The unsteady characteristics and local loss mechanisms of a single-blade and a two-blade pump are investigated by a combined experimental and numerical study. These pumps are designed for solid-laden fluids and clogging-prevention and thus have particular large flow channels with a weak flow guidance, which cause highly three-dimensional fluctuating flow fields and low efficiencies, so that their operation cannot be adequately described by stationary characteristics only. Thus, additional unsteady characteristics in terms of time-resolved pressure, impeller deflection and flow rate are analyzed. For evaluating the flow rate fluctuations, a new measurement method is presented based on an electromagnetic flow meter. With ensemble-averaging, interfering signals acting on the time-resolved measurement signals are filtered out. The validity of the new measurement technique is assessed by accompanied 1D circuit simulations. Due to the clogging-resistant impeller design, common design concepts for centrifugal pumps cannot simply be adopted and the sole evaluation of the efficiency is not sufficient for few-blade pump optimizations. Thus, a local loss analysis based on local entropy production is presented and applied to the single-blade and two-blade as well as a conventional multi-blade pump. A finite volume method and a statistical turbulence model are employed for the 3D simulations. The simulation results are validated by time-resolved measured characteristics of the pumps. A wall function for entropy production in isothermal flow is derived, implemented in the flow solver ANSYS-CFX and validated on standardized turbulence model test cases. The local loss analysis revealed distinctive pump type specific loss mechanisms in all three pumps.