| 摘要 |
PURPOSE:To enable complete drainage at a low water level and the prevention of the backflow of water in a piping and the like by separating or bringing the periphery of a cup-shaped resilient membrane of a swing valve from or into close contact with a cone-shaped pressure receiving surface on a bottom plate, thereby opening or closing a passage, respectively, when the swing valve is operated to be turned up and down. CONSTITUTION:Since a negative pressure is generated under the impeller of a submersible pump when the pump is started at a water level l1, a swing valve 7 is operated to be turned up, the peripheral portion 13 of a cup-shaped resilient membrane is separated from a cone- shaped pressure receiving surface 14 on a bottom plate 4, and suction ports 9...9 and the suction opening 3 of the pump fall in communicative condition. In result, a passage 17 from the peripherals bottom edge of an annular seat portion 11 to the suction opening 3 of the pump is opened and the water sucked through narrow gaplike passages 12...12 provided in extremely low positions is discharged from a discharge opening (not shown) via the passage 17 and the inside of a pump casing 1. An, since the swing valve 7 is operated to be turned down by the pressure of return water in the pump casing 1 and a piping for drainage and the periphery 13 close the cone-shaped pressure receiving surface on the bottom plate 4 when the submersible pump is stopped at a water level l1 whereat the drainage is terminated, demonstrating a backflow preventing function.
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