The Kingsbury thrust bearing in a steam turbine is designed to maintain which type of shaft alignment?

• A. Radial positioning
• B. Angular positioning
• C. Axial positioning of the rotor shaft
• D. Torsional alignment

Answer: (C)

The question is testing what a Kingsbury thrust bearing is primarily meant to do in a steam turbine. It is designed to maintain axial positioning of the rotor shaft. This type of bearing supports the axial thrust that the rotor experiences from steam pressure and inertia, keeping the rotor centered along the shaft axis so there’s a stable, correct distance between the moving rotor and stationary components like diaphragms and seals. Maintaining this axial position is crucial for proper clearances, smooth operation, and preventing rubbing.

Radial positioning and angular positioning are handled by other bearings and alignment systems that deal with side-to-side movements and tilting of the rotor, while torsional alignment relates to twisting along the shaft, which is not the primary function of a thrust bearing. The Kingsbury design uses a hydrostatic or hydrodynamic oil film with tilting pads to provide stiffness in the axial direction, helping keep the rotor in the correct axial location even under varying loads.