DEVICE FOR CONTROLLING THE WEIGHT ON AN EARTH DRILL BIT

摘要

A device for controlling weight on bit of a drilling assembly for drilling a borehole in an earth formation, is provided. The device includes a fluid passage for the drilling fluid flowing through the drilling assembly, and control means for controlling the flow resistance of drilling fluid in the passage in a manner that the flow resistance increases when the fluid pressure in the passage decreases and that the flow resistance decreases when the fluid pressure in the passage increases.