Patent ID: 6789804
Filing Date: 2004-09-14
Classification: F04D,F16J

Abstract:
In a dry gas seal for centrifugal compressors of the type having a pressure chamber which houses a rotating compressor member that is driven by a compressor drive shaft, the improvement comprising:a housing having a generally hollow interior shaped to receive the compressor drive shaft therethrough, and an annularly-shaped channel disposed concentric with the compressor drive shaft and including an open end thereof opening into said housing interior, and a base end thereof configured to communicate with the compressor pressure chamber and associated process pressure therein; means for pressurizing said housing with a buffer gas during compressor operation; a rotor disposed within said housing, configured to be received on and connected with the compressor drive shaft at a predetermined location thereon, and having a radially extending sealing surface disposed a predetermined, spaced apart axial distance from said housing channel; a sleeve disposed within said housing, configured to be received on and connected with the compressor drive shaft at a predetermined location thereon, and having a generally smooth, cylindrically-shaped exterior surface; a circumferential shaft seal supported on said housing and sealingly engaging the exterior surface of said sleeve to restrict the flow of contaminates from the compressor into said housing interior, and regulate the flow of buffer gas into the compressor pressure chamber; an annularly-shaped shutdown piston slidably received in said housing channel for axial shifting therein between a retracted, open position, and an extended, closed position; said shutdown piston including a cylindrical outside surface, a cylindrical inside surface, an interior end face communicating with said housing interior and an exterior end face shaped to communicate with the compressor pressure chamber and associated process pressure therein; a circumferential piston seal operably positioned between said housing channel and said outside and inside surfaces of said shutdown piston to resist fluid flow between the compressor and said housing interior, yet permit said shutdown piston to shift axially between said open and closed positions; an end seal disposed on said interior end face of said shutdown piston, and sealingly abutting said sealing surface of said rotor when said shutdown piston is in said closed position; and a biasing member operably connected with said shutdown piston and resiliently urging the same toward said open position, whereby during compressor operation, the forces generated by said biasing member combined with the force generated by the pressure of the buffer gas acting on said interior face of said shutdown piston retain said shutdown piston in said open position, and during compressor shutdown, when the pressure of the buffer gas drops to a predetermined level, the pressure of the process gas acting on said exterior face of said shutdown piston generates sufficient force to overcome the combined forces of said biasing member and the buffer gas acting on said interior face of said shutdown piston, so as to shift said shutdown piston to said closed position to prevent contaminates from entering said housing interior.