| 摘要 |
PURPOSE:To impart sufficient airtightness to junction surfaces without inferiority, by providing annular projecting streaks on at least one junction surface of the base plate of a piston and a holding plate, and holding a sealing plate between both parts. CONSTITUTION:Many projections 3 and one or two annular projecting streaks, which cut into the sealing plate 5 so as to secure airtightness, are formed on a piston base plate 2 in protruding patterns. Many holes 6, which correspond to the projections 3, are provided in a soft-resin sealing plate 5 and a hard-resin holding plate 7. Under the state, the base plate 2 and the holding plate 7 are strongly compressed, they are caulked. Then the projecting streak 4, which is provided on the front surface of the base plate 2, is made to cut into the surface of the sealing plate 5. Thus, perfect airtightness is kept at the junction surfaces of the base plate 2 and the sealing plate 5.
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