| 摘要 |
A pneumatically operated underground piercing tool that includes an elongate cylindrical body carrying an anvil at one end and with a striker slidably received within a chamber defined by the body. An end cap, threadedly engaged with another end of the body, captures a striker within the chamber. A valve assembly controls the communication of pressurized air to and from the body and is operator adjustable in order to produce forward or rearward movement of the piercing tool. A strong threaded engagement between the body and the end cap is provided by a tapered buttress thread. The striker defines a plurality of balancing grooves which aid in the uniform distribution of pressurized fluid around the striker. A recess is formed in an end wall of the striker to inhibit pressurized fluid from being trapped between the striker and the end cap when the striker is reciprocated within the body. The striker includes oblong or slot-shaped radial ports in which the long dimension of the port is parallel to a centerline of the striker. A tail adaptor is threadedly secured to the end cap using tapered buttress thread configurations and an exhaust bushing received by the end cap is secured in its operative position by the tail adaptor. The valve assembly includes a detent mechanism including a finger member slidably held on a valve spool support. Flats formed on the support are engaged by internal flat surfaces formed on an inside bore of the finger member which permits sliding movement while resisting relative rotation. The control spool is coupled to an end of said valve support by structure which includes a spherical element formed on the support that is held in an elastomeric socket which, in turn, is received by an internal bore in the valve spool. A snap ring maintains the socket within the bore of the valve spool. An improved exhaust bushing carried by the valve assembly includes a plurality of peripheral notches or recesses through which air is exhausted during tool operation.
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