| 摘要 |
PROBLEM TO BE SOLVED: To hold sludge concentration to prescribed concentration when drain of sewage is started by driving a sewage pump installed on a bottom part of a sewage tank in a reverse direction for a constant time before the sewage pump is driven in normal, agitating sludge deposited on a bottom part of the sewage tank, and then draining sewage water by switching into driving of normal rotation. SOLUTION: A sewage pump 2 is driven in a reverse direction for a constant time before the sewage pump 2 is driven in a normal direction for draining sewage water in a sewage tank 1. Namely, sewage water stored in a drain pipe 3 flows (makes reverse flow) into the sewage tank 1, and sludge deposited on a bottom part of the sewage tank 1 is agitated. After deposited sludge is uniformly dispersed in sewage water, the sewage pump 2 is switched in the normal driving. Sludge concentration is held to a prescribed concentration especially when drain of sewage water is started. In this time, existence of sewage water in the drain pipe 3 is detected by a sensor 6, reverse driving of the sewage pump 2 is stopped when sewage water in the drain pipe 3 is eliminated, and thereby, racing and failure of the sewage pump 2 are prevented.
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