Pneumatic impact piercing tool

1. 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 blind 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 blind discharge ports.

2. The tool of claim 1 , wherein each exhaust passage comprises a frontwardly opening, rearwardly extending first blind hole in the tail nut, wherein the first blind hole is intersected by a second blind hole proximate the rear end of the first blind hole and perpendicular thereto, extending radially inwardly and forming the outlet port at the inner end thereof.

3. The tool of claim 2 , wherein there are several discharge ports at spaced positions intersecting the rear end of each first blind hole.