Axial Thrust of Mixed-Flow and AxiaL-Flow Impellers
The axial thrust in radial impellers is produced by the static pressures on the impeller shrouds. Axial-flow impellers have no shrouds, and the axial thrust is created strictly by the difference in pressure on the two faces of the impeller vanes. In addition, a difference may exist in pressure acting on the two shaft hub ends, one generally subject to discharge pressure and the other to suction pressure.
With mixed-flow impellers, axial thrust is a combination of forces caused by the action of the vanes on the liquid and those arising from the difference in the pressures acting on the various surfaces.Wearing rings are often provided on the back of mixed-flow impellers, with either balancing holes through the impeller hub or an external balancing pipe leading back to the suction.
Except for very large units and in certain special applications, the axial thrust developed by mixed-flow and axial-flow impellers is carried by thrust bearings with the necessary load capacity.