Importance or tubing type for CO2?

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m3B.eer

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Hi all,

I've noticed I may have CO2 leaks off of my manifold, and off the bard on the gas disconnect. Interestingly, it's not consistent, and not at the same time. I notice the leak happens quite certainly between 20 and 30PSI. I noticed it last night, dropped it at 20PSI, and it seemed okay (spray test on both end). It's a clear vinyl tube, and I clamped the hell out of it on both ends (screw clamp),
Can you use clear vinyl for gas lines, or does it often creates leak? I'm tempted to go get some braided vinyl for my gas lines if not, but unfortunate because I have quite an amount of clear tubing...
I'm pretty sure the ID is correct (3/8").
 
m3B.eer said:
I'm pretty sure the ID is correct (3/8").
Click to expand...
If your gas barbs are 1/4" OD, there's no way you can make a tight seal using 3/8" ID tubing.

You should avoid PVC, vinyl tubing, it's very oxygen permeable. Oxygen ruins your beer.

The best tubing to use, even for gas, is Oxygen Barrier tubing, the queen of all being EVA Barrier tubing. It comes in 4mm and 5mm ID (8mm OD) and 6mm ID (9.5mm OD).
Possibly even wider than those 3 common sizes, but those won't be very useful for homebrewers.

For example:
https://www.williamsbrewing.com/Hom...ing-Tubing-Accessories/DuoTight-Tubing-System
https://www.birdmanbrewing.com/tubing/
 
You can certainly get vinyl tubing to be functionally leak-tight for CO2. As IL said, you need the right tubing size: if you can fairly easily slide the tubing over the barb, the tubing ID is too large. Best is if it has to be coaxed on after warming the tube carefully (perhaps with hot water.). In that case, the hose clamps should be more of an afterthought.

I used EVABarrier for the gas lines for my second keezer, but vinyl for my first (both had barrier liquid lines.) My experience is that flavor stability over months has been just fine for both. I am unconvinced by those who say that there will be oxygen ingress into a PVC line that is pressurized with CO2.
 
IslandLizard said:
If your gas barbs are 1/4" OD, there's no way you can make a tight seal using 3/8" ID tubing.

You should avoid PVC, vinyl tubing, it's very oxygen permeable. Oxygen ruins your beer.

The best tubing to use, even for gas, is Oxygen Barrier tubing, the queen of all being EVA Barrier tubing. It comes in 4mm and 5mm ID (8mm OD) and 6mm ID (9.5mm OD).
Possibly even wider than those 3 common sizes, but they're not very useful for homebrewers.

For example:
https://www.williamsbrewing.com/Hom...ing-Tubing-Accessories/DuoTight-Tubing-System
https://www.birdmanbrewing.com/tubing/
Click to expand...
I confirm my gas barb is also 3/8" (0.38), that's why I said it works.

AlexKay thanks for the recommendation. I also thought of warming the tube and tighten up the clamp. I'll give it a try and monitor see if I see bubbles again.
What do you mean the hose clamp should be more of an afterthought?
 
fwiw, O2 doesn't care how much pressure CO2 is under. If the line is permeable, ingress shall happen.
It's all about partial gas pressure laws. One should always respect the law :)

I used the same 3/16" ID Bevlex 200 solid PVC line for both beer and gas for over a decade. In 2019 I switched everything to EVAbarrier tubing, beer and gas. The one immediately obvious change was beers that sat overnight in the line no longer had an oxidized character that increased with the time since the last pour. With a six faucet keezer, that's important...

Cheers!
 
day_trippr said:
fwiw, O2 doesn't care how much pressure CO2 is under. If the line is permeable, ingress shall happen.
It's all about partial gas pressure laws. One should always respect the law :)
Click to expand...
That’s the argument that leaves me unconvinced!
As a law, it only describes the state of the system at equilibrium, not how long it takes to get there. The rate of diffusion absolutely depends on the CO2 pressure, as well as the pressure differential. That it’s a pressure differential across very small, probably tortuous channels only makes the situation more complicated.

There’s a misconception that because gases behave ideally in some respects, that they can be viewed as non-interacting in all respects. Collisions between molecules at atmospheric pressure occur over nanometer length scales (and within picoseconds.)
 
I've always used 5/16" ID gas lines/tubing for my setup. The barb should be snug on the tubing. You then clamp it to be sure it won't leak/fail under pressure. I've been using oetiker clamps since shortly after I started kegging. Mostly because the worm clamps SUCK for making tight, leak free, connections. The oetiker clamps, once crimped, are pretty much fool proof (provided you use the correct clamp size and crimp them correctly). I use the oetiker clamps on more than just my gas and beer lines. Anywhere I need to be 100% sure the connection won't leak, I use them. Including the lines to/from my glycol chiller. I tried worm clamps there at the start, but they leaked right away. So those got ditched and the oetiker went on. Zero leaks from that point forward.

I'm sure there are plenty of people who've had good results with worm clamps, I'm just not one of them.
 
I confirm that it the tube is cold, It's quite hard to put on the barb, even harder to pull it out. I always manipulate it after passing them under hot water.
I have tried warming them up and tighten them more (with the worm clamp). It seems that there are no more leak, even going up to 30PSI. I've been monitoring twice today and it looks good.

I have a 10# tank, filled it last week. In general, how many kegs can a 10# CO2 tank take care of? With no leaks.

I'm still tempted to get a braided tube, if I just need 1 or 2 feet, won't be much of a cost...
 
AlexKay said:
That’s the argument that leaves me unconvinced!
As a law, it only describes the state of the system at equilibrium, not how long it takes to get there. The rate of diffusion absolutely depends on the CO2 pressure, as well as the pressure differential. That it’s a pressure differential across very small, probably tortuous channels only makes the situation more complicated.

There’s a misconception that because gases behave ideally in some respects, that they can be viewed as non-interacting in all respects. Collisions between molecules at atmospheric pressure occur over nanometer length scales (and within picoseconds.)
Click to expand...

The way I read Fick's law is the only driving force for oxygen diffusion through the hose in question is the concentration gradient. In this case that is the concentration of oxygen outside the tubing vs inside and is independent of the concentration or pressure of other gasses. That the gasses do not interact is the idea behind the term ideal gasses. Your assertion that they do interact only happens under extremely high pressures and gasses with very large molecules which is not the case here. Simply put the amount of CO2 pressure inside your hose has zero effect on the diffusion of oxygen into it.
 
Last edited:
Bilsch said:
The way I read Fick's law is the only driving force for oxygen diffusion through the hose in question is the concentration gradient. In this case that is the concentration of oxygen outside the tubing vs inside and is independent of the concentration or pressure of other gasses. That the gasses do not interact is the idea behind the term ideal gasses. Your assertion that they do interact only happens under extremely high pressures and gasses with very large molecules which is not the case here. Simply put the amount of CO2 pressure inside your hose has zero effect on the diffusion of oxygen into it.
Click to expand...
Even though for some experiments, gases at atmospheric pressure behave ideally, there are in fact many interactions. Figure that the density of air at atmospheric pressure is about 1 kg/m3, or 1/1000 that of water: each gas molecule, then, is separated from its neighbor on the order of 10 times its diameter. That's diffuse, but not that diffuse: mean free path is on the order of tens to hundreds of nanometers. The kinetic theory of gases might have you thinking that molecules were bouncing like billiard balls off the walls of their container; they're in fact colliding millions of time with other molecules, and more or less performing a random walk. This is why effusion rates (expansion into a vacuum) are orders of magnitude larger than diffusion rates (travel through another medium.)

I thought (I could certainly be wrong!) the diffusion coefficient itself had a pressure dependence? In any case, I don't think Fick's law is applicable when you have (a) a porous medium like a thick-walled polymer tube, and (b) net flow from higher pressure inside the hose to outside.
 
I checked going to bed last night, and it seemed okay. This morning I check, tiny bubbles leaking off of the disconnect.
Could it be related also to the amount of beer in the keg (pretty full) and the pressure building up inside?
Haha, sorry for not topping up its chemistry topic ^^
 
AlexKay said:
In any case, I don't think Fick's law is applicable when you have (a) a porous medium like a thick-walled polymer tube, and (b) net flow from higher pressure inside the hose to outside.
Click to expand...

Ah ok, now I understand your argument and where you are sort of going off the rails. The problem is in assuming that the tubing polymer is porous when it definitely is not. It is permeable but not porous, an important distinction. This means the molecules of gasses aren't traveling through pores but instead diffusing. This a process where the molecules of gas, in this case oxygen, adsorbs into the surface of the tubing polymer, slowly moves through the material and then desorbs on the other side. This is a good thing for us in keeping CO2 in and O2 out since the molecules move orders of magnitude slower while diffusing through the plastic than they would quickly bouncing through pores.

Anyway lots of great info on the net about gas permeability of polymers. Here is one that describes applicability of Ficks law quite well.
https://www.witpress.com/Secure/elibrary/papers/EID20/EID20020FU1.pdf
 
That's interesting -- so the process involves solvation of the gas in the polymer, diffusion through the polymer as a solute through a solvent, and then release back into the gas phase on the other side. I hadn't thought of it like that.

Can we then agree that the argument "CO2 and O2 are ideal gases and therefore diffusion of O2 doesn't depend on CO2" is not relevant here, then? Because really what you need is for them to be acting as ideal solutes, which is a totally different thing: the chemical potential of O2 in the polymer has be linear in its concentration, and independent of the amount of CO2 present. My hunch (just a hunch) is that it wouldn't be: while sometimes you have to work a bit to find deviations from the ideal gas law, non-ideal solutions are more the rule than the exception.

I still think it matters that you're never at equilibrium: there's going to be a steady flow of CO2 from the high-pressure region inside the tubing, through the wall and then out.

In any case, the point I'll come back to is that the physics here is not, in fact, simple, as evinced by the fact that people are still studying it. The argument "you have to use barrier tubing for gas lines because ideal gas law" is ... not convincing.
 
m3B.eer said:
I checked going to bed last night, and it seemed okay. This morning I check, tiny bubbles leaking off of the disconnect.
Could it be related also to the amount of beer in the keg (pretty full) and the pressure building up inside?
Haha, sorry for not topping up its chemistry topic ^^
Click to expand...
Which QD is leaking?? You shouldn't have ANY leaks/bubbles at the QDs or anywhere really. Beer should only come out from the faucet (to your glass).
 
Sorry to hijack your thread with all this, m3B! For what it's worth, I don't think you're going to see any improvement in things going to braided tubing (though my experience with braided tubing isn't extensive). Switching from worm-drive pipe clamps to oetikers is going to give you more bang for your buck. Amazon sells knock-off kits including an assortment of sizes and a crimping tool for about $20 ... anyone have experience with these?
 
AlexKay said:
That's interesting -- so the process involves solvation of the gas in the polymer, diffusion through the polymer as a solute through a solvent, and then release back into the gas phase on the other side. I hadn't thought of it like that.

Can we then agree that the argument "CO2 and O2 are ideal gases and therefore diffusion of O2 doesn't depend on CO2" is not relevant here, then? Because really what you need is for them to be acting as ideal solutes, which is a totally different thing: the chemical potential of O2 in the polymer has be linear in its concentration, and independent of the amount of CO2 present. My hunch (just a hunch) is that it wouldn't be: while sometimes you have to work a bit to find deviations from the ideal gas law, non-ideal solutions are more the rule than the exception.

I still think it matters that you're never at equilibrium: there's going to be a steady flow of CO2 from the high-pressure region inside the tubing, through the wall and then out.

In any case, the point I'll come back to is that the physics here is not, in fact, simple, as evinced by the fact that people are still studying it. The argument "you have to use barrier tubing for gas lines because ideal gas law" is ... not convincing.
Click to expand...
And what about the rest of the system?? Are the o-rings O2 barrier as well?
 
I've bought just the clamps from Amazon (made sure they're stainless and have the correct clamping range). I don't recall where I bought the crimping tool I use most often. It's a ratcheting version, so maybe McMaster. McMaster also sells the clamps in 25 count bags. For most/many people, a bag for gas lines and another for beer lines would last a long time. I make it a point to have [at least] enough on hand to completely replace all the tubing in my setup at all times.

I used some last night when I changed the dual body regulator, on the 20# CO2 tank for the keezer, to one of the single body regulators that was in the fermenting room. I'm now using that dual body (on another 20# tank since my 10# ran really low and I swapped it out for the larger size) for carbonating, transfers, and CO2 purge for canning. The dual body means I no longer need to have two bottles and regulators in that area.
 
Golddiggie said:
Which QD is leaking?? You shouldn't have ANY leaks/bubbles at the QDs or anywhere really. Beer should only come out from the faucet (to your glass).
Click to expand...

My gas one, I have gas leaks.


AlexKay said:
Sorry to hijack your thread with all this, m3B! For what it's worth, I don't think you're going to see any improvement in things going to braided tubing (though my experience with braided tubing isn't extensive). Switching from worm-drive pipe clamps to oetikers is going to give you more bang for your buck. Amazon sells knock-off kits including an assortment of sizes and a crimping tool for about $20 ... anyone have experience with these?
Click to expand...

Haha no worries. I found it always interesting to see how deep things can do. Though I'm still fairly new to beer and kegging and haven't had time to really push into the science of it.


I'm not super excited to switch to ear clamps, though it seems it has a better seal. It seems you need a tool to tighten them - can you also un-tighten them or you need to cut them off?

What I did today is go to the brew store and get a flare swivel nut that was 3/8" instead of 5/16", and used it on a 5/16" tubing.
Also I realized I had a 3/16" ID tubing, to which I pushed in a 1/4" barb. IT was real hard, clamped it as hard, and it seems fine. My gas line is pretty short though, less than 2 feet, but I think it should be fine. So I'm using a smaller ID for this beer line. No big deal?
 
Oetiker clamps are one use items. They're cheap enough (per item if you buy smart) that it rarely matters. A good set of side cutters removes them as well.

The cheapest option would probably be this (or something like it): Oetiker Clamp Tool with three most used Oetiker clamps for beer applications
You can also get the tool, then however many of the clamps you want:
https://www.kegconnection.com/search.php?search_query=oetiker&section=product
I use this to crimp the clamps: https://smile.amazon.com/gp/product/B004O3MGX8 Not available via Amazon right now. Not sure where you could locate one, but it kicks ass. Advantage is you don't over crimp the clamps with it. It stops when it reaches max compression. You can also release it if you have a clamp that's not really the right size (will close more than you need).

I'd compare prices with McMaster before buying the tool and clamps. Make sure you are getting stainless clamps either way. I know McMaster (and Amazon) have ones that are NOT stainless. Read the entire description for ones on Amazon.

BTW, I bought the tool (linked above on Amazon) in 2012. Still works perfectly. I have other ones from KegConnection that I rarely use.
 
You really want a tool that the live edges are parallel. Like the ones I linked to earlier. Side cutters are not parallel. Which means the crimp won't be even. Unless you crimp from both sides, which is making more work for you. The actual tools that crimp properly can be had for short enough money (again, see links from earlier) that it just makes more sense (to me) to actually get the right tool for the job.

I've used the crimp tool to also cut the bands. But, after a lot of them, they started to wear. I invested in a really good pair of cutters for removing the clamps. These are the ones I'm currently using to remove the clamps:
https://smile.amazon.com/gp/product/B0002RI9OA
Keep in mind, I probably removed 50 (or more) of the clamps before I got the Klein cutters for removing them. I was using them on the tubing on the brewing system as well as the kegging setup (several redo's of both). I used them on tubing from my air compressor during one version of that setup.
 

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