A
line shaft pump includes a drive unit and a hydraulic unit. A riser tube of the hydraulic unit includes an outer surface and an inner surface, and is arranged vertically between an
impeller section and a
discharge head. An essentially impermeable
lubricant retention tube is arranged within the riser tube and surrounds a
line shaft, providing an essentially
vertical channel delimited in a radial direction by the
line shaft and the
lubricant retention tube. A hydraulic section includes a centralizer to receive the riser tube, the centralizer is in intimate contact to the outer surface. Radial dimensions of the centralizer are smaller than radial dimensions of an inner well surface, and the radial distance between the outer surface and the inner well surface is essentially constant in all radial directions at an axial position of the centralizer, and the centralizer includes an additional axial through hole.