| 摘要 |
A valve member (E) for a shut-off valve has a stem tip seal (F) and is adapted for selective movement axially towards and away from an associated valve seat (76). A generally cylindrical sleeve (80) is carried by the valve member (E) and has an end defining an outer annular seal surface (91) adapted for cooperative sealing engagement with the seat (76). Mounted centrally within the sleeve (80) for limited axial movement is a rigid cylindrical body (88) that defines an inner annular seal surface (90) adapted for engagement with the seat (76) at a location radially inwardly of the outer annular seal surface. Formed between the sleeve (80) and the rigid body (88) is an annular chamber (96) which opens axially inwardly from a narrow slot (94) located between the inner annular seal surface (90) and the outer annular seal surface (91). A mass of resilient packing material (97) substantially fills the chamber (96) and extends axially outwardly of the slot (94) to define a medial annular seal surface (103). Means are associated with the rigid body (88) for generating pressure on the packing material (97) when the body is forced axially towards the valve member (E). In addition, the inner annular seal surface (90) is configured to engage the seat (76) prior to engagement by either the medial annular seal surface (103) or the outer annular seal surface (91). |
