Patent ID: 7299872

Claim:
A jar mechanism which comprises: a housing having a fluid chamber therein containing a fluid; a piston movably mounted in the fluid chamber for movement between a first position and a second position; a jar member movably mounted in the housing; and whereby a push force exerted on the jar member moves the piston from the first position to the second position within the fluid chamber against the resistance of the fluid, and the action of the push force exerted on the jar member actuates a release device, the jar member being releasably coupled to the piston by the release device such that when the piston is in the first position in the fluid chamber the jar member is coupled to the piston by the release device for movement therewith and actuation of the release device enables the jar member to be uncoupled from the piston, wherein the piston is retained in the second position by a retainer member when the jar member is uncoupled from the piston; and a balance piston facing the fluid in the fluid chamber and which operates to accommodate for any expansion of the fluid.