Closed Transfer: What About the Jumper Lines?

[mac_1103]

I can definitely notice the beer start to drop off when it gets hooked up to the tank gas for serving.

How fast?

 

[mac_1103]

The bad news is that I have no idea where their 30 ppb number comes from. A little Googling instead gives 30 ppm as a typical value, though that's a maximum and not typical value.

Typo? The reference that they took the table from says ppm.

 

[Pacific Electric]

I use a double sided jumper to purge my transfer line with CO2. Then I ‘purge’ the line with beer from my fermenter, and discard a few ounces that might get a bit of O2 exposure. After that I connect to my keg and transfer, and hope it was enough.

 

[Dland]

Well, all this has got me thinking I ought to get EVA lines, especially for the one from gas tank to kegs. I picture it now sitting there coiled around the tank in the cellar, absorbing O2 and plotting to stale my beer...{ ; Good thing I tend to drink it pretty fast once tapped. .

A lot of things about brewing can be seen as rabbit holes, or can be seen as things that could be improved, even if only incrementally at some point. For me this is better than being content with the other extreme; making and drinking mediocre beer year after year...

How pure tanked CO2 probably varies, may not live up to published specs, and there's always plenty of room for quality control lapses at the bottling plant. Pretty sure what I get and lots of others get is industrial grade. The only gas in separate category from the different industrial/welding gas choices I have seen is the medical oxygen.

Maybe the CO2 that beverage distributors supply is beverage grade, it came from a different supply chain when I was in restaurant business. But no way would the Coca Cola dealer sell it to me now unless I was buying their soda syrup and leasing their dispensers.

So if one is in pursuit of quality enough to be worried about EVA lines and Buna-N seals, one also ought to consider spunding. Using gas from "over spunded" kegs to help dispense seems a good practice too, but will only get one so far.

 

[AlexKay]

Well, all this has got me thinking I ought to get EVA lines, especially for the one from gas tank to kegs. I picture it now sitting there coiled around the tank in the cellar, absorbing O2 and plotting to stale my beer...{ ; Good thing I tend to drink it pretty fast once tapped. .

There's a pretty universal consensus 'round these parts that EVA or other barrier tubing is necessary for liquid lines. Plenty of people will tell you it is necessary for gas lines, as well. My personal experience (anecdote does not equal data) is that PVC gas lines (and, for that matter, tank O2) don't cause a severe oxidation problem, at least as measured by my own taste and the taste of judges at competitions I enter, at least for non-hoppy beers.

So if one is in pursuit of quality enough to be worried about EVA lines and Buna-N seals, one also ought to consider spunding. Using gas from "over spunded" kegs to help dispense seems a good practice too, but will only get one so far.

I think this is a pretty fair statement. I just ordered a spunding valve because of this thread.

 

[Bassman2003]

I think over spunding is a good approach if you can pour successfully. EVA is cheap, so you might as well do both gas and liquid.

How fast does the downhill slide go? It is tough to say. Maybe 2-4 weeks the beer is a lesser percentage from when it started. These are gradual changes kind of like a frog in slowly rising temp water but the malt character goes to more sweet and the hop aroma fades away. The color goes darker too. Some styles this is not bad at all like a Scottish ale.

 

[Dland]

Just to be clear, when I over spund, the keg in question will be over carbed and pour that way, all foam. What I do is hook a jumper from gas post of over-spunded keg to gas post on another keg in freezer that is being dispensed. The over spunded beer is fresh and still lagering, but I get dispensing gas from it as it's carbonation is reduced to desired level. This works out as I typically have a pipeline of at least 12 kegs going most of the time. It does take some paying attention to, but most of us here are used to that regarding our beer.

 

[Yesfan]

Well, all this has got me thinking I ought to get EVA lines, especially for the one from gas tank to kegs. I picture it now sitting there coiled around the tank in the cellar, absorbing O2 and plotting to stale my beer...{ ; Good thing I tend to drink it pretty fast once tapped. .

A lot of things about brewing can be seen as rabbit holes, or can be seen as things that could be improved, even if only incrementally at some point. For me this is better than being content with the other extreme; making and drinking mediocre beer year after year...

How pure tanked CO2 probably varies, may not live up to published specs, and there's always plenty of room for quality control lapses at the bottling plant. Pretty sure what I get and lots of others get is industrial grade. The only gas in separate category from the different industrial/welding gas choices I have seen is the medical oxygen.

Maybe the CO2 that beverage distributors supply is beverage grade, it came from a different supply chain when I was in restaurant business. But no way would the Coca Cola dealer sell it to me now unless I was buying their soda syrup and leasing their dispensers.

So if one is in pursuit of quality enough to be worried about EVA lines and Buna-N seals, one also ought to consider spunding. Using gas from "over spunded" kegs to help dispense seems a good practice too, but will only get one so far.

From my own personal experience, I could tell the difference between EVA and PVC when I made the switch to EVA/Duotight. At the time of the switch, I had two kegs of the same beer (from a 10 gallon batch) so I decided to hook both to two open taps. One line had the recently cleaned/sanitized PVC Beverage line and the other the new EVA with Duotight push to connect style (like John Guest) fittings, which were also cleaned/sanitized.

In the past, I would always purge the beer in the beer line as those first few ounces in the line always tasted off. This was the biggest thing I noticed with the EVA. The beer in the EVA line after going a day without drinking tasted the same. Nothing off. So I changed both beer/gas line to EVA/Duotight.

Three other advantages of the EVA/Duotight line/fittings are:

1 The ability to use shorter runs of beer line without the worry of foamy pours. This is because of the smaller 4mm ID of the EVA line.

2 Cost. The EVA line is much cheaper than the more expensive Ultra barrier stuff I had been using.

3 PTC style fitting are easier to build lines vs dealing with MFL swivel nuts, otiker and/or worm gear clamps.

I've more or less replaced every kind of line with this stuff and not looked back.

 

[Biggz1313]

I have floating dip tubes ready to go, too! So do folks like this metal one, or this Duotight one, or something else?

I have multiple of the duotight ones and love them. I use them at the end of my daisy chain so CO2 from my All Rounder during fermentation is pushing Star San out of a keg that wall filled to the brim. That star san is being pushed into another empty cleaned all rounder and then the gas post for the star san all rounder has a spunding valve attached to it. that way i'm using fermentation co2 to purge my clean star san keg and not store bought CO2 and then my next fermenter is also being sanitized in the process and the starsan is kept in a CO2 only closed environment further extending it's shelf life.

edit: Duotight spunding valve is also super easy to clean.

 

[tracer bullet]

In the past, I would always purge the beer in the beer line as those first few ounces in the line always tasted off. This was the biggest thing I noticed with the EVA. The beer in the EVA line after going a day without drinking tasted the same. Nothing off. So I changed both beer/gas line to EVA/Duotight.

I basically noticed this as well. The first couple ounces or whatever poured since the previous night were not sweet and lacking hop flavor after my change to EVA. I'd pick up pretty much where I left off. This got me to switch the other keg line and the CO2 line as well.

After a week or something (I've been on a trip perhaps), I do think I get some oxidation for some reason. But it takes FAR longer.

 

[Yesfan]

On a unrelated topic......I'm pretty sure the Kegland disconnects (red/grey gas & black/yellow beer) are universal. I know they are with the Kegland colored posts on my All Rounder fermenter. You'd think they would still be post specific for your run of the mill corny. One of the gas disconnects (the red/grey one) I could swap between each post with no effort. The old school CMB style disconnects only work one way (grey to gas, black to beer).

I wished I'd known this when I ordered my universal posts for my kegs. The Kegland disconnects are $2 cheaper than the universal posts and you don't have to have the adapter to use them with the EVA barrier lines.

 

[Bassman2003]

Yes, it is very nice to have the disconnects that are made to interface with EVA tubing.

 

[AlexKay]

I’ve had some trouble with them. Gas ones not fitting on posts, liquid ones not releasing poppets when you take them off (mess!)

 

[Yesfan]

I’ve had some trouble with them. Gas ones not fitting on posts, liquid ones not releasing poppets when you take them off (mess!)

With what? Universal posts? Poppits? Kegland's disconnects? Don't know if you're replying specifically to me so thought I'd ask.

The set of universal posts/poppits I put on one of my kegs seem to work. I pressure tested it and it's still sitting at 10psi. I think the universal posts don't work with all kegs (according to More Beer), but most of my kegs are Super Champion and Challenger VI cornys if that helps.

 

[AlexKay]

With what? Universal posts? Poppits? Kegland's disconnects? Don't know if you're replying specifically to me so thought I'd ask.

The set of universal posts/poppits I put on one of my kegs seem to work. I pressure tested it and it's still sitting at 10psi. I think the universal posts don't work with all kegs (according to More Beer), but most of my kegs are Super Champion and Challenger VI cornys if that helps.

Kegland disconnects. They're sleek and low-profile, but both gas and liquid have given me problems.

 

[Yesfan]

Kegland disconnects. They're sleek and low-profile, but both gas and liquid have given me problems.

Gotcha. I'll keep an eye on mine then. Appreciate the heads up.

 

[Bassman2003]

I have had good experiences with the normal disconnects. I ordered two of the plastic adjustable type and they do not seem to create a good seal as I had bubbles and foam in the keg lines. I am still checking them out but have been too busy to dive in. My stainless adjustable from Kegland works great.

 

[segallis]

Even if the ambient air pressure is far less than the CO2 pressure in the line, you will still get O2 going into the line, into the CO2 filled area.

The reason is because, strictly from the standpoint of the O2, there's some O2 outside of the line and therefore some O2 pressure outside of the line. But none inside the line. Lots of Co2 pressure inside, but no O2 pressure inside. And so the O2 will indeed permeate through the line and get inside until it balances out.

I would like to understand the physics behind this. If you are correct then it would seem any additional O2 molecules introduced into the higher pressure CO2 line would increase the pressure even further (more moles of gas total), which would seem to violate the Boyle's Law (among others). Everything I have read on permeability and diffusion seems to imply the pressure would cause things to move the opposite direction. E.g. This is how some gas separators work. In fact, Nitrogen would be much more likely to permeate into the line since it is both much more concentrated/higher partial pressure and also a lighter molecule. Obviously, without a pressure difference, an area of greater oxygen concentration would tend to move into an area of lower concentration (all the gases would mix in both directions until the partial pressure of each component is equal).

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years, not to mention the recent explosive popularity of barrel aged beers.

 

[mac_1103]

I would like to understand the physics behind this.

Google "partial pressure."

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years

It's true that people have been enjoying beer for thousands of years, but people have also been putting up with flat oxidized beer for most of that time.

 

[AlexKay]

I would like to understand the physics behind this. If you are correct then it would seem any additional O2 molecules introduced into the higher pressure CO2 line would increase the pressure even further (more moles of gas total), which would seem to violate the Boyle's Law (among others). Everything I have read on permeability and diffusion seems to imply the pressure would cause things to move the opposite direction. E.g. This is how some gas separators work. In fact, Nitrogen would be much more likely to permeate into the line since it is both much more concentrated/higher partial pressure and also a lighter molecule. Obviously, without a pressure difference, an area of greater oxygen concentration would tend to move into an area of lower concentration (all the gases would mix in both directions until the partial pressure of each component is equal).

Actually, this entire thread and things like agonizing over ppm's of O2 and purging jumper lines with one thousandth the total volume has me wondering how people have actually been enjoying cask ales for thousands of years, not to mention the recent explosive popularity of barrel aged beers.

Maybe this will help frame the problem.

There's no question what the equilibrium state is for this system: the gas mixture inside and outside the tube will be the same composition and pressure. The only question is how long it takes for this to happen, and that depends on the tube's permeability: an impermeable metal tube will keep equilibrium from ever occurring, whereas a highly permeable silicone tube will let you get there relatively quickly. On the way to equilibrium, a CO2-filled tube will leak CO2 out into the atmosphere, at the same time as O2 (and yes, N2) from the atmosphere diffuse in.

The counter-intuitive case you're proposing is that diffusion into a tube increases its pressure. In most cases this won't happen, because other gases will be diffusing out at the same time. In the extreme cases (say, helium through a glass tube), it does indeed happen, but to say that things get counter-intuitive in extreme cases doesn't refute the underlying principles.

Diffusion through a permeable polymer is essentially a solvation process: gases dissolve in the polymer, diffuse through its bulk, and evaporate from the other side. Fick's law describes an idealized system where solutes don't interact: the amount of CO2 in the tube has no effect on the diffusion rate of O2 into it. I think there's a colorable argument to be made that the system will be non-Fickian.

 

[segallis]

Google "partial pressure."


It's true that people have been enjoying beer for thousands of years, but people have also been putting up with flat oxidized beer for most of that time.

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

 

[Biggz1313]

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

I agree and think you're correct that there is a much higher chance and amount of oxidation happening to these BA beers, but I think the styles that are typically BA and the flavors the BA impart on the finished project are going to be much stronger then the sort of flavors a limited amount of oxidation will bring to those particular beers. This is just me implying some reasoning in my own mind and is basically my opinion so there is no research (that I'm aware of) to back this up, but to me it makes sense.

 

[segallis]

The counter-intuitive case you're proposing is that diffusion into a tube increases its pressure. In most cases this won't happen, because other gases will be diffusing out at the same time. In the extreme cases (say, helium through a glass tube), it does indeed happen, but to say that things get counter-intuitive in extreme cases doesn't refute the underlying principles.

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

 

[Broken Crow]

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

...it's the O2 Gnomes... They delight in mining through barely porous material carrying oxygen and dumping in the brews of the O2CD brewers on here.

 

[tracer bullet]

Hmmm, what I see are statements that "partial pressure" describes the contributions of individual gas components on the combined pressure of a mixed gas (usually relating the two for a specific absolute pressure). I don't see any formula (or experiment) that demonstrate this given a continually supplied pressure difference (other than blanket statements to that effect on forums). All the supported arguments I can find having to do with O2 intrusion include things about permeability and diffusion. The mixing of a specific gas from higher concentrations to lower concentrations is explained by the free, unhindered motion of gas molecules and the large space between gas molecules which is also why different gas mix. I also see articles demonstrating that absolute pressure differences affects (and can overcome) much of this interaction.

I would not necessarily equate flat beer to oxidized beer. While I'm sure many would prefer their own homebrew to the cask ales of a century ago, some of the best beers I have had, as well some of the most expensive and most in demand beers I have seen professionally offered, are modern barrel aged ales (which likely introduces a billion times more risk for oxidation than the things discussed on these threads). I'm curious how this part of the industry is enjoying so much success and growth to where they can't age enough B.A. Quads and Wee Heavys, meanwhile a few ppb of O2 are destroying so many homebrews?

You aren't wrong about the general definition of partial pressure. It's not the "one thing" to point at for all of the explanation. The gist is that the partial pressure of the gasses on each side of a barrier will want to be equal. The partial pressure of O2 on the outside of the line will want to try to enter the inside of the line until they are equal (regardless of what other gasses are on each side, or their pressures). So partial pressure is sort of the reason but you can't just go search for the definition and get the whole explanation being looked for.

Your 2nd half I'm not sure what to say, it's a bit of a strawman. O2 gets into beers and oxidizes them. It's up to the person, particularly with the beer type, to decide if they care. A homebrewer that transfers a hazy IPA into a keg through a tube with a lot of splashing will have crappy beer that lost its intended hop flavors in a matter of just days. Minimizing O2 ingress keeps things better, longer. At some point it gets to be a silly chase, but keeping out O2 makes a difference. I'd hope you agree, if not then you'd be welcome to make a hazy IPA and see how much O2 you can introduce and how it tastes afterwards.

If you can agree that a beer can be oxidized, and change flavor (better or worse is in the eye of the beholder), then I'd think you can start to see why some people care for some beers and go through the work. to minimize it, for certain beer types where they want a particular outcome (hazy NEIPA that they want to keep the smell and flavor around on day 30 like it was on day 1).

Some people conversely "age" beer, i.e. their Imperial Stouts and it could be that they are simply preferring some oxidation. I've always thought this to be the case, actually, that we prefer these beers to be oxidized. Flavors may not "mellow" or hops" smooth out" in these beers, maybe they simply oxidize away, or at least change, in a way we believe is better. So you can't put a blanket statement on oxidation, or say that... since it's OK for an aged quad that it must therefore be OK for a hazy IPA. Apples to oranges comparison. Or quads to hazies comparison.

If O2 diffuses into a pressurized CO2 line, then it would seem the same could be said for fermentation purging of a keg over time. Wouldn't O2 permeate through the blowoff water and tube walls and then along that open channel inside the tube back into the keg, so that the keg is being continually replished with more O2 since there wasn't enough in there compared to the surrounding air???

I can see where O2 can intrude (through the water and tube wall) once CO2 is no longer being produced, but it seems that the steady production of CO2 during fermentation is what keeps the O2 out. If I am missing something then please explain how this purging removes and then keeps O2 out, while a CO2 bottle can't?

I can undertand that the number of mols of different gasses on two different sides of a hose can be rearranged such that the partial pressures on boths sides are at equillibrium, and the aboslute pressures maintain the same different numbers you started with. But I don't underatnd what force casues those molecules of O2, for example, to diffuse throught that hose when there is higher pressure on the other side?

The no membrane case is explained by the rapid and unobstructed motion of gas molecules (i.e. mixing). And the case of a ballon deflating over time explains how molecules of a gas want to move in one direction through a membrane from a higher pressure to a lower pressure (rather than just the exchange of dissimilar molecules).

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

If you have a silicone blow-off tube, it absolutely will allow O2 into your fermenter. Not sure about how fast it'll come through a liquid, but yes, it will come through there as well. O2 will get into the water you have your blow-off tube inserted into and it will come out the other side in the blow-off tube that way as well (unless of course it's already become equal in partial pressure inside the fermenter and out but this would take a long while). I can't say how fast, or if anyone should care, but yes it happens.

CO2 generation in the fermenter will of course be blown out, but it doesn't keep the O2 from coming in at the same time. Some O2 will get carried out by the CO2 of course, but it will continue to come in 24/7/365 regardless. As fermentation slows, it'll stay in the fermenter longer.

No idea what you are asking about purging and CO2 bottles.

Diffusion of O2 into a beer line that it can permeate through is a counter intuitive thing but it does do it. And YES it can raise the pressure inside the line, all else being equal. It's probably in real life balanced by the CO2 escaping from the line, or being absorbed into the beer, and things like that. But it doesn't HAVE to be balanced by CO2 removal. O2 will still permeate through, and even if the existing CO2 in the line doesn't go anywhere, it'll come in, and it'll raise the overall pressure in the line. The fact that the CO2 pressure is higher inside than the "air" pressure outside is not enough to prevent this permeation. O2 partial pressure in the air will find its way to having a similar O2 partial pressure inside the line, even if the line has a higher "overall" pressure. This is where partial pressure comes into play again. That O2 doesn't care what's already there, it's coming anyhow, like it or not.

 

[mac_1103]

But what force physically moves molecules of a gas from low pressure, through a membrane into a high pressure area???

The concentration gradient of that specific gas across that membrane. You wouldn't be able to breathe if it didn't work this way.

 

[AlexKay]

It certainly won't hurt to use EVABarrier for the blowoff tube, for connecting kegs to the fermenter for purging, and everything else. As with anything else, it's a matter of degree -- EVA is still permeable, but it's substantially better than PVC (and let's not talk about silicone.)

As far as oxygen making it through the airlock, you will absolutely have 9 ppm of O2(aq) in the airlock/blow-off-tube water. It's a relatively slow process to equilibrate with O2(g), though. Eventually, you'll equilibrate to the same gas composition on both sides of an airlock, despite the presence of the water, but I suspect this takes a very long time.

Also, there's a significant distinction to be made between diffusion through a permeable material and diffusion of one gas through another. The latter process is quite slow (root time) in the absence of convection (free or forced).

Give or take a factor of 2, professionals target ~100 ppb O2(aq) as total package oxygen -- dissolved, headspace, everything. That's achievable in home brewing, though not without going to some trouble. Targeting <10 ppb probably isn't, and the folks who think they're getting there are probably missing some avenues of ingress.

 

[segallis]

The concentration gradient of that specific gas across that membrane. You wouldn't be able to breathe if it didn't work this way.

Not to go too far down a bunny trail, but the exchange of gases inside the lungs is a gas-to-liquid transfer across a membrane, and does not involve much pressure difference (the pressure difference existes to move air in and out of the lungs). If anything there would be higher pressure in the inhaled air tending to move gas into the avioli when you inhale, and then lower pressure on the air side of the membranes when you exhale tending to move CO2 out. The differing solubility for various gases in these tissues is also a factor.

Regardless, "concentration gradient" is not a cause - it is an effect. Take a container divided into two halves, O2 on one side, CO2 on the other. Now remove the divider. Sure there is a concentration (partial pressure) difference. The gases will mix and the partial pressures will equalize on both sides over time. That is a an EFFECT. The cause for that mixing and equalizing of partial pressures is the fact that the gas molecules are in constant and unobstructed motion. The fact that the concentration equalizes is a simple consequence of statistical motion. O2 molecules from the right side are moving in all directions, so some move to the left side. Once there is 10% concentration on the left side, there will be 1/10 as many molecules moving back towards the right side as are moving to the left. Eventually the gases are completely mixed and there are as many O2 molecules moving from the right side to the left side as from the left side to the right. Simple statistical probability results in equal concentrations. But the concentration has ZERO to do with why that condition is eventually established. The "effect" of equal concentrations is "caused" by the random motion of the gas molecules.

Attributing the final effect of equalizing gases on two sides of a barrier to "gases want to be the same everywhere" is popular, but cannot be explained with facts. (Sort of like people asserting that a plane can fly due to the airfoil shape of a wing). The gas on the outside of a hose isn't "motivated" to get to the other side because there are fewer molecules of that type inside the hose - it is simply random motion and statistics.

Anything that impedes or prevents (e.g. a barrier) that motion of molecules will impede or prevent the equalization of concentrations (partial pressures). At zero pressure difference, diffusion is unimpeded and we see mixing of gases in relatively little time. Add a barrier and the effect is slowed. Random motion of a gas molecule will cause some to penetrate the surface of a hose. Random motion will cause it move in various directions, some of which will exit the hose material on the other side. Again - random motion is the cause. But it is obvious that there are things that can impede or prevent that random motion across certain barriers (e.g. EVA). The question is whether pressure can do so?

Which brings me back to the example of a latex balloon. The balloon will deflate over time - regardless of what the gas concentrations are inside vs outside the balloon. And for one simple reason: the higher pressure inside the balloon results in gas molecules moving through the membrane in (nearly) one direction. If molecules were traveling in both directions in equal number, the balloon would never deflate.

If this can't be explained, then dismissing the effect of pressure appears to be without basis.

 

[tracer bullet]

Not to go too far down a bunny trail, but ... Attributing the final effect of equalizing gases on two sides of a barrier to "gases want to be the same everywhere" is popular, but cannot be explained with facts. (Sort of like people asserting that a plane can fly due to the airfoil shape of a wing). The gas on the outside of a hose isn't "motivated" to get to the other side because there are fewer molecules of that type inside the hose - it is simply random motion and statistics.

Well, there's always the possibility you can't believe something that's actually true and just don't really know you're talking about.

 

[segallis]

Well, there's always the possibility you can't believe something that's actually true and just don't really know you're talking about.

Or the possibility that some are believing something that isn't true and regurgitating it with nothing to prove it. A law of physics is explained with facts and backed by empirical evidence - as opposed to, say, an old wives tale.

What specifically did I say that is not true? Show me a balloon that stays inflated. Explain why it deflates if the number of molecules through the membrane are equal in both directions? Please show me why you know what you're talking about - I'm always open to learn truth. If you are going insult me, then at least offer a fact or two to support your opinion, or answer one of these questions I have asked.

And for the record, it is proven fact that the mixing of gases is the result of random molecular movement (which was my claim regarding cause). The laws of thermodynamics and entropy are also well proven and demonstrable. Just as it can be shown that areas of high pressures will flow to lower pressures (i.e. the movement of molecules).

"If a man has the correct answer but he has no idea why, is he really right?"