The performance of a mixed-flow three-stage pump having a stage specific speed Ns = 2630 (rpm, gpm, ft) or nq = 53 (rpm, m3/s, m) — commonly known as a “bowl” pump — was improved by nearly five (5) percentage points by substantially increasing the number of vanes in the bowl-type diffuser. analysis showed a large field of unintended swirling flow emerging from the exit of the original diffuser. The solidity of the improved diffuser was much greater than conventional design practice would indicate. Yet this was needed to eliminate separation of the radially inward diffusing flow from the vanes as they effectively guide the fluid into the axial direction, thereby enabling the following stage(s) to generate the intended head and so achieve the intended efficiency. This apparently radical approach appears to be necessary in order to overcome the tendency of the circumferential velocity component of the flow from the impeller to increase as it is transported to the smaller radii of this radial inflow diffuser configuration.