PURPOSE:To make it possible to disassemble and assemble easily by a method wherein a frame is provided between two opposed plates to form a chamber as well as a predetermined bolt and constraint means are provided between two plates to fix a cyclone element. CONSTITUTION:In disassembling a pressure container forming a chamber 6, a bolt 4 and a nut 5 are unscrewed firstly and, subsequently, if a bolt 9 is rotated to a direction wherein a distance of the first plate 1 and the second plate 2 is widen, because the bolt 9 can not moved to an axial direction against the second plate 2 by the action of the constraint means 14, the engagement of the second permeating pores 22 and the cyclone elements 16 is disengaged. If the bolt 9 is rotated moreover to the same direction, the bolt 9 is disengaged from a screw bore 7. Then, the second plate 2 is perfectly separated from the first plate 1 and the frame 3 to expose the chamber 6. In this condition, washing is carried out to remove the cloggings and the assemblage is carried out in a reverse order against above described order.