An impeller will produce hydraulic radial thrust due to its developed head. The equation for calculating hydraulic radial thrust load is:
T = [ Kq x Kt x D2 x B2 x H x SG ] / [ 2.31 ]
T - hydraulic radial thrust load, pounds Kq - empirical capacity factor Kt - empirical radial thrust factor D2 - outer diameter (OD) of impeller, inches B2 - width of impeller opening at D2, inches H - developed head, feet SG - specific gravity of liquid 2.31 - conversion factor
Values for Kq are [ * ] and Kt are [ * ]
This equation applies to radial flow - not to axial flow or to positive displacement pumps.
In mixed flow pumps, the thrust acts at some angle from the shaft centerline so it has to be resolved to its radial and axial components. Many prefer not to do this to simplify the calculation and to use a conservative value of radial thrust.
Radial thrust acts in radial direction (perpendicular) to the shaft and will cause the shaft to deflect more. It is important to reduce radial thrust to minimize the shaft deflection and prevent the premature failures of thrust bearings and mechanical seals.
Radial thrust is used in evaluating shaft deflection, sizing and selection of thrust bearing, and in vibration and critical speed analysis.
Steps that can be taken to reduce radial thrust are included in a full version of this article [ * ].