TITLE: A DOWNHOLE WEIGHT CONTROL DEVICEFOR IMPACT ROCK DRILLING TOOLABSTRACT OF THE DISCLOSUREA downhole weight control device is described forconnecting to the upper end of a downhole, pneumatically-operated, impact rock drilling tool for applying a downwardforce on the tool sufficient to maintain the drill bit in theclosed working position. The weight control device has apiston member that has an effective area related to the sur-face area of the hammer piston in the drilling tool to effec-tively counterbalance an upward force of the tool tending tolift the tool. The control device also prevents exertingexcessive weight on the drill bit. The control device hasmeans for automatically decreasing the working pressureshould the drill string be fed for a period of time at a rategreater than the penetration rate of the tool.
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