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I just set up a new kegerator with a corny and 5 lb CO2 tank. I turned the tank on and at first I had a leak I could hear/feel, but I tightened everything and sprayed with starsan and don't see any bubbles now.

However, every few hours since I started carbonating (it's been about 10 hours) the pressure on the keg decreases from 15 psi where I started down to 10 psi. The pressure on the CO2 tank started at 50 psi and is down to 45 or so. I haven't been able to find info on whether this is normal. The beer and CO2 may have decreased in temperature since I started, because it had only been in the fridge a few hours when I started carbonating.

Is this normal, i.e. the CO2 is absorbing, or is it possible that I have a leak?

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    is the Carbon Dioxide tank in the refrigerator with the beer? If so, the pressure will decrease on the tank as the temperature decreases.
    – baka
    Commented Jul 26, 2012 at 19:15
  • @baka: This should probably be the answer. I experienced the same thing when I first started kegging.
    – Dustin Rasener
    Commented Jul 26, 2012 at 19:33
  • Yes it is in there. It's a 5 cu. ft. chest freezer, so it all fits in there.
    – paul
    Commented Jul 26, 2012 at 19:54
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    @baka I think this is the answer. Someone else posted it after you, but if you post it as a formal answer I would give it to you because you were first. On further consideration, if I remembered basic laws of physics governing gases this could have been obvious, since pressure is proportional to temperature and it almost definitely got colder.
    – paul
    Commented Jul 27, 2012 at 4:03

3 Answers 3

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You have multiple effects at work here:

For one, the carbonation is about absorbing CO2 into the beer. This process lowers the CO2 pressure in the keg.

The second point is, that while cooling the beer and the tank, you make the beer able to absorb more CO2, while also reducing the volume of the gas - both in the keg and in the tank. That will lead to a somewhat lower pressure in the tank.

The third thing is, that allthough you have the first two point at work almost certainly (I cannot think of a reason why not) you still might have a leak.

I would leave the gas connected for a while and check regulary if the pressure is still falling in the tank. After about 1-2 weeks of this, you shouldn't have it falling anymore, and a significant slowdown before that. If you are good with math, you can calculate how much the pressure should fall if you are carbonating, but I don't have any formulas for this at hand.

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  • After a few weeks, the pressure has stabilized so there were no leaks. It seems like the answer was mainly the drop in temperature (en.wikipedia.org/wiki/Gas_laws), though CO2 absorption could have also played a role. Would like to give some credit to baka who answered this in a comment first, but I'd like to mark this as answered and this answer is more complete. Thanks Flyhard & @baka.
    – paul
    Commented Aug 20, 2012 at 19:41
  • +1 for details, and information about what to look for in the future, as well as the immediate info. Thanks!
    – nrobey
    Commented Jun 3, 2013 at 23:31
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Its likely the decrease in perceived pressure as the tank is chilling in the fridge.

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    What do you mean by "perceived pressure" - it seems like it's the actual pressure.
    – paul
    Commented Jul 27, 2012 at 4:05
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This is normal. The pressure will decrease significantly when cold but don't know the specifics on why this happens.

When you place it back in room temp, the regulator show the pre-cooled temp after a few hours.

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