More great info. Was the regulator one of the smaller 'stock' auto units? My reason for asking is mine is a rather large Mallory unit that's supposed to handle truly massive flows (the manual specs supply and return line sizes up to 1200 HP...). So with 3/8" pressure and return lines, and the return being only a few inches long,I'd hope my pressure changes will be minimal (will test, of course) .
BTW, I picked it not for capacity, but because it has 4 in/out ports and very flexible mounting possibilities.
The pressure rise with fuel flowing through the -4 vent line is sobering. Some form of 'nearing full tank' alert or cutoff is certainly called for, and I'll look at implementing that, as well. With 2 aux tanks, I really have no choice about transferring fuel.
Others have plumbed main & aux tanks together & re-routed vent systems to force the main tank to draw from the aux, but I have multiple 'issues' with that idea, including, I don't want to alter the stock mains vent arrangement, and the fact that an air leak in the main's filler cap can prevent transfer from the aux.
Thanks for the great data.
How about an update on your plane?
Charlie