Tractor with improved valve system
View Patent ↗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 positioned along said body and configured to detect advancement of said body relative to said aft or forward gripper assembly, respectively;
wherein said aft and forward mechanically actuated valves are in fluid communication with said gripper control valve such that 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.
2. The tractor of claim 1 , further comprising an aft vent valve which allows fluid to flow from said aft mechanically actuated valve to said gripper control valve only when a pressure in the fluid exceeds a pre-selected threshold pressure.
3. The tractor of claim 2 , further comprising a forward vent valve which allows fluid to pass from said forward mechanically actuated valve to said gripper control valve only when a pressure in the fluid exceeds a pre-selected threshold.
4. The tractor of claim 1 , further comprising aft and forward vent valves, said aft and forward mechanically actuated valves being configured to direct fluid to pilot said aft and forward vent valves, respectively, said aft and forward vent valves being configured to direct fluid to pilot said gripper control valve.
5. The tractor of claim 4 , further comprising a propulsion control valve, said propulsion control valve having a first position in which said propulsion control valve directs 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.
6. The tractor of claim 5 , wherein said propulsion control valve is piloted by fluid pressures in said aft and forward gripper assemblies and wherein pressure exerted by said surfaces of said aft or forward gripper assembly exceeds a pre-selected threshold before said propulsion control valve changes positions.
7. The tractor of claim 1 , wherein said aft and forward propulsion assemblies comprise aft and forward cylinders, respectively, and wherein said body further comprises aft and forward pistons which are slidably housed within said aft and forward cylinders, respectively, said aft and forward pistons being configured to be displaced by the pressurized fluid within said aft and forward cylinders for advancing said body through the borehole.
8. The tractor of claim 1 , further comprising a propulsion control valve, said propulsion control valve having a first position in which said propulsion control valve directs 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.
9. The tractor of claim 8 , wherein said propulsion control valve is piloted by fluid pressures in said aft and forward gripper assemblies and wherein pressure exerted by said surfaces of said aft or forward gripper assembly exceeds a pre-selected threshold before said propulsion control valve changes positions.