The application relates to the technical field of downhole tools for
well cementing, in particular to a packoff type grading collar for
well cementing operation of oil and gas wells. The packoff type grading collar comprises a grading collar main body and an action sliding sleeve slidingly arranged in the grading collar main body. A sliding groove is coaxially arranged on the inner wall of the grading collar main body, the action sliding sleeve is slidingly arranged in the sliding groove, a
piston cavity is coaxially arranged in the grading collar main body, a communication groove is arranged on the groove bottom of the sliding groove, the communication groove is communicated with the
piston cavity, an installation groove is coaxially arranged on the outer
peripheral wall of the grading collar main body, the installation groove is communicated with the
piston cavity through a communication flow channel, a linkage rod is slidingly arranged in the communication groove, a
piston ring is slidingly arranged in the piston cavity, an expansion sealing rubber tube is arranged in the installation groove, the end of the linkage rod is fixedly connected with the
piston ring, the action sliding sleeve and the linkage rod are linked through a fixing column, the expansion sealing rubber tube is matched with the installation groove, the inner
peripheral wall of the expansion sealing rubber tube is open and is fixedly connected with the groove bottom of the installation groove, and the effect of reducing control steps and improving
well cementing operation efficiency is achieved.