A pump is a mechanical device that converts mechanical energy into hydraulic energy. The aim of the current work is to examine the behavior of fluid flow inside a rotary sliding vane pump and assessing the performance by studying the effect of change of the rotational speed, number of vanes and the radial clearance gap size between vane tips and stator surface on the performance of the pump. The commercial finite-volume solver ANSYS Fluent was used to simulate flow behavior in the pump with an additional C source code for the description of the dynamic mesh motion. Pump flow has been studied using lubricating oil, 5W-30, as the working fluid. Several computational configurations were used for the numerical simulation. The numerical results showed that 100% increase of the number vanes decreases the overall efficiency by 46.5%, while increasing the clearance gap size from 0.025 to 0.05 decreases the overall efficiency by 9.72%, and results in a 42.85% increase in the internal leakage within the pump.