Author Topic: Quick, quick carbing question?  (Read 4205 times)

Offline tschmidlin

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Re: Quick, quick carbing question?
« Reply #30 on: November 05, 2011, 11:02:59 PM »
I think where you're going wrong is assuming that the line resistance is 3 psi/ft, In my experience the resistance of most line is 2 psi/ft or less. So at 15 psi, you're looking at a 7.5 ft line. I always start too long and cut it back until I get the pour I like. So maybe start with 9-10 ft and go from there.
This this this, 100x this.

3 psi/ft is way off IME, the stuff I get from morebeer is supposed to be 2.2 psi/ft but my experience says it's less.  Start with a longer line and cut it until you get the pour you want.
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Re: Quick, quick carbing question?
« Reply #31 on: November 06, 2011, 12:05:08 AM »
If I remember correctly 3/16 line has a resistance of 1.8 lbs per foot.  I typically run 12 psi serving pressure with a 6' line.
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Offline dzlater

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Re: Quick, quick carbing question?
« Reply #32 on: November 06, 2011, 04:40:41 AM »
I found this info here http://www.beersmith.com/blog/2011/07/14/keg-line-length-balancing-the-science-of-draft-beer/
   * 3/16″ ID  vinyl tubing = 3 psi/ft
    * 1/4″ ID vinyl tubing = 0.85 psi/ft
    * 3/16″ ID Polyethylene tubing = 2.2 psi/ft
    * 1/4″ ID Polyethylene tubing = 0.5 psi/ft
    * 3/8″ OD Stainless tubing = 0.2 psi/ft
    * 5/16″ OD Stainless tubing = 0.5 psi/ft
    * 1/4″ OD Stainless tubing = 2 psi/ft

The tubing I have is Bevlex which is PVC , I assumed it was vinyl.
OK so let's say it's 2.2.
That would mean serve at 11psi. Which would give a good pour and keep the beer carbed at around 2 volumes.
I do understand to get it really dialed in I  would need to play around with the line lengths. I am just trying to get it working a bit better with what I have.


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Re: Quick, quick carbing question?
« Reply #33 on: November 06, 2011, 09:16:00 AM »
3 psi/ft is way off IME, the stuff I get from morebeer is supposed to be 2.2 psi/ft but my experience says it's less.  Start with a longer line and cut it until you get the pour you want.

I agree. The big problem is that resistance per unit length will change based on the length of the line. It may be 2.2 psi/ft for a 5 ft run, but in my experience with longer runs it's more like 1.5 psi/ft. I serve my "standard" beers at 13 psi with 7.5 ft lines, and sometimes I wish they were a little longer.
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Offline tschmidlin

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Re: Quick, quick carbing question?
« Reply #34 on: November 06, 2011, 10:53:47 AM »
3 psi/ft is way off IME, the stuff I get from morebeer is supposed to be 2.2 psi/ft but my experience says it's less.  Start with a longer line and cut it until you get the pour you want.

I agree. The big problem is that resistance per unit length will change based on the length of the line. It may be 2.2 psi/ft for a 5 ft run, but in my experience with longer runs it's more like 1.5 psi/ft. I serve my "standard" beers at 13 psi with 7.5 ft lines, and sometimes I wish they were a little longer.
That's interesting, and something I hadn't considered.  Do you think the flow is less turbulent over long lengths, decreasing the psi/ft?  And do you think it would be affected by whether the line is straight or coiled? (my kegerator isn't even 7 feet long).
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Re: Quick, quick carbing question?
« Reply #35 on: November 06, 2011, 12:08:02 PM »
That's interesting, and something I hadn't considered.  Do you think the flow is less turbulent over long lengths, decreasing the psi/ft?  And do you think it would be affected by whether the line is straight or coiled? (my kegerator isn't even 7 feet long).

I think the major factor is actually the turbulence induced by the keg coupler and the faucet/tap. Within the tubing itself, the flow should always be turbulent, and pressure drop should be constant. For a flow rate of 40 mL/s (a 12 s pour), Re ~ 10,000. Solving for pressure drop using a Moody chart gives f ~ 3.1e-2, so dP/l = 1.6e4 Pa/m, or 0.71 psi/ft.

So if you assume that a 5 ft line is balanced at 10 psi, the flow resistance due to the tubing is actually only ~3.5 psi, with the other 6.5 psi being dropped by the fittings. Ignoring the fittings gives a resistance of 2 psi/ft.

Try to carbonate to 16 psi assuming that same value, though, and you have problems because the actual pressure drop is 6.5 + 8*0.7 = 12 psi. There's 4 psi of excess pressure coming out at the tap. In order to balance that system, you'd need (16-6.5)/0.7 = 13.6 ft of tubing. That actually squares up pretty well with what I've seen in practice, so I'd guess that using the 6.5 psi drop for the hardware will get you pretty close.

Coiling the tubing shouldn't have any effect as long as the radius of the bending is large relative to the diameter of the tubing. I think that would always be the case for vinyl tubing, which you can't coil tighter than what, 6 inches or so?
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Offline maxieboy

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Re: Quick, quick carbing question?
« Reply #36 on: November 06, 2011, 01:04:23 PM »
3 psi/ft is way off IME, the stuff I get from morebeer is supposed to be 2.2 psi/ft but my experience says it's less.  Start with a longer line and cut it until you get the pour you want.

I agree. The big problem is that resistance per unit length will change based on the length of the line. It may be 2.2 psi/ft for a 5 ft run, but in my experience with longer runs it's more like 1.5 psi/ft. I serve my "standard" beers at 13 psi with 7.5 ft lines, and sometimes I wish they were a little longer.

Way off IME aIso. I use 10' lines w/ picnic taps @ 12 psi. Great pours.
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