| 摘要 |
The present invention relates to bypass valves for use in wellbores, particularly but not exclusively to bypass valves used during the setting of hydraulic anchor packers. A bypass valve (2) is provided with a piston (30) slidably mounted adjacent a body member (4) having at least one opening (20) extending therethrough. The piston (30) is moveable between a first position establishing a passage from the interior of the body (4) to the exterior thereof via the at least one opening (20) and a second position isolating th e interior of the body (4) from the exterior thereof. Means are provided for increasing, in response to a predetermined fluid pressure differential acros s the length of the piston (30), the force exerted on the piston (30) by a giv en flow of fluid through the bypass valve (2) such that the resultant force on the piston (30) is insufficient to move the piston (30) to the second position. Thus, the bypass valve (2) is adapted to provide an indication at the surface of an imminent closure. Once said indication is received, the bypass valve (2) may be closed, without the need for remedial action, by simply increasing the rate of fluid flow.
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