A self supported cylindrical corrugated filter. The cooling fin is mounted on the plurality of fin supports. A control system receives signals from a speed sensor operatively coupled to the rotor, and is configured to regulate the hydraulic rams, thereby controlling the opening and closing of the cage in response to rotation of the rotor. A second lever member pivotally attached to the base member bears on the first lever member to bring the punch member into cooperation with the punch hole thereby perforating the collar stay.