| 摘要 |
PURPOSE:To ensure conveniences for compact design and mass production, and flow rate accuracy by applying a short size to a peripheral groove formed near the axis of a closer and a long size to a peripheral groove formed away therefrom. CONSTITUTION:A plurality of flow passages 22 are opened and closed via the rotation of a closer 18 and the combination of the flow passages 22 allowing a gas flow can be selected to the predetermined state, depending upon the rotational stop position of the closer 18. The groove 21 of the closer 18 is made to have a short peripheral length near the axis 26 thereof and a long peripheral length near the tip thereof away from the axis 26. When the external surface of the closer 18 is machined, therefore, the closer 18 comes to have high strength against a deflection, as there are only short grooves 21b and 21c near the axis 26 of the closer 18. According to the aforesaid constitution, it becomes possible to obtain stable machining precision for the closer 18, including circularity, straightness and surface roughness.
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