| 简介 |
PROBLEM TO BE SOLVED : To provide a sand removing method which can reduce the frequency of start and stop of a sand pump and enables use of an ordinary low-cost pump.
SOLUTION : In the sand removing method where water is jetted from nozzles for sand collection provided in a settling basin in a state where water is discharged, to collect deposited earth and sand into a sand collecting pit, and when the water surface of the pit is equal to or higher than a predetermined high water level, a sand pump is operated and when it becomes a predetermined low water level, the sand pump is stopped, thereby pumping up the earth and sand, the control of switching valves for switching between supply and stopping supply to nozzle headers comprises a first process for opening switching valves of nozzles for troughs and the sand collecting pit for a predetermined time, a second process for specifying the order of blocks to which water is jetted from the nozzle headers, a third process for opening the nozzles of the specified block for a predetermined time, a fourth process for waiting until the water surface in the sand collecting pit decreases to a predetermined water level, a fifth process for determining whether the order of the block at completing the fourth process is the last order or not, a sixth process for returning to the first process when the order of the block is not the last order, and a seventh process for waiting until the water surface in the sand collecting pit decreases to a predetermined low water level when the order of the block is the last order.
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