Patent ID: 7182131

Claim:
A centralizer, connectable in a tubing string, comprising: a sub, having a first end and a second end opposite the first end, the sub having at each end thereof thread means for threadably connecting the sub in a tubing string; a pair of collars, spaced apart from each other, and rotatably mounted on the sub; the pair of collars comprising a first collar and a second collar; the first collar and the second collar being capable of axial movement along a length of the sub; the first collar being located closer to the first end of the sub than the second collar; the second collar being located closer to the second end of the sub than the first collar; a plurality of bow springs, having a relaxed and a compressed state, fixed to each of the pair of collars, and which in their fully compressed state, hold the collars at their furthest distance apart along the sub; a pair of shoulders, fixed to the sub and spaced apart from each other, and extending essentially around the exterior circumference of the sub; the pair of shoulders comprising a first shoulder and a second shoulder; the first shoulder being located closer to the first end of the sub than the second shoulder; the second shoulder being located closer to the second end of the sub than the first shoulder; the pair of shoulders being positioned between the pair of collars; the length of axial movement of the first collar when moving in the direction toward the first end of the sub being limited solely by the abutment of the second collar with the second shoulder and the compressed state of the bow springs; the length of axial movement of the first collar when moving in the direction toward the second end of the sub being limited solely by the abutment of the first collar with the first shoulder; the length of axial movement of the second collar when moving in the direction toward the second end of the sub being limited solely by the abutment of the first collar with the first shoulder and the compressed state of the bow springs; the length of axial movement of the second collar when moving in the direction toward the first end of the sub being limited solely by the abutment of the second collar with the second shoulder.