| 摘要 |
A tractor (20) for moving within a borehole comprises body and two propulsion assemblies (24, 26) that are longitudinally movably engaged with the body. The tractor body has annular pistons (34, 36, 38, 40) configured to receive hydraulic thrust to propel the body longitudinally. Each propulsion assembly includes a gripper (42, 52) and propulsion cylinders (44, 46, 48, 50). The gripper has an actuated position in which the gripper limits relative movement between the gripper and the inner surface of the borehole, and a retracted position in which the gripper permits free relative movement between the gripper and the inner surface of a borehole. Each propulsion cylinder contains one of the pistons. The tractor includes a control assembly (30) having valves and hydraulic circuitry which control the sequencing of fluid distribution to the propulsion cylinders, and of the actuation and retraction of the grippers. A throttle valve (54) controls the fluid flowrate to the pistons.
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