| 摘要 |
PURPOSE:To remarkably reduce vibration and noise so as to relax the harmful effect to the title pump by interposing a valve body in an intake passage for intercommunicating an impeller to the inside of a pit at a minimum level and connecting the valve body or a valve body actuating source with a valve body opening/closing mechanism. CONSTITUTION:As a water level becomes a minimum water level LWL, a valve body 11 is opened so as to speedily introduce a large quantity of air inside an intake bell-mouth 3. That is, since an impeller 1 is intercommunicated to the air, thus operating the pump in the air so as to avoid the occurrence of air intake swirl and respiration phenomena so that it is possible to remarkably reduce the vibration and noise. Since the operation changing timing can be relayed with the valve body actuating source only during the water level is varied in a region A ranging from the minimum water level LWL to a pumping starting water level HWL, it is unnecessary to frequently perform the change between the air operation and pumping operation in a short cycle. Thus, it is possible to reduce the frequency of the impact generated each change and remarkably relax the harmful effect to the pump. |
