How to calculate PSI for line-length?

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olie

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I see a zillion answers for how to calculate the right line length for a given pressure, but that's not what I need. I have a line length, and I need to know what PSI to put behind it to get the pour I want.

Example:
  • It's 2.5' (30") up from keg to tap.
    • (Ooo, does this change as the keg gets emptier? Is the distance from top-of-keg or top-of-beer?)
  • I have 3/16" vinyl beer line.
  • There's 20' of it between the keg & the tap.
  • If it were a 2' "picnic tap", I'd use 8-9psi.
  • I want to pour 8-10second pints.
  • What pressure to I use to drive this line?

But, really, I don't want the answer to my example; I want to know the formula, in case I raise or lower the taps, or have a different beer that serves higher or lower from a picnic tap, or I change to 1/4" lines, or 15' or 25', etc.

Thanks!
~Ted
 

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First, you're doing it backwards. In order to get the carbonation right, you MUST have the correct psi for the carbonation level which is temperature dependent.

So, you have an IPA that you want at 2.5 volumes, and your beer temperature is 39 degrees- you must have the regulator set to 12 psi. That's just the way it is.

However, now you want to serve the beer in a long run. So you need Mike Solty's line length calculator. Determining Proper hose length for your Kegerator (Scroll down to tubing and flow rate for info).
 

Tobor_8thMan

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When I was building my keezer I did a LOT of research. I found the following very helpful.

 
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olie

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No, I'm not doing it backwards -- I have a different problem than the one you're solving. :)

I already have a keg of beer at the proper level of carbonation. Now I want to put it under my bar that already has lines installed (or will, once it's built). So I want to know what pressure I need to set my regulator at to get the pour I want.

NOTE: while you are technically correct in your statement that ends with "...you must have ...12 psi.", that's 12 psi at the tap. My whole question is about what I have to set my regulator to in order to get 12psi at the tap, given my pre-existing carbonated beer and lines.

On the page you link, under "Alternate: Set Pressure/Temperature based on Hose Length", is a picture of the exact spreadsheet I want. Sadly, I'm too blind to see a link to where I get that spreadsheet.

The important thing is: the answer to my question changes if I have 5' of line or 25' of line. It changes if the line is steel or vinyl. It changes if the line is 3/16" or 1/4". It changes if my taps are 2' or 3' above the keg. (I did notice that the spreadsheet takes an average and measures from center-of-keg -- I kind-a figured the weight of beer in the spear might affect the elevation portion of the calculation.)

I'd love to get a link to this spreadsheet, or any sort of web-calculator like it.

Thanks!

Screen-Shot-2012-09-17-at-8.28.42-PM.png
 

bracconiere

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12 psi at the tap? if it's twelve in the keg, then you just don't want to "shake the can" sorta say, and want to pour it gently.....just because it comes out slowly doesn't mean it's not still 12 psi.....i think?
 

Tobor_8thMan

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No, I'm not doing it backwards -- I have a different problem than the one you're solving. :)

I already have a keg of beer at the proper level of carbonation. Now I want to put it under my bar that already has lines installed (or will, once it's built). So I want to know what pressure I need to set my regulator at to get the pour I want.

NOTE: while you are technically correct in your statement that ends with "...you must have ...12 psi.", that's 12 psi at the tap. My whole question is about what I have to set my regulator to in order to get 12psi at the tap, given my pre-existing carbonated beer and lines.

On the page you link, under "Alternate: Set Pressure/Temperature based on Hose Length", is a picture of the exact spreadsheet I want. Sadly, I'm too blind to see a link to where I get that spreadsheet.

The important thing is: the answer to my question changes if I have 5' of line or 25' of line. It changes if the line is steel or vinyl. It changes if the line is 3/16" or 1/4". It changes if my taps are 2' or 3' above the keg. (I did notice that the spreadsheet takes an average and measures from center-of-keg -- I kind-a figured the weight of beer in the spear might affect the elevation portion of the calculation.)

I'd love to get a link to this spreadsheet, or any sort of web-calculator like it.

Thanks!

View attachment 698007
Oh, sorry, then you just need the minimum amount of CO2 to push to the tap. In my experience, this means the CO2 cylinder is off and the beer pours fine for a while. Then, need to turn the CO2 cylinder back on, low psi, to push to the tap.
 
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olie

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I apologize, I realize this is not a normal homebrew/kegerator kind of question, where configurations are somewhat limited and similar.

It turns out that beer line has resistance. Longer beer lines have more resistance. There's a point at which, if you have enough beer line --even if it's only 1' above the keg -- no beer will come out the other end at 12psi. Additional pressure needs to be added in order overcome line resistance. (I don't know what that point is, but I imagine that, if you have 1000' of 3/16" line and you try to push beer through it at 12psi, you'll be in for a very disappointing pour, even if the tap is even with the keg.)

Btw, separate from my problem*, this also comes up if you use a jockey box. A box with 20' of cooling line needs different pressure than one with 50' or 75'. It also matters if the cooling line is 3/16", 1/4" or 3/8". I've made it work with trial and error, but I think it'd be cool to be able to do the math, to get things really close to start, then tweak from there. In the past, my system as been to guess, then tweak from there, and my guesses aren't always good starting points! :)

Thanks again!


* Where I have a long bar with many kegs under it, and, rather than have different length lines, all requiring different pressures, I'm just making all the lines the length of the longest one, so I can run the same pressure to each. Big-ACK: that different gravity beers also affect the math, but I'm ok being a few % off; I just want to get my main pressure close.
 

day_trippr

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I don't really get the need for a "reverse line length calculator" because - for example - the specific physical system characteristics given in the OP will never be solved appropriately - that is, without the keg eventually being epically over-carbonated. That 8-10 second pour over that long a 3/16" ID run is the issue: the line length * ID really needs a lot more pressure than "chart pressure" to meet that flow rate.

Rather than fight physics, I suggest falling back on the classical method: find your chart pressure, then solve the line length vs diameter to make it meet the pour spec desired. There will be a lot less pain involved...

Cheers!
 
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olie

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[T]he specific physical system characteristics given in the OP will never be solved appropriately.
So are you suggesting that there's no such thing as a bar with a keg that's 20' away from the tap?

As above: it's ok if y'all don't know. I recognize that this is not a typical homebrew/kegerator problem. But it *is* solvable, as 10s of 1000s (more?) of brewpubs all across the country can attest, not to mention every single jockey box user, everywhere.

The Beersmith link and Mike's line calculator (above) both mention that it's perfectly possible & reasonable, they just don't offer (or I was too blind to see) a link to the calculator.

All I'm asking for is the math.

Thanks!
 

day_trippr

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So are you suggesting that there's no such thing as a bar with a keg that's 20' away from the tap?
If you don't want help, just say so. But from all appearances, you need a lot of it here.

Bars with cold rooms use specified diameter beer lines for the distance and height gain needed. They don't force-fit lines, they do the same math that Solty's calculator does, then use appropriate ID lines. Ideal solutions may well involve a short run of small ID "choker" tubing for fine tuning when non-FC faucets are involved. As well, often long line systems require the use of mixed-gas - primarily nitrogen - to provide propulsion without adding carbonation.

There are lots of solutions - when your feet aren't in cement...

Cheers!
 
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olie

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Thanks, Tobor_8thMan -- that's pretty close. I'd seen that one before, and what I can do is guess at pressures until I get the line-length to come out to the number I want (so, in my example above, for a 1.020 beer, it'd be 23-24psi for 10s, 34+ for 8s). And that's cool. I was just hoping to bookmark a link that led to a straight-up calculator (with the math "reversed" to give pressure).

Thanks!
 
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Tobor_8thMan

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Thanks, Tobor_8thMan -- that's pretty close. I'd seen that one before, and what I can do is guess at pressures until I get the line-length to come out to the number I want (so, in my example above, for a 1.020 beer, it'd be 23-24psi). And that's cool. I was just hoping to bookmark a link that led to a straight-up calculator (with the math "reversed" to give pressure).

Thanks!
I do believe we're dealing with "There is no 1 right answer" as it depends. It's frustrating, but it always depends...
 
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olie

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Science you can do at home:
  • Rent (or buy, or borrow) a jockey box with 50' coils.
  • Hook up your keg.
  • Give the good ol' 12psi.
  • Have a pour.
  • Report back.
  • Bonus points: get the one with 120' coils. :D
I have seen day_trippr's posts in the past and he's normally very knowledgible. This particular branch of physics is one where he seems to have his "feet stuck in cement", as they say. The dozens of brewhouse owners and GCs who have built brewhouses that I've been talking to this past year all tell me his answers are way off the mark.

Maybe what he describes is how they solve the problem on the other coast. Like I said, he seems pretty smart, so I don't doubt that he's got some reference point, there.

But complete dismissal of the jocky box experiment demonstrates a certain level of ..."cement-ness". As mentioned (earlier reply), even the kegerator page works-out the math for me if I'm willing to hunt & peck a bit.

How about we all just have a beer and be ok with saying "I don't know". That's where I started from. :)
 
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olie

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Science you can do at home:
  • Rent (or buy, or borrow) a jockey box with 50' coils.
  • Hook up your keg.
  • Give the good ol' 12psi.
  • Have a pour.
  • Report back.
  • Bonus points: get the one with 120' coils. :D
I have seen day_trippr's posts in the past and he's normally very knowledgible. This particular branch of physics is one where he seems to have his "feet stuck in cement", as they say. The dozens of brewhouse owners and GCs who have built brewhouses that I've been talking to this past year all tell me his answers are way off the mark.

Maybe what he describes is how they solve the problem in other parts of the country. Like I said, he seems pretty smart, so I don't doubt that he's got some reference point, here.

But complete dismissal of the jocky box experiment demonstrates a level of ..."cement-ness". As mentioned, even the kegerator page works-out the math for me (earlier reply).

How about we all just have a beer and be ok with saying "I don't know". That's where I started from. :)
 

bracconiere

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That kind of pressure will result in a VERY over-carbonated beer!

Edit: @day_trippr beat me to it.

not if your line is long enough and pushing up far enough! maybe a nitro tap i've been learning about would help.....or beer gas in general if you need really high pressure to really push it, i hear nitro doesn't dissolve in water......lol
 

Pkrd

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The keg pressure should be regarded as a constant as that determines the carbonation level in the poured beer.

But yeah, let us know how you get on. Hefes and Lambics are pretty good for a while...
 

camonick

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not if your line is long enough and pushing up far enough! maybe a nitro tap i've been learning about would help.....or beer gas in general if you need really high pressure to really push it, i hear nitro doesn't dissolve in water......lol
I understand line length and carbonation levels quite well. I run 3 standard taps balanced at the proper length with CO2 and 1 mixed gas nitro tap. I’m referring to the OP’s statement that he’ll need 24 psi to achieve his ideal pour with the fixed length of line he is insisting on.... that’s not how it works as stated by many people above. You must determine the carbonation level you desire and adjust your line length and or inside diameter to achieve a balanced system for the desired pour time you’re after.
 

bracconiere

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I understand line length and carbonation levels quite well. I run 3 standard taps balanced at the proper length with CO2 and 1 mixed gas nitro tap. I’m referring to the OP’s statement that he’ll need 24 psi to achieve his ideal pour with the fixed length of line he is insisting on.... that’s not how it works as stated by many people above. You must determine the carbonation level you desire and adjust your line length and or inside diameter to achieve a balanced system for the desired pour time you’re after.

but if you dilute the co2 with nitrogen....you can get the proper carb at the length right? without overcarbing.....
 

camonick

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but if you dilute the co2 with nitrogen....you can get the proper carb at the length right? without overcarbing.....
Yes. @day_trippr addressed this above
Bars with cold rooms use specified diameter beer lines for the distance and height gain needed. They don't force-fit lines, they do the same math that Solty's calculator does, then use appropriate ID lines. Ideal solutions may well involve a short run of small ID "choker" tubing for fine tuning when non-FC faucets are involved. As well, often long line systems require the use of mixed-gas - primarily nitrogen - to provide propulsion without adding carbonation.
But that’s not what the OP is willing to accept.
Rent (or buy, or borrow) a jockey box with 50' coils.
I’ve never dealt with a jockey box, but all the 50’ versions I’ve seen have 3/8” diameter coils
 

rsquared

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Thanks, Tobor_8thMan -- that's pretty close. I'd seen that one before, and what I can do is guess at pressures until I get the line-length to come out to the number I want (so, in my example above, for a 1.020 beer, it'd be 23-24psi for 10s, 34+ for 8s). And that's cool. I was just hoping to bookmark a link that led to a straight-up calculator (with the math "reversed" to give pressure).

Thanks!
What you're looking for can be done, but it only works for a short time. If you're looking for a single event (e.g. a jockey box at a beer fest), sure that 34 psi will probably do you just fine. The problem is that if you've got that level of pressure sitting on the keg for days or weeks at a time, the beer then becomes overcarbonated. That's why the calculators don't work in this direction, because it doesn't hold up over time. For a permanent line, your CO2 pressure should be balanced to your beer carbonation level, then the line diameter and length chosen to match that. Bars with long runs (e.g. your 20'+ example) are using a larger ID line so that they can do those runs down in the 10-15 psi range without overcarbing their beers.
 

Tobor_8thMan

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What you're looking for can be done, but it only works for a short time. If you're looking for a single event (e.g. a jockey box at a beer fest), sure that 34 psi will probably do you just fine. The problem is that if you've got that level of pressure sitting on the keg for days or weeks at a time, the beer then becomes overcarbonated. That's why the calculators don't work in this direction, because it doesn't hold up over time. For a permanent line, your CO2 pressure should be balanced to your beer carbonation level, then the line diameter and length chosen to match that. Bars with long runs (e.g. your 20'+ example) are using a larger ID line so that they can do those runs down in the 10-15 psi range without overcarbing their beers.
Not so sure as the lines between the kegs and the tap will lose CO2 over time. I know this from experience and not from a book or theory.
 

Vale71

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So are you suggesting that there's no such thing as a bar with a keg that's 20' away from the tap?
Yes, there is. But if everything was done properly then the line diameter was adjusted so that, in combination with the line length, it would offer the right amount of flow resistance in order to be able to set the correct pressure so that the beer's carbonation would not change while the keg is being tapped.

The reason there is no "reverse calculator" is because there is really no reason for one. All you need to do is just connect a keg, open the tap and slowly increase pressure until beer starts flowing at an acceptable rate. You'll then be able to read the pressure at the regulator. That and also the fact that if you design your system this way you will most certainly run into severe overcarbonation problems.

One of the reasons why the Keykeg and similar systems where invented is that they allow extreme setups, such as very long runs or large height differentials, without running the risk of overcarbonation as the gas is only compressing the inner bladder but never touches the beer itself.

In any case, if you're really set on letting your system determine the carbonation of your beer, this article has all the information you need to calculate the minimum serving pressure based on line lenght and diameter:

 
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Vale71

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but if you dilute the co2 with nitrogen....you can get the proper carb at the length right? without overcarbing.....
That is correct but of course there is increased cost and complexity when using beer gas.
 

kydan47

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Yooper

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How about we all just have a beer and be ok with saying "I don't know". That's where I started from. :)
Because some of us certainly DO know. Some of us, and some of our friends, actually design beer line runs for brewpubs. The fact that you don't agree with physical science and experience doesn't make us wrong.

You asked, some of us answered, and you don't like the answers. That's fine.
 

ClaudiusB

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I see a zillion answers for how to calculate the right line length for a given pressure, but that's not what I need. I have a line length, and I need to know what PSI to put behind it to get the pour I want.

Example:
  • It's 2.5' (30") up from keg to tap.
    • (Ooo, does this change as the keg gets emptier? Is the distance from top-of-keg or top-of-beer?)
  • I have 3/16" vinyl beer line.
  • There's 20' of it between the keg & the tap.
  • If it were a 2' "picnic tap", I'd use 8-9psi.
  • I want to pour 8-10second pints.
  • What pressure to I use to drive this line?

But, really, I don't want the answer to my example; I want to know the formula, in case I raise or lower the taps, or have a different beer that serves higher or lower from a picnic tap, or I change to 1/4" lines, or 15' or 25', etc.

Thanks!
~Ted
but if you dilute the co2 with nitrogen....you can get the proper carb at the length right? without overcarbing.....
You are correct. In the non hobby world a gas blender is used to make up for the additional pressure required. Nitrogen and CO2 are mixed to achieve the correct pressure.
 

Mtrhdltd

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If you have the equation for balancing your draft system then you already have what you are asking for. Solve for the variable you want, basic algebra. (Instead of solving for line length, solve for psi, they are all variables). I think you are way overcomplicating this.
Everyone is trying to show areas you seem to be ignoring due to lack of experience or knowledge. It's up to you to listen to their experiences or learn from your own. Good luck!
 

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Day Tripper and Yooper are correct. Listen to their advice. My system from Keezer to taps is 12 feet up with 18 feet of line. I went through those same calculations in order to arrive at using 5/16” line... that is the variable, not the psi. Long runs in bars vary the line size or the blend of CO2 with nitrogen. If you have to take the psi much above 12 then you have to blend the CO2 down... not something home brewers want to invest in. Use the online resources as a starting point for line resistance but use the manufacturer’s values before finalizing as they do vary for the same size.
 

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How about we all just have a beer and be ok with saying "I don't know". That's where I started from. :)
For starters, if you actually want to have a dialog and learn something, you should cut the condescending crap. You only know just enough to stick your foot in your mouth and it's showing.

You have a 20 foot run but unfortunately with 3/16" ID lines, it is very likely that the pressure required to make an 8 second pour will be too high for the carbonation level you want. That's speculation because we don't know if you're pouring a bitter or a hefewiesen and those two beers are ideally very differently carbonated.

If the required pressure is too high, you have two options:
1. Move up to 1/4" ID lines which are lower resistance per foot so it allows a lower pressure for the same flow rate.
2. Switch over to beer gas at whatever ratio makes sense. If you want a beer carbonated to a level that is achieved by 12psi of CO2 but you need 16psi for a good pour, you'd run 16psi of 75/25 Nitro/CO2 beer gas. This is exactly how bars handle long draw systems. This is the answer closest to the question you're asking, but I don't believe you're asking the question you think you are. I believe that you think it's fine to just adjust the CO2 pressure upwards to make the pour look right but that keg is going to overcarbonate.

The other issue you're going to run into is the beer is going to be pretty foamy without active cooling of that long line, or at least it will be for the first 2 pints given any long lag between pours.

The last thing I'll address is the great jockey box anecdote. One of the reasons the coils are offered at longer lengths, such as 120ft, is precisely because the keg is expected to be warm. For starters, it needs a lot of surface area to be fully cooled in one pass but that's not really why the coil is long. It's long because in order to maintain 2.5 volumes on a beer that's 70F, you need about 30psi. That 120 feet of coil is to hold enough back pressure to make the pour tolerable when there is 30 psi at the keg.

The reason your challenge has mostly been ignored in this regard is because we all know that you're not going to be able to put 30 psi on your cold kegs.

This is likely the best option for your situation, assuming the beers are going to be carbed to typical 2 to 2.5 volumes at normal kegerator temperatures:

Get the 39ft rolls for each faucet and leave them long as you test. If the pour is too slow, cut a few feet off and try again.
 
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jddevinn

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Jocky boxes are normally temporary setups for events and the beer gets drank or removed from tap before it becomes over carbonated. Long draw draft systems almost always use a CO2 and Nitrogen mixture to prevent overcarbonating.
 

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