29 psi cant be right

[JONNYROTTEN]

According to the formula I need 29psi.
L=(P-)H x .5)-1)/R
This formula doesn't include temp,so how does that work?Should I assume its for 38 deg?

my setup:
Length 10 ft
Pressure 29
Height 2 ft
Resistance 2.7 (3/16 line)
Will achieve 2.7 volume.
How can this be right?
The tap came with 5 ft line,I added 5 ft as per instructed here.If I went back to 5 ft that all taps come with I would be at 14.5 psi which sounds right.
Is my math off or am I missing something?
If I drop the pressure back to 14 with the same 10 ft lines will that effect anything besides a slower pour?(like less volume)

 

[cbrown9064]

Are you talking about hooking up a commercial keg or carbing/serving your own?

 

[JONNYROTTEN]

commercial keg.At 29 psi I should be forced carbing a corny,something is off OR maybe theres a reason that all kegerators come with a 5ft line.Are longer lines only for homebrew?

 

[cbrown9064]

Ok, here we go...


Commercial beer is kegged with a certian Volumes of CO2 (VV). To properly dispense the commerical beer, you need to know what VV it was kegged at. For instance A-B is usually 2.6 VV (used to be higher). Then you use that chart located at the URL below to determine what PSI to run depending on the tempature. That is called a "balanced" setup. It is balanced when you are applying the same volumes of CO2 as the brewer intended and was kegged at.

Once I figured this out on commercial kegs, the beer dispenses much better.

Also, when taking the temp of the beer, use the 2nd glass out of the tap. Not the air temp of the inside of the cooler or the temp of a glass of water. For whatever reason (not known to me, nor am I that interested in finding out), the temp of the beer in the keg may not be the same as the temp of water in a glass. So, draw two glasses of beer and measure the temp in the 2nd glass to find your beer temp.

Longer line length will help reduce your foam problems, but at 29psi you are way out of the range of a commercial keg. Depending on how long you had the keg at that pressure, you may have induced more volumes of co2 and changed the beer from the brewery.

Chris


http://www.kegerators.com/carbonation-table.php

 

[BigFloyd]

Forget about the calculator for now. With the 10 ft lines at 38*F, 11-12 psi is where you want to start.

I have no clue how you came up with 29psi, but that's way out. It would only work if you were pushing a stout out of a foamer faucet with 70/30 beer gas.

 

[JuanMoore]

According to the formula I need 29psi.
L=(P-)H x .5)-1)/R
This formula doesn't include temp,so how does that work?Should I assume its for 38 deg?

my setup:
Length 10 ft
Pressure 29
Height 2 ft
Resistance 2.7 (3/16 line)
Will achieve 2.7 volume.
How can this be right?
The tap came with 5 ft line,I added 5 ft as per instructed here.If I went back to 5 ft that all taps come with I would be at 14.5 psi which sounds right.
Is my math off or am I missing something?
If I drop the pressure back to 14 with the same 10 ft lines will that effect anything besides a slower pour?(like less volume)

There are two major problems here, number one, you're using the formula backwards, and number two, the formula is flawed.

The formula is not intended to calculate serving pressure given the line length, it's intended to calculate the minimum line length given the serving pressure. The serving pressure is determined by the carbonation and temperature of the beer, using a chart like the one linked above. Unless your beer is coming out too fast at the proper pressure, and causing excessive foaming, don't worry about using the formula to determine the minimum line length.

 

[JONNYROTTEN]

If the formula is flawed could I get the formula everyone uses here.The chart is great but useless without the correct formula to use it with.Yes,I ran the numbers backwards because everything is setup and connected with the 10 ft lines and I wanted to see where I was at.It came up as 29 psi.I just ran the numbers off the chart above(using my formula) and it came back 4' 3"lines .Which is basicly what the tower came with.That would in theory give me a perfectly balanced keg.So Im wondering why almost everyone runs long lines to eliminate foam when the shorter lines are what the charts call for.Every beer is different but some here are running 15 ft 3/16 lines.I cant imagine anything on the chart would call for that.Im really just curious why if the chart and fomula is for a perfect balance,why the longer lines

 

[JuanMoore]

If the formula is flawed could I get the formula everyone uses here.The chart is great but useless without the correct formula to use it with.Yes,I ran the numbers backwards because everything is setup and connected with the 10 ft lines and I wanted to see where I was at.It came up as 29 psi.I just ran the numbers off the chart above(using my formula) and it came back 4' 3"lines .Which is basicly what the tower came with.That would in theory give me a perfectly balanced keg.So Im wondering why almost everyone runs long lines to eliminate foam when the shorter lines are what the charts call for.Every beer is different but some here are running 15 ft 3/16 lines.I cant imagine anything on the chart would call for that.Im really just curious why if the chart and fomula is for a perfect balance,why the longer lines

There is a lot of really misleading information out there about "line balancing". The first misleading thing is the name, which implies there's some sort of balance you're trying to reach, and that anything greater or less than some "balanced" line length will cause problems. This is simply not true. That equation does only one thing, it calculates the line length required to result in a flow of 1 gal/min. Why 1 gal/min? Because the formula was designed for use in commercial systems, and bars and restaurants want to be able to pour as fast as possible without excessive foaming, which for commercial serving parameters (~36°, <2.7 vol, relatively low FG) is ~1 gal/min.

The problem with the formula? Not everyone wants to use commercial parameters, and for warmer or more highly carbed beer, the flow needs to be slower/gentler to prevent the CO2 from coming out of solution and causing excessive foaming. You quoted a resistance figure for 3/16" ID line of 2.7 psi/ft, but that resistance figure is only valid at a flow rate of 1 gal/min. Line resistance changes with fluid velocity, so to decrease the flow rate slightly, much longer lines are required.

The only side effect of extra long lines is a slightly slower pour. Once again, since resistance decreases when the flow rate decreases, even doubling or tripling the line length doesn't change the time it takes to fill a pint by very much. Since most of us aren't running a bar or restaurant where the time it takes to pour a pint effects our bottom line, having extra long lines is generally a good idea. It allows you to serve beer at a wider variety of temperatures and carb levels without excessive foaming, and only adds a second or two to the time it takes to fill a pint. If I have time to drink a beer, then I usually have an extra two seconds to wait for it to pour.

FWIW there is only one "line balancing" calculator I've seen that doesn't ignore the basic laws of fluid dynamics. You input your pressure, line diameter, and desired pint fill speed, and it will tell you the length of line required-

https://docs.google.com/a/email.arizona.edu/spreadsheet/ccc?key=0ApGb-vIKLq7FdGtzN3BrY2xZSldORzQ2bHVVX0hzaEE#gid=0

 

[JONNYROTTEN]

Thanks for the info.I wouldn't have thought of getting the beer out faster to make more money.Ill leave things as is and go with the chart.Tweaking the pressure as needed.

 

[cbrown9064]

Remember though, to use the chart I posted earlier, you need to know the volumes of CO2 the brewery carbed the keg at. Bud products are usually 2.6vv, but can vary and not all brewers are the same.

"Balancing" the keg in the way I described has nothing to do with line length and all to do with pressure on the beer. Until you know the vv of keg, you are just guessing with the chart.

Longer lengths of 3/16 line will slow down the flow, compensating for a poorly balanced keg.

All that being said, 10-14 psi depending on temp, will get you in the ballpark.

Chris