The blade slip factor significantly influences the prediction accuracy of the self-closure one-dimensional flow model for side chambers of centrifugal pumps. Wiesner's and Stodola's slip factors, which are used to formulate the blade outlet pressure and served as the boundary condition for the model, are examined, which is an improvement of the previous study (Gu et al., 2020, “A Pressure Model for Open Rotor–Stator Cavities: An Application to an Adjustable-Speed Centrifugal Pump With Experimental Validation,” ASME J. Fluids Eng., 142(10), p. 101301). Both computational fluid dynamics (CFD) simulations and experiments for the centrifugal pump are conducted to support the improvement. A good agreement exists between the performance at the best efficiency points (BEPs) of different rotating speeds obtained by simulations and experiments. Through the CFD analysis, the flow in the impeller remarkably deviates from the blade-congruent flow, especially in the quasi-triangular regions downstream of the throats. Meanwhile, the reason for pressure over-predictions of the side chamber one-dimensional flow model that embeds Wiesner's slip factor (FMW) is that Wiesner's expression underestimates the impeller flow deflection and overestimates pressure boundary. By contrast, the side chamber one-dimensional flow model with Stodola's slip factor (FMS) is closer to CFD in terms of relative flow angle and chamber inlet pressure. Compared with the side chamber pressure measurements, the accuracy of FMS is upgraded approximately by 3.5% than FMW. At the BEPs of different rotating speeds, FMS generates lower shroud thrust coefficients but slightly greater volumetric efficiencies than FMW. This work provides a simple approach to better calculate flow characteristics in the side chambers.