Effects of Hydraulic Forces in Annular Pressure Seals on the Vibrations of Centrifugal Pump Rotors

Abstract

In centrifugal pumps, the annular clearance spaces of the leakage path, i.e. impeller seals and balance piston seals, act as powerful hydrostatic bearings with turbulent flow. In the present discussion, the dynamic forces due to these bearings acting on the rotor are analysed, including the effect of squeeze action, i.e. the effect of velocities of separation or approach of the bearing and journal surfaces. Synchronous forced whirling is analysed in a simple idealization comprising a single mass rotor, including the estimation of amplitudes as well as critical speeds. Large damping forces due to squeeze action are found, in qualitative agreement with experimental work by Marcinkowskij and Karincev (3)†. A simplified treatment of the effects of fluid rotation is included in the analysis of rotor vibrations, leading to an analysis of high speed whip instability onset.