This paper presents experimental and numerical results obtained with micro rotary shaft pumps (RSP). Impellers with a diameter of 2.5 mm, different outlet widths and blade number were coupled with semicircular volutes with different eccentricities. Experimental data for every impeller–volute couple were reported and include the flow rate, head and overall efficiency. Different rotational speeds were tested up to 24 000 rpm, obtaining pressure increases up to 5.7 kPa and flow rates up to 80 ml min⁻¹. The non-dimensional performance was also computed obtaining the maximum head coefficient of 0.49 and the maximum flow coefficient of 0.138. Furthermore, experimental data were compared with 3D time-dependent CFD simulations. The focus of the simulation was to study the flow field structure inside the impeller and in the volute. Moreover, CFD data allowed for the calculation of the hydraulic efficiency of the pump and for the impeller to highlight the stator rotor interference influence on the pump characteristics, as well as to show the distribution of losses inside the volute.