| 摘要 |
PROBLEM TO BE SOLVED: To provide a butterfly valve which can grasp small amount of water (fluid) when water flows down, at flooding work time or the like to downstream of a pipeline. SOLUTION: A pair of protrusions 20, 20, provided with a sphere 19 opposed through a small clearance 18 to a valve element seat 2A in the external periphery of a valve element 2 in a small opening region of about 30 degrees, are provided in an inner surface of a valve casing 1, a single through-hole 21 is provided in these protrusions 20, 20. In the case of opening the valve element 2 by a small degree of opening, a small amount of water is made to flow down from the upstream to the downstream side of the valve casing 1 through the through-hole 21. The small amount of water flowing down is grasped by the sum of a passage sectional area of the through-hole 21 in the protrusions 20, 20.
|
