The Correct Pressure for Your Beer Dispense Lines: The Science

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Draft beer being pulled

Perhaps one of the more vexing questions for draft beer dispense, other than ensuring a beer clean line using, of course, Draftec,  is guaranteeing that you have the correct pressure. But, how do you calculate that? What is the correct procedure? Too high a pressure and the beer pours too fast, is wild and too foamy and the waste can be huge! Too low a pressure and the beer will become flat. The answer? Well, it IS a little complicated. This blog tackles the “Science” - the next blog will tackle the “Practice."
 
The longer the beer the beer line from the keg to the tap, the lower the serving pressure at the tap. However, this is very general;  it is literally all about balance! Nature hates imbalance.
 
 

First and foremost, we need to gather some information.

  1. The length of the beer line.

    This is the distance in feet from your draft beer tap shank to the coupler

  2. The line resistance.

    Depending on the material (vinyl or stainless steel) and the diameter of the beer line there is a set resistance value per foot.

    • 3/16” ID vinyl tubing = 2.2psi/ft
    • 1/4” ID vinyl tubing = 0.85psi/ft
    • 5/16” ID vinyl tubing = 0.4psi/ft
    • 3/8” ID vinyl tubing = 0.2psi/ft
    • 3/16” ID polyethylene tubing = 2.2psi/ft
    • 1/4” ID polyethylene tubing = 0.5psi/ft
    • 5/16” ID stainless steel = 0.3psi/ft
    • 3/8” ID stainless steel = 0.12psi/ft

  3. Gravity.

    This has nothing to do with the gravity of the beer (!) but refers to the rise or fall in feet between two horizontal planes, i.e., the center of the keg to the tap. For each foot, assign a value of 0.5 PSI.

  4. Temperature & Pressure.

    The higher the temperature, the more the restriction and, therefore, the higher the subsequent pressure will have to be.

  5. Altitude.

    There is a big difference working at high altitude (think Denver or Johannesburg) rather than sea level. Carbon dioxide will only stay dissolved in beer if the temperature and pressure are in balance.

  6. The desired carbon dioxide (in vols) in the beer to be dispensed (for most American lagers this is around 2.7 vols).

Watch for the next blog from AC Technologies - Clean Once, Clean Right!

A free sample of Draftec's beer line cleaner is available for professional line cleaners and beer distributors. To request a sample, please email us at info@draftec.com or call us at (888) 226-8228.