Patent ID: 7066279

Claim:
A ground piercing tool, comprising an elongated tubular tool housing, including a front anvil having a lengthwise bore therein; a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to an impact surface of the anvil for driving the tool forwardly through the ground; a chisel including a front head and a rearwardly extending chisel shaft slidably disposed in the bore of the anvil, which chisel is movable between a rearwardmost position at which a rear end portion of the chisel shaft protrudes from the bore of the anvil to receive an initial impact from the striker, and a forwardmost position at which the striker impacts on a rear impact surface of the anvil; and a distributing mechanism that reciprocates the striker in response to a supply of compressed fluid, wherein the housing and chisel shaft cooperate to define a front chamber that decreases in volume as the chisel moves forward relative to the housing, and the distributing mechanism includes passages that conduct compressed fluid to the front chamber, which front chamber is configured to form a gas spring using such compressed fluid.