Shaft seal assembly for a rotary machine

In a fluid-to-fluid shaft seal assembly wherein a high pressure sealing fluid is maintained between shaft and a machine to prevent a working fluid contained within the machine from passing therebetween, apparatus for reducing the pressure of said high pressure fluid comprising:

• an annular seal member encircling the shaft within the sealing region and including an annular breakdown bushing having a close running fit with the outer periphery of said shaft for throttling said sealing fluid moving from a high pressure fluid injection regin to a regin of lower pressure, said breakdown bushing including an axially extending pressure, said breakdown bushing including an axially extending step-like portion of constant diameter spaced a relatively small distance from the outer periphery of said shaft and disposed immediately adajacent to said fluid injection region to restrict the flow of fluid moving from said region, the flow of fluid through said restricted flow path developing a radially acting hydrostatic force on the surface of said step-like portion to move said seal member radially outward with respect to said shaft, and an annular seal ring intergrally connect to said breakdown bushing to prevent the working fluid from escaping into said flow pressure region, the center of gravity of said seal member being positioned radially above the center of said step-like portion whereby said radially acting hydrostatic force acts in opposition to the radially acting force generated by the weight of said seal member to radially center said seal member with respect to said shaft.