Seal ring for valve stem

A sealing ring disposed with a plurality of ring elements in a gap between a valve stem and a valve housing for the stem to prevent fluid under pressure from flowing between the stem and the housing, said sealing ring comprising:

• i) a relatively rigid annular base of generally rectangular cross-section circumscribing a central axis and directed toward a downstream direction between the two members, and a pair of relatively flexible sealing lips formed in one piece with said base and extending outwardly from a side of said base in an upstream direction, said sealing lips defining an annular cavity disposed in a plane substantially normal to said central axis and opening toward the upstream direction and each of said sealing lips has a sealing edge on an outer surface thereof in sealing contact with one of said valve stem or said valve housing, and
• ii) an expander ring disposed in the cavity between the sealing lips,
• each of said sealing lips narrowing down between said base and said sealing edge to a cross-sectional dimension which is between 0.033 inches and 0.041 inches at the narrowest point along the lip,
• said expander ring also having a maximum cross-sectional dimension at the midpoint of the expander ring in a direction normal to the central axis which is between 74% and 94% of said predetermined distance, and each of said sealing lips having a maximum radial dimension about a plane through said midpoint and normal to said central axis which is between 3% and 13% of said predetermined distance.