| 摘要 |
PURPOSE:To prevent cavitation in a cut-off valve and abnormal vibration and noise in a pump, by providing a bypass pipe having a check valve, for communicating one or both of a pump and a communicating pipe with a main discharge pipe. CONSTITUTION:A bellmouth 8 and a communication pipe 5 inserted in a pit 14 are connected, respectively to the suction and discharge sides of a pump 1 having an impeller 2 driven by a drive unit 3. A shut-off valve 11 and a check valve 12 are disposed in a bypass pipe 9 communicating between the top of the communication pipe 5 and the top of a main discharge pipe 6. When the level L of suction water lowers to such a degree that a pump 1 is stopped, a water cut-off valve 4 is fully closed. Since the pumping-up of water in a small amount is possible even if the water cut-off valve 4 is fully closed and therefore the level of suction water is regulated in accordance with the inflow rate of water, there is no risk of abrupt lowering of the level of suction water.
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