The HMJ incorporates a latch mechanism to keep the jar locked in the neutral position and eliminate unexpected jarring while tripping or racking on the derrick.

The built-in mechanical latch keeps the jar locked in a neutral position, which prevents stroking of the jar downhole and unintentional firing of the jar while drilling or tripping. When latched, the mandrel and housing act integrally, eliminating seal and inner-tool wear. The latch eliminates the need for a safety collar and special handling/precautions on the rig floor.

The hydraulic valve provides delay when jarring up, allowing drillers to vary overpull and control impact force. The valve resides in its own oil seal chamber for increased reliability, and a robust metering device controls delay times across operating temperatures.

Down strokes use the mechanical part of the jar, while upward strokes use the hydraulic part with hydraulic delay. The mechanical latch actuation force can be adjusted and set during the jar assembly upon customer request.

The HMJ is normally operated in the latched position to reduce unexpected jarring while drilling and eliminate movement between jar components increasing service life.
The spline drive and latch mechanism are enclosed in a single sealed oil chamber without ports to the annulus. Such ports on other jars may become filled with cuttings/debris and restrict the down jar stroke.
With the latch mechanism in the latched position the inner mandrel and outer housing work integrally essentially eliminating seal and inner tool wear during normal drilling conditions. There is no need to un-latch or open the jar before running in the hole.
The HMJ can be run in tension or in compression within the preset latch setting.