Beer Line Balancing

There are several factors that go into pouring the perfect glass of draft beer, but most of the important math is done in regard to balancing the actual beer lines. The length of the beer lines you can use to pour your draft depends on:

  • The placement of your keg.
  • The placement of your tap in relation to the keg.
  • The type of line you use.

By balancing out all of the elements that go into a balanced beer line draft system, you can get the perfect pour every time. Let's take a look at the math involved in determining what kind of line you will use and how long your line will be.

Tubing Resistance

Every beer line has resistance based on the type of tubing used and the pressure at both ends of the line. Before we can calculate the actual amount of line you will need, we first need to establish the resistance numbers for the different types of popular tubing. Let's stay with the 3/16-inch and 5/16-inch diameter tubing of polyethylene, vinyl and stainless steel.

  • 3/16-inch vinyl line (ID): 3 psi/ft
  • 3/16-inch polyethylene line (ID): 2.2 psi/ft
  • 5/16-inch stainless steel line (ID): 0.5 psi/ft

Each line type has its own resistance, so it is always a good idea to find the actual psi/ft number before you start investing in line. Anything that is smaller in diameter than 3/16-inch is going to give too much resistance, so you should avoid it.

Calculating The Length Of Line Needed

The formula you want to use to calculate line length is:

Line Length = (Pressure of the Keg - Tap Pressure) / Line Resistance

If you have your keg set up properly, then you have it at around 40 degrees with a carbonation level of around 2.5 CO2 volumes. That gives you a keg pressure of around 12 psi. If your carbonation and temperature numbers match up with this example, then you can use the 12 psi number. But if you have your keg balanced differently, then calculate your keg pressure and use it in this formula.

There has to be some kind of pressure on your tap to draw the beer to the glass. So, for this example, it is safe to use 1 psi for your tap pressure. If you want to use a 3/16-inch polyethylene line for your beer line, then the amount of line you would need for the perfect pour is:

(12 psi - 1 psi) / 2.2 psi/ft = 5 feet of line

Balancing An Unbalanced System

What if your keg and tap are not in perfect line? It is generally accepted that you lose around 0.5 psi/ft for every foot that your keg and tap are not in line. So if your keg is a foot lower than your tap, then the keg loses 0.5 psi/ft in pressure.

To balance an unbalanced system, we simply need to add a factor into the equation that takes the distance into account. The new formula is:

Line Length = (Pressure of the Keg - Tap pressure - (Height difference / 2)) / Line Resistance

Using our original example, and adding in the idea that the keg is three feet lower than the tap, we get:

(12 psi - 1 psi - (3/2)) / 2.2 psi/ft = 4.32 feet of line

Try it out and see if this results in the best pour you have ever had.