Abstract—The known information of satisfactory correlation of calculated and measured stator part performances is a foundation for the numerical investigation. Stator parts «Vane (vaneless) diffuser + crossover + return channel» of stages with different specific speed were designed in accordance with standard recommendations and investigated by CFD calculations. Flow structure demonstrated advantages and disadvantages of design. Flow separation in crossovers was eliminated by its shape modification for stages with diffusers relative width of diffusers. The stage with medium flow rate and low loading factor was designed with traditional and modified crossovers. Calculated efficiency performance becomes better. The information obtained is useful for design method better calibration.