I'm in the process of cutting new lines for a keezer, and am trying to calculate the proper line length for a nitro faucet. I used to get way too much head on stouts poured from my nitro system (1.5-2 inches, easily), and turning the pressure down gave a better result (~1 inch) but invariably resulted in the keg going flat since it didn't have enough applied CO2 pressure. I was running 7 ft lines on a kegerator that, on a good day in the summer, could only get down to 45º or so.
I'll probably be running the new system (a keezer) at 42-44º, but can't quite figure out how to calculate the proper line length for a stout (assuming 42º, 2 vol works out to 7.8psi). I read through this excellent resource, but the formula in Appendix C that purports to give you the proper applied pressure for a blended gas system (75 N2/25 CO2) seems to want me to put the keg under 75 psi to get 7.8 psi of applied CO2 pressure:
Applied = (Ideal CO2 Pressure + 14.7)/.25 -14.7
Applied = (7.8+14.7)/.25 - 14.7
Applied = 22.5/.25 - 14.7
Applied = 90 psia - 14.7
Applied = 75.3 psig of N2/CO2
Since most everything I've ever read has said blended systems do well at 30-40 PSIA, what am I missing here? I know the stout restrictor plate adds a bit of resistance, but I can't imagine it is enough to compensate for an extra 60 psi over what most 12" systems can comfortably handle. Not to mention 75 psig seems absurdly high... Thoughts?
[Edit] It occurs to me that 2 vol is a bit high for a stout (it's what the program I use, Beer Alchemy, suggested...), but even at 1.5 volumes the formula still suggests 53.3 psia of beer gas so the problem persists...