It would seem the line from the fuel pump to the header tank will have fuel in it because of header tank slosh back from taxi, turns, climb and turbulence, etc. unless a check valve is in the line. 

Rob, et al,

 

Hmmmm...

 

Let me describe my setup and experience.

 

1. Automatic "header full" system keeps the header tank between 8.25 and 9 gallons at all times.  Lower level sensor must remain at the lower level for about 15 seconds before the pumps are started (avoiding start/stop cycles in turbulence).  This assures me of about 1 hour flight time in case of complete power failure, etc.  Indicators show the header full and another for "timer running."

 

2. Both pumps (located in the stub wings) are simultaneously engergized.  There are check valves at each header entry point for a variety of safety reasons - siphoning, negative pressure, etc.  The wings are emptied evenly meaning that lateral trim does not change thru the flight unless I throw the passenger out. 

 

3. Each pump has its' own pullable breaker and manual on/off switch.  This allows for non-automatic operation.  There is no fuel selector for KISS.

 

4. VM EPI 800 fuel probes are in all three tanks. They are very accurate.  All tanks produce a warning (I have annunciator lights) when they are below 4 gallons.  I would be gasping for air if the header falls below 4 gallons (ask the Don about this).  The Gallons indicator shows zero (by design) when below 2 gallons.  There is a fuel totalizer running off the fuel flow sensor, generally 2-3% high, that is another low fuel warning source.

 

5.  The automatic system is manually turned off when the header does not refill after dropping to 8 gallons and the wings have been zero for a while. This probably means the pumps are running "dry" for no more than 15-20 minutes.  Slosh, etc. probably means the pumps are not really dry for that length of time.  I have flown in this condition about ten times (including the Kitty Hawk to Dayton race leg, 10 minutes before crossing the finish line) and the pumps are still working.  The wings have been emptied in level flight with not much more than a cup of fuel remaining in each wing as later measured on the ground.

 

6.  The panel is placarded "Do Not Take Off With Less Than 8 Gallons In The Header."  There is no experience maneuvering when the header contained less than 4 gallons, although the header is throughly baffled. 

 

In flight I cannot hear the pitch of the pumps change when thay run dry because of their stub wing location - perhaps you can hear them as they are under the seat.  Maybe you could hook up an aural sensor switched into the audio panel or use a stethoscope, checking heart rate and pump pitch, when you think the wings are dry.