Patent ID: 7607495

Claim:
A tractor assembly, comprising a tractor for moving within a borehole, the tractor configured to be powered by pressurized operating fluid received from a conduit extending from the tractor through the borehole to a source of the operating fluid, the tractor comprising: an elongated body having a thrust-receiving portion longitudinally fixed with respect to the body, the body having an internal passage configured to receive the operating fluid from the conduit; a gripper assembly longitudinally movably engaged with the body, the gripper assembly having an actuated position in which the gripper assembly limits relative movement between the gripper assembly and an inner surface of the borehole, and a retracted position in which the gripper assembly permits substantially free relative movement between the gripper assembly and said inner surface, the gripper assembly configured to be actuated by the operating fluid; a control assembly on the body, the control assembly including a valve system configured to receive fluid from the internal passage of the body and to selectively control the flow of operating fluid to at least one of the gripper assembly and the thrust-receiving portion; and a tractor isolation apparatus being controllable from a location of the source of operating fluid, the isolation apparatus configured to bring the tractor to a non-operational state in which the gripper assembly is assured of being in its retracted position; wherein operating fluid in the internal passage of the body is permitted to flow through the control assembly to one or more components connected downhole of the tractor when the isolation apparatus has the tractor in said non-operational state.