Pneumatic impact piercing tool

A reversible, pneumatic ground piercing tool according to the invention includes:

• an elongated hollow body having a front nose and a rear opening;
• a striker disposed for reciprocation within an internal chamber of the body to impart impacts thereto for driving the body through the ground, the striker having a rearwardly opening recess and a rear radial passage through a wall enclosing the recess, a front portion having a front bearing thereon for sliding contact with a first inner surface of the body and passages permitting flow of pressure fluid to a front, variable-volume pressure chamber ahead of the striker, and a rear portion having a rear bearing thereon rearwardly of the radial passage for sliding contact with a second inner surface of the body;
• a stepped air inlet conduit which cooperates with the striker within the internal chamber of the body to reciprocate the striker and impart blows to a front end wall of the internal chamber under the action of a pressure fluid fed into the rear recess in the striker, followed by reverse movement of the striker when the rear radial passage moves past a front edge of the step of the stepped air inlet conduit, and exhaust of compressed air when the rear radial passage moves past a rear edge of the step of the stepped air inlet conduit;
• reversing mechanism by which the tool is switched from forward to reverse travel and back;
• and
• a tail assembly mounted in the rear opening of the body that secures the air inlet conduit in the body, wherein the tail assembly includes a tail nut threadedly secured in the rear end opening of the tool body and a tail cone disposed over the rear end opening of the tool body and secured to the tail nut, the tail nut having a lengthwise opening extending therethrough which opening opens rearwardly when the tail cone is in position over the tail nut,
• wherein the tail nut has exhaust passages therethrough, at least a portion of each exhaust passage angling radially inwardly and ending in a discharge port that communicates with a central hole at the rear end of the tail cone, whereby exhaust escapes through the central hole, and the tail cone has a radially inwardly extending flange on the inner periphery of the central hole, which flange is rearwardly spaced from and covers the discharge ports.