US Patent 7066251 Hydraulic jar lock

An internal, positive engagement lock that locks a tool, such as a hydraulic drilling jar, in the fully open position when the tool is racked back and when tripping in and out of the hole close to the surface. The lock mechanism is spring biased into a locked position that provides a positive engagement between two axially translatable components, thus preventing any actuation of the tool. As the tool is run in the hole, increasing hydrostatic pressure within the tool will cause the locking mechanism to shift to a disengaged position and the tool will operate normally. The spring-biased locking mechanism will return to the locked position as hydrostatic pressure decreases as the tool is retrieved to the surface.