The multi-piped impeller (MPI) is a completely new, patented approach to the design of the impellers of pumps operating with a very low specific speed n(q) < 10. Such a construction is a development of the concept of a pumping disc with drilled holes (a drilled impeller). In order to identify the flow phenomena in such an impeller, numerical calculations were done taking into account the influence of the grid size and turbulence model on the accuracy and time of the calculations. The numerical model was validated by comparison with experimental results. The calculation results were presented and discussed. (C) 2013 Elsevier B.V. All rights reserved.