We have experimentally investigated the evacuating characteristics of a molecular viscous stage of a combined turbomolecular pump. This study has been conducted for a stage with trapezoidal channels operating in viscous or transient regimes of gas flow. The paper describes the experimental stand used to obtain the experimental data, namely, measured speed of the pump in a wide range of pressures. The obtained experimental data have been used to analyze the influence of the velocity parameters of the pump stage on its operational speed. The ways of increasing the operational speed of the pump have been determined without changing the overall dimensions of the pump as a whole. The obtained results allow to improve the evacuating characteristics of combined turbomolecular vacuum pumps and the parameters of the high-vacuum system where they are installed.