Extension type slidingly sealing device

The utility model discloses an extension type slidingly sealing device, which comprises an outer drum provided with a central hole. An upper connector is in threaded connection with the top end of the outer drum, a lower connector is in threaded connection with the lower end of the outer drum, and an annular groove is respectively formed on the inner wall where the top end of the outer drum and the upper connector are connected and the inner wall where the bottom end of the outer drum and the lower connector are connected. A central pipe penetrates through the central hole of the outer drum, and two ends of the central pipe respectively penetrate out of the upper connector and the lower connector. A split sealing annular group is contained in each annular groove and arranged on the outer side of the central pipe in sealing mode. The extension type slidingly sealing device not only can seal an inner pipe and an outer pipe of a concentric layering steam injection tubular column in annular mode so as to achieve