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Thread: draft line sizing

  1. #1
    Join Date
    Aug 2004
    Location
    Soldotna, AK
    Posts
    44

    draft line sizing

    I'm setting up my draft line in a new brewpub and need help from fellow probrewers.

    First of all, do you need to factor in head pressure for 7 bbl. serving tanks that are on the same floor as the draft tower? The top of the beer in the serving vessel should never be above the taps in my scenario(It's almost at the same level as the tower taps)
    According to my equation from the ABG dispense chapter regarding choker lenth(y):
    Dispense pressure=tank pressure-line lenth*line resistance-tap loss-3psi/ft(y-unknown choker length)
    So, in my case for my longest run,
    .5 psi=(12)-(54ft)(.06psi/ft-5/16" barrier tubing)-(.5psi)-(3psi/ft)(y)
    .5psi=(12psi)-(3.24psi)-(.5psi)-3ft(y)
    .5psi=(8.26psi)-3psi/ft(y)
    3psi/ft(y)=7.76psi
    y=2.58ft. choker hose

    Does this look right?
    Do I need to add any head pressure to this?
    Anything i'm missing?

    Thanks,
    Zach Henry
    St. Elias Brewing Company
    Soldotna, Alaska

  2. #2
    Join Date
    Apr 2006
    Posts
    87

    Balancing draft line from bright tank

    Quote Originally Posted by zachjenny
    I'm setting up my draft line in a new brewpub and need help from fellow probrewers.

    First of all, do you need to factor in head pressure for 7 bbl. serving tanks that are on the same floor as the draft tower? The top of the beer in the serving vessel should never be above the taps in my scenario...
    Doesn't look you should factor in the head pressure: a head pressure in an equilibrium system (closed tank) is equal to a gas pressure in beer.

    In a balanced system a dispense [CO2 tank] pressure should be equal to tank beer/head pressure and to provide a necessary flaw rate this pressure is to be restricted by sufficient piping.

    What seems should be taken into consideration are vertical runs from the tank to the line (ascending, descending) and from the line to the tap.

    Leonid Lipkin

    Libira Brewery
    Haifa, Israel
    Last edited by Hofer; 01-28-2008 at 05:38 AM.

  3. #3
    Join Date
    Apr 2006
    Location
    Chicago, IL
    Posts
    185
    generally, the idea is to balance the gas pressure (head pressure) and have "gravity pour" from the serving tank -- i.e. if you open a tap off the bottom of the tank and beer freely flows out. After balancing the gas, the pouring pressure is the hydraulic pressure from the liquid level in the tank.

    This is the assumption bars/distributors work with. (and they also work with kegs, which are a lot shorter than serving tanks.)

    What they do is to balance gas pressure (head pressure) to the total system restriction (including vertical change, of the draft system), and leave the hydraulic pressure to do the pouring work.

    Obviously, with the height of a serving tank, you will have a lot more hydraulic pressure to pour than using a keg, until the tank level gets low enough to be comparable to a keg -- faster pour that is. But I wouldn't try to correct it with a choke.



    Oh, and I just noticed that, 5/16" barrier tube usually have -0.10 psi/ft restriction instead of -0.06 (3/8").

    I also didn't see you accounting for the restriction of your beer tower (often ~ -7psi!)

    Still, if you have 7.76 psi left unbalanced for your system and needing ~ 3' of choke, I would recommend you down sizing your barrier line to increase system restriction and reduce beer waste sitting in the beer line!
    1/4" barrier tube = -0.3 psi/ft with 1/3 oz beer inside/ft
    5/16" barrier tube = -0.1 psi/ft with 1/2 oz beer inside/ft
    3/8" barrier tube = -0.06 psi/ft with 3/4 oz beer inside/ft


    Also, head pressure should be determined by your serving temperature and carbonation level, not merely to meet up with the draft system restriction, if that's what you mean by "adding head pressure to this".
    Last edited by jarviw; 02-01-2008 at 10:07 AM.

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