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I was forced to rethink my comment about sinking floats by Bob Chesley and
I stand corrected.  "G" loads will not cause the float to sink from lack of
buoyancy.  Thanks Bob for your physics lesson. But none the less my float switch would cause a fuel transfer whenever I
went into a turn or got into turbulance.  I now suspect that this was due
to  the fuel tank deforming due to the "G" loading and causing an apparent
lower fuel level and tripping the upper float switch or some other force
like surface tension.  In any event the optical float sensing device cured
the problem perhaps because of its lower profile in the tank or perhaps
because it has a built in time delay.

A couple of cautions if using floats or optical switches for header tank
level control.  The floats I got from A/C Spruce would not float in 100LL
so I had to add estensions.  The floats were not made of a material
compatable with fuel which I think has since been corrected.  After all my
problems with floats I scrapped the whole concept and switched to optical
which BTW fit into the same tank hole threads as the floats. If you are using a lower float to start the transfer system, locate it at a
mid tank position so as to have enough fuel to get you to the nearest
suitable in the event of a transfer failure and use an annunciator to
advise you when the tank is about half full rather than empty.  If it is
empty because the transfer system failed its is too late anyway.

Jim Frantz
angle-of-attack.com