Back pressure pipes are situated on the final cell discharge of a flotation bank. The pressure drop across the valve is commonly exaggerated due to the downstream pipework arrangement. To improved performance of the final cell and to reduce the pressure drop across the final valve, a back pressure pipe is used to decouple the downstream pipework from the cell. This not only assists the performance of the valve, but will also recover half the height of the cell across the entire bank. For commonality of spares, the valve can now be identical to the intermediate valves upstream.