Patent ID: 7059417

Claim:
A self-propelled tool for moving within a passage, comprising: a body configured to convey a working fluid for powering movement of the tool; a gripper movably engaged with said body, said gripper including at least one gripper portion having a first position in which said gripper portion limits movement of said gripper portion relative to an inner surface of said passage and a second position in which said gripper portion permits substantially free relative movement between said gripper portion and said inner surface; a thrust-receiving member longitudinally fixed with respect to said body and longitudinally movable with respect to said gripper portion of said gripper, said body being longitudinally movable within said passage when the working fluid is directed to apply a thrust onto said thrust-receiving member with said gripper portion in said first position; a control pack comprising a valve having one position in which said valve permits the working fluid to flow through said valve to a first side of said thrust-receiving member to impart said thrust, and another position in which said valve prevents the working fluid from flowing to said first side of said thrust-receiving member, the position of said valve being controlled by fluid pressure forces acting on said valve; wherein said control pack is configured to prevent said thrust on said thrust-receiving member from exceeding a set threshold value regardless of a pressure of the working fluid flowing through the valve, by internally continuously controlling fluid flow within the tool.