Mike Wills wrote:

At 11:56 PM 6/7/99 -0700, you wrote:

VMAZDA@aol.com wrote:

 Have been reading the e mail about fuel return. I am using two fuel pumps,
one between the wing and the air frame at each wing. I am using a switch to
turn on either or both pumps. My fuel return will go through what use to be
the fuel selector valve and back to each tank. I will also have a balance
tube from tank to tank with a manual valve. The balance tube is used in

case

one of the pumps fail or I forget to switch the fuel return to the right
tank. Here is a picture of how I attached them to the plane.

VMazda
Vince Hearn

Guys,

 I had pretty well settled on using Ed Anderson's unvented header tank
approach until seeing some of the comments regarding vapor lock in this
approach. I seriously doubt that vapor lock would be a problem in my
application since the header tank is on the cockpit side of the firewall.
But now I'm wondering if I'm simply adding unnecessary complication and
weight.

 Funny thing is I originally intended to switch both supply and return
lines so when I built my fuel tanks I installed return lines in both, so
returning to that option is easily accomplished. The major reasons I bailed
out on that approach in the first place were:

1) Couldnt find a ganged selector that was of decent quality. That is
resolved by the selector from Andair mentioned yesterday or by using
Vince's approach above.

2) The header tank solves the problem of unporting a fuel pick-up. In the
RV tanks I can visualize how this could easily cause a problem in a
sustained turn when the up wing tank is selected. I'm not sure in practice
just how big a problem this would be.

Only if you are sliping Mike. In a coordinated turn the gravity vector
points stright down relative to the airplane. The same as stright
and level flight.

 So the question is what is the down side of the approach that Vince
describes above with a high pressure pump on each tank fed to a simple T
and relying on the pump's internal check valve to prevent pumping fuel from
one tank to another?

This discussion has been one of the most valuable Ive seen since joining
this list.

Thanks,

Mike Wills

Assuming you are running both pumps on take off
I can think of only one and that is if one pump fails in the
air and that is the fullest tank you have no way for the other
pump to transfer fuel from the fullest tanks. No real problem
if you have enough fuel in the tank with the good pump to find
a place to land. Perhaps another subtle problem would be if you
forget and slip the airplane with the active pump/wing tank 
down the pickup could become uncovered and the engine could quit.

Whereas a vented sump tank being gravity fed from both wing tanks 
and dual pressure pumps sucking from/or immersed in that one tank 
would solve those particular problems.

You could have one return line feeding a selector so the fuel could
be returned to the fullest tank minimising the heating of the fuel.
No real need for a ganged selector.

For handling slips gravity ball check valves could prevent flow out
of the sump tank into the low wing tank.

Only two pumps would be required and one of course could act to back up
the other. The size of the sump tank need not be very large.

Paul 

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