| 摘要 |
PROBLEM TO BE SOLVED: To prevent filtering capacity from being limited by enabling air in a filtration tank to automatically leave out without especially providing an air vent valve. SOLUTION: An uppermost part of a lidded manhole 11f for maintenance provided at an obliquely upper part of the filtration tank 11 and an outlet piping 21 are joined by an air vent hose 40. Thereby air in the filtration tank 11 is discharged into the outlet piping 21 via the air vent house 40 due to pressure difference between the inside of the filtration tank 11 and the inside of the outlet piping 21 when filtered water passes through the outlet piping 21 by pump pressure.
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