Author Topic: Keg System pressure  (Read 4525 times)

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3833
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Keg System pressure
« Reply #15 on: December 05, 2012, 08:31:15 AM »
1/4" line should restrict about 0.6 psi per foot, and you're pushing at ~10.  A 4' line will make the beer foamy weather it is homebrew or a commercial keg.  Get some 3/16" line, that restricts more like 2 psi per foot.

Those should be about 0.2-0.3 psi/ft and 0.7-1.1 psi/ft, respectively.

http://seanterrill.com/2011/11/11/a-more-accurate-approach-to-draft-system-balancing/
Sent from my Microsoft Bob

Beer is like porn. You can buy it, but it's more fun to make your own.
seanterrill.com/category/brewing | twomilebrewing.com

Offline tschmidlin

  • I must live here
  • **********
  • Posts: 8197
  • Redmond, WA
    • View Profile
Re: Keg System pressure
« Reply #16 on: December 06, 2012, 12:03:31 AM »
1/4" line should restrict about 0.6 psi per foot, and you're pushing at ~10.  A 4' line will make the beer foamy weather it is homebrew or a commercial keg.  Get some 3/16" line, that restricts more like 2 psi per foot.

Those should be about 0.2-0.3 psi/ft and 0.7-1.1 psi/ft, respectively.

http://seanterrill.com/2011/11/11/a-more-accurate-approach-to-draft-system-balancing/
It depends on the source and material.  micromatic says 3 psi/foot for 3/16" vinyl, morebeer says 2.2 psi/foot for 3/16" vinyl.  micromatic also says 0.5 psi/foot for 1/4" poly, 0.3 psi/foot for 1/4" barrier, and 0.85 psi/foot for 1/4" vinyl, while morebeer shows 0.65 psi/foot for 1/4" vinyl.  For all we know it varies by manufacturer and lot, not just material.

You could do some tests if you trust your pressure gauge.  Get a 10' section, hook it to a corny, and run it as straight up and down as possible.  Account for the static resistance at 0.5 psi/foot of elevation, then slowly apply pressure until water is coming out the top.  The pressure, minus 5 psi (0.5 psi/foot * 10 feet), divided by 10 feet of tubing gets you the resistance per foot.  So if it takes 20 psi to get water to the top, you've got 1.5 psi/foot resistance in the line.  It will read slightly high because of the poppet/fitting it has to run through, but you could account for that with a second test with a longer tube.
Tom Schmidlin

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3833
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Keg System pressure
« Reply #17 on: December 06, 2012, 09:21:30 AM »
It depends on the source and material.  micromatic says 3 psi/foot for 3/16" vinyl, morebeer says 2.2 psi/foot for 3/16" vinyl.

I'm going to do some testing next time I have an empty keg. It just seems clear to me that these values are inaccurate. Anecdotally, we all know that a 3' run of 3/16" line will be nowhere near balanced at 10 psi.
Sent from my Microsoft Bob

Beer is like porn. You can buy it, but it's more fun to make your own.
seanterrill.com/category/brewing | twomilebrewing.com

Offline neemox

  • Cellarman
  • **
  • Posts: 33
    • View Profile
Re: Keg System pressure
« Reply #18 on: December 06, 2012, 11:13:44 AM »
I love that every time I have a question about brewing, their is a scientific solution if there is not someone who has already done the tests. Thank you for pointing out the theory behind my broken keg system. Know I understand the balancing issue, so I'll do some tests on my kegs and system and report back.

Offline tschmidlin

  • I must live here
  • **********
  • Posts: 8197
  • Redmond, WA
    • View Profile
Re: Keg System pressure
« Reply #19 on: December 06, 2012, 11:56:43 AM »
It depends on the source and material.  micromatic says 3 psi/foot for 3/16" vinyl, morebeer says 2.2 psi/foot for 3/16" vinyl.

I'm going to do some testing next time I have an empty keg. It just seems clear to me that these values are inaccurate. Anecdotally, we all know that a 3' run of 3/16" line will be nowhere near balanced at 10 psi.
I agree that they are high, but then I don't get my hose from micromatic so I don't know how off their number is.  But that's also the example number they give in the DBQM, so lots of people are looking at that.

In my system I find that for 12 psi, 6 feet of 3/16" line gives me a pour I like.  That's 2 psi/foot, not accounting for losses in the fittings, shank, faucet, or that the faucet is more than a foot higher than the center of the keg.
Tom Schmidlin

Offline Jimmy K

  • Official Poobah of No Life.
  • *
  • Posts: 3630
  • Delaware
    • View Profile
Re: Keg System pressure
« Reply #20 on: December 06, 2012, 02:27:57 PM »
In my system I find that for 12 psi, 6 feet of 3/16" line gives me a pour I like.  That's 2 psi/foot, not accounting for losses in the fittings, shank, faucet, or that the faucet is more than a foot higher than the center of the keg.
Now I'm thinking, hold my beer...
 
Everyone talks about it like resistance should equal psi, but shouldn't there be some unmet resistance. Else the beer would just dribble out of the faucet and not foam much at all. I know if I set my psi too low, the pour is really slow with no head. Raise it up 2psi and it pours much better. I'm just wondering if anyone knows what the ideal pressure at the faucet is, I'm guessing it is not zero.
Delmarva United Homebrewers - President by inverse coup - former president ousted himself.
AHA Member since 2006
BJCP Certified: B0958

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3833
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Keg System pressure
« Reply #21 on: December 06, 2012, 02:53:05 PM »
I'm just wondering if anyone knows what the ideal pressure at the faucet is, I'm guessing it is not zero.

I think if you look in the DQM it recommends 5 psi of over-pressure, because bars are happy to trade foam for a faster pour (up to a certain point, anyway). For a more "natural" pour without any spillage, I'd say probably 1-2 psi.
Sent from my Microsoft Bob

Beer is like porn. You can buy it, but it's more fun to make your own.
seanterrill.com/category/brewing | twomilebrewing.com

Offline tschmidlin

  • I must live here
  • **********
  • Posts: 8197
  • Redmond, WA
    • View Profile
Re: Keg System pressure
« Reply #22 on: December 06, 2012, 11:02:19 PM »
Yeah, I don't know what the pressure should be really. I just do some math, add a foot or two, and see how the pour is.  Then adjust as necessary.
Tom Schmidlin