| 摘要 |
In a ball valve including a cylindrical housing having a flow passage, a rotatable ball for selectively blocking the flow passage, and an external actuating handle, a fire safe stem seal comprising a stem having a selected diameter with a larger diametered shoulder portion on one end which is keyed for engaging the ball, and an opposite end for engagement with the actuating handle, the housing having a stem bore for matingly receiving the stem therethrough within a selected tolerance, a first interior step concentric with the stem bore and selectively sized to accommodate the stem shoulder, a second smaller selectively sized interior step concentric with the stem bore having a selected axial depth, a deformable heat-resistance second seal ring having an axial thickness substantially greater than the axial depth of the second step for engagement with the housing in the second step, a heat-destructible primary seal and bearing ring for engagement with the housing and the heat-resistant ring in the first step, and means to draw the stem shoulder against the heat-destructible primary ring in the first step which thereby compacts the heat-resistant ring in the second step and into the tolerance to effectively functionally lock the heat-resistant ring in a desired position around the stem.
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