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Xtant · 01-20-2013, 09:25 PM

Not volume or a level. It's gas. Bottle pressure. There was very little change in bottle pressure until the bottle was empty.

**JuanMoore** · 01-20-2013, 09:59 PM

Quote:

Originally Posted by Xtant

Now that it is outside, it accurately shows how full the bottle is.

No, it doesn't.

Quote:

Originally Posted by Xtant

Not volume or a level. It's gas. Bottle pressure. There was very little change in bottle pressure until the bottle was empty.

It's going to behave the same way with the tank stored at room temperature. The high pressure gauge reads the vapor pressure in the bottle, which will remain the same (assuming constant temperature) until all of the liquid CO2 is gone, and the tank is almost empty. As soon as the liquid CO2 is gone, the pressure will quickly drop to zero as the remaining vapors are used. No matter what temperature you store the tank at, the gauge has little to no relation to how much CO2 is in the tank.

The ONLY way to know how much CO2 you have in the tank is to weigh it.

agslax · 03-07-2013, 12:46 PM

Quote:

Originally Posted by JuanMoore

No, it doesn't.

It's going to behave the same way with the tank stored at room temperature. The high pressure gauge reads the vapor pressure in the bottle, which will remain the same (assuming constant temperature) until all of the liquid CO2 is gone, and the tank is almost empty. As soon as the liquid CO2 is gone, the pressure will quickly drop to zero as the remaining vapors are used. No matter what temperature you store the tank at, the gauge has little to no relation to how much CO2 is in the tank.

The ONLY way to know how much CO2 you have in the tank is to weigh it.

I will admit that I took thermodynamics twice, but this is all wrong. As you fill a tank with CO2, the pressure inside increases because you are adding molecules into a fixed space. The more you add, the more compact you force them to be (ie, a larger pressure). As you use the CO2, that pressure decreases accordingly and that is how the empty/full gauge works.

If you change the temperature of your gas, it will drastically change the pressure. Even if you keep your CO2 tank at a constant cold temperature, that is not the pressure level that your gauge is set to show when it is getting low. In my mind, it would prematurely show an empty tank as cold gas takes up less volume than warmer gas. Regardless, I would not trust the high pressure gauge to determine how much is left in a tank when the tank is at a colder climate than intended. For this reason, homebrew stores are not allowed to fill your tank unless it is at room temperature so they do not risk over pressurizing it.

pabloj13 · 03-07-2013, 01:09 PM

Quote:

Originally Posted by agslax

I will admit that I took thermodynamics twice, but this is all wrong. As you fill a tank with CO2, the pressure inside increases because you are adding molecules into a fixed space. The more you add, the more compact you force them to be (ie, a larger pressure). As you use the CO2, that pressure decreases accordingly and that is how the empty/full gauge works.

If you change the temperature of your gas, it will drastically change the pressure. Even if you keep your CO2 tank at a constant cold temperature, that is not the pressure level that your gauge is set to show when it is getting low. In my mind, it would prematurely show an empty tank as cold gas takes up less volume than warmer gas. Regardless, I would not trust the high pressure gauge to determine how much is left in a tank when the tank is at a colder climate than intended. For this reason, homebrew stores are not allowed to fill your tank unless it is at room temperature so they do not risk over pressurizing it.

Yeah, no. Your description assumes a fixed ratio of gas:liquid. A 1/4 full tank and a full tank both have the same pressure (assuming equal temperature). I agree that a cold tank will have a lower vapor pressure than a warm tank, but what difference does that make? And the time difference between the two tanks (warm versus cold) after the liquid runs out is insignificant.

**JuanMoore** · 03-07-2013, 08:14 PM

Quote:

Originally Posted by agslax

I will admit that I took thermodynamics twice, but this is all wrong. As you fill a tank with CO2, the pressure inside increases because you are adding molecules into a fixed space. The more you add, the more compact you force them to be (ie, a larger pressure). As you use the CO2, that pressure decreases accordingly and that is how the empty/full gauge works.

If you change the temperature of your gas, it will drastically change the pressure. Even if you keep your CO2 tank at a constant cold temperature, that is not the pressure level that your gauge is set to show when it is getting low. In my mind, it would prematurely show an empty tank as cold gas takes up less volume than warmer gas. Regardless, I would not trust the high pressure gauge to determine how much is left in a tank when the tank is at a colder climate than intended. For this reason, homebrew stores are not allowed to fill your tank unless it is at room temperature so they do not risk over pressurizing it.

If the CO2 in the tank was all in gas form, you'd be correct, but most of it is in liquid form. If you took thermodynamics, you should know that most liquids are considered for all practical purposes to be incompressible. The vapor pressure of CO2 at any given temp is more or less a constant. Think of a recently filled tank, and let's imagine that the liquid CO2 takes up 80% of the volume of the tank, and above that is CO2 vapor. What's the pressure in the headspace? It's whatever the vapor pressure of CO2 is at that temperature. Now imagine the tank is nearly empty, with the liquid only taking up 5% of the tank volume. What's the pressure in the headspace? Just like before, it's the vapor pressure of CO2 at that temperature. So at constant temperature, the pressure will be constant as long as there's still liquid CO2 in there.

I'm simplifying things slightly above, but in general that's the way the tank pressure will behave. If you think it has any meaningful correlation to how full the tank is, you're mistaken.

**TrickyDick** · 03-07-2013, 09:37 PM

you should always try to put you cylinder OUTSIDE the fridge for many reasons. I hit a coolant line building my kegerator, but I had it repaired. It can be done.

TD

danielbt · 03-07-2013, 10:24 PM

Any tips to figuring out where the coolant lines run on the sides of a fridge?

LazyCat · 03-07-2013, 11:34 PM

I used our Fire Dept. Thermal imaging camera to find mine

brewinginnc · 03-08-2013, 01:12 PM

I called my local fire station to see if they would come out and tic my fridge but for some reason they wouldn't.

broadbill · 03-08-2013, 01:37 PM

Quote:

Originally Posted by TrickyDick

you should always try to put you cylinder OUTSIDE the fridge for many reasons. I hit a coolant line building my kegerator, but I had it repaired. It can be done.

TD

what are those "many reasons"?