| 摘要 |
PROBLEM TO BE SOLVED: To prevent a catalyst from depositing in recesses defined between the back seats and bleed bushing of a butterfly valve. SOLUTION: A butterfly valve involves, in its valve casing 1, a valve element 2 pivotally supported on a valve stem 3, back seats 4 projecting from the inner periphery of the valve casing 1 so as to receive the peripheral portions 2a of the valve element 2, a bleed bushing disposed between the bearing cylinder 1a of the valve casing 1 and the valve stem 3 so as to butt or abut against the end faces 4a of the back seats 4 at its outer periphery, and purge gas supply passages 6 passing through the bearing cylinder 1a and a bushing 20 up to a clearance gapαdefined between the bleed bushing 5 and the valve stem 3. The bearing cylinder 1a is formed with purge gas passages 13 which branch off from the purge gas supply passages 6 and open on recesses 11 defined between the back seats 4 and the bleed bushing 5.
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