Shaft seal assembly for high speed and high pressure applications

Abstract

A seal assembly is provided for reducing the escape of fluids from between a housing and a shaft rotatably mounted in the housing. The seal assembly comprises a pair of seal rings resiliently connected to each other and disposed in side-by-side relationship. In each seal ring, both the internal bore surface and the radial face which faces away from the other seal ring are provided with a plurality of equi-spaced recesses known as Rayleigh step pads. The seal faces referred to are located adjacent a seating surface of the housing. Under normal operating conditions, the seal assembly is stationary with respect to the housing, and the recesses generate lift, keep the assembly spaced from the rotating shaft and allow slip therebetween. Due to expansion of the shaft resulting from rubbing contact with the seal assembly, the seal assembly can seize on the shaft, and slip will then occur between the radial faces and the housing. The shaft will subsequently cool down due to the reduction or elimination of rubbing contact between the shaft and the seal assembly, and the seal assembly will heat up with resultant thermal expansion due to rubbing contact with the housing. As the seal assembly expands, slipping once again occurs between the seal assembly and the shaft. Thus, the seal ring assembly provides thermal stabilization. Preferably metallic bands are shrunk fit about each of the seal rings which are comprised of carbon graphite, so as to match the coefficient of expansion of a metallic shaft and the seal assembly.