Refrigerated CO2

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Ol' Grog

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Well, for now at least, I got one keg and my 10 pounder CO2 tank in the 4912. Notice, which I know will happen, that the pressure drops, A LOT. If I have my regulator set at 12 psi inside the refrigerator, am I really getting 12 psi to the keg? When they were warm, I dropped it to 12, but it changed when it got cold.
 
The regulator is right. Since the cold tank has less pressure in it, the regulator will need to be readjusted. Think of it like a garden hose hooked up to a hand sprayer. If you adjust the sprayer to the desired flow with the water turned on fully, and then you turn down the water pressure at the spigot, you'd have to readjust the sprayer to get the same flow.
 
If you are keeping the gas turned on, the pressure should not vary in your keg. CO2 tank yes, keg no.

The regulator's sole function is to keep output pressure (not flow as mentioned above) constant irrespective of the input pressure.
 
I've had the same problem in the past. My tank was filled at 1000 PSI, when refrigerated, it dropped about to about 550.

Regardless, the regulator will keep you honest, and keep the desired amount of CO2 on the beer.
 
Whatever the regulator reads on the outlet side is the pressure your keg has in it. Adjust it back to 12 and check it again in a few hours.

When you put the cylinder/regulator in the fridge, the regulator setting that worked at room temperature will result in a too low an outlet pressure when cold. A chilled regulator tends to be a bit finicky, but there's nothing wrong with it being cold as long as you adjust it properly.
 
Ol' Grog said:
Well, for now at least, I got one keg and my 10 pounder CO2 tank in the 4912. Notice, which I know will happen, that the pressure drops, A LOT. If I have my regulator set at 12 psi inside the refrigerator, am I really getting 12 psi to the keg? When they were warm, I dropped it to 12, but it changed when it got cold.

The setting for 12 psi cold and 12 psi warm are two different things. Adjust the setting when the temp stabilizes and all will be well in the world
 
Yuri_Rage said:
When you put the cylinder/regulator in the fridge, the regulator setting that worked at room temperature will result in a too low an outlet pressure when cold.

Explain please- what's the physics behind this?
 
skunked169 said:
So if you increase temp, volume must increase as well, or volume will decrease with a decrease in temp.
Or, an increase in temp with no change in volume will result in increased pressure, and vice versa. You're forgetting that portion of the equation...which is the important part in this discussion.
 
Yuri_Rage said:
Or, an increase in temp with no change in volume will result in increased pressure, and vice versa. You're forgetting that portion of the equation...which is the important part in this discussion.


Sorry, but that is exactly it , if the volume is constant like with a CO2 bottle pressure in the bottle will increase or decrease dependent on temperature, in a proportional fashion...I told you I was trying to forget Physical Chemistry...
 
Yuri_Rage said:
Simple - the Ideal Gas Law - pressure and volume vary with temperature. Given the same gas volume, pressure will lower proportionally with temperature.

Uuum. Nope. That explains why the pressure in the CO2 tank changes with temperature, but the question is why does the pressure output of a regulator change with temperature.

The regulator doesn't know about the Ideal Gas Law and doesn't care. It's a mechanical device whose sole job is to keep downstream pressure constant, irrespective of supply pressure. That's why it's called a 'regulator' and not a 'reducer' or 'restrictor'. The ones we use are adjustable, but that's a side point. Most gas regulators, like used on a propane BBQ, turkey fryer or domestic gas supply are at a fixed output pressure.

It works by balancing pressure on one side of a diaphragm against mechanical spring pressure on the other. If the downstream gas pressure decreases, the spring pushes open a metering valve to allow more gas to flow and restore the desired pressure. If the downstream pressure is already too high, the metering valve stays shut.

We all know that downstream pressure to a keg ( or BBQ) will remain constant until the pressure in the supply tank has dropped to almost nothing- which shows that it does indeed do it's appointed job.

If the only additional variable is the temperature of the gas, why does this have the affect of changing downstream pressure?

BTW- my 5 regulators are NOT affected by temperature. Why some and not others?
 
Wow. Thanks for all the responses. Now I just wonder when I'll need to order gas. The tank pressure dropped to just above the "re-order" gas line on the guage. I know it's about 750 at room temperature but dropped to about 500 or so. Guess when it gets really low, say around 100 or so, get ready to order. Is that what ya'll have been doing???
 
Ol' Grog said:
Wow. Thanks for all the responses. Now I just wonder when I'll need to order gas. The tank pressure dropped to just above the "re-order" gas line on the guage. I know it's about 750 at room temperature but dropped to about 500 or so. Guess when it gets really low, say around 100 or so, get ready to order. Is that what ya'll have been doing???

Yep. Pretty much. I wait until it gets pretty low. Mine has been sitting at 500 for weeks.
 
I just keep two tanks at all times. When one goes down, I will slap the other into the kegerator and keep going. Then, I can get the other filled at my leisure.
 
Mikey said:
Uuum. Nope. That explains why the pressure in the CO2 tank changes with temperature, but the question is why does the pressure output of a regulator change with temperature.

The regulator doesn't know about the Ideal Gas Law and doesn't care. It's a mechanical device whose sole job is to keep downstream pressure constant, irrespective of supply pressure.

It works by balancing pressure on one side of a diaphragm against mechanical spring pressure on the other. If the downstream gas pressure decreases, the spring pushes open a metering valve to allow more gas to flow and restore the desired pressure. If the downstream pressure is already too high, the metering valve stays shut.
You are correct in that a good regulator should not be affected by temperature (which kinda had me puzzled as I wrote the post about the Ideal Gas Law, but it was the most logical explanation I could think of). Two more possible explanations for why some regulators definitely are affected:

1. Some regulators might not be as accurate as they should, so a large pressure drop on the inlet side does cause a pressure drop on the outlet side.

2. As the regulator mechanism gets cold, the spring is the most affected part since it is a long, thin piece of metal. The spring decreases in length, reducing the tension on the spring, resulting in a lower outlet pressure.
 
The reason that the outlet pressure setting appears to change when the regulator is cold is due to the fact that the elastomer that is used for the diaphragm in the regulator responds more slowly to changes when cold.

For example, if your tank is in the fridge and you set the regulator for an output of 12 psi, the low pressure gauge will read 12 psi. When you come back and check it later you will find that the pressure will have overshot your setting of 12 psi by a few psi or more. This is the elastomer that the diaphragm is made of reacting more slowly to a change in output due the the colder temperature.

John
 
That's EXACTLY what happened. So, with that in mind, do I need to crank it up a bit? If I want 12 psi, then crank to 14 or so?
 
Ol' Grog said:
That's EXACTLY what happened. So, with that in mind, do I need to crank it up a bit? If I want 12 psi, then crank to 14 or so?

No, you want to do the opposite. If your regulator is already in the fridge and cold, and you want 12 psi on the keg, set it to about 10 psi or so and it will stabilize at about 12 psi. You may have to experiment a little to find out just how much the pressure will creep up from your initial setting, but I have found that setting the regulator about 2 psi below what you want will get you pretty close.

Keep in mind, I am only referring to making regulator output adjustments on a tank and regulator that is stored in the kegerator. This delay in response to a change in output pressure should not occur at a "normal" room temperature.

John
 
Just an FYI, for anyone that is interested. Here is a pressure/temperature chart for CO2 that shows the relationship between the pressure inside the CO2 tank and the ambient temperature that the tank is exposed to.

John

CO2_liquid_gas_chart.gif
 
johnsma22 said:
The reason that the outlet pressure setting appears to change when the regulator is cold is due to the fact that the elastomer that is used for the diaphragm in the regulator responds more slowly to changes when cold.

For example, if your tank is in the fridge and you set the regulator for an output of 12 psi, the low pressure gauge will read 12 psi. When you come back and check it later you will find that the pressure will have overshot your setting of 12 psi by a few psi or more. This is the elastomer that the diaphragm is made of reacting more slowly to a change in output due the the colder temperature.

John
Dammit, I hate being wrong. I thought I was making so much sense. Guess I'll go drink more beer.
 
Yuri_Rage said:
Dammit, I hate being wrong. I thought I was making so much sense. Guess I'll go drink more beer.

I don't think you were wrong. The stiff elastomer theory would make sense in transient/slow response time scenario, but under steady condition, it should still eventually settle at the original setting.

By the way, part of my job is to troubleshoot aircraft engine fuel supply systems which operate in environments of -60*F to +175*F. Does it show? :tank:
 
Mikey said:
By the way, part of my job is to troubleshoot aircraft engine fuel supply systems which operate in environments of -60*F to +175*F. Does it show? :tank:
That is also part of my job. But my fixes tend to be more urgent and less permanent.
 
Guys, I don't think anyone posted important info;

Most of the Co2 in the tank, (if it is mostly full) is LIQUID carbon Dioxide. The liquid will boil off, at a pressure determined by the temp. If you lower the temp, the pressure will also drop.

On a 2 stage regulator, the higher gauge will read bottle pressure, and the lower gauge will read delivery pressure. It has been my experience, with good gauges and regulators, that the lower pressure will remain static (unless you adjust it) until the upper pressure drops below the boil pressure, for the temp. (That usually means that the liquid Co2 has boiled away.) Then, the upper pressure will start to drop, and when it hits the lower pressure, both of them drop to zero.

If you put the bottle in the refrigerator, the boil pressure will drop below the "re-order" level, but stay there, until you run out of liquid Co2. Just watch the upper gauge for movement, (not influenced by temp swings) and re-fill when it drops.

steve
 
skou said:
Guys, I don't think anyone posted important info;

Most of the Co2 in the tank, (if it is mostly full) is LIQUID carbon Dioxide. The liquid will boil off, at a pressure determined by the temp. If you lower the temp, the pressure will also drop.

That was brought up on page 1 of this thread- ideal gas law.
 
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