HIGH FREQUENCY FLUIDPRESSURE DRIVEN DRILL HAMMER FOR PERCUSSION DRILLING IN HARD FORMATIONS

摘要

A fluid pressure driven, high frequency percussion hammer for drilling in hard formations is presented. The hammer piston (20) of the percussion hammer has a relatively large and longitudinally extending bore (41 ) that provides minimal flow resistance for a drilling fluid flowing through the bore (41 ) during the return stroke of the hammer piston (20). The bore (41 ) is closeable in the upstream direction by a valve plug (23) that follows the hammer piston (20) during the stroke. The valve plug (23) is controlled by a relatively long and slender valve stem (49) that is mechanically able to stop the valve plug (23) by approximately 75 % of the full stroke length of the hammer piston (20) and separates the plug (23) from a seat ring (40). Thus the bore (41 ) opens up such that the bore fluid can flow there trough, and the inherent tension spring properties of the valve stem (49) returns the valve plug (23) so rapid that it will be good through flow during return of the hammer piston (20).