Keg Pressures and Beer Line Info

[captdavid]

Not a home brewer, but we serve LOTS of craft beers, and build and maintain our own keg equipment. I see lots of questions on the forums concerning correct keg "gauge" pressures, beer line diameter and length. The Brewers Association Draught Beer Quality Manual http://www.draughtquality.org/f/DBQM_Full.pdf is available online as a pdf file and will tell you more than you ever wanted to know about draught systems. It covers lots of commercial applications such as glycol and beer pump systems that don't pertain to home systems but their chapter on "A matter of balance" explains the dynamics of carbonation and how the combination of temperature, applied or "gauge" pressure and system resistance combine to affect the pour quality. While the explanation can seem complicated, it is really quite simple as seen by the following example.
• Beer Conditions:
o Beer temperature: 38°F
o Beer carbonation: 2.8 volumes of CO2 per volume of beer
o Dispense gas: 100% CO2
o Gas pressure needed to maintain carbonation = 14.5 psig
• Static Pressure:
o Vertical lift = 5 ft. (Tap 5 ft. above the center of the keg)
o Static resistance from gravity = 5 ft. x 0.5 pounds/foot = 2.5 pounds
• Balance
o Applied pressure of 14.5 psi must be balanced by total system resistance
o Since static resistance equals 2.5 psi, a total of 12 pounds of system resistance will be needed:
Restriction = 14.5 – 2.5 = 12 pounds
o To achieve this: 4 ft. of 3/16” polyvinyl beer line (choker) @ 3 pounds per foot = 12 pounds)

May save a lot of headaches trying to figure out why one will pour and not another. We use 1/6 sankey kegs and have spent the extra to regulate each keg as line conditions will vary dramatically depending on the keg carbonation volume

Also have some info on our systems including a thru the wall three tap kegerator on our patio and a home brew walkin cooler (34-40 degrees) we use to store products. Getting ready to build a 10 tap keezer for the front of the house in March.

Good Luck
Capt David ONeill
Tybee Island Ga

 

[mcberry]

Don't you also need to account for pressure loss at the tap and shank? Additionally, if done as above, doesn't that leave no dispensing pressure? I've seen desired dispensing pressures from anywhere between 1psi and 5psi. I'm trying to get this all sorted out in my head, as I'm kegging for the first time in 2 weeks.

Thanks

 

[BendBrewer]

I've seen desired dispensing pressures from anywhere between 1psi and 5psi.

Your beer would want to balance out with your system meaning it would lose carbonation. If you want your beer at 12 psi, then serve it at 12 psi.

 

[captdavid]

Yet another quote from the "Beer Manual"

The “ideal gauge pressure” for a beer is the pressure
at which CO2 is not diffusing from beer into the
headspace and excess CO2 is not absorbing in the
beer. This value varies from account to account depending
upon factors such as temperature, altitude
and carbonation level of the beer. Because beer carbonation
can vary with the temperature of your cooler
and the pressure applied to the keg, you must take
care to maintain steady values suited to your system
and beers.

Point behind beer line diameter and length is to maintain the "gauge" pressure on the keg while the faucet is open (faucet and shank resistance is negligible for purposes of calculation) Really would suggest getting online and reading the chapter on balancing as it explains it far better and in more detail. Also has a nifty method of determining optimum gauge pressure if you do not know the original carbonation volume in a keg.