Improvements in and relating to impact-action self-propelled mechanism for driving holes in the earth

摘要

A pneumatically operated impact-action self-propelled mechanism for driving holes in the earth comprising a cylindrical housing assembly (10) with an anvil member (11) located at the forward end thereof. An impact piston (12) is reciprocal in the housing to deliver successive impacts to the anvil member and shaping with the housing a forward chamber (15) of variable volume. A control assembly comprises a forwardly extending sleeve (23) which is slidably received within a rear space of said impact piston to form a rear chamber (16) of variable volume. A central passage is connected to said sleeve for continuous supply of compressed air into said rear chamber and therefrom into said forward chamber through apertures (18) in a side wall of the rear chamber of said impact piston. Means is provided for locating said sleeve longitudinally with respect to said apertures for providing forward or reverse movement of said mechanism. An elastically deformable shock-damping bush (20) is located within the rear of the housing assembly which houses an annular metallic member (21) having longitudinal apertures (22) formed therethrough, through which air is exhausted. IMAGE