And there is no problem with venting the sensor to atmosphere as the tank shouldn't be pressurized while standing still.  What I don't know is whether anyone would be willing to buy such a thing (probably about $100).  Might be a good stocking stuffer for the pilot who has everything else.  Any potential interest?

Gary,

 

Everybody's past experience leads them to different sensibilities.  I accumulated over 1100 hours in a Skymaster while I was building my Lancair.  With extended range tankage, I had six tanks, three to a side, wired to the "brain" to compute fuel gauge displays that were never accurate no matter how much money was invested in the system.  They weren't accurate even when they read empty (a random gaming event).  The fuel flow was implied by measuring the fuel pressure.  While it had selector valves, they were only needed for cross feed if flying a long distance on one engine.  It was a simple system, everything on the Right meant something to the Rear, everything on the leFt meant something to the Front.  One flew by time, fill up to the 122 gal limit, consider 118 as usable, roughly guess 22 gals per hour unless flight time had to be stretched and then verify the time vs usage value at each top up.  High wing tanks provided a gravity boost to the pumps.

 

I learned that I liked simple and I preferred accurate.  No timing tank switching for me.

 

Thus, on the Lancair, the VM fuel reporting system satisfied the accuracy requirement for all tanks and the fuel flow rate. A "keep the header tank full" automatic system satisfied the simple requirement.  Pumping from both wings simultaneously meant that the lateral trim never has to be adjusted (ergo, no aileron trim on the stick) once trim is set for the flight.  There is no selector valve.  The wings can be pumped "dry" during level flight - all but a cup of the fuel is usable from those sources.  The header tank is a deep sump, properly baffled so that all 8+ gallons, but for a quart or two, is usable regardless of pitch, except under extreme uncoordinated flight.  The boost pump and engine pump never have to suck up, just assist gravity.  If the main aircraft power is completely lost, there are at least 8 gals in the header to get me somewhere suitable for landing or crashing, whichever comes first.  Careful tank calibration and a fuel flow sensor give very accurate level readings and total fuel used values, verified at each top up.  Uh, I still fly by time though, just as a backup.

 

I have everything I want relative to fuel (except a CO2 energy pump) and my plump body has stuffed my stockings quite nicely.  I am not a candidate for your clever and sophisticated device.  Others may have different requirements.