The Metso DR flotation machine is the first mechanical open type machine to incorporate a vertical circulation of pulp, made possible by combining a “recirculation well” with the distinctive top feed impeller. 

This arrangement provides positive vertical circulation of pulp similar to the action in a propeller agitator. 

Pulp from an intermediate zone of the cell is circulated down into the eye of the impeller, mixed with air, and diffused out over the entire bottom of the cell, creating a uniform upward current. 

This principle varies from most other mechanical open type cells which circulate pulp by lifting it up from the bottom of the cell into the centre of a rotating element.