Upgrading kegerator to duotight/evabarrier questions

[Bobby_M]

Is there science to show a significant oxygen gets in through Standard oxygen porous gas tubing? I’d think diffusion across plastic tubing would be Slowed down since there is co2 under pressure.

Similar to fick’s law. Fick's Law | Pathway Medicine
“ Fick's Law essentially states that the rate of diffusion of a gas across a permeable membrane is determined by the chemical nature of the membrane itself, the surface area of the membrane, the partial pressure gradient of the gas across the membrane, and the thickness of the membrane.”

In both replies you demonstrate a misunderstanding of the nuances in the law. "of THE gas across membrane" rather than "any gas".. It means a particular gas's propensity to migrate is based on the pressure differential OF THAT GAS on either side of the membrane. That is to say, CO2 is on the inside and there is little to no oxygen in there. But there IS oxygen outside and that differential will cause migration.

The good news is that you don't have to take anyone's word for it or even spend time researching. Make up a 5 foot picnic tap line out of clear PVC tubing and out of EVA. Dispense beer through both and then leave them both disconnected but inside your kegerator for a few days. Then hook them both back up and dispense exactly 1 ounce of beer into cups through both lines. Taste them blindly and discover what we're talking about.

 

[Vale71]

Similar to fick’s law. Fick's Law | Pathway Medicine
“ Fick's Law essentially states that the rate of diffusion of a gas across a permeable membrane is determined by the chemical nature of the membrane itself, the surface area of the membrane, the partial pressure gradient of the gas across the membrane, and the thickness of the membrane.”

No need to look for something similar as this is actually governed by Fick's law. I've highlighted the part you have missed and that is most relevant to the discussion.

 

[Vale71]

I don't follow. CO2 pressure inside the tubing means that there will be some CO2 loss through a permeable tubing to the atmosphere. This is only a cost issue, but is negligible for the trivial volume of CO2 lost.

The partial pressure of O2 inside the tubing is essentially ZERO, and the partial pressure of O2 at sea level is 21% x 14.7 psia = 3.1 psia, which is thus the O2 gradient from outside the tubing into the tubing. Therefore, there is a propensity to have oxygen enter a permeable tubing -- even under high co2 pressure. Am I missing or misinterpreting something here?

Not at all. As a matter of fact you're spot on.

The CO2 loss could be an issue in packaging in case of prolonged storage (especially if stored warm, where both permeability and pressure are significantly increased) where the loss of carbonation could become noticeable. That's one more reason why keg gaskets are made of low-permeability rubber such as Buna or EPDM, both to prevent O2 ingress as well as avoiding significant carbonation loss.

 

[Gozie Boy]

Not at all. As a matter of fact you're spot on.

The CO2 loss could be an issue in packaging in case of prolonged storage (especially if stored warm, where both permeability and pressure are significantly increased) where the loss of carbonation could become noticeable. That's one more reason why keg gaskets are made of low-permeability rubber such as Buna or EPDM, both to prevent O2 ingress as well as avoiding significant carbonation loss.

Good point about CO2 loss from the keg. The small diameter of EvaBarrier tubing (i.e. much less surface area), plus its inner liner, means that this product must have a much lower CO2 loss from the keg (at least relatively) versus, say, 5/16 vinyl tubing. [And, by the same reasoning, much lower O2 ingress.].

Having said that, I now often remove the disconnects from my kegs if my system will not be in use for a few days or more. All it took was one odd leak in the system (which had held firm for a couple of years) and a drained beer gas tank to keep me on guard. Turned out to be a flare swivel connection that worked itself just loose enough to leak (probably my fault for not having wrenched it tightly enough). I hope the DuoTight connects are a little more robust (and idiot proof!).

 

[Yesfan]

..........The good news is that you don't have to take anyone's word for it or even spend time researching. Make up a 5 foot picnic tap line out of clear PVC tubing and out of EVA. Dispense beer through both and then leave them both disconnected but inside your kegerator for a few days. Then hook them both back up and dispense exactly 1 ounce of beer into cups through both lines. Taste them blindly and discover what we're talking about.

I can personally attest to this. When I made the switch to EVA, instead of using the picnic tap test I just hooked up a second keg of the same beer to a tap with the EVA line. Like with the old line, I flushed both lines of the first few ounces to get fresh beer from the keg. Took samples from both and noted they tasted the same. Both were good.

Then I did another taste a couple of days later but this time didn't flush the lines like I used to do with the PVC lines. The beer from the Bevflex line tasted awful, very stale like. The EVA line showed no change and tasted the same as the previous day.

 

[fun4stuff]

In both replies you demonstrate a misunderstanding of the nuances in the law. "of THE gas across membrane" rather than "any gas".. It means a particular gas's propensity to migrate is based on the pressure differential OF THAT GAS on either side of the membrane. That is to say, CO2 is on the inside and there is little to no oxygen in there. But there IS oxygen outside and that differential will cause migration.

The good news is that you don't have to take anyone's word for it or even spend time researching. Make up a 5 foot picnic tap line out of clear PVC tubing and out of EVA. Dispense beer through both and then leave them both disconnected but inside your kegerator for a few days. Then hook them both back up and dispense exactly 1 ounce of beer into cups through both lines. Taste them blindly and discover what we're talking about.

Thanks for the clarification. Can always count on someone on an online forum to put you right if you say something wrong... Cunningham’s law.

I was not talking about whether oxygen gets the the beer side line. I switched to EVA awhile back after it came out and it definitely prevents oxidation of the beer that’s left in the line.

I was questioning the need to replace the gas side with Eva line to stop/slow down oxidation. Would the pressure of co2 in the tube slow down the the diffusion of oxygen into the tube and into the beer. But as you pointed out, there’s no oxygen (or very little) in the tubing so the concentration gradient would favor oxygen to flow into the tube... unless for the some reason the co2 pressure in the tube would slow down oxygen influx.

I’m still questioning whether high pressure of co2 would slow down the diffusion of oxygen into the gas side.

 

[day_trippr]

Stop wondering. There are actual gas laws that say one gas will ignore the partial pressure of another...

Cheers!

 

[Vale71]

I was questioning the need to replace the gas side with Eva line to stop/slow down oxidation. Would the pressure of co2 in the tube slow down the the diffusion of oxygen into the tube and into the beer. But as you pointed out, there’s no oxygen (or very little) in the tubing so the concentration gradient would favor oxygen to flow into the tube... unless for the some reason the co2 pressure in the tube would slow down oxygen influx.

Except no such reason exists nor will it ever exist...

I’m still questioning whether high pressure of co2 would slow down the diffusion of oxygen into the gas side.

In that case feel free to do your own research and publish a peer-reviewed paper that contradicts the work that Adolf Fick did in 1855 and the scientific community will gladly accept it, because that is how science works. If you were to manage that you might even get on the fast track for a Nobel in Physics, trip to Sweden included.

Until you manage to pull that off all you're doing with your posts is flaunting your own stubborness and steady refusal to learn, which means that anybody who's tried to repeatedly point you in the right direction has just been wasting his/her time (myself included).

 

[eric19312]

Short possibly friendlier answer

go ahead and swap out your gas lines when you get a chance. Cost is modest, gas lines tend to be pretty short. Cold side oxygen is a non controversial enemy of beer. Plus duo tight is fun.

 

[Bobby_M]

I was not talking about whether oxygen gets the the beer side line. I switched to EVA awhile back after it came out and it definitely prevents oxidation of the beer that’s left in the line.

I’m still questioning whether high pressure of co2 would slow down the diffusion of oxygen into the gas side.

There are a lot of true things in the world that are counterintuitive.

Now you know the truth and are still resistant. Ok, dont do it. Drink the slightly oxidized beer.

 

[Yesfan]

I asked the same question when I was changing out my lines. The cost of the Duofit fittings and EVA line isn't much more with beer lines only vs both sets so I did all of mine (5mm for gas, 4mm for beer).

A cheap piece of mind option whether you believe the science or not.