Radial force generally means a force exerted in a radial direction towards the centre or away from the centre. When a body or fluid element with mass moves in a circular path, an equilibrium exists in the radial direction between the outwardly directed centrifugal force (inertia force) und the inwardly directed centripetal force (acceleration force).
In centrifugal pumps, radial force (also radial thrust) is the term used to designate the force acting on the pump rotor. The radial force at the rotor of a centrifugal pump determines the bending load and resulting bending deformation of the shaft and the load on the radial bearings.
The resulting radial force at the rotor of a centrifugal pump comprises the hydraulic radial force generated by hydrodynamic processes, and mechanically influenced components from the effect of an unbalance and (in the case of a non-vertical pump shaft) the weight of the rotor parts themselves.
The hydraulic radial force at the impeller of a centrifugal pump is (in the case of radial and mixed flow impellers) assumed to act on the centre of the impeller width at the outlet. In relation to the fixed reference system of the casing, it is possible to distinguish between non-rotating and rotating (e.g. rotating at the pump's rotational speed, like the unbalance force) and, in terms of time dependence, between steady and non-steady (mainly periodic) force components. The hydraulic radial force at an impeller contains both steady and non-steady components.