| 摘要 |
A valve has upstream and downstream seat assemblies each having a pair of spaced annular face seals in concentric relation to form inner and outer face seals. A movable valve member (26, FIG. 2; 88, FIG. 8) has a main bore therethrough and is mounted in a valve chamber between the seat assemblies for movement between open and closed positions. A pair of auxiliary fluid passageways (72, 74, FIG. 2; 112, 114, FIG. 8) are located in the valve member at opposite ends of the main bore. Each of the auxiliary passageways has its outer end opening to the side of the valve member radially outward of the main bore and an inner end opening into the main bore. Upon opening of the valve the valve member is temporarily positioned so as to locate the outer end of each auxiliary passageway between the associated face seals so fluid can leak past the inner face seal on the upstream seat assembly into the area between the inner and outer seals, thence flow through one auxiliary passageway into the main bore and valve chamber, and then through the other auxiliary passageway to leak past the outer face seal at the downstream seat assembly to the downstream side of the valve. This fluid motion functions to equalize and reduce the pressure differential across the valve before the valve member is moved to the open position with the main bore moving across both face seals of the seat assemblies.
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