Converting a fridge to a kegerator. CO2 tank on the inside or out?

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jcole

jcole

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I'm in the process of converting an old fridge I have to store two kegs with mounted faucets.

I have room for the CO2 on the inside and would actually like to keep it on the inside, unless there is a good reason not to.

Thoughts?

thanks,
John
 
Berserker_Brew said:
it is fine to keep it on the inside. lots of people do. the tank's guages reading will be off though
Click to expand...

How will it be off?

Pressure decreases as temperature decreases. That's just physics...

Or am I over thinking your post?
 
lilzaphod said:
How will it be off?

Pressure decreases as temperature decreases. That's just physics...

Or am I over thinking your post?
Click to expand...

That's kind of what I was getting at and wondering in the original post.

Its easier for me to keep it inside, but if I'm going to lose a lot of pressure or suffer other negative effects, then I would consider going to the trouble of mounting it outside.
 
You will loose pressure when it's in the fridge. But the amount of CO2 in the tank will not change.
 
You get the same amount of gas, but the gauge won't be right until you're just about out of gas (my experience anyway).
 
MoRoToRiUm said:
You get the same amount of gas, but the gauge won't be right until you're just about out of gas (my experience anyway).
Click to expand...

How is it "off" though?

It shows lower pressure? It shows higher pressure(doubtful)?

Unless you have a mechanical issue with the gauge, you should have the pressure you have, and it would be off by the offset in
PV=RT (Ideal gas law), I believe.

If you wanted the "same" pressure cold as what the tank is when you fill it, you would need to fill the tank at the same temperature as you hold it at in the fridge. Otherwise, the temp change will lower the pressure slightly.

Now if the gauge is acting/reading funky, that may be a mechanical thing, but I'm not versed enough on this equipment to say what or why.

But the gas itself isn't doing much except contracting a little, and so you will lose some psi in the tank. And I would have to think it's miniscule....
 
lilzaphod said:
How is it "off" though?

It shows lower pressure? It shows higher pressure(doubtful)?

Unless you have a mechanical issue with the gauge, you should have the pressure you have, and it would be off by the offset in
PV=RT (Ideal gas law), I believe.

If you wanted the "same" pressure cold as what the tank is when you fill it, you would need to fill the tank at the same temperature as you hold it at in the fridge. Otherwise, the temp change will lower the pressure slightly.

Now if the gauge is acting/reading funky, that may be a mechanical thing, but I'm not versed enough on this equipment to say what or why.

But the gas itself isn't doing much except contracting a little, and so you will lose some psi in the tank. And I would have to think it's miniscule....
Click to expand...

How do you think the "amount in the tank" gauge works?

Pressure.

If the gauge is calibrated for room temperature and you have it 40 degrees, the apparent pressure is lower, so the gauge will be off.
 
Cpt_Kirks said:
How do you think the "amount in the tank" gauge works?

Pressure.

If the gauge is calibrated for room temperature and you have it 40 degrees, the apparent pressure is lower, so the gauge will be off.
Click to expand...

What's "room temperature" again? Oh yeah, what ever you set it at.

You're always going to have a little fudge factor in these types of gauges. IMO, it's not worth drilling a hole in the side of a refrigerator so you can get "more accurate" readings.

The post I was referencing made it sound like the gauge was going to be way off if you kept it cold, and that's just not the case unless there is something mechanically different in these gauges than other high pressure gauges. As in something like a unsealed unit getting frost inside and hindering the movement.

This is my first tank of gas in my kegerator, but I do know a little bit about gas, tank pressure and temp changes due to the scuba classes I used to teach.
 
lilzaphod said:
What's "room temperature" again? Oh yeah, what ever you set it at.

You're always going to have a little fudge factor in these types of gauges. IMO, it's not worth drilling a hole in the side of a refrigerator so you can get "more accurate" readings.

The post I was referencing made it sound like the gauge was going to be way off if you kept it cold, and that's just not the case unless there is something mechanically different in these gauges than other high pressure gauges.

This is my first tank of gas in my kegerator, but I do know a little bit about gas, tank pressure and temp changes due to the scuba classes I used to teach.
Click to expand...


"Room Temperature" is generally considered to be 71 to 81 degrees.

The inside of a kegerator is about 40 degrees, so you would be looking at a roughly 50% reduction in temperature. Now, I'm no expert, but once again using the Idea Gas Law, a 50% reduction in temperature should lead to a considerable (though not a 50%) reduction in indicated pressure.

The gas line is usually brought in though the drain hole. You have to drill holes for the taps.

ETA: Some quickie anecdotal research indicates the tank capacity gauge is not terribly useful. No real change in pressure happens until the liquid CO2 is exhausted.
 
As stated in the last post, don't take too much notice of the 'tank' pressure gauge. The 'PSI' gauge of the keg is good but the tank pressure gauge can remain at a set figure right up until the tank is virtually empty. If the tank pressure gauge drops to near zero and you are still getting CO2 pressure then I'd look into getting it refilled soon but otherwise don't rely on it.
 
It's been explained in other post before, but CO2 is a liquid gas. The tank (high pressure) gauge when refrigerated won't be accurate until you tank is almost empty, and the liquid has enough free space to turn into gas (similar at room temp too).

Moral of the story- Having an extra tank filled is quite handy
 
no- no -no - you guys got it all wrong. nothing wrong with the guages they read the actual pressure inside the tank. When a tank is cold, the pressure in the tank will be lower then when it is warm (with the same amount of CO2 in the tank.

PV=nrT

PV/nrT=PV/nrt (inside a cylinder, nr are equal, and V-volume does not change so cancel those)

that leaves P1/T1=P2/T2 (with P1,T1 being warm) P2,T2 being cold)

solve for P2 - P2=P1*T2/T1

P1=4000 psi, T1=75 deg F which is 298.1K, T2=35 deg F wich is 274.8K

so P2=4000*274.8/298.1

P2= 3687 psi

So a tank at 4000 psi when at room temp will read 3687 psi in the fridge. But the amount of CO2 in the tank is exactly the same.
 
More practical way to look at this is gas expands when temp goes up. this is what makes a hot air balloon work. they heat up the air in the balloon, the air expands (which makes it less dense) and the balloon rises.

Similarly, gas contracts when it cools. So when you fill a tank at room temp to a certain pressure. You stick it in the fridge and the gas contracts, making the pressure in the tank lower without changing the amount of gas in the tank.
 
As to the OP...

Nothing wrong with having the tank inside the fridge. The issue you will run into is that the regulators don't like to work when cold. The diaphragm inside the regulator gets stiffer at colder temps.The best thing to do for this is to set them low when you first put them in (like at 5 PSI) and then come back the next day and it may have crept upward, adjust it a few times over the next few hours to get it where it will stay at your desired pressure, and don't mess with the pressure anymore.
 
^ this is the best answer to the question. The only question now is whether the apparent "decrease" in quantity will affect the longevity of the Co2 Cylinder between fills (which is what i think the OP was originally looking to figure out).
 
techbrewie said:
^ this is the best answer to the question. The only question now is whether the apparent "decrease" in quantity will affect the longevity of the Co2 Cylinder between fills (which is what i think the OP was originally looking to figure out).
Click to expand...

It won't. There's a decrease in pressure because the vapor pressure of liquid CO2 decreases with temperature. Unless you need to push CO2 out above 450-500 psi, this is fine. You still have the same amount of CO2 that you had when the tank was warm.

As mentioned above, the only downside is the regulator can respond a little slower.
 
In my experience, I have enjoyed having the tank of the outside of my kegerator. It allows me to monitor keg pressure without having to open the fridge and allows me to make adjustments quickly. The tank pressure gauge is pretty worthless IMO, regardless of tank temperature or whether mounted in/out of the fridge. My tank filled around 8 kegs worth of beer, and lasted little over a year (I alternate bottling/kegging depending on the beer in question).
 

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