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Jim Frantz wrote about float switches not being good because they are affected

by G-loads and turbulence causing the float to probably sink.



Actually that isn't the case.  The same centripetal force acting on the

float as

acting on the surrounding fluid not only canceling any effect but multiplying

the buoyancy of the float by the increase in 'g'.  So if it floats, it'll

float

even better under higher g's. If it sinks, it'll sink harder under g's.  In

fact

the The better way to think of it is simply by comparing densities (which is

unaffected by gravity because it's MASS divided by volume).  



I've got 3 float switches in my tank (Matteson is the mfgr - same as in

Aircraft

Spruce) the lowest (at about the half mark) to turn on pumps, the middle to

turn

off pumps and the highest to signal a light.  I also have a both wing tanks

plumbed through a fuel flow transducer feeding a panel gage so that I will

know

if flow to the header tank isn't nominal.  I'm planning to use the VM-1000

system to warn of low fuel should a pump or relay fail.  The Lancair Avionics

people did the design and put a nice little relay and harness package

together.

But I didn't think about what I would do if a relay fails and I get the

warning

but I only have a few gallons left.  I'll have to think that failure mode

through.  Thanks for the warnings.



Ed de Chazal

Rochester Michigan