How to calculate PSI for line-length?

[Vale71]

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:

https://content.kegworks.com/blog/determine-right-pressure-for-your-draft-beer-system/

 

[Vale71]

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]

Have you checked out the Draught Beer Quality Manual? Specifically pg 39 diagram 4.1? I find that 3/16" tubing runs about 1.8 psi resistance per foot rather than the higher estimates.

https://brewersassoc.s3.us-west-2.a.../2019/03/Draught-Beer-Quality-Manual-2019.pdf
Seems like you might need some secondary regulators for the individual kegs.

Good Luck,
Dan F.

 

[Yooper]

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]

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]

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!

 

[Granite03]

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.

 

[Bobby_M]

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:
https://www.morebeer.com/products/e...tubing-1564-6-mm-id-38-95-od-placeholder.html
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.

 

[jddevinn]

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.