| 摘要 |
PURPOSE: To suppress a leak amount of exhaust gas to a minimum limit by a method wherein a clearance previously provided between a pipe passage and a valve body is reduced to a low value as much as possible. CONSTITUTION: In a butterfly valve device formed in such a manner that a pipe passage 4 is opened and closed in such a way that an oval disc-form valve body 6 contained in the pipe passage 4 for the flow of exhaust gas of a valve holding body 3 is rotatably supported by rotary shafts 7 and 8 crossing the pipe passage 4 at right angles, the valve holding body 3 is molded by using cast iron having the coefficient of thermal expansion in a range of 9.2×10<-6> -11.8×10<-6> , and the valve body 6 is molded by using a heat resisting steel having the coefficient of thermal expansion of 9.9×10<-6> -11.0×10<-6> .
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