Patent ID: 7229076

Claim:
A method for operating a mechanical seal interposed between a housing for an apparatus having a rotary shaft and the rotary shaft, and operative to seal an endo-fluid region against a sealing-fluid region and an atmospheric region, the mechanical seal including: a rotary seal ring mounted to the rotary shaft; a first stationary seal ring in axially opposing relation with the rotary seal ring for cooperatively defining therebetween a seal face constituting a primary seal portion for establishing a seal between said endo-fluid region and the sealing fluid region; a secondary stationary seal ring in axially opposing relation with the rotary seal ring for cooperatively defining therebetween a seal face constituting a primary seal portion for establishing a seal between the sealing-fluid region and the atmosphere region; a seal case mounted to the housing for axially movably retaining the first stationary seal ring, and including a groove extending circumferentially of a portion thereof in close proximity to and in opposing relation with the first stationary seal ring; an elastic member retained by the seal case and urging the first stationary seal ring into movement toward the rotary seal ring; and, a seal member mounted in the groove and interposed between the first stationary seal ring and the seal case for constituting a secondary seal portion for establishing a seal between the endo-fluid region and the sealing-fluid region, the method comprising the steps of: having the first stationary seal ring designed to have a predetermined balance ratio K 1 defined by K 1 =S 2 /S 1 wherein S 1 is an area of the seal face and S 2 is a pressure receiving area subjected to a pressure of sealing fluid for pressing the first stationary seal ring in a direction to close the seal face to thereby obtain an intrinsic nature for inhibiting the seal face from being opened; having the first stationary seal ring designed to have a predetermined balance ratio K 2 defined by K 2 =S 3 /S 1 =(S 1 −S 2 )/S 1 wherein S 3 is a pressure receiving area subjected to a pressure in the endo-fluid region for pressing the first stationary seal ring in the direction to close the seal face; supplying the sealing-fluid region with a pressure of sealing fluid higher than a pressure of the endo-fluid region during a normal operation of the mechanical seal to thereby permit the seal face to be slightly opened when a dynamic pressure is generated by rotation of the rotary seal ring; and supplying the endo-fluid region with steam of a predetermined pressure and bringing the sealing-fluid region into an exhausting state to thereby permit the seal face to be opened when the rotary seal ring is at standstill for a sterilization operation of the mechanical seal.