Patent ID: 7311149

Claim:
A jar having an adjustable preload, comprising: a housing having an anvil surface and defining a fluid chamber; a mandrel moveable relative to the housing under an applied load and having a hammer surface to impact the anvil surface; a trigger sleeve axially positioned within the housing; a collet engaging the mandrel and releasing the mandrel to cause the hammer surface to impact the anvil surface upon being moved into registration with the trigger sleeve; a spring disposed within the housing to permit a preload to be applied to the mandrel without producing longitudinal axial movement of the collet relative to the trigger sleeve; a piston moveable within the fluid chamber to cause a build up of pressure in the fluid chamber in resistance to longitudinal, axial movement of the collet relative to the trigger sleeve upon application of a load to the mandrel in excess of the preload until the collet releases the mandrel; and an adjustment mechanism carried by the housing and coupled to the spring to adjust compression of the spring and thereby adjust an amount of preload permitted to be applied to the mandrel.