Abstract: The invention relates to a pumping set for plants carrying water, comprising a split-tube motor and a rotary pump driven by the same, the impeller of which is located on the extremity of the shaft present in the pumping space, said shaft being carried by two radial anti-friction bearings situated at either side of the rotor stack of laminations, and consists of ceramic material at least in the area of these anti-friction bearings and is longitudinally movable with respect to the ceramic bearing rings of the radial anti-friction bearings under forces acting axially on the impeller, the maximum length of this longitudinal displacement being limited by two axial anti-friction bearings. An annular groove is provided in the shaft directly adjacent to each of the two bearing areas of the radial anti-friction bearings, that is to say in each case adjacent the extremity of these bearing areas directed towards the impeller, and that the said distance is smaller than the width of the annular grooves.