| 摘要 |
A ground piercing tool (10, fig 1) comprises an elongated tubular body that includes a front anvil (29, fig 1) having a lengthwise bore (23, fig 1), and a striker (16, fig 1) disposed to impart impacts to a rearward impact surface 30 of the anvil. The tool also includes a chisel, which includes a front head assembly mounted on a bit shaft (11, fig 2) slidably disposed in the bore of the anvil, movable between a rearward position (fig 2), and a forwardmost position (fig 4). A distributing mechanism is provided that reciprocates the striker in response to a supply of compressed fluid, where the body and bit cooperate to define a front chamber 13 that decreases in volume as the chisel moves forward and a rear chamber 17, which increases in volume as the chisel moves forward. The distributing mechanism includes one or more passages 15 that conduct compressed fluid to the front chamber, which is configured to form a gas spring. The tool further comprises a valve including a passage (26, fig 5) that permits communication between the front chamber and the rear chamber when the bit shaft is in its forwardmost position where it contacts a front stop (20, fig 5), 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. |
