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Pneumatic impact tool

  • US 8,955,613 B2
  • Filed: 05/01/2009
  • Issued: 02/17/2015
  • Est. Priority Date: 05/03/2008
  • Status: Active Grant
First Claim
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1. A ground piercing tool, comprisingan elongated tubular tool body, including a front anvil having a lengthwise bore therein;

  • a striker disposed for reciprocation within an internal chamber of the body to impart impacts to a rearward impact surface of the anvil for driving the tool forwardly through the ground;

    a chisel including a front head and a rearwardly extending bit shaft slidably disposed in the bore of the anvil, which chisel is movable between a rearward position at which a rear end portion of the bit shaft protrudes from the bore of the anvil to receive an initial impact from the striker, and a forward position at which the striker impacts on a rear impact surface of the anvil;

    a distributing mechanism that reciprocates the striker in response to a supply of compressed fluid;

    wherein the body and bit shaft cooperate to define a front chamber that decreases in volume as the chisel moves forward relative to the body and a rear chamber increases in volume as the chisel moves forward relative to the body and a rear chamber, the distributing mechanism including one or more passages that conduct compressed fluid to the front chamber, which front chamber is configured to form a gas spring using such compressed fluid; and

    a valve including a passage that permits communication between the front chamber and the rear chamber when the bit shaft is in a forwardmost position wherein it contacts a front stop, which valve permits compressed air to pass from the front chamber to the rear chamber, negating the gas spring when the bit shaft is in the forwardmost position.

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