| 摘要 |
A valve assembly includes a valve stem which is connected with a valve. A drive member is disposed in engagement with the valve stem. A gear assembly is operable to rotate the drive member to effect axial movement of the valve stem. The gear assembly is driven by an electrical motor. In the event of a power failure, the valve may be moved to a closed condition by either a return spring or an auxiliary source of electrical energy. To facilitate movement of the valve between the open and closed conditions, the valve is pressure balanced.
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