If for any reason one strake is reluctant to transfer, I can de-select the tank that's transferring OK and suck fuel from the reluctant tank (this would be impossible if the sump were vented).

Both "suck" and "reluctant" are relative terms since the head pressure between the strake and the sump is quite small - 0.3 psi with full strakes, 0.1 when empty.

That's why I believe sumps should be a closed system .... Jim S.

I’d say what works for you is what works. But before adding potential problems of electric valves, the requirement to use them, and the potential for air or vapor locked in the sump tank, I would determine why I had “reluctant” gravity. There has got to be a reason, you just haven’t found it yet. Agreed. I thrashed my brains out for over a year. Spent a LOT of time on the Cozy and Velocity lists (as you know). Nobody had ANYTHING that I hadn't already tried - except going from 3/8" to 1/2" or 7/16" lines from the strake to the sump. The valves were my last gasp, and much more of a workaround than a solution. As you know, assymetric transfer is quite common in Velocitys - mine is just the worst and most persistent. You have a good ‘work around’ that you are willing to manage, and that’s fine; I just wouldn’t generalize that to be the best approach in all cases. Agreed. I didn't mean to suggest that everyone would encounter what I did gravity feeding a sump. But lots of people have lesser problems. Assymetric/reluctant flow is something you have to watch out for gravity feeding a sump from multiple sources. Reluctant flow could give you problems if sump is vented. LARGE lines from strake to sump should be a solution (that I might yet incorporate - I'm just reluctant to open the bulkhead between the wing tank and the cabin).

You also said: Your sump basically recycles completely every 4 minutes or so. Your fuel could be really REALLY hot just when you begin your takeoff roll.

Do you have any reason to believe this;Sort of; like any measurement? I estimated (key word) a 30-35 gph pump, 2-gal sump (your Vel?), 2 gph idle usage => >30 gph return => turns over 2-gal tank 15 times / hr. Pump capacity and sump volume are BIG variables. 2 gph from main tank doesn't put much of a dent in 30 gph return. There is always some fresh fuel coming from the mains. How much heat is the fuel line really picking up? With a 3 gallon sump and a 30 gph pump the recycle is clearly less than once every 6 minutes. Yeah, if I was on the taxiway more than 20-30 minutes I might be concerned. By then I’d probably have turned off my engine a few times while I waited. I’ll plan on getting some temp measurements on my sump tank temp and we’ll see. Good idea. Measured numbers always better than SWAGs.

BTW, my comment about a power runup before takeoff was to bring fresh cool fuel into the sump before takeoff. And as soon as I apply full power for takeoff roll the fuel temp in the sump tank is going down. (Very little recycle, fuel flowing in from the mains) If there were to be an issue, wouldn’t I know it at the beginning of the takeoff roll? I don't think so. With a 2-gal sump and 20 gph usage, it will take upwards of 5 min to replace the sump fuel. Any problem is going to happen long before that IMO. Paul’s issue in the earlier version was not just pumps higher than the sump, but also restrictive flow into the sump. I think badly located pumps and restrictive flow (not quantified) were not his main issues. I believe his biggest problem was returning fuel to a [small] sump. Was his sump < 2-gal?

I have no objection to returning fuel to the mains; that’s fine. I’m not at all convinced that is a requirement that needs to be backfit. I'll be better able to speak to that when I retrofit 5/8" lines from my strakes to my sump :o)

I’m headed of on vacation in the morning for about 10 days, so you can say anything about me that you wantJ. At the risk of repeating myself, by now we have a pretty good handle on the down side of returning fuel to sump. I don't recall hearing the up side (aside from it's already in place - sort of like my 3/8" feed lines :o)