Fuel leaking BETWEEN main tanks?

[skymstr02]

Please see the attached fuel system schematic for an O-2A. Check to ensure that the "EMERGENCY CROSS-FEED SELECTOR VALVE" is fully rotated to the "CLOSED" position. This is the only way that you can cross feed the AUX tanks. It is also a sole source of uncommanded fuel transfer in an unlevel condition.

It could also be leaking internally.

The only check valves in the fuel system are used in the return fuel from the fuel pumps to the main tanks, and the maint tank vents, so don't chase ghosts looking for leaking check valves.

Myself, I turn both fuel selector valves to the "CLOSED" position in my shut down checklist. This also helps to keep the valves from binding.