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> Balancing a Tap System, contributed by TomoMeier
cj in j
post Apr 9 2005, 06:51 AM
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Balancing a Tap System To Reduce Foaming
Contributed by TomoMeier

Q: What do I need to know about pouring foam-free beers?
A: There are three basic things you need to do.
1) Use "Beverage Grade" tubing for the liquid line -- not the "Food Grade" stuff because it has irregularities inside the tubing which will cause the CO2 to come out of solution when dispensing. The Beverage Grade tubing has smoother insides and a thicker wall thickness. I get Beverage grade tubing from Rapids Wholesale Equipment (800-472-7431) great people that'll help you -- they know the draft beer stuff because they supply the bars and pubs with it.
2) Use 3/16" ID tubing for the liquid line because it has the greatest pressure drop when dispensing, therefore, you'll need less line length than if you used a 1/4" ID tubing.
3) You can keep your kegs at the same pressure AND dispense without having to adjust the regulator AND it won't foam. You just need to BALANCE your system.

Q: Can you give me an example?
A: Sure. Here's what works with MY SYSTEM -- I have a frig with 4 taps in the door.

1) There has to be enough pressure to push the beer up to the level of the taps. I've found that it takes ~0.2 psi to push the beer vertically up 6" of 3/16" Beverage Grade (BG) vinyl tubing (I'm sure that number will change depending on the viscosity (SG) of the fluid, but apparently it's not enough to worry about with beer). Measure the height from the middle of the keg (I'll explain that in a sec) up to the taps and figure the pressure needed to get the beer up to that point. For instance, if the elevation gain is 2'6", then you'll need about 1 psi to get the beer up that high.

The reason I chose the middle of the keg: The weight of the beer surrounding the dip tube would be enough to push the beer in the dip tube up to the same level without extra force. Example: If the keg was open and full, and you pushed the poppet down on the liquid side, the beer would come up the dip tube to the same level as the surrounding beer. If the keg were half full, the beer in the dip tube would then go to that level. I chose the middle because the beer level will change as it's dispensed and since you can't constantly compensate for it, choosing the middle seems to be the best.

2) The pressure of the beer has to be dropped before getting to the glass, but not too fast or too slow or else you can get a foamy flat beer. The beer also needs to have enough pressure to make it through the faucet. Most bars and pubs seem to pour a pint in about 8 to 10 seconds. With the 3/16" ID BG vinyl tubing, I get great results when I use a figure of 1.8 psi drop per foot of vinyl tubing and a figure of 0.65 psi drop for the faucet. This will drop 16 oz in about 10 seconds on my system at any carbonation level. Sorry, I can't comment on the "Cobra" faucets.

So to sum it up, I use:
  • 0.2 psi drop/0.5 ft of elevation gain from middle keg to faucet
  • 1.8 psi/ft drop for 3/16" ID Beverage Grade vinyl tubing*
  • 0.65 psi drop for thru-door faucet
*Note that the 1.8 psi/ft drop is an estimate that worked in this example. Different tubing, even of the same diameter, will present different amounts of resistance to flow, thus a little trial and error may be required on your part.

Example: You have a keg carbonated to 16 psi @ 45F and the faucet sits 2'6" above the middle of the keg.

16 psi (keg) - 1 psi (elev diff keg/faucet) - 0.65 psi (faucet) = 14.35 psi

The hose needs to drop that 14.35 psi so 14.35/1.8 = 7.97 ft

It would take 7 feet, 11.5 inches of 3/16" ID BG vinyl tubing to drop that pressure without foaming and without ever having to jocky the serving pressure.

Of course, this is how it works in MY SYSTEM -- it may not work like this in other peoples systems, but I'll bet it's pretty damn close if they've got it balanced to where they can carbonate & serve at the same pressure with no foaming.

Q: Do you have any other tips to avoid foaming?
A: Foaming beer can mean several things:

1) The beer coming out of the faucet should fill the faucet opening completely when pouring: no huge bubble hung in the middle of the pour stream, or an uneven pour stream. These problems are the result of too long of a beer line (too much restriction) or to low of a serving pressure and usually results in flat, foamy beer. Either shorten the line length or increase pressure.

2) It should take about 8-12 seconds to pull a pint. If it's faster than 6-8 seconds, the beer is coming out too fast, knocking the CO2 out of solution, foaming, and causing a flat beer. This is due to improper balance between the pressure and line length/diameter. Longer pour times may also cause the CO2 to come out of solution in the lines, resulting in foamy, flat beer.

3) Other causes of foaming include: use of non-beverage grade tubing, tubing pinch, tube warming, dirty lines/faucet, any constriction in the lines, air leak in connections, and carbonation not matching serving pressure.

It's a damn shame to see people talking about having to drop the regulator to pull a pint, then run the pressure back up to keep the beer carbonated. You don't have to do this if you take the time to figure out where the balance is when using the right type of tubing. Anyone should be able to take this info and easily balance his/her system with a little work. After you get this stuff down and see how it works, it's all just common sense.
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