Double acting hydraulic jar

A jar mechanism comprising an outer body member;

• an inner body member movably mounted on the outer body member;
• a fluid chamber defined by the inner and the outer body members;
• and a resistance mechanism in fluid communication with the fluid chamber;
• the inner and the outer body members being movable relative to each other between a first configuration in which the resistance mechanism resists relative movement between the inner and the outer body members, and a second configuration in which the resistance mechanism resists relative movement of the inner and the outer body members to a lesser extent than the first configuration;
• the resistance mechanism comprising two valve devices, each valve device resisting movement of fluid within the fluid chamber in one direction and the valve devices being arranged to resist the movement of fluid in opposite directions, wherein the inner body member is moveable with respect to the valve devices, and the valve devices divide the fluid chamber into three sections such that the fluid is capable of flowing between the three sections of the fluid chamber.