Abstract: A hydraulically powered tractor adapted for advancement through a borehole including an elongate body, aft and forward gripper assemblies, and a valve control assembly housed within the elongate body. The aft and forward gripper assemblies are adapted for selective engagement with the inner surface of the borehole. The valve control assembly includes a gripper control valve for directing pressurized fluid to the aft and forward gripper assemblies. The valve control assembly also includes a propulsion control valve for directing fluid to an aft or forward power chamber for advancing the body relative to the actuated gripper assembly. Aft and forward mechanically actuated valves may be provided for controlling the position of the gripper control valve by detecting and signaling when the body has completed an advancement stroke relative to an actuated gripper assembly.

Abstract: An expandable gripper assembly may be configured for anchoring a tool in a passage. The expandable gripper assembly includes first, second, and third pivotally connected links that are coupled to a tool. The third link is adapted to engage an inner wall in the passage. An actuation mechanism causes the third link to move radially outward from the tool for engagement with the inner wall. The actuation mechanism may comprise a roller mechanism that pushes on an inner surface of the first link for causing the first link to pivot outward away from the body. As the first and second links pivot outward, the third link moves in a radial direction for engagement with an inner wall.