Flow resistance (4mm)

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uSlackr

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I built a great keezer base on all the design ideas I found here. I used duotight everywhere and 4mm ID EVA barrier tubing. I'm suddenly feeling the need to ensure it is balanced correctly. I have most beers carbed at 2.5 volumes and using ~12 psi to push. What I cannot find is the flow resistance for the 4mm tubing. Lots of talk about it, but I cannot find a stated figure. Can you point me to a source?
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day_trippr

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I don't have that number and haven't see it published.
But, playing with Mike's calculator using my own empirical data leads me to believe the value isn't much different from solid PVC.

fwiw, I'm running 6.5 feet of the 4mm on the four faucets I dispense with 11 psi at the kegs (12 psi indicated at the reg with 2 check valves in the path) and the pours could not be better. A fifth faucet runs at 15 psi (wheat beer) at 9 feet total length, and the sixth faucet for my nitro stout is back to the 6.5 feet length. All six have flow meters at the keg ends (~10" of tubing from the QD to meter inputs)...

Cheers!
 

whattabrau

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My experience with 4mm ID tubing is that for ~2.5 vol beers I get good pours with the line practically just reaching from the keg to the tap with a small amount of wiggle-room (slightly over 1m or 4ft). The story changes completely for 3.5 vol beers, where I need in the order of 3.5m or 11ft of line. I was expecting to need seriously less 4mm line for 3.5 vols, but reality didn't agree with my expectations. (data point: I used 6ft / 15ft of 3/16" ID in my previous keezer, so 4mm vs. 3/16" doesn't seem to scale linearly as a function of keg pressure)

That said, lines with Duotights are so easy to swap out, that I'd just spend half an hour of active time to figure out the best line length; cool-downs between experiments may give more realistic results. Remember, the calculator should be working for you, not vice versa. If you get good pours with different line lengths than those suggested by a calculator, the calculator is wrong, not reality.

Well, and I actually measure line in "keezers": low/mid carb is 1 keezer and high-carb is 3 keezers -- I'm good at misplacing my in-house measuring tapes, but I've never misplaced my keezer.
 
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uSlackr

uSlackr

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Well, and I actually measure line in "keezers": low/mid carb is 1 keezer and high-carb is 3 keezers -- I'm good at misplacing my in-house measuring tapes, but I've never misplaced my keezer.
Love it. Is that the L, W or H of the Keezer?
 

odie

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Since that line usually comes by the roll, I just used the whole roll and ended up with about 10ft lines for maximum flexibility. More than the "rule of thumb" but longer lines don't hurt anything and you can't serve higher carb'd beer on short lines without foam issues...but you can serve low carb beers on long lines without any issues.
 

whattabrau

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More than the "rule of thumb" but longer lines don't hurt anything and you can't serve higher carb'd beer on short lines without foam issues
Actually .. or theoretically .. you can't serve high-carb beers (>=3.5 vol) on a too long line without foaming. It's the same phenomenon as when dropping the CO2 pressure causes more foaming: the pressure towards the tap-end drops too low, and CO2 comes out of solution in the line. Now, granted, it's difficult to accidentally install 50ft of beer line, so as a rule of thumb the "too long" (= a few feet too long) line works line. It's quite easy to observe the problem with a flow control disconnect, though. You need to have the flow restriction and the line length in balance, or you'll get foamimg in the line. With a short line and properly adjusted flow control, you get both no foam in the line and reasonable exit velocity.
 
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