Impact-action self-propelled mechanism for driving holes in the earth

Claim 1

A pneumatically operated impact-action self-propelled mechanism for driving holes in the earth comprising a cylindrical housing having a forward and a rear end and an anvil member located at the forward end; an impact piston reciprocal in the housing to deliver successive impacts to the anvil member and forming within the housing a forward chamber of variable volume; said impact piston having a rear space defined by a rearwardly extending side wall; a control assembly comprising a forwardly extending sleeve which is slidably received within the rear space of said impact piston to form a rear chamber of variable volume; a tube having connecting means for connection to a compressed air supply and a central passage connected to said sleeve for continuous supply of compressed air into said rear chamber and therefrom into said forward chamber through apertures in the side wall of the rear chamber of said impact piston; and means for lockably locating said sleeve longitudinally with respect to said apertures for providing forward or reverse movement of said mechanism, said control assembly further comprising a rearwardly extending cylindrical member connected to said sleeve and tube, said cylndrical member carrying a pin extending diametrically therefrom to engage in a generally Z-shaped slot formed in a further cylinder which partially surrounds said rearwardly extending cylindrical member and is located in a fixed position relative to the housing, the rearwardly extending cylindrical member being normally resiliently urged in a forward direction for providing forward motion of the mechanism, and being lockable by rotation of said tube in a rearward location relative thereto for providing rearward motion of the mechanism.