| 摘要 |
A valve 10 has at least one annular seal 56 surrounding a stem 18 to effect the seal between the stem and casing 12. Valving 110 and/or porting 100, is provided for introducing a pressure equal to or greater than the line pressure into a first chamber 76 whereby the pressure acts on an annular rim 48, to move the stem 18 in an axial direction to compress the annular seal(s) 56 which are alternate layers of polytetrafluoroethylene and graphite. The seals may be formed by winding ribbons of polytetrafluoroethylene 51 and graphite 53 on a former 55 to provide a ring which is then axially compressed before inserting into the valve 10. <IMAGE> |
