Mechanical seal

Abstract

A balance ratio for a stationary seal ring is designed to allow a seal face to be opened when, with a rotary seal ring at standstill, steam of a predetermined pressure is supplied to an endo-fluid region while a sealing-fluid region is brought into an exhausting state. On the other hand, an O-ring constituting a secondary seal portion is retained by a groove formed in a flange portion of a seal case, thereby preventing a force on the O-ring from affecting the stationary seal ring even when the steam is supplied to the endo-fluid region.

What is claimed is:  
     
         1 . A mechanical seal interposed between a housing of an apparatus having a rotary shaft and the rotary shaft, and operative to seal an endo-fluid region against an exo-fluid region, the mechanical seal comprising: 
 a rotary seal ring mounted to said rotary shaft;    a stationary seal ring in axially opposing relation with said rotary seal ring for cooperatively defining therebetween a seal face constituting a primary seal portion for establishing a fluid seal between said endo-fluid region and said exo-fluid region, the stationary seal ring having a balance ratio designed to permit said seal face to be opened by supplying steam of a predetermined pressure to said endo-fluid region and by bringing said exo-fluid region into an exhausting state when said rotary seal ring is at standstill;    a seal case mounted to said housing for axially movably retaining said stationary seal ring, and including a groove extended circumferentially of a portion thereof in close proximity of and opposing relation with said stationary seal ring;    an elastic member retained by said seal case and urging said stationary seal ring into movement toward said rotary seal ring; and    a seal member mounted in said groove and interposed between said stationary seal ring and said seal case for constituting a secondary seal portion for establishing a fluid seal between said endo-fluid region and exo-fluid region.    
     
     
         2 . A mechanical seal according to  claim 1 , wherein an exhaust hole extended through said seal case has one open end located near a place where droplets fall, the droplets being formed by condensation on a surface of said stationary seal ring exposed to said exo-fluid region.