| 摘要 |
An apparatus for reducing pressure surges in a wellbore comprising a body having a bore therethrough, the bore providing a fluid path for wellbore fluid between a first and second end of the body, at least one fluid path permitting the wellbore fluid to pass between the bore and an annular area formed between an outer surface of the body and the walls of a wellbore therearound, and a number of closure mechanisms whereby the at least one fluid path is selectively closable to the flow of fluid.
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