CLOSED IMPELLER C043
The impeller vanes are enclosed by two shrouds. Replaceable wear rings restrict internal recirculation to the suction side of the impeller. Closed impeller pumps need wear rings because you cannot adjust the impeller clearances against the volute or back plate.
In a closed impeller pump the suction eye diameter is taken as the smallest inside diameter of the shroud. In determining the area of the suction eye the area occupied by the impeller shaft hub is deducted. The hub is the central part of the impeller that is bored out to receive the impeller shaft.
Closed impellers are very efficient as long as the wear ring clearance is within tolerance, but the shrouded vanes can clog up easily with “stringy” material or solids.