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Hi
Paul;
I was going to ask you to draw a detailed sketch of your
system to ensure that we are all on the same page while trying to diagnose your
problems, but your latest description along with the photo makes it pretty
clear. However it wouldn't hurt to have a good drawing.
I'm very happy without a header tank but I feel that you
could make a sump tank work for you by simply adding the vents. I'd use a 3/8"
line from the top of your sump going to a "T" then on to the very top of both
wing tanks. Do not just tie this into your existing main tank vent lines. Any
flow up this line would flow to the tank in use as it would be drawing fuel out.
I would expect that fuel would fill this line to equalize the level in the main
tank as what you would have created would be a "U" tube manometer, however any
vapour that appeared in the sump tank should flow up the vent line to the mains.
I'd use a 3/8" line rather than a 1/4" line for the vent as there is a chance
that there could be enough surface tension of fuel inside a smaller vent line to
impede flow. Since you still have the Facet pump in the feed line from the mains
to the sump you can always turn that on at critical flight phase to ensure
circulation, forcing any possible vapours back to the main tanks. This should be
all that is needed to make your sump tank work.
However it may be less work to just get rid of the sump
tank. I don't know how hard it will be for you to add return lines to your
mains? Either way it should be done, whether you are using them to return fuel
or to vent your sump tank. Since you only use 2 tanks you can buy a duplex valve
that switches feed and return flows ($$$$), that would help to manage this. I
didn't go with this route since I have 6 tanks to manage. Tracy method is also
another possibility and several others are using it. I didn't go this route just
because I didn't really like the idea of only having one source and having to
keep transferring fuel on a regular basis. But there really is nothing wrong
with it and it definitely is less workload than the fuel management that I did
when I had the header system.
My system isn't a true returnless system as found in late
model cars, as that is designed to have only one main tank however it is as
close as I could make it. Rather than adding unnecessarily to the archives I'll
just add the link to the original post and drawing.
It has
been working great for me, but my needs were a little different as I am managing
6 tanks. With only two tanks to manage I would seriously consider using a
conventional fuel return system with a duplex valve and no sump tank. You will
also be shaving off a few more precious pounds by ridding yourself of
it.
Todd (I might as well only have one tank for all the
flying I have time for lately)
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