SELF-CENTERING SYSTEM FOR A TOOL TRAVELLING THROUGH A TUBULAR MEMBER

摘要

A self-centering system (249) for a down hole running tool (14) is provided with four metal balls (250) equally spaced about the circumference of the tool (14). Each ball (250) is seated in a corresponding cavity (252) formed about the periphery of an upper portion (150) of the tool (14). Each cavity (252) is closed by a threaded cap (254) which has a central opening through which each ball (250) can extend. However, the diameter of the opening is less than the diameter of the ball thereby preventing the balls (250) from falling out. A pad of resilient material (256) is disposed beneath each ball (250) so as to force it radially outwardly. Due to the resilience of the pads (256), the balls are able to move between a first position in which they can contact an inner surface of a drive sub (12) and a second position radially inward of the first position. For exemple, in the second position the balls (250) may be flush with the external surface of the tool (14). The pads (256) are of a resilience so as to ensure substantial centering of the tool within the drive sub (12) irrespective of its inclination.