Thanks for the input.

Both tanks are above the sump and most of the sump is above the fuel pumps.  The "hump"  or length of tubing would probably mot be longer than 6".  Main tanks feed the sump through a 2" X 3" opening.  If the fuel level is at the point where the tubes exit sump to feed the pump there is less than a pint of fuel on board.  Buly, the Limo EZ is a stretched Long EZ.

Joe

 

Joe;

 

A hump in the plumbing is not necessarily and issue, but your situation as I understand it is questionable.  The head at the pump inlet (neglecting line losses) is the difference between the level of the surface of the fuel and the pump inlet.  Any hump should not go higher than the surface of the fuel when the fuel is at its lowest point.

 

If I understand your case correctly, you would have to rely on siphoning to get gravity feed from your tank below the level of where the tube exits the tank; or if you are pumping out of the tank, the pump could normally draw that last 1.5 of fuel out, but in either case I d say this is not a desirable condition, as it will take a negative pressure, however slight, to get it out.  With 100LL it would probably not be a problem as it is formulated with a higher vapor pressure than mogas.

 

The other issue with a high spot in the plumbing is the potential for trapped air.  When you fill from an empty condition there will be air trapped at the high point.  That s not necessarily an issue; if it has some place to go, like the sump tank with a vent, and enough head to push it through.  If you partially filled your tank with air trapped in the line you may get no flow.

 

The supply line from the tank needs to go steadily down hill, either to a pump or gravity feed to a sump tank. Any air in the line should be able to migrate back to the tank.

 

FWIW - I don t know the details of your system, so can only speak in generalities.

 

Al