Abstract: A drill hit for drilling a borehole into an earth formation is provided. The drill bit has a central longitudinal axis and a bottom surface facing the borehole bottom during drilling with the drill bit, and comprises primary fluid injection means (10) arranged at the bottom surface and located at a selected radial distance from the central longitudinal axis, the primary fluid injection means being arranged to eject a primary stream of fluid into the borehole, the primary stream having a component in a transverse plane of the drill bit, directed from the fluid injection means to the central longitudinal axis.

Abstract: A hydraulic accumulator for use in a drill string having a fluid passage for supply of fluid to a hydraulic drill string tool is provided. The accumulator comprises a body provided with connecing means for connecting the accumulator to the drill string and an expansion chamber in fluid communication the fluid passage when the accumulator is connected to the drill string by the connecting means. The expansion chamber is expandable between a first volume and a second volume which is larger than the first volume. Further, the expansion chamber is provided with means for moving the expansion chamber from the first to the second volume upon a fluid pressure increase in the fluid passage and for moving the expansion chambe from the second to the first volume upon a pressure decrease in the fluid passage.