Patent ID: 7343982

Claim:
A tractor for moving a component through a borehole, comprising: an elongate body including an internal passage configured to receive pressurized fluid from a supply line when the supply line is connected to the body; aft and forward gripper assemblies longitudinally movably engaged with said body, said aft and forward gripper assemblies each being hydraulically actuated and defining engagement surfaces configured to selectively engage an inner surface of the borehole; aft and forward propulsion assemblies configured to advance said body through the borehole relative to said aft and forward gripper assemblies, respectively; a gripper control valve having a first position in which said gripper control valve directs the pressurized fluid to said aft gripper assembly and a second position in which said gripper control valve directs pressurized fluid to said forward gripper assembly; a propulsion control valve having a first position in which said propulsion control valve directs the pressurized fluid to said aft propulsion assembly and a second position in which said propulsion control valve directs pressurized fluid to said forward propulsion assembly; and a pressure relief valve disposed within said body of the tractor for limiting fluid pressure in said internal passage of the body, the internal passage configured to convey fluid toward said gripper control valve and said propulsion control valve.