To provide a vertical pump unit which can prevent the increase of water level in a suction pipe by exclusion of air in the suction pipe due to air exclusion of the pump impeller, even if there is water leakage from a flap valve which is provided at a pump discharge to prevent backflow during stand-by operation of the pump in the atmosphere.
In the vertical pump unit that is equipped with the vertical pump 4 whose suction opening 3a is opened at a lower position than the minimum operating water level of a suction sump 1 and that the impeller of the pump 4 is located at a higher position than the minimum operating water level of a suction sump 1, an air return pipe 10 communicating with the pump 4 impeller discharge pipe 5 and the pump 4 impeller suction pipe 3 is provided for preventing water filling.
NIIJIMA KEIICHI
SENDO TSUTOMU
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