The running wheel has a turning centre and a number of scoop elements (1) to convey a substance through a passage zone. Each scoop element has a head zone (8) and a downstream root zone (9). There are projections (2) in the root zone of at least one scoop element, projecting over a surface (5) defined by the reverse or obverse side of the scoop. The projections have a head zone facing upstream and a root zone facing downstream. The head zone narrows and the root zone may do the same. The projections may be of streamlined cross section, e.g. in the shape of an NACA profile.
