Originally Posted by pmoneyismyfriend
This can't possibly be correct
That depends on your definition of correct. The goal of that set of calculations is to result in a pour speed of ~1gal/min, and 2.2' of line would result in something very close to that given your figures, so in that sense it's correct.
Those equations and calculators ignore many of the basic laws of fluid mechanics, but they get away with it for commercial systems by making a few assumptions. They assume that the beer will be stored very cold (~36°), the carb level will be 2.5-2.7 vol, and the goal is to pour as fast as possible without losing a ton of beer to excessive foaming (which happens to be ~1 gal/min for 2.7 vol and temps <38°). Since those assumptions often don't apply to home systems or homebrewers, the equations and formulas are pretty useless for a lot of us.
Raising the temp just a couple degrees means that the flow needs to be slower/gentler in order to keep the CO2 from breaking out of solution. The same thing goes for carb levels over ~2.7vol. And since line resistance decreases as flow rate decreases, you need a much longer line to slow the flow down just a little bit.
Most of us don't really care if the average pint pour time is 1.5 seconds longer like a bar does. Instead, having a system that's flexible and capable of serving beers at a wider range of temperatures and with a wider variety of carb levels is typically more important, and well worth waiting an extra second or two for a pint to fill. This is the main reason you see many suggestions to avoid the calculators and formulas that result in a 1 gal/min flow rate, and instead to just use some extra long lines.
If you're interested, there is one line length calculator that doesn't ignore the laws of fluid mechanics. It doesn't do all of the work for you, but if you know the flow rate that won't cause excessive foaming for your specific beer temp and carb level, you can input that (in terms of time to fill a pint) and it will calculate the length of line required to achieve that flow rate. For many of us serving in the 2.3-2.6 vol and 38°-42° ranges, a 10-11 second pint fill time seems to work pretty well.https://docs.google.com/spreadsheet/...VX0hzaEE#gid=0