Stem seal for a fire safe ball valve

Claim 1

In a ball valve including a cylindrical housing having a flow passage, rotatable ball means for selectively blocking said flow passage, and external actuating means, a fire safe stem seal comprising: a stem having a selected diameter with a larger diametered shoulder portion on one end including means for engaging the ball means, and an opposite end for engagement with the actuating means, the housing having a stem bore for matingly receiving said stem therethrough within a selected tolerance, a first interior step concentric with said stem bore and selectively sized to accommodate said stem shoulder, and a second smaller selectively sized interior step concentric with said stem bore having a selected axial depth, a deformable heat-resistant secondary seal ring having an axial thickness substantially greater than said axial depth of said second step for engagement with the housing in said second step, a heat-destructible primary seal and bearing ring for engagement with the housing and said heat-resistant ring in said first step, and means to draw said stem shoulder against said heat-destructible primary ring in said first step which thereby compacts said heat-resistant ring in said second step and into said tolerance to effectively functionally lock said heat-resistant ring in a desired position around said stem, whereby said heat-destructible ring acts to seal the housing between said first step and said stem shoulder and serves to retain said heat-resistant ring in position to protect it from abrasive stem shoulder rotation while serving as a bearing for said stem shoulder, and whereby when the valve is subjected to intense heat and said heat-destructible ring disintegrates, said heat-resistant ring acts to seal said housing between said stem bore and second step and said stem and stem shoulder.