Patent ID: 6550554
Filing Date: 2003-04-22
Classification: E21B

Abstract:
A reverse circulation rock drill comprising:a backhead; a cylinder extending from the backhead; a piston having an axial bore and an outwardly extending circumferential shoulder providing a driving surface forming a drill hammer movable axially within the cylinder; a drill bit assembly with its bit mounted to project from the opposite end of the cylinder to the backhead and located to be struck by the piston; and a sample tube extending from the drill bit through the piston into the backhead; characterized in that; the outer wall of the sample tube is profiled partway along its length to form with the bore through the piston an air flow path for air to lift the piston; the external wall of the piston is profiled to form with the cylinder a second air flow path for the supply flow of air to the driving surface on the piston; and both air flow paths extending to open through the drill bit.