| 摘要 |
<p>A downhole tool operable by means of a pressure flow of circulating mud is activated and deactivated remotely by a temporary or transient increase in circulation rate effective to shift a spring-biassed (17) annular piston (14) through which normal circulation passes. The piston (14) engages a latching means (19, 20) operative sequentially to locate the piston (14) so that it opens and closes a duct (22) for supplying the tool from the main circulation flow.</p> |
