Bubbles in the keg beer line? What does it mean?

[JDGator]

Your right about one thing, this thread is way off topic.

So in your scenerio 1 or 2, it has nothing to do with displacement. I can play the terminolgy dictionary game too. You already cover the definition of both speed and velocity.

Lets get this back to beer related items.

If you pour a beer from your tap and have every teast piece of equipment in the world, what units are you going to come up with?

If i pour a beer i'm going to say something like "it filled my glass in 10 seconds". I wouldnt say anything along the lines of the beer flowed out of my tap at 25FPS.

You also a have already proved that when you open your tap, flow begins and your pressure drops.

Am i correct so far?

 

[JuanMoore]

It is true that at a constant flow rate, the pressure drop will increase and the pressure decreases. I stated this in my earlier post. My problem is with making that statement in general and using the term pressure without differentiating between the supplied (regulated) pressure, the pressure in the line, and the pressure drop in the line. Taken literally and in a general sense, this statement is false.

I absolutely agree that when making comparisons about pressure you need to differentiate between applied pressure and the internal pressures in the system. I tried to make that distinction in my posts to avoid confusion.

"If the pressure increases then the flow decreases" is incorrect. All other things equal, if the pressure on a keg is increased, the beer flow rate will increase. This is a fact.

It depends on how the pressure is being increased. If you increase the applied pressure from the regulator, then yes, the flow rate will increase. If beer is flowing through the faucet and you increase the internal system pressure by placing a restriction in the line, then the flow rate will decrease. If you remove a restriction, the flow rate will increase, and the system pressure will decrease. Same goes for other methods of adding and removing resistance to the flow, including changes to exit line diameter, internal roughness, etc.

"Flow" refers to the mass or volumetric flow rate (which are the same for an incompressible liquid, ex gallons per minute) and "speed" or "velocity" refer to the linear velocity (ex feet per second).

In my fluid mechanics textbooks, "flow" is an extremely ambiguous term that simply indicates that a fluid is moving, and as such has no units. The continued use of such an ambiguous term is likely responsible for much of the confusion in this thread. Flow rate (volumetric flow rate, V dot, Q) is the volume of fluid passing a specific point in a system per unit of time. Mass flow rate (m dot) is flow rate multiplied by the fluid density, and is expressed in mass per unit of time, and is not the same thing as flow rate even for incompressible fluids. I think I understand what you were getting at though, since they have a linear relationship due to the fact that incompressible fluids have a constant density. Flow velocity can be a bit confusing since it actually describes a vector field, but can also be used to describe other things depending on context. In the context of the Bernoulli equation describing flow through pipes, it's the average of the instantaneous velocities of every streamline connected by a plane orthogonal to all streamlines at a specific point in the system. In other words, it's the average of the velocity vector field emanating from a cross sectional area of the pipe. Flow speed typically refers to the magnitude of a specific velocity vector within the flow velocity vector field, or along a single streamline.

 

[Callacave]

Haha this whole thread has gone way off topic. No, I work a little closer to Boston, you can PM me for more details. I know one or two people that work at Millipore though.

There's someone at Millipore who's a homebrewer. I don't know who it is, but was just curious.

 

[spaceyaquarius]

Ohm's Law is surely taught at every university, though it is not used as an analogy for fluid flow. There would be no reason to do that, as fluid transport has its own equations and laws (as it should).

 

[JDGator]

i have read through the post a few times now and have to admit i am somewhat wrong and somewhat right. So here me out:

1. in the case of a hydraulic system (which is what i work with daily) the statement, when flow is increased, pressure is decreased, and when flow is decreased, pressure is increase is a correct statement.

Here is a quote from Vickers Mobile Hydraulics Manual M-2990-A:

Page 13- A basic rule of hydraulics is that wherever there is flow, there must be a pressure difference or pressure drop. Conversely, where there is a difference in pressure, there must be either flow or at least a difference in the level of fluid.

The hydraulics definition of flow: Page 11

Flow is the movement of hydraulic fluid caused by a difference in pressure at two points.

A few paragraphs further it explains Velocity and Flow rate:

Velocity of a fluid is the average speed of its particles past a given point. usually FPS

Flow rate is the measure of how much volume of the liquid passes a point in a given time. usually GPM.

Now here is where i am wrong: Listen cuz i don't want to say i'm wrong again. LOL

Because our kegs setup (the whole reason for this post) is not an actual hydraulic system, some of this principals don't apply exactly. you can increase the pressure and therefore increase the flow. but you are only able to increase the pressure until either your relief goes off or you blow a hose. Because there is no work being performed like a hydraulic system.

There were a ton of other words that were brought up that have no real reason to be in this thread and i'm a guilty as anyone for that. displacement, velocity, applied pressure and internal pressure etc.

anyways, i hope this cleared somethings up. i did really enjoy this debate because it made me hit my books again. i'm like you Zach and that i hate to be wrong. but in this case i sure wasn't totally right!!

Cheers

 

[zachattack]

Yeah I think this whole thing is just us confusing terminology. I didn't understand what you posted originally, and thought it was wrong because you were using different terminology than I'm used to. I don't think that we're disagreeing about anything from a physics/fluids standpoint though. Though it is fun to argue about

I disagree with nothing in your above post

I'll try and bring this back a bit on topic.

Spacey, sorry you haven't gotten any help with your foaming and we've just been bickering at each other. Did you check the diptube o-ring as JuanMoore suggested? I've found that Juan is one of the best keg troubleshooters on this forum. I agree with him in that there are only a few things that can cause bubbles to form in the line when you aren't pouring.

1) The beer is overcarbed relative to your current pressure
2) The lines are significantly warmer than the keg
3) You dip tube or dip tube o-ring are compromised, and gas from the headspace is directly entering the line.

I think you ruled out #2 already, right?

I'd first check the dip tube and its o-ring. Vent the keg, unscrew the "out" post and remove the dip tube. Check it for any tiny pinholes. Does the o-ring look OK? Is it squished or torn at all? Replace the o-ring with a new one, hit it with a tiny bit of keg lube, and make sure you don't overtighten when you reinstall the post. It needs to be tight, but really cranking on the post with a wrench can easily shred the o-ring.

If that doesn't solve the problem, it's time for another round of de-carbing. Use agitation as Juan said earlier.

 

[Bigscience]

Another issue I've seen is if you get a little bit of something, like part of a hop, in the poppet you'll get bad pours. This includes the quick disconnect as well as the post (and cobra if using one). May not be your problem but still it's best practice to take these apart and clean/inspect regularly.

 

[spaceyaquarius]

I'm actually just going to order a brand new keg. I changed out all the o-rings, cleaned the dip tube, inspected the posts, tightened them with a wrench and hammer, and the acid/metal taste has never gone away after 5 kegs.

 

[spaceyaquarius]

Resolution:

The problem was a combination of old seals on the so-called "reconditioned keg", and a faulty regulator that was reading a lower PSI than actually existed.

I have also learned that you can get off-flavors from beer that is only partially carbonated (even though the head from the pour looks like it is carbonated). High head in your beer glass means that you need to wait longer - and/or that your PSI is too high. My recipe called for 7-10 days of bottle conditioning, so I was drinking my kegged beer at 7 days. 2.5 to 3 weeks is more like it if you are doing the "set it and forget it" method.

 

[JeffWScott]

It most likely means the beer still has more carbonation in it than 1.9 vol (5 psi @ 38°). The serving pressure needs to match the carbonation level. If the serving pressure is high, the carbonation will increase until it matches the pressure. If it's lower, the gas will come out of solution and form bubbles/pockets of gas in the lines.

The only other possibilities are that you either installed a faulty liquid side diptube o-ring, or somehow messed it up during the install, or the lines are much much much warmer than the beer in the keg.



This. And it would never go completely flat without agitation. Even if you left the lid off and let it come to equilibrium with no pressure, at 38° it would still hold on to ~1.5 vol of carbonation.

If you had a beer that needed to be highly carbinated. Would you use a longer beverage line so that you could crank up the serving pressure??

I usually serve at around 5psi. Anything more than that and I pour too much head.

I never thought that I might need to increase the pressure while serving to prevent air in the beverage line.

Some more info on this would be very helpful please!!

 

[GilSwillBasementBrews]

If you had a beer that needed to be highly carbinated. Would you use a longer beverage line so that you could crank up the serving pressure??

Yes you would need the longer line otherwise you'd be pouring glasses full of foam.

I usually serve at around 5psi. Anything more than that and I pour too much head.

I usually run around 10-12PSI and have 10ft lines and don't have much problems with foam. So yes as stated above the logger line would aid in not pouring foam from higher pressure.

I never thought that I might need to increase the pressure while serving to prevent air in the beverage line.



Some more info on this would be very helpful please!!

I'm not sure that's what he meant. If you're serving at a lower pressure than the beer is carbed at you're gradually decreasing pressure in the headspace of the keg the co2 dissolved in the beer will seek to balance the pressure of co2 in the liquid with pressure of co2 in the headspace. So co2 will be coming out of solution which may lead to bubbles in your serving line. If your serving at a higher PSI than the beer is carbed at you will gradually be increasing the PSI in the headspace of the keg which will lead to higher volumes of co2 dissolved into the beer which may lead to foamy pours if your serving lines aren't balanced with your system.

In short, if you serve and carb your beer at the same levels, your lines are the proper length to avoid foamy pours at that serving pressure you will be fine as your system will be "balanced". If you change one or more of those variables they can lead to some of the problems being discussed.

 

[JuanMoore]

If you had a beer that needed to be highly carbinated. Would you use a longer beverage line so that you could crank up the serving pressure??

I usually serve at around 5psi. Anything more than that and I pour too much head.

I never thought that I might need to increase the pressure while serving to prevent air in the beverage line.

Some more info on this would be very helpful please!!

Yes, the higher your carbonation level and/or serving temperature, the longer your lines need to be too pour without foam at serving pressure. Serving pressure should be whatever corresponds to the carbonation level and temperature. If you have to reduce pressure to prevent foam, your lines are likely too short. And reducing pressure can often result in gas coming out of solution in the lines, resulting in a foamy first pour of every drinking session, as well as a slow loss in carbonation as the keg empties.

Yes you would need the longer line otherwise you'd be pouring glasses full of foam.

I usually run around 10-12PSI and have 10ft lines and don't have much problems with foam. So yes as stated above the logger line would aid in not pouring foam from higher pressure.

I'm not sure that's what he meant. If you're serving at a lower pressure than the beer is carbed at you're gradually decreasing pressure in the headspace of the keg the co2 dissolved in the beer will seek to balance the pressure of co2 in the liquid with pressure of co2 in the headspace. So co2 will be coming out of solution which may lead to bubbles in your serving line. If your serving at a higher PSI than the beer is carbed at you will gradually be increasing the PSI in the headspace of the keg which will lead to higher volumes of co2 dissolved into the beer which may lead to foamy pours if your serving lines aren't balanced with your system.

In short, if you serve and carb your beer at the same levels, your lines are the proper length to avoid foamy pours at that serving pressure you will be fine as your system will be "balanced". If you change one or more of those variables they can lead to some of the problems being discussed.

Exactly.

 

[JeffWScott]

Yes you would need the longer line otherwise you'd be pouring glasses full of foam.

I usually run around 10-12PSI and have 10ft lines and don't have much problems with foam. So yes as stated above the logger line would aid in not pouring foam from higher pressure.





I'm not sure that's what he meant. If you're serving at a lower pressure than the beer is carbed at you're gradually decreasing pressure in the headspace of the keg the co2 dissolved in the beer will seek to balance the pressure of co2 in the liquid with pressure of co2 in the headspace. So co2 will be coming out of solution which may lead to bubbles in your serving line. If your serving at a higher PSI than the beer is carbed at you will gradually be increasing the PSI in the headspace of the keg which will lead to higher volumes of co2 dissolved into the beer which may lead to foamy pours if your serving lines aren't balanced with your system.

In short, if you serve and carb your beer at the same levels, your lines are the proper length to avoid foamy pours at that serving pressure you will be fine as your system will be "balanced". If you change one or more of those variables they can lead to some of the problems being discussed.

Makes total sense. I appreciate all of this.

I'd love to see some kind of beverage line to volumes of c02 chart. God that would be so helpful.

 

[day_trippr]

Makes total sense. I appreciate all of this.

I'd love to see some kind of beverage line to volumes of c02 chart. God that would be so helpful.

You would need a three-dimensional chart/plot to account for the many ways to hit a given volume of CO2 - and the result wouldn't actually account for any specific dispensing system configuration.

But it's actually pretty simple to come up with a balanced dispensing system with two easily accessible tools.

First, use our favorite carbonation table, plug your preferred dispensing temperature into the Y axis at the left, scan across that row to find your desired carbonation level (with 2.4 to 2.5 being about middle of the road for most ales), then run up that column to find the CO2 pressure that will eventually result in that level of carbonation - and maintain same.

Take that value and your dispensing system configuration to the only line length calculator worth using, and out pops a line length that will balance your system to provide 10 second pints.

Or, take the short-cut, and just use one foot of 3/16" conventional PVC beverage line (eg: Bevlex 200) per PSI.
If using PET-lined barrier tubing (eg: Bev Seal Ultra Series 235) use 1.5 feet per PSI...

Cheers!

 

[stevenkimbell]

Hmmm, seems this thread has lived a long time, so I guess my issue is not so unique, however,,,,,,,
First, let me say, without going into detail on on my setup, I have had no issues until now. My kegs carb and pour just fine. This is a situation with a stout that I have in the keg now, but it is the same recipe I have stored and dispensed from this keezer at least 5 times this year. Further, it worked great for the first week or so in the keezer. That said.......
I have a keg of stout in my keezer (lucky me!) and it had a small leak at the QC going to the tap. I disconnected the QC, cleaned up the leak, replaced the poppet and o-rings and put it all back together.
Suddenly, I have bubbles in my line going to the tap. Not good I say to myself, assuming it is a leak of some type (pulling air in since I dont hear gas escaping or see liquid coming out?)
I disconnected the QC and double checked my fittings, no issues. I connected it to another tap and still got bubbles. NOW, I am confused. It isnt a leak, it happens on other taps, gotta be the keg, but was NOT happening before I had the seepage of beer from the outflow fitting.
I read several posts (who am I kidding, I was supposed to be working and spent over 3 hours looking, chasing rabbits, learning new stuff) - anyway - I read about venting the gas from the beer since it might be overcarbed and trying to equilibrate in the lines. I removed the gas and vented the keg; it sat for 24 hours, regassed and immediately had bubbles when I pulled a glass.
Not to be outsmarted by my own creativity, I removed the gas, vented the keg, and left it for 4 days while I was on a trip. When I returned, the first thing I did was vent the keg again, but there was no gas to vent. Nope. Nada. No hiss, no fizz, no, just nothing. Hooked the gas up again, lo and behold! bubbles in the tap line.
To be sure, it doesnt affect the beer, it tastes fine.
I however, am at wits end. I have no idea what to do or check next. Ideas?

 

[passedpawn]

Hmmm, seems this thread has lived a long time, so I guess my issue is not so unique, however,,,,,,,
First, let me say, without going into detail on on my setup, I have had no issues until now. My kegs carb and pour just fine. This is a situation with a stout that I have in the keg now, but it is the same recipe I have stored and dispensed from this keezer at least 5 times this year. Further, it worked great for the first week or so in the keezer. That said.......
I have a keg of stout in my keezer (lucky me!) and it had a small leak at the QC going to the tap. I disconnected the QC, cleaned up the leak, replaced the poppet and o-rings and put it all back together.
Suddenly, I have bubbles in my line going to the tap. Not good I say to myself, assuming it is a leak of some type (pulling air in since I dont hear gas escaping or see liquid coming out?)
I disconnected the QC and double checked my fittings, no issues. I connected it to another tap and still got bubbles. NOW, I am confused. It isnt a leak, it happens on other taps, gotta be the keg, but was NOT happening before I had the seepage of beer from the outflow fitting.
I read several posts (who am I kidding, I was supposed to be working and spent over 3 hours looking, chasing rabbits, learning new stuff) - anyway - I read about venting the gas from the beer since it might be overcarbed and trying to equilibrate in the lines. I removed the gas and vented the keg; it sat for 24 hours, regassed and immediately had bubbles when I pulled a glass.
Not to be outsmarted by my own creativity, I removed the gas, vented the keg, and left it for 4 days while I was on a trip. When I returned, the first thing I did was vent the keg again, but there was no gas to vent. Nope. Nada. No hiss, no fizz, no, just nothing. Hooked the gas up again, lo and behold! bubbles in the tap line.
To be sure, it doesnt affect the beer, it tastes fine.
I however, am at wits end. I have no idea what to do or check next. Ideas?

I don't see how beer under pressure can pull IN anything. If there was a leak, beer would be going OUT.

I figure it's got to be one of two things. Beer line is warmer than the keg. So, add a fan inside your keezer. Or, some sort of nucleation point inside the disconnect is causing the CO2 to come out of the solution. Try a different disconnect.

 

[william_shakes_beer]

I get bubbles in my lines whenever the keg rests for a while. I have my system set up with long lines and low pressure. The burst of bubbles at the beginning of the first pour makes a nice little head.

 

[stevenkimbell]

Wish I could say I havent tried that yet, but...
I installed a fan when the keezer was built, and, I dont have this issue with my other two kegs. Also, it didnt happen for the first week the keg was in the keezer. I already tried it with BOTH of the other taps as well. This is why I am so stumped.

 

[day_trippr]

It has something to do with this:
"I disconnected the QC, cleaned up the leak, replaced the poppet and o-rings and put it all back together."

My guess is the small O-ring under the dip tube flange is either missing or damaged.
Either will allow CO2 in the keg head space to be injected directly into the beer stream at the Out post.
It's a classic bug...

Cheers!

 

[stevenkimbell]

It has something to do with this:
"I disconnected the QC, cleaned up the leak, replaced the poppet and o-rings and put it all back together."

My guess is the small O-ring under the dip tube flange is either missing or damaged.
Either will allow CO2 in the keg head space to be injected directly into the beer stream at the Out post.
It's a classic bug...

Cheers!

Thinking I checked this, but maybe not. Thanks for the info, I will check it later today and update. Appreciate it!

 

[stevenkimbell]

It has something to do with this:
"I disconnected the QC, cleaned up the leak, replaced the poppet and o-rings and put it all back together."

My guess is the small O-ring under the dip tube flange is either missing or damaged.
Either will allow CO2 in the keg head space to be injected directly into the beer stream at the Out post.
It's a classic bug...

Cheers!

Thanks day_trippr, you hit it right on the head. I would not have thought of this (obviously) because it did not get disturbed when I pulled the fitting off and replaced it - I only worked with the fitting. Sure enough, there is a small tear in the o-ring under the dip tube flange. Guess the removal and replacement of the fitting either tore it, or moved it in such a way it was able to pull co2 from the tank around the flange.
Good Call!

 

[day_trippr]

Yup, a classic.

fwiw, that o-ring is sealing three items all at once - the threaded keg riser, the dip tube, and the post - so it's subjected to both compression and rotation forces, which can be tough on the o-ring.

Any time you install a rubber o-ring or gasket that is subject to rotational forces you should make sure it's at least wet, if not carry a film of silicone grease (aka "keg lube"). The last bit of rotation when tightening the adjacent fitting can be enough to tear the rubber...

Cheers!

 

[passedpawn]

Yea that was a great diagnosis trippr. I have to remember that.