Patent ID: 7156190

Claim:
An impact tool comprising: a body having a longitudinal axis, a central longitudinal passageway defined by an inner surface of the body, a striking end and a closed end; an annular orifice ring in the central longitudinal passageway, the orifice ring being positioned in mid-portions of the central longitudinal passageway and having a center opening; a tubular valve having an outer wall spaced from the inner surface of the body to form an annular passageway, said tubular valve having a center bore and a first end that forms an orifice seal around the center opening on a first side of the orifice; a piston sealably fitted around the tubular valve, and within the annular passageway on the first side of the orifice ring, the orifice ring closing one end of the annular passageway; a piston sleeve in which the piston is mounted, said piston sleeve being mounted inside the central longitudinal passageway and spaced from the inner surface of the body to form an annular gas chamber surrounding the piston sleeve, and a piston chamber surrounding the tubular valve; a block closing the central longitudinal passage at the closed end of the body, said block having a central bore in which a second end portion of the tubular valve slides, and an annular valve seat at the closed end, the tubular valve having a length so a second end of the tubular valve is moved away from the annular valve seat to open the center bore of the tubular valve to an exhaust port when the first end of the tubular valve is engaging the orifice ring; and a flow opening from a first end portion of the piston chamber of the piston sleeve to the annular gas chamber, whereby movement of a first end of the piston toward the block under hydraulic pressure in a second end portion of the piston chamber acting on a second opposite end of the piston compresses gas within the first end portion of the piston chamber and the annular gas chamber to provide a driving force on the first end of the piston when the hydraulic pressure on the second opposite end of the piston is relieved by the piston moving the first end of the tubular valve away from the orifice ring to open the orifice seal.