| 摘要 |
PURPOSE: To thin a bottom flap and to prevent biting of aggregate at the bottom flap portion by attaching a freely opening and closing bottom flap to a bottom of a valve housing, and forming a portion opposite to a tubular swirl valve body into a shape substantially identical to a curved surface of a swing face of the lower portion of the valve body. CONSTITUTION: A tubular swirl valve body 34 placed in a valve housing 18 is mounted in the manner that it can be turned about an axis 36. The valve housing 18 has an opening with an area equal to or larger than a lateral swinging range of the valve body 34, and a bottom flap 50 for closing the opening. The bottom flap 50 is mounted rotatably about the axis at a place of a rear wall 52, and a side opposite to the valve body 34 is formed in the shape substantially identical to a curved surface of a lower portion of the valve body in a cross direction, or is formed in the shape substantially identical to a lower swinging face of the valve body 34 in a longitudinal direction. Therefore, during the swinging of the tubular swirl valve body 34, abrasion can be reduced since aggregate is not bitten between the valve body 34 and the bottom flap 50, and thus a thickness of the flap 50 can be thinner and also a sufficient strength can be secured.
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