Can the inlet be fed from a tube

that goes into a tank close to the bottom 1.5" but is bent down in a 90

degree bend? The sump is lower than the tanks and the pumps would be at the

level of the bottom of the sump. My concern is how much of a "hump" in the

plumbing will the pump tolerate?  Thanks for any help.

 

Joe Berki

 

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