GB2332921A - Double acting hydraulic jar - Google Patents

Abstract

A jar mechanism is described as comprising an outer body member (2, 4, 9, 10, 14, 17), an inner body member (1, 5, 11) which is movably mounted on the outer body member (2, 4, 9, 10, 14, 17), and a fluid chamber (35, 37, 42) which is defined by the inner (1, 5, 11) and outer body members (2, 4, 9, 10, 14, 17). Firstly, a resistance mechanism (12, 13, 48, 50) is described which is in fluid communication with the fluid chamber (35, 37, 42). The inner (1, 5, 11) and outer body members (2, 4, 9, 10, 14, 17) are moveable relative to each other between a first configuration in which the resistance mechanism (12, 13, 48, 50) resists relative movement therebetween, and a second configuration in which the resistance mechanism (12, 13, 48, 50) substantially does not resist relative movement therebetween. The resistance mechanism (12, 13, 48, 50) comprises two valve devices (58), where each valve device (58) resists movement of fluid within the fluid chamber (35, 37, 42) in one direction and the valve devices (58) are arranged to resist the movement of fluid in opposite directions. A releasable locking mechanism (5, 8) is secondly described for locking the inner body member (1, 5, 11) with respect to the outer body member (2, 4, 9, 10, 14, 17), where a piston section (48, 50) permits a load to be applied between the body members after the locking mechanism (5, 8) has released. Optionally, there is at least one flow passage to permit fluid located in the annulus between the body members in flow from one side of the locking mechanism (5, 8) to the other.