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"Not to debate the subject, but the return line teed back to the fuel line
between the selector valve and the aux pump is a short simple run. The
mechanical/aux pumps give redundancy. That is how factory, low wing, fuel
injected planes work."

I'm not sure I understand this plumbing configuration completely. The
return line is used to reduce the chance of vapor lock by keeping the fuel
moving through the line, right? Is there a check valve required anywhere in
the lines using a return as you describe, and are the engine-driven and
electrical pumps in series? Thanks.

Mike Reinath
San Jose, CA

[The logical location for the fuel pressure regulator on an injected
engine is downstream of the fuel distribution manifold which feeds the
injectors.  Depending on the injectors used, they will require some fixed
pressure to deliver the proper amount of fuel over a given injection pulse
time period.  The fuel pump is delivering fuel at some higher pressure
than that which is required of the injectors... the regulator bypasses
the excess fuel to maintain the proper pressure, and that is the return
line we are talking about here.  I hope this helps answer at least that
part of your questions.    <Marv>  ]
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