The only safe way to have a "Both"-selection for a low wing would be (IMHO), to have a low pressure pump in each tank feed a fairly large sump ( 2 gallons +) with a system as described by Georges below:

EFI pump picking up at the bottom of the sump, with a return to the top and baffels, not just separating the top from the bottom, but also side from side, so when a tank pump starts to pump air into the sump, it can vent to the top of the sump and out through the vent, which would have to go to both main tanks.

With some additional cross-feed line from one tank to the other with a manual valve, one could use one tank pump as the back-up for the other:

Open the crossfeed valve and slip the plane accordingly for a while. That should push the fuel into the other tank, in case one of the pump fails.

One question remains: How would you prevent or equalize overflow from the sump to the tanks?

Thomas J.

----- Original Message -----

From: Echo Lake Fishing Resort (Georges Boucher)

To: Rotary motors in aircraft

Sent: Sunday, May 29, 2005 8:07 PM

Subject: [FlyRotary] Re: will EFI pumps pump air was Re: Fuel Tank Selection

Group FWIW

Call it a sump or header tank, if its large enough say 3 liters oops! I mean quarts with both pumps picking up fuel at the bottom 1/4 of the tank with the fuel return pointing at the cover to avoid aerating the fuel in the header (possibly a baffle below it & a vent pipe to each tank) Gravity feed would work in a high wing , in a low wing I think you still need a low pressure transfer pump to push fuel to the header tank from the mains. I don't think it is safe to have "Both" position in the fuel selector except in a gravity system with carburetors, not with EFI, the possibility of "sucking air "is unavoidable without check valves ( more weight, more cost & more possibility of problems).

Georges B. ( Not really stirring the pot, maybe just a little)

-------Original Message-------

From: Rotary motors in aircraft

Date: 05/29/05 17:42:01

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: will EFI pumps pump air was Re: Fuel Tank Selection

   Now I'm not so worried, because each high pressure fuel
pump draws from it's own tank and the only point of inter- connection is where the lines join at the fuel rail(s).

This brings up a question that I've had before, and I'm not sure this is exactly what anyone is doing, so it's not meant that way.

Say you have two tanks, with an EFI pump for each tank.   You then connect the output of each pump together, feeding into one line running to the fuel rail.   The question is: What happens when one tank runs out of gas? Will the EFI pump move enough air through it to disturb the fuel rail pressure that's being delivered from the other pump, or would it just stop pumping at that point, and do no harm (other than maybe burning the pump up eventually)?

Yep, still trying to figure out how to fix my fuel transfer system.

Cheers,

Rusty

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