Design analysis of Rayleigh-step floating-ring seals

The analysis and design of a 50-mm diameter floating-ring helium buffer seal are described. The seal rings incorporated Rayleigh-step lift pads to provide hydrodynamic forces to separate the rings from the shaft. Maximum surface speed is 183 m/s (600 fps) and maximum buffer gas pressure is 1389 kPa (200 psia). An operating range map was computed as a function of speed and pressure. Contradictory problems arise due to excessive friction preventing ring tracking at low-speed, high-pressure conditions and insufficent friction to retard inertia driven motions at high-speed, low-pressure conditions. Steady-state and dynamic analyses and performance are described, as well as the results of thermal studies.