Patent ID: 7241122

Claim:
A positive-displacement pump, comprising a centering body having a cylindrical cavity, a rotor rotatably mounted with centered coupling without interference inside said cylindrical cavity, and an idle sprocket rotatably mounted with centered coupling without interference on a pin, wherein said rotor comprises a cylindrical peripheral surface for defining said centered coupling into said cylindrical cavity and has a plurality of peripheral teeth, wherein said idle sprocket comprises a body from which a plurality of teeth extend radially and are meshed with said plurality of peripheral teeth of said rotor, wherein said rotor has peripheral notches provided on said cylindrical peripheral surface to define said plurality of peripheral teeth, wherein a central opening of said idle sprocket comprises a series of centering portions of a centering wall which define the centered coupling of said idle sprocket to said pin and wherein said central opening of said idle sprocket further comprises portions of undercut regions spaced from the peripheral cylindrical portion of said pin and which are interposed between said curved centering portions.