The numerical and experimental investigation of impact of stay vane number on the flow patterns and efficiency of a pump-turbine model at heads up to 200 m in turbine and pump modes are presented. The study was conducted for two variants of flow parts, which consisted of spiral casing with stay vanes, guide vanes, runner, and draft tube, and differed in the number of stay vanes: 20 in the original variant and two times less in the modernized one. Numerical studies of incompressible viscous flow were carried out using the Ansys CFX software. The flow structure was presented and analyzed, the distribution of radial and circumferential velocity components was compared, as well as the flow angle in the gap between the stay vanes and the guide vanes blades. Experimental tests were performed on the hydrodynamic test stand of the IEMS hydraulic machinery laboratory. The blades and rim of the runner were manufactured using 3D printing technology. The efficiency hill chart in turbine mode at the given speeds, which correspond to the best efficiency mode and the minimum, nominal, and maximum heads at the Dniester PSP are shown. In pumping mode, a comparison of efficiency and head at the optimal opening of the guide vanes is given. It is concluded that the double reduction of the stay vanes worsens the energy characteristics in turbine mode, but improves them in pump mode.