HYDRAULICALLY EXPANDING UNDERREAMER Russian patent published in 2004 - IPC

FIELD: boring technology. SUBSTANCE: device has cylindrical body, in inner longitudinal channel of which elastic sleeve is placed, and in side walls of which longitudinal ports are made, in which radially moveable extending blades with rock destroying means on outer surface are placed. Channel inside the body is made through with diameter no less than inner diameter of elastic sleeve. On the outer side on upper and lower ends of extending blades from their faces grooves are made, said grooves being covered by limiting bushings mounted outside the body. Outer surfaces of extending blades are inclined to their upper and lower ends. Blades are placed in longitudinal ports of body in such a way, that their inner surfaces along all height of blade are in direct contact with outer surface of elastic sleeve, under which butterfly governor is mounted in body channel. In transferring position extending blades are buried into the body and fixed there by shear pins. Width of each extending blade is no less than 0.3 of inner diameter of elastic sleeve, and its length is no less than two such diameters. Underreamer is a part of boring column construction. EFFECT: simplified construction and operation, high operation reliability. 9 cl, 3 dwg