To prevent downward effluence of an effluent gate and generation of cavitation.
A diameter-reduction part 12 is formed in an effluent pipe line 1, an induced face 12a toward the upstream side and a water-tight face 12b toward the downward side are provided in the diameter-reduction part 12 and the water-tight face 12b is made to be a valve seat 2, a shielding plate 10 brought into contact with the valve seat 2 or separated therefrom is supported through a downstream side axis 11 to make it possible to open or close it. The shielding plate 10 has a spherical face 10a around the axis 11 and at the periphery of the rear face of the spherical face 10a, a taper face 10b reducing the diameter downwards at an inclination larger than the induction face 12a is formed. When the valve hole is finely opened, the shielding plate end edge 10c facing the valve hole goes ahead to a little upstream side than the valve hole along the peripheral face 10a, the peripheral edge of the rear face of the shielding plate positioning at the downstream side of the valve hole is reduced in the diameter, and therefore, the water stream is discharged downstreams smoothly. Further, in a finely opened state, the stream passage can pass the stream in the short distance through the valve hole, and hence, it does not cause the cavitation.
Higashio Masahiro
Torii Kazuhisa
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