Centrifugal pump

Claim 1

A MULTISTAGE CENTRIFUGAL PUMP COMPRISING FIRST AND SECOND RADIAL FLOW IMPELLERS FOR GENERATING VELOCITY ENERGY IN FLUID, POWER MEANS CONNECTED TO DRIVE THE IMPELLERS, WALL MEANS FORMING AN ESSENTIALLY OPEN AND SUBSTANTIALLY UNOBSTRUCTED ANNULAR INTERSTAGE RETURN PASSAGE FOR DIRECTING FLUID FROM THE FIRST TO THE SECOND IMPELLER, THE WALL MEANS INITIALLY FORMING A DIVERGING PORTION OF THE PASSAGE FOR THE FLUID LEAVING THE FIRST IMPELLER TO DIFFUSE THE VELOCITY ENERGY IN THE FLUID AND TRANSFORM IT TO PRESSURE ENERGY AND THEN FORMING A GENERALLY CONSTANT PORTION OF THE PASSAGE TO EFFECTIVELY PRESERVE SUCH PRESSURE ENERGY AND DIRECT THE FLUID RADIALLY INWARDLY TO THE SECOND IMPELLER, THE LATTER PORTION OF THE PASSAGE BEING VANELESS TO AVOID SUBTRACTING ENERGY FROM THE FLUID THEREIN, AND MEANS MOUNTING THE WALL MEANS FOR ROTATION TO DECREASE THE RELATIVE SPEED BETWEEN THE WALL MEANS AND THE FLUID FLOWING FROM THE FIRST TO THE SECOND IMPELLER TO REDUCE SKIN FRICTION LOSSES IN THE ANNULAR INTERSTAGE RETURN PASSAGE.