Abstract: Erosion of parts owing to cavitation in the part-load region of operation of a centrifugal pump is reduced or eliminated by equipping the pump with an annular diffuser which is installed upstream of the annular intake of the impeller. The impeller portion immediately downstream of the inlet edge, where the vanes begin, is bounded by a surface which diverges at an angle of 8 to 20 degrees, as considered in the direction of fluid flow in the impeller. The diffuser has a smaller first cross section which is remote from and a larger second cross section which is nearer to the impeller. The area of the smaller cross section is between one-half and nine-tenths of the area of the larger cross section. If the diffuser has a conical internal surface, the angle of divergence of such conical surface (as considered in the direction of fluid flow toward the impeller) is between 5 and 15 degrees. If the diffuser is internally stepped, the ratio of its length to the diameter of the larger cross section is between 0.