Importance

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Abstract

A wellbore underreamer has a tubular body, a central body cavity, and pivotally mounted blades in slots on the periphery of the tubular body. A translatable piston in the central body cavity is urged away from cam surfaces on the blades by a biasing spring. The piston has an orifice restricted fluid passage and translates in response to fluid pressure determined by the selected piston orifice and biasing spring. Fluid circulates through the piston fluid passage and fluid passages in the underreamer while piston movement is restrained by the spring. At a predetermined fluid pressure, the piston moves to engage the blade cam surfaces to pivotally extend the blades outward from the blade slots. The blades are held in the slots by a spring biased ball until they are extended by the piston.

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First Claim