PURPOSE: To economize electric power for pumps required for returning by dividing a storage tank to plural tank chambers provided with returning means, passing the water into the other tank chamber when one tank chamber is filled and starting return from the tank chamber where the water level is highest.
CONSTITUTION: When only the weirs 11b and 11c are closed and other weires are opened, the sewage flowed through a water passage 12 overflows from the bottom part 15a, is flowed into a tank chamber 10a and stored. When the water level in the chamber 10a rises higher than the part 15d, the sewage overflows from the part 15d and flows into a tank chamber 10b where it is stored. When the inflow continues further, the water level in the entire part of the three tanks rises up to h2. All of three pumps are used to return the water. When the water level in the chamber 10a drops equal to the water level in the tank 10b, a water distributing valve 13b is opened to return the water simultaneously from the chambers 10a and 10b. A water distributing valve 13c is also opened to return the water from all of the tanks 10aW10c.
FUJINAWA AKIO
FUJITA SHIGEO
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