Determining the ideal top pressure a draft system

[Brewmaster Pat]

I am collecting data to determine the ideal top pressure that is required in a draft system that takes into account the pressure needed to maintain the CO2 in solution (equilibrium pressure) as well as pressure needed overcome resistance in the line. My assumption is that you need to determine both of these factors independently and then add them up. Consider a 100 foot glycol-chilled trunk-line system and a 38 degree cooler with a beer at 2.70 volumes of CO2. First we determine the equilibrium pressure required to be 14 psi at 38 degrees. Then we calculate the resistance in the lines to be about 16 psi in a 100 ft glycol trunk. Do we then add these two pressures to get (14 psi + 16 psi) 30 psi as the ideal pressure or do we just use the higher pressure of 16 psi to maintain equilibrium AND overcome the resistance in the line?

[PremiumVADraftTech]

Im not fancy on figuring that all out, but if using straight C02 the max PSI is 17lbs I believe, you need mixed gas for anything higher

But in those 100 feet, is it all one one level? or up/down 1 level? There are numerous factors

[spdbump]

Definattely would need to use mixed gass or beer pumps in this aplication. What size trunkline 5/16 or 3/8

[mikejferrari]

You're thinking of it the wrong way- You're not adjusting the pressure to overcome the line restriction; you're setting the pressure to maintain the level of carbonation in the keg (determined by carbonation level, elevation, and ambient temperature) and then you design your lines and components to achieve a 1:1 ratio of applied pressure and system restriction which gives you the ideal flow rate of 1 gallon/minute. Increasing the applied pressure would only serve to over-carbonate the kegs. For 100 feet of line, you will definitely need a gas blend, because your applied pressure is already less than your trunk line restriction. You probably want a 70/30 CO2/N2 blend with an applied pressure of 22psi. In that case, you already have 16 pounds of line restriction, so you would need 6 pounds of additional restriction, which would require 2 feet of 3/16" vinyl choker line installed between your barrier tubing and your faucet. That would give you 22psi vs 22 pounds of restriction- a balanced system. Do you have any vertical lift or drop between your walk-in and your taps? What kind of tap tower are you using? What size tubing are you using for your jumper line between the keg and the barrier line? These factors will also affect your system balance. I would find someone in your area with draft install experience to help you out with this.