i wanted to revisit this issue from May this year.  My velocity plans
   call for a low, wide sump tank mounted on the cabin floor near to
the firewall.
   I would guess it is only a few gallons in capacity.
  Am I correct in abandoning the sump in favor of plumbing the system
   so that the fuel selector routes the return fuel back to the tank
from which it is drawn,
   as in your drawing below?  What is the purpose of the sump tank anyway?
jeremy solomon



No kidding. "A long wide sump". That is dumb. I guess you are not supposed to slip or make uncoordinated turns. EFI engines will quit right now if the fuel
pickup becomes uncovered. What you want is something like one of these illustrations.

No dwg was included. If you want one sump tank make it tall and skinny
mounted in the center as low as possible. Can be mounted on the engine
side of the firewall.

The purpose of a sump tank is so a one layer  selector valve can
be used and return fuel is sent back to the sump tank.

Paul Lamar

Isn't there a danger of over pressurizing the sump if the fuel is
returned to it?  My thinking is to use a twin selector and lose the
sump, thereby simplifying(?) the fuel system.  I pulled the attached
diagram from an earlier post.
jeremy solomon

No. More fuel is used out of the sump tank than goes back to it or
the engine will quit.

It is possible that gravity feed will keep the tank full but
the pressure in the tank cannot be higher than the gravity head
From the strake tanks which is probably not more than 10 to 18 inches.
What you want to be careful of is don't face the tank vents into the air stream.
With some configurations that can empty a tank in a few minutes.

Again with no sump tank you can uncover the fuel pick up in a slip, a steep decent or an uncoordinated turn. This is particularly true when the tank is near empty. Not as good a configuration. Stick with the tall skinny sump tank. That is best.

Jerry Hey can weld one up for you.


Paul Lamar