CO2 and regulators

[kev211]

OK, so this very well could be a dumb, one and done question but its kind of a semi emergency so here we go...

I'm going on a camping trip this weekend. It was requested that I bring some beer. Great! I'll do that! I had an empty keg and spare co2 tank so all I needed to do was purchase a regulator and brew some beer. Fast forward to now. My kegerator is full so I'm carbing in my chest freezer/ferm chamber. The co2 tank and keg fit in there perfectly. Got everything all hooked up, peachy.

So tonight I go to check the carb level and I noticed that the regulator is reading about 500psi in the tank (carbing at around 15psi). The tank was full when I attached it. So the question is... Will a regulator read lower tank pressure when the tank is cold? I googled it and found some half baked answers but couldn't find a definitive answer. I'm leaving on my trip tomorrow night and will need to refill the tank if it is in fact empty (or close to it).

I have it sitting out to warm up right now to test the theory but I wanted to ask y'all.

So to summarize... Will cold temps make regulators read lower co2 levels? At ~38 degrees when my tank reads 500 psi is it actually a full tank or is it close to being empty? Thank you guys for your help!

 

[doug293cz]

OK, so this very well could be a dumb, one and done question but its kind of a semi emergency so here we go...

I'm going on a camping trip this weekend. It was requested that I bring some beer. Great! I'll do that! I had an empty keg and spare co2 tank so all I needed to do was purchase a regulator and brew some beer. Fast forward to now. My kegerator is full so I'm carbing in my chest freezer/ferm chamber. The co2 tank and keg fit in there perfectly. Got everything all hooked up, peachy.

So tonight I go to check the carb level and I noticed that the regulator is reading about 500psi in the tank (carbing at around 15psi). The tank was full when I attached it. So the question is... Will a regulator read lower tank pressure when the tank is cold? I googled it and found some half baked answers but couldn't find a definitive answer. I'm leaving on my trip tomorrow night and will need to refill the tank if it is in fact empty (or close to it).

I have it sitting out to warm up right now to test the theory but I wanted to ask y'all.

So to summarize... Will cold temps make regulators read lower co2 levels? At ~38 degrees when my tank reads 500 psi is it actually a full tank or is it close to being empty? Thank you guys for your help!

The pressure in a CO2 tank is a strong function of temperature. 500 psi when refrigerated is about right.

The flat portions of the curves below show the pressure at various temperatures for CO2 tanks that have any amount of liquid CO2 in them.



Brew on

 

[kev211]

The pressure in a CO2 tank is a strong function of temperature. 500 psi when refrigerated is about right.

The flat portions of the curves below show the pressure at various temperatures for CO2 tanks that have any amount of liquid CO2 in them.

View attachment 328047

Brew on

Great thanks! I figured it was a PV=nRT type of thing but its been a while since I took chem. And I didn't feel like doing any mental stuff right now 😀

 

[doug293cz]

Great thanks! I figured it was a PV=nRT type of thing but its been a while since I took chem. And I didn't feel like doing any mental stuff right now 😀

Actually, it's not a PV=nRT thing. It's a liquid/vapor equilibrium thing.

Brew on

 

[kev211]

Is pv=nrt not the relation ship to a particular amount of gas at specific temperatures? Not trying to get argumentative, I'm just starting to feel the need to learn all of a sudden haha

 

[mikescooling]

Yes, a cold tank will read lower, by about 200 or 300 PSIG, I think

 

[doug293cz]

Is pv=nrt not the relation ship to a particular amount of gas at specific temperatures? Not trying to get argumentative, I'm just starting to feel the need to learn all of a sudden haha

PV=nRT is the "ideal gas law" that applies to compression/expansion of gases when the gases are not in equilibrium with a condensed phase (usually liquid, but sometimes solid.) However, inside a CO2 tank that has any amount of liquid, you have equilibrium between the gas and liquid. The pressure in the tank is then the equilibrium vapor pressure of CO2 at the temperature of the liquid. Once the CO2 content of the tank is low enough that there is no liquid at the pressure and temperature of the tank, then the pressure approximately follows the ideal gas law. CO2 is not a very ideal gas. The fact the the PV curves are not linear in the lower left of the chart is because of the non-ideality of CO2 (i.e. compressibility.)

Brew on

 

[kev211]

Well I guess that makes sense. This is why I took one semester of chem in college to fulfill my G.E. requirements and never looked back haha