GB643196A - Fluid operated underreamers - Google Patents

Abstract

643,196. Earth-boring apparatus; under-reamers. DEHN, S. G. (Baker Oil Tools, Inc.). April 13, 1948, No. 10259. [Class 85] A tubular plunger 20 of an under-reamer controls, through levers 23, the pivoted blades 15 by its movement in the bore 13 of the reamer body 10, the upper portion 25 of the bore being enlarged. In this enlarged portion 25 is a spring 28 which is maintained in compression between the bottom of the chamber and a piston-head 26 formed on the plunger so that, unless fluid pressure is exerted on the piston-head to overcome the spring 28, the blades are withdrawn into the slots 14 of the body 10. A restriction 32 is screwed into the bore 30 of the plunger and a sleeve 35 of hard metal, such as tungsten carbide, and of greater internal diameter than the passage 33, is positioned within the restriction, it being maintained there by a spacer sleeve 37 resting on a shoulder 38 formed in the bore 30. When the tool is in the desired position, fluid is pumped through the drill string 12 and pressure built up on the plunger head until the resistance of the spring is overcome and the resultant downward movement of the plunger forces the blades outwardly of the body 10. The fluid passes through the restriction leaving it with a high velocity resultant upon the decrease in pressure experienced, but since it impinges against the sleeve 35 expending energy thereon, when it subsequently flows through the bore 30, passages 31, 18 onto the blades no erosion or scoring occurs.