Down hole bypass valve

摘要

PCT No. PCT/GB96/03027 Sec. 371 Date Jun. 4, 1998 Sec. 102(e) Date Jun. 4, 1998 PCT Filed Dec. 9, 1996 PCT Pub. No. WO97/21020 PCT Pub. Date Jun. 12, 1997The invention relates to bypass valves for use in wellbores, particularly but not exclusively to bypass valves used during the setting of hydraulic anchor packers. The invention provides a bypass valve for selectively isolating the interior of a down-hole assembly from the exterior thereof, the bypass valve comprising guide pin in received slot being adapted to permit movement of a piston (30) from a first position to a second position in response to a predetermined pressure differential between a bore (58) of the piston (30) and the exterior of a body (4) but normally preventing movement of the piston (30) to a third position in which the bore (58) of the piston (30) is substantially isolated from the exterior of the body (4), and an extension of the guide slot for overriding the guide pins in the slot, so as to permit movement of the piston (30) to the third position. The invention thereby provides a bypass valve which resists any tendency to close prematurely and which communicates any such tendancy to the surface.