dmcmillen
Well-Known Member
The concept of balancing a keg dispensing system is basically pretty simple. You're looking to balance the keg pressure with an equal resistance from the other elements of the system: tap, shank, gravity (resistance due to height of tap above center of keg), and line resistance, taking into consideration some additional flow pressure required for a proper flow rate.
The variable we are calculating is the the length of beer line needed to balance the system given everything else is fixed. The basic formula is:
L = (Keg_Pressure - 1 - System_Resistances) / Beer_Line_Resistance
L = Length of beer line required
1 = Overpressure reqd for the proper flow rate (ususally 1 for homebrewers)
System_Resistances = Total resistance in the given system: tap, shank, gravity, and line resistance
Beer_Line_Resistance = Resistance of the beer line used. E.g., 3 psi/foot for 3/16" line.
However, I see ths formula applied using two different ways of calculating what I am calling System_Resistances
Method 1
L = (Keg_Pressure - 1 - (Height/2) / Beer_Line_Resistance
Height/2 = resistance due to gravity and Height is the distance in feet from center of keg to center of tap
Here the only resistance being considered is the one due to gravity.
Two articles that recommend this method are:
http://beersmith.com/blog/2011/07/14/keg-line-length-balancing-the-science-of-draft-beer/
http://www.brewersfriend.com/2009/07/18/getting-a-good-pour-kegged-beer-co2-line-length-and-pressure/
Method 2
L = (Keg_Pressure - 1 - (Height/2) - Shank_R - Faucet_R ) / Beer_Line_Resistance
Shank_R = Resistance due to shank = 1 psi
Faucet_R = Resistance due to faucet = 2 psi
Here the resistance being considered is that due to gravity, shank and faucet so we have an additional 3 psi resistance to consider. This means for my system where I use 3/16" beer line, this method recommends a beer line that is 1 foot shorter.
Two articles that recommend this method are:
https://byo.com/yeast/item/164-balancing-your-draft-system-advanced-brewing
http://www.winning-homebrew.com/dispensing-your-beer.html
Please note that these two articles do not put forward this formula but this is effectively the formula they are using.
I am curious. Which is correct? Does it matter? I.e., is the science inexact enough that a foot here or there doesn't matter?
The variable we are calculating is the the length of beer line needed to balance the system given everything else is fixed. The basic formula is:
L = (Keg_Pressure - 1 - System_Resistances) / Beer_Line_Resistance
L = Length of beer line required
1 = Overpressure reqd for the proper flow rate (ususally 1 for homebrewers)
System_Resistances = Total resistance in the given system: tap, shank, gravity, and line resistance
Beer_Line_Resistance = Resistance of the beer line used. E.g., 3 psi/foot for 3/16" line.
However, I see ths formula applied using two different ways of calculating what I am calling System_Resistances
Method 1
L = (Keg_Pressure - 1 - (Height/2) / Beer_Line_Resistance
Height/2 = resistance due to gravity and Height is the distance in feet from center of keg to center of tap
Here the only resistance being considered is the one due to gravity.
Two articles that recommend this method are:
http://beersmith.com/blog/2011/07/14/keg-line-length-balancing-the-science-of-draft-beer/
http://www.brewersfriend.com/2009/07/18/getting-a-good-pour-kegged-beer-co2-line-length-and-pressure/
Method 2
L = (Keg_Pressure - 1 - (Height/2) - Shank_R - Faucet_R ) / Beer_Line_Resistance
Shank_R = Resistance due to shank = 1 psi
Faucet_R = Resistance due to faucet = 2 psi
Here the resistance being considered is that due to gravity, shank and faucet so we have an additional 3 psi resistance to consider. This means for my system where I use 3/16" beer line, this method recommends a beer line that is 1 foot shorter.
Two articles that recommend this method are:
https://byo.com/yeast/item/164-balancing-your-draft-system-advanced-brewing
http://www.winning-homebrew.com/dispensing-your-beer.html
Please note that these two articles do not put forward this formula but this is effectively the formula they are using.
I am curious. Which is correct? Does it matter? I.e., is the science inexact enough that a foot here or there doesn't matter?