Patent ID: 7481391

Claim:
An air shaft comprising: a hollow cylinder; an inflatable airtight bladder in the hollow cylinder; a plurality of movable members provided externally of the bladder, each of the movable members having a portion radially passed through the hollow cylinder; and a plurality of curved members provided on an outer surface of the hollow cylinder and between both ends thereof, the portion of the movable member radially passed through the hollow cylinder being secured to an outer surface of the curved member; wherein each of the curved members comprises a plurality of first projections formed on one side, the first projections being disposed axially and overlaying the hollow cylinder, a plurality of first slots each disposed between adjacent first projections, a plurality of second slots formed on the other side and lined up with the first projections, the second slots being disposed axially and overlaying the hollow cylinder, and a plurality of second projections formed on the other side and lined up with the first slots, the second projections being disposed axially and overlaying the hollow cylinder; the first projections are adapted to fit into the second slots, and the second projections are adapted to fit into the first slots; and prior to inflating the bladder, tops of the first and second projections are substantially flush with tops of the first and second slots, and the curved members are pushed outwardly by the movable members after inflating the bladder such that the tops of the first and second projections are substantially flush with the tops of the first and second slots.