Anordning og fremgangsmate for mekanisk avstengningsventil i en bronn

A shut-off valve is disclosed for use in a downhole string of tools in a well. The valve has a housing adapted to be connected between adjacent tools of the string, defining a bore and a passage for hydraulic communication between the adjacent tools. The passage is arranged to intersect the bore, and a piston is slidably disposed within the bore and arranged to block hydraulic communication between the passage and the piston bore. The piston is further arranged to, in a first position, permit hydraulic communication along the passage, and to, in a second position, block hydraulic communication along the passage. The piston also has a bore for ballistic communication between the adjacent tools, such that it can be employed between a firing head and a gun, for instance. Some embodiments also permit circulation flow from the tubing to the well bore after the valve has closed. Methods of use and tool strings containing such valves are also disclosed.