| 摘要 |
A rotary valve assembly comprising a valve body having a stem passageway in communication with the valve body cavity which contains a closure member for selectively closing or opening the fluid flow passageway intersecting the valve body cavity. A valve operator consisting of a reciprocatable and rotatable stem passing through the stem passageway is connected to the closure member so that when the stem rotates, the closure member rotates together with the stem. The stem is provided with a back-seat and the valve operator reciprocates the stem to unseat and reseat the stem onto the stem seat located on the valve body surrounding the stem passageway in order to seal the stem passageway from the valve body cavity. Sealing of the stem passageway isolates the stem packing from the fluid in the valve body cavity, prevents fugitive emissions related to stem leakage and prolongs the useful life of the stem packing.
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