<... Jim, this is exactly the system I have been thinking of except for the sump to tank vent. Why do you suggest not venting the sump? It seems to me that any gasses or vapor that do get in the sump will eventually displace the fuel ...> 
In my scheme the only path to the only access to the sump is from the main "Supply" tank.  All you can draw into the sump is what's in the lowest point of the Supply tank.  OTOH, if fuel is "reluctant" (for any reason - like a leaking fuel cap on the low pressure surface of the wing) to gravity feed to the sump, the pump will "suck" it down from the Supply tank.  That's exactly how I worked around the transfer problems in my Velocity - I installed electric valves between each strake and the sump.  If for any reason one strake is reluctant to transfer, I can de-select the tank that's transferring OK and suck fuel from the reluctant tank (this would be impossible if the sump were vented). 

Both "suck" and "reluctant" are relative terms since the head pressure between the strake and the sump is quite small - 0.3 psi with full strakes, 0.1 when empty.

That's why I believe sumps should be a closed system .... Jim S.


Tim Andres


Tim Andres wrote:

Jim Sower wrote:

 
My own (personal) recommendation is:

Large (>1/2") gravity feed from Right ("supply") strake to Sump;
Sump feeds engine; return from rail to Right strake;
Have a facet pump that transfers fuel from Left ("transfer") strake to Right;
Sump vent is capped off (and only uncapped to initially fill the sump);
ONLY fluid path into sump is from "supply" tank;
"Transfer" tank feeds ONLY the "supply" tank.

Dirt simple, as reliable as it can be, does require some fuel management (which if I can't handle, I shouldn't be flying unsupervised :o).  Simple warnings and other simple gizmos can assure more timely fuel management.

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