Abstract: A centralizer for use in oil well wireline toolstrings comprising a central mounting rod and floating spring mechanisms between which a number of jointed centralizer arms are connected. The jointed centralizer arms have a section with a concave profile disposed near to their pivot points so that a closing force acting on the arms acts at a greater distance from the pivot, thereby increasing the closing moment and making the centralizer easier to draw into a borehole with a narrow cross-section. The floating spring mechanisms also have a linkage to the presser plate of the spring such that an axial force pulling the centralizer apparatus into a borehole is transferred directly into a force on the spring, thereby reducing the opening moment the springs exert on the centralizer arms.

Abstract: An improved centralizer apparatus for use in oil well wireline toolstrings comprising a central mounting rod (20) and floating spring mechanisms (30, 90) between which a number of jointed centralizer arms (120, 140) are connected. The jointed centralizer arms (120, 140) have a section with a concave profile (64, 84) disposed near to their pivot points (50) so that a closing force acting on the arms (60, 80) acts at a greater distance from the pivot, thereby increasing the closing moment and making the centralizer easier to draw into a borehole (200) with a narrow cross-section. The floating spring mechanisms also have a linkage (99) to the presser plate (98) of the spring (96) such that an axial force pulling the centralizer apparatus into a borehole is transferred directly into a force on the spring (96), thereby reducing the opening moment the springs exert on the centralizer arms, making them easier to close.