Another Buoyancy Concept

[not2smart]

Sorry if this has already been proposed. 

Basic idea is a submerged U-shaped tube, flooded on one side and pumped full of air on the other, closed at the top with an airlock. 

1) heavy buoyant spheres are dropped from an air lock down the air -filled side of the shaft.
2) momentum carries them around the curve of the tube where they float back to the surface on the opposite submerged side of the tube. 
3) The buoyancy of spheres collecting in the tube provide the energy to push the top spheres back up a set of rollers onto the top of the air lock. 
4)repeat.

So the only energy input requirement is operating the airlock against the air pressure in the tube below.  Is there any way this system can create enough energy to do that?