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. 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.
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; like any measurement? 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.
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? Paul’s issue in the
earlier version was not just pumps higher than the sump, but also restrictive
flow into the sump.
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’m
headed of on vacation in the morning for about 10 days, so you can say anything
about me that you wantJ.
Al