US Patent 7836976 Underground piercing tool

A pneumatically operated underground piercing tool including an elongate cylindrical body carrying an anvil and a striker slidably received within a 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. The body and an end cap are connected by a tapered buttress thread. The striker defines a plurality of balancing grooves. 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. A tail adaptor is threadedly secured to the end cap using tapered buttress thread configurations. The valve assembly includes a detent mechanism and an improved exhaust bushing. The control spool is coupled to an end of said valve support by structure which includes a spherical element held in an elastomeric socket.