| 摘要 |
PROBLEM TO BE SOLVED: To enhance economy by enabling stable operations and a constant selection of power adequate for operation specifications by means of a manhole drainage system for appropriately pumping up and discharging waste water, though an excess of rated power of a pump occurs due to an increase in discharge flow rate of the pump. SOLUTION: In the manhole drainage system, a submergible motor pump is disposed in the manhole so as to appropriately pump up and discharge the waste water flowing into the manhole. A pump having limit-load characteristics is used as the submergible motor pump. An air-vent branch pipe, which is mounted midway along a pumping-up pipe, is made to descend in a state of being parallel to the pumping-up pipe, and an end of the branch pipe is disposed near an opening of a waste-water suction pipe of a submergible motor pump part, so as to generate a spiral flow in the waste water of the submergible motor pump part.
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