Kegging CO2 Pressure Questions

[odium]

I am doing my first 5 gallon soda-keg and I have a question:

My CO2 tank started at 725psi, and went to around 500psi overnight. Does this mean I have a leak in my tank that I have to fix? Do I need to install new O-rings, or does it really use this much CO2!?

The guy behind the counter at the shop I used said to put it in a refrigerator and pressurize it to ~30psi for 24-72 hours. After that, I should release pressure and serve at the appropriate psi found in the charts for the beer I've made. Is this right?

If not, what do I do?

 

[user 4295]

I'm assuming from your post that you have your CO2 tank in the fridge hooked to your keg, correct? If so, CO2 has a direct pressure/temperature relationship. Meaning that the pressure in the tank will change depending on the temperature that the tank is sitting at.

Also, CO2 exists in your tank in a liquid/vapor state. The pressure will stay the same in the tank, as long as the temperature of the tank does not change, until all the liquid has been vaporized. Once there is only vapor in the tank the pressure will drop rapidly. See the pressure/temperature chart for CO2 below. 567 psi is correct for a 40˚F fridge temp.

Another important thing to note about the valve on a CO2 tank is that when it is open it must be open all the way and snugged up on its back seat. Otherwise it can leak.

John

 

[Mikey]

The guy behind the counter at the shop I used said to put it in a refrigerator and pressurize it to ~30psi for 24-72 hours. After that, I should release pressure and serve at the appropriate psi found in the charts for the beer I've made. Is this right?

If not, what do I do?

The above step in unnecessary and can lead to grossly overcarbonated beer. Set your regulator to the final serving pressure as soon as its connected to a freshly kegged batch. That's it. The CO2 will take about a week to achieve equlibrium and will benefit from having time to settle and clear.

 

[odium]

This forum is great!

Thanks.

 

[Chairman Cheyco]

Another important thing to note about the valve on a CO2 tank is that when it is open it must be open all the way and snugged up on its back seat. Otherwise it can leak.

I was always told that if you open all the way to the back seat, you will compress the packing around the stem of the valve and cause a leak over time. Thus you should always open all the way gently and close it a 1/4 turn.

 

[user 4295]

I was always told that if you open all the way to the back seat, you will compress the packing around the stem of the valve and cause a leak over time. Thus you should always open all the way gently and close it a 1/4 turn.

That is not correct. There are two basic types of cylinder valves used for compressed gas cylinder valves -
packed valves and diaphragm valves. Packed valves come in 2 different types: pressure seal valve (backseating packed valve) and the nonbackseating packed valve.

Diaphragm valves are used for highly toxic gases and high purity gases (I use this type of valve for lithium bromide absorption refrigeration systems). Nonbackseating packed valves are used for corrosive and reactive gases (I use this type of valve for standard refrigerant systems). Backseating packed valves, also known as pressure seal valves, are used for inert gases such as CO2, nitrogen(N2), and also for O2 and H2.

Pressure seal valves must be in the fully open position and snugged, not cranked against the backseat. This pulls the lower stem up to the upper stem driving the upper stem seal ridge to the packing ring, improving the seal and reducing the chance for a leak. This is called “backseating”. See photo below:

John

 

[Chairman Cheyco]

Sweet, thanks John. I stand corrected. Does the same apply to propane tanks?

 

[user 4295]

Sweet, thanks John. I stand corrected. Does the same apply to propane tanks?

No! Propane valves are not double seated. They are of the nonbackseating packed valve style. The valve stems are sealed whether 1/4 turn open or full open.

John

 

[david_42]

John - Thanks! I never took a close look at the valve. Maybe that's where the slow leak is in my system. I've had a problem with CO2 leakage since I moved the bottle outside the fridge. I backseated the valve & we shall see.

 

[user 4295]

John - Thanks! I never took a close look at the valve. Maybe that's where the slow leak is in my system. I've had a problem with CO2 leakage since I moved the bottle outside the fridge. I backseated the valve & we shall see.

You are more than welcome David. I hope this solves your slow leak. I wrestled with a leak for a little while and I know how frustrating it can be when you can't locate it, but you know it's there. I finally submerged every component, except the regulators, in my bathtub full of water while pressurized to 60 psi. The bubbles led me to the leak on the stem of one of my shutoff valves.

John