| 摘要 |
The present invention provides a robust, durable and reliable cylindrical valve having closable, radially extending openings for use in cementing, injection, including hydraulic fracturing, and production in wells having high pressures and large pressure differences. The valve may comprise scraping rings in order to remove deposits and the like when it is to be closed after use. Magnets or other suitable means indicates whether the valve is in an open or closed position.
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