I'm building an LNC2 with a header tank.  I want to use the Pillar Point fuel
sensor to determine when the wing tanks are empty.  I would send this signal
to Jim Frantz's annunciator panel -- when the yellow light goes on I can turn
off the fuel pump.

By the way, Pillar Point makes a nice system that does all this automatically
but I already have an "automatic" fuel transfer system (Wayne Lanza built it
for me well before Pillar Point built theirs) that monitors header tank level
and cycles the Facet pumps as required.  Unlike the Pillar Point system,
though, it has no way of knowing when the wing tank is empty, so the pump would run
indefinitely.

My plan is to put one of these infrared gizmos in the fuel line between the
wing tank and the header tank.  It would be okay to put this in the line
between the wing tank and the fuselage-floor-mounted Facet pump, but it would be
easier to put it downstream of the Facet pump.  (The wiring would all stay in the
fuselage and I've already made the aluminum tubing inside the fuse that
connects to the pump inlet, plus mounted the pump to the floor.  Changing this
would be a pain.)

My question is whether there will ever be air downstream of the Facet pump.  
Or will the line between the pump and the header tank inlet always have fuel
in it?

Thanks in advance for the comments.

- Rob Wolf