...snipped
> One point that I should clarify, so that my ruminations here would not
> seem so pointless.  I've been considering a returnless system.  A single
> tank is located high in the back of the airplane.  If I locate the
> pumps, filters and gascolator back under the tank (advantageous for W&B
> and positive head to the pumps), and just run the single supply line up
> front, then I would have to find a valve that would reliably operate
> under elevated pressures.  But having a pump that blocks flow when it
> isn't running immediately begs the question of, "What is the point of
> the valve?"  Not thinking for a moment that I know it all, I present the
> question here.
..snipped

Ball type valve will always work - at least under the pressures you will be
using in a gasoline engine application!
As mentioned, what if you can't shut off the pump, because your the
electrics just got burned?
"Putting out fire with gasoline ?!!"

Thomas J. (listening to a David Bowie classic..:))