Tractor with improved valve system

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. Aft and forward sequence valves may be provided for controlling the propulsion control valve by detecting when the gripper assemblies become fully actuated. Furthermore, a pressure relief valve is preferably provided along an input supply line for limiting the pressure of the fluid entering the valve control assembly.

1 . A tractor for moving a component through a borehole, comprising:
 an elongate 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 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; and   aft and forward mechanically actuated valves configured to detect advancement of said body relative to said aft or forward gripper assembly, respectively;   wherein fluid pressure causes said gripper control valve to change positions after said body has completed an advancement stroke through the borehole relative to said aft or forward gripper assembly.