 
then your regulator gauge is wrong. Science dictates the psi of CO2 WILL be 'x' value at 'y' temperature. Period. And it'll stay that psi until you're down to the last few ounces of liquid CO2.

A CO2 tank with a pound left is still going to be about 1,000 psi at room temperature, as is a full tank at room temperature, even if one is 5lbs total and the other is 50lbs.

I agree, just never thought about it that way and have always read the gauge. good thing I am building a new one.
 
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