Fluid operable hammer

In a fluid operable hammer assembly, the improvement comprising:

• a body member having an elongated bore therein, a piston reciprocably movable within said bore in oppositely directed axial strokes to form two axially spaced variable volume chambers therein, said body member having a gas accumulator in continuous gas flow communication with one of said variable volume chambers to form therewith a sealed gas system with said piston being move periodically through one of said strokes by expansion of gas within said gas system, said body member having a hydraulic fluid chamber, said body member having means to selectively control the supply of a hydraulic fluid to the other of said variable volume chambers to move said piston periodically through the other of said strokes upon completion of said one strokes and to selectively place said hydraulic fluid chamber in fluid flow communication with said other of said variable volume chambers to receive hydraulic fluid discharged from said other of said variable volume chambers when said piston is movable through each of said one stroke, said gas accumulator substantially encompassing the axial extent of said one of said variable volume chambers, and said hydraulic fluid chamber encompassing the axial extent of said gas accumulator.