Patent ID: 7343987

Claim:
A system for excavating a subterranean formation, the system comprising: a drill string for receiving a suspension of impactors and fluid; a body member for discharging the suspension in the formation to remove a portion of the formation; and means in the drill string for controlling the flow of suspension between the drill string and the body member; wherein the means is a valve assembly that moves between an open position in which it permits the flow of the suspension from the drill string to the body member, and a closed position in which it prevents the flow; wherein the valve assembly comprises two tubular members adapted for relative movement with respect to each other, and at least one valve member for moving between the open and closed positions in response to the relative movement; wherein the valve member is pivotally mounted to one of the tubular members and is engaged by the other tubular member during the relative movement to pivot the valve member to one of the positions; and wherein one tubular member extends inside the other tubular member, and further comprising means for introducing pressurized fluid into the one tubular member to cause relative movement between the tubular members to move the valve member into the open position.