Annular Pressure Seals and Hydrostatic Bearings

The lecture introduces annular seals and hydrostatic bearings in liquid pumps. The analysis details the physical principle for generation of a direct stiffness in these mechanical components. Annular seals as neck ring seals and interstage seals restrict leakage but also generate force coefficients, stiffness-damping-inertia, greatly affecting the rotordynamics of liquid turbopumps, in particular those handling large density fluids. Highlights on the bulk-flow analysis of annular seals are given with details on the performance of two water seals long and short, featuring the advantages of an anti-swirl brake to enhance the seal rotordynamic stability. Hydrostatic bearings rely on external fluid pressurization to generate load support and large centering stiffnesses, even in the absence of journal rotation. The load capacity and direct stiffnesses of hydrostatic bearings do not depend on fluid viscosity, thus making them ideal rotor support elements in process fluid pumps. Current applications intend to replace oil lubricated bearing with hybrid bearings to improve efficiency with shorten rotor spans and less mechanical complexity. Current cryogenic liquid turbopumps implement hydrostatic bearings enabling an all fluid film bearing technology with very low number of parts and no DN limit operation. Details on the bulkflow analysis of turbulent flow hydrostatic bearings are given along with the discussion of performance characteristics, static and dynamic, for hydrostatic bearings supporting a water pump. Angled liquid injection produces a hydrostatic bearing with unsurpassed dynamic force and stability characteristics.