CO2 Pressure and Dissolution

[beerd]

I am trying to pressure/leak test a fermenter. The fermenter had some amount of water in it. I have the fermenter completely sealed and pressurize it to, say, 2 PSI with CO2, then disconnect the CO2 tank The pressure gauge on the fermenter slowly over an hour or more drops to 0.

I realize that CO2 will dissolve in water - so I am not sure how to judge if this is a leak or not. Practicality dictates just draining the water. But now I am curious...

I had dumbly expected the head pressure to "equalize" above the water at 1 PSI (half of the 2 PSI I put in). Reading a bit it sounds like CO2 solubility in room temperature tap water is much higher than the dissolved CO2 based on equilibrium with atmospheric concentrations? Depending on the ratio of headspace to water in the fermenter (assuming it is airtight), I could presumably pressurize it to 2 PSI several times before the water becomes saturated with CO2 and the PSI in the headspace remains at 2 PSI even after disconnecting the CO2 tank? Any sort of calculator or napkin math that covers this?

 

[bracconiere]

5 gallons of co2 weighs 1.23oz's, and according to residual carbonation charts, at like 85f water can hold around 0.6 volumes, and at 50f, like 1.2? not sure if that helps....

maybe try it with hot water? instead cold/room temp?

 

[Bobby_M]

It's all about the ratio between the headspace and liquid space. If the container is 2 gallons and you have 1 gallon of water, 2 PSI blasted into the headspace and disconnected will equalize down to 1PSI in the water and 1PSI in the headspace. Top up the headspace to 2psi again and now the midpoint is 1.5 psi after some time.

Or you could hook up 2psi and shake the hell out of the fermenter for a couple minutes and then everything will be at 2psi.

 

[balrog]

Get your bike pump out and pump up the fermenter using that instead of co2.

 

[Golddiggie]

Anytime I'm pressure testing a vessel I make sure it's as empty as possible of liquid. I'm looking at how it holds gas pressure, not liquids. I also use more than 2psi to test with. Granted all my fermenters have working pressure of at least 15psi (latest conicals are rated to 15psi working pressure). Typically, I'll hit them with 5-10psi (again, just CO2 with as little liquid inside as possible). At 10psi you should hear any leaks that are large enough to be a major concern. You'll also want to have them someplace that's fairly temperature stable (not swinging more than a few degrees F during the day, or time you're testing). Since temperature can influence pressure levels. Worst case, hit them with pressure when the area is the coolest it will be. Since the pressure level can increase as things warm up (degreasing as they cool).

You can also use a spray bottle of Starsan solution to find significant leaks (that you cannot hear). Or soapy water, also in a spray bottle. I like to use Starsan since I typically have a spray bottle of it on hand at all times.