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Old 04-09-2010, 01:13 PM   #1
goswell
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Default Newb kegging question

I kegged up my first batch last night...Here's what I did.

Racked the beer into the keg and sealed it up, used keg lube on all gaskets.
When the beer was a room temp I set the regulator to about 10.5 psi to check for leaks, which I didn't detect any.
I then put everything in the kegerator and went to sleep. When I woke up, the pressure dropped to about 5 psi, according to the regulator. I opened the valve a bit more and it's now back to 10.5 psi.
Why did that happen? Is it because the beer temp dropped from room temp to 38f? The tank regulator says I have about 600 lbs left, which is low, did that cause it? I guess I expected the regulator to stay at 10 psi no matter what is happening with the beer.



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Old 04-09-2010, 01:23 PM   #2
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at lower temps liquids absorb more co2



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Old 04-09-2010, 01:33 PM   #3
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at lower temps liquids absorb more co2
I know that, but why would that have anything to do with the psi on the regulator gauge? If the beer cools down and absorbs more co2, shouldn't the regulator keep up with that and maintain the 10.5 psi?
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Old 04-09-2010, 02:17 PM   #4
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Did you put the CO2 into the fridge, or turn the fridge on? As the CO2 cools in the tank, the tank pressure will drop from ~850 to ~500-600. This is NORMAL, you don't have a leak. Also, as the regulator cools, its internal workings will cool, and the pressure it is outputting will change. I have my reg outside my fridge, and now that spring is coming and temps are warming, I have to keep an eye on it to make sure a warm day doesn't spike me up to 15 psi.

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Old 04-09-2010, 02:20 PM   #5
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Thanks for the input. I also just put my first batch of beer on pressure and had the same concern. I am putting it at about 11 PSI and just leaving it there for a few weeks.

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Old 04-09-2010, 03:05 PM   #6
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Quote:
Originally Posted by shortyjacobs View Post
Did you put the CO2 into the fridge, or turn the fridge on? As the CO2 cools in the tank, the tank pressure will drop from ~850 to ~500-600. This is NORMAL, you don't have a leak. Also, as the regulator cools, its internal workings will cool, and the pressure it is outputting will change. I have my reg outside my fridge, and now that spring is coming and temps are warming, I have to keep an eye on it to make sure a warm day doesn't spike me up to 15 psi.
Yep, I think that might be what is happening. When you say the tank pressure will drop from 850 to 500 - 600, is that throughout the life of the tank, i.e., will the tank read 600 no matter if there is 2000 psi or 900 psi actually in the tank? Or is 850 psi actually the max they get into the cylinder? Will it stay at 500 - 600 for a long while before dropping to zero? So many question from the newb....
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Old 04-09-2010, 04:12 PM   #7
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Originally Posted by goswell View Post
Yep, I think that might be what is happening. When you say the tank pressure will drop from 850 to 500 - 600, is that throughout the life of the tank, i.e., will the tank read 600 no matter if there is 2000 psi or 900 psi actually in the tank? Or is 850 psi actually the max they get into the cylinder? Will it stay at 500 - 600 for a long while before dropping to zero? So many question from the newb....
CO2 in a tank is mostly liquid, with a bit of vapor on top. The gauge is reading the vapor pressure, which you can think of like the pressure that the liquid CO2 is making while trying to boil. As you pull CO2 out of the tank (dispensing beer), more liquid CO2 boils into vapor to replace what you take.

The vapor pressure of the CO2 depends on temperature. So, at 70F, it will read like ~850 PSI, (going from memory here, but you could look these up). At 38F, it will read 500 PSI. It will CONTINUE to read that pressure until the tank is almost empty, at which point all of the CO2 liquid will have boiled, and the vapor pressure will start to drop as you use the last bit of vapor.

What this means is, your tank will stay at 500-600 PSI the entire time it's in the fridge, until JUST before it runs out, (before you use up all your CO2), at which point it will drop very quickly to 0 PSI.

The gauge is not like the gas gauge in your car. It basically only tells you if you have CO2 or not, not how much you have left.

If you don't use your CO2 for 20 years, (don't pull any pints), and don't have any leaks, it will stay at 500-600 PSI that entire time, (if in the fridge), and at any time if you remove it from the fridge it will jump back up to 850 PSI. As you use it, and keep pulling pints, and keep pulling CO2, it will stay at 500-600 PSI until it suddenly drops to 0, at which point you need a refill.
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Old 04-09-2010, 04:17 PM   #8
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Sorry to post in here but it kinda has to do with the original question.

I set my beer at 12 psi this morning, came bac a few hours later and it jumped to 15 psi. how did this happen?

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Old 04-09-2010, 04:18 PM   #9
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Quote:
Originally Posted by shortyjacobs View Post
CO2 in a tank is mostly liquid, with a bit of vapor on top. The gauge is reading the vapor pressure, which you can think of like the pressure that the liquid CO2 is making while trying to boil. As you pull CO2 out of the tank (dispensing beer), more liquid CO2 boils into vapor to replace what you take.

The vapor pressure of the CO2 depends on temperature. So, at 70F, it will read like ~850 PSI, (going from memory here, but you could look these up). At 38F, it will read 500 PSI. It will CONTINUE to read that pressure until the tank is almost empty, at which point all of the CO2 liquid will have boiled, and the vapor pressure will start to drop as you use the last bit of vapor.

What this means is, your tank will stay at 500-600 PSI the entire time it's in the fridge, until JUST before it runs out, (before you use up all your CO2), at which point it will drop very quickly to 0 PSI.

The gauge is not like the gas gauge in your car. It basically only tells you if you have CO2 or not, not how much you have left.

If you don't use your CO2 for 20 years, (don't pull any pints), and don't have any leaks, it will stay at 500-600 PSI that entire time, (if in the fridge), and at any time if you remove it from the fridge it will jump back up to 850 PSI. As you use it, and keep pulling pints, and keep pulling CO2, it will stay at 500-600 PSI until it suddenly drops to 0, at which point you need a refill.
Great info, thanks!


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