| 摘要 |
An underreamer for earth boring operations has a tubular body with a passage extending through it. Arms are pivotally mounted to the body and movable between retracted and extended positions. An actuator mandrel, located within the passage in the body, pushes the arms outward when drilling fluid is pumped downward in the drill string. Ports are located in the sidewall of the body and in the actuator mandrel. The ports align with each other when the mandrel moves to its downstream position. The ports divert a portion of the drilling fluid out to jet it across the cutting elements on the arms. The remaining portion of the drilling fluid passes downward to the drill bit and out nozzles of the drill bit. |
