JP6755466B2 - Sand removal device for sand basin - Google Patents

Description

The present invention relates to a sand removal device for a sand basin.

The bottom of the sand basin is divided into multiple areas in the direction of the water flow in the sand basin, and the water in the sand basin is discharged by the drainage pump (drainage state), and the low pressure water from the water supply pump is discharged from the nozzles provided in each area. A low-pressure sand collection type sand removal device that sequentially injects and collects the sediment that has settled in the area through the main trough to the sand collection pit, and pumps up and removes the collected earth and water with a sand lifting pump installed in the sand collection pit. Is disclosed in Patent Document 1.

The sand removal device starts the operation of the sand lifting pump when the height of the water surface in the sand collecting pit is higher than the predetermined high water level, and when the height of the water surface drops to the predetermined low water level due to the pumping by the sand lifting pump. Stop the operation. Then, when the sand collection area (sand collection target area) is sequentially changed, the switching valve corresponding to the nozzle in the first-order region is closed and the switching valve corresponding to the nozzle in the next-order region is opened, but the switching valve is opened and closed. Takes 30 seconds to 1 minute or more. In addition, the discharge amount of the sand lifting pump is set to be slightly larger than the discharge amount of the water supply pump. At the beginning of water injection to one area, the amount of sediment flowing into the sand collection pit is large and decreases over time. The amount of sediment that settles on the bottom of the sand basin is larger toward the upstream side of the sand basin and smaller toward the downstream side. Therefore, the water level of the sand collection pit during changing the sand collection target area from the earliest region to the last region fluctuates relatively greatly with the passage of time.

Therefore, what is the reference for setting the switching timing of the sand collection target area becomes a problem. That is, when the switching valve corresponding to the nozzle in each region is uniformly switched by the timer, the water level in the sand collecting pit may become low before the sand collection in the entire region is completed, and each time. There is a problem that the sand lifting pump is stopped. If the sand pump is stopped frequently, the load on the sand pump increases and the life of the pump is shortened.

In order to overcome the weakness of the switching valve control by this timer, when it is detected that the water level of the sand collection pit has reached the intermediate water level between the high water level and the low water level during the sand collection operation for a certain area, the sand collection target area It was proposed in Patent Document 2 to perform the switching. According to this method, since the switching of the sand collection target area depends on the water level of the sand collection pit, it is necessary to avoid the water level of the sand collection pit from becoming low before the end of sand collection in the entire area.

However, during heavy rains such as torrential rains, the amount of sediment deposited in the sand basin is particularly large. In such a case, it often takes time for the earth and sand and water collected from the area immediately after the switching of the sand collection target area to arrive at the sand collection pit. Therefore, since the opening / closing time of the switching valve is relatively long, the closing operation of the switching valve in the first-order region and the closing operation of the switching valve in the next-order region are based on the fact that the sand collection from the first-order region is completed and the intermediate water level is detected. It is inevitable that the water level in the sand collecting pit will become low while the switching valve is opened. In addition, since there is a large difference in the amount of sediment accumulated in each area of the sand basin, it is necessary to set the intermediate water level appropriately so that the water level in the sand collection pit does not become low during the switching operation of the switching valve. Have difficulty. Therefore, even in the sand removal method in which the sand collection target area is switched when the intermediate water level is detected, the effect of reducing the stop frequency of the sand lifting pump during sand removal is limited.

Japanese Patent No. 3315489 Japanese Unexamined Patent Publication No. 2014-217843

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an effective sand removal device for further reducing the frequency of stopping the sand lifting pump during sand removal.

In order to achieve the above object, the present invention starts the operation of the sand basin pump provided in the sand basin when the water surface in the sand basin reaches a predetermined high water level or higher, and keeps the sand basin in a drainage state. Low-pressure water is sprayed onto the bottom of the sand basin by a nozzle to flush the sediment accumulated on the bottom of the sand basin to the main trough, and then collect it in the sand collection pit, and the collected sediment is collected together with water by the sand basin pump. In a sand basin sand basin remover that pumps up and stops the operation of the sand basin when the water level in the sand basin reaches a predetermined low water level, the water surface in the sand basin is between the high water level and the low water level. A water level detecting means for detecting that the water level has fallen below the intermediate water level, a water supply means other than the nozzle for supplying water to the sand basin from the outside of the sand basin, and a water level detecting means for detecting that the water level has fallen below the intermediate water level. when, and a water supply control unit for supplying water a certain time to the settling basin by the water supply means other than the nozzle, the prior SL predetermined high level, the magnitude of the volume of the water uptake capacity and the settling basin of the Agesuna pump in response, characterized in that set between the lowest point of the highest point and the main trough of the bottom of the sand basin.

According to the present invention, it is possible to prevent the sand pump from being stopped until the sand collection is completed.

It is a vertical sectional view of a rainwater treatment facility including a sand basin. It is a partially omitted plan view of the range of XX of FIG. FIG. 2 is a cross-sectional view taken along the line Y1-Y1 of FIG. FIG. 2 is a sectional view taken along line Y2-Y2 of FIG. FIG. 2 is a cross-sectional view taken along the line Y3-Y3 of FIG. It is a water supply system diagram. It is a control system diagram which illustrates the control apparatus in 1 Embodiment. It is sectional drawing which shows the detected water level by the water level sensor of a sand collecting pit. It is a perspective view of the bottom surface of a sand basin. It is a flowchart of the sand lifting pump control means. It is a flowchart of a switching valve control means. It is a time chart showing the relationship between the opening / closing timing of the switching valve in the sand collection of each block, the height of the water surface of the sand basin, and the operating state of the water supply pump and the sand lifting pump.

Subsequently, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a rainwater treatment facility, which has a sand basin 2 and a pump well 3 formed between side walls Wa and Wb (see FIG. 2). The sand basin 2 is connected to an inflow culvert 4 in which sewage such as rainwater and sewage is collected from a sewer pipe (not shown). A dam device 5 is installed at the downstream end of the inflow culvert 4 to allow or prevent the inflow of sewage from the inflow culvert 4 to the sand basin 2, and on the downstream side of the dam device 5, the sand basin 2 is installed. A screen 6 for capturing contaminants is installed immediately before the upstream end of the dam.

As described above, the bottom surface 2a of the sand basin 2 is inclined so that a part thereof, for example, the center is the deepest, and the sand collection pit 7 is located at the center of the bottom of the sand basin 2 in order to collect low-pressure sand. Is formed, the main trough 8a is formed in the center of the bottom of the sand basin in the width direction so that the sand collection pit 7 side is deep, and further parallel to the bottom surface of the sand basin from the vicinity of the side walls Wa and Wb to the main trough 8a. A large number of small troughs 8c are formed. When the width of the bottom of the sand basin is small, the main trough 8a may be formed at a position closer to either one of the side walls Wa and Wb instead of the center in the width direction. 8b of FIG. 2 is an inclined surface (also referred to as a sand collecting pit inclined surface in the present specification) that inclines downward from the side walls Wa and Wb to the bottom surface of the sand collecting pit 7.

A drainage pump P1 described later and a water supply pump P2 also serving as a stagnant water pump are installed in the pump well 3, and a sand lifting pump P3 described later is installed in the sand collecting pit 7. FIG. 1F is a filter installed at the downstream end of the sand basin 2.

Further, as shown in FIG. 2, nozzles 9a are installed at the upper end of the main trough 8a and the upper end of the sand collecting pit inclined surface 8b, and the bottom surface of the sand basin 2 is placed on both sides of the main trough 8a to flow water in the sand basin 2. As shown in FIGS. 5 and 6, nozzles 9b are installed at the upper end of the region (block) B divided into a plurality of directions (8 divisions in FIGS. 2 and 6). A plurality of nozzles 9b installed in the region B are installed at equal intervals in the nozzle header NH installed in the vicinity of the side walls Wa and Wb in each region. FIG. 5 shows an example in which nozzle headers NH1, NH2, ..., Which are formed by attaching a plurality of water supply nozzles 9b to the mother pipe 10 at predetermined intervals, are used. Preferably, a sediment stirring nozzle 9c is installed in the sand collecting pit 7.

Then, as illustrated in FIG. 6, the pressurized water from the water supply pump P2 of the pump well 3 is automatically supplied (passed) to each nozzle 9a, 9b, 9c, and the supply is stopped (stopped). A switching valve group VG1 and VG2 composed of valves are provided. The switching valve groups VG1 and VG2 include a switching valve Va for trough nozzles, a switching valve Vb for each nozzle header, and a switching valve Vc for a nozzle for earth and sand stirring, respectively. As illustrated in FIG. 6, when the bottom surface 2a of the sand basin 2 is divided into eight regions, eight nozzle header switching valves Vb (Vb1 to Vb8) are used.

One end of the relief circuit 11 is connected to the pipeline connecting the water supply pump P2 and the switching valve groups VG1 and VG2, and the other end of the relief circuit 11 opens in the sand basin 2, for example, at the upper end of the main trough 8a. I'm letting you. The relief circuit 11 is provided with a switching valve Vd. The relief circuit 11 and the switching valve Vd correspond to water supply means other than the nozzles (9a, 9b, 9c).

The water mixed with earth and sand pumped from the sand collecting pit 7 by the sand lifting pump P3 is transferred to the sewage sedimentation basin 13 after the earth and sand are separated by the known sand settling basin 12.

As illustrated in FIG. 7, an operation panel 101 having a sand removal start button (not shown) is added to the control device 100 provided in the sand removal device according to the embodiment of the present invention, and a drainage pump control circuit is added. PCON1, water supply pump control circuit PCON2, sand pump control circuit PCON3 are built-in, and a switching valve control circuit VCON is also built-in.

The switching valve control circuit VCON includes, as illustrated in FIG. 7, and as will be described later, a sand collection order designation unit 102 that sequentially specifies the order of the area to be collected by injecting water from the nozzle header. Each time an intermediate water level detection signal from the water level sensor 14 is input, the order determination unit 103 that determines whether or not the sand collection order designated by the sand collection order designation unit 102 at that time is the last, and the relief circuit 11 The determination result of the first switching valve control unit 104 that controls the opening and closing of the switching valve Vd and the ranking determination unit 103 after the input of the sand removal operation start command signal or when the intermediate water level detection signal from the water level sensor 14 is input. When it is not the last, the second switching valve control unit 105 that opens the switching valves Va and Vc for nozzles on the main trough and the inclined surface of the sand collecting pit for a predetermined time, and the switching valves Vb1 to Vb8 for the nozzle header in the designated area. Each has a third switching valve control unit 106 that opens for a predetermined time. Then, these switching valve control units 104, 105, 106 give a control signal for causing the group of switching valves Va, Vb, Vc, and Vd to open or close in a predetermined order.

Further, the control device 100 detects whether the water surface of the sand basin at the installation position of the sand collecting pit 7 is at a predetermined high water level HWL or higher, an intermediate water level MWL, or a low water level LWL conceptually shown in FIG. 8A. A water level sensor 14 (see FIGS. 7 and 8A) as a water level detecting means for outputting a detection signal is electrically connected.

The sand lifting pump P3 pumps water from the sand basin, lowers the height of the water surface in the sand basin, and injects low-pressure water from each nozzle 9a, 9b, 9c with the bottom surface of the sand basin exposed from the water surface. It is used to pour and collect the earth and sand on the bottom surface into the sand collection pit 7. The sand lifting pump control circuit PCON3 starts the operation of the sand lifting pump P3 based on the signal output when the water level sensor 14 detects the high water level HWL.

The height at which the water surface in the sand basin 2 is set as the high water level HWL depends on the water absorption capacity of the sand pump P3 and the scale of the sand basin, that is, the size of the volume of the sand basin. When the volume of the sand basin is small compared to the water absorption capacity of the sand pump P3, set the high water level HWL so that the water level does not reach the low water level LWL within a short time from the start of operation of the sand pump P3. To do.

The high water level HWL can be set to the highest point H0 (see FIGS. 8A and 8B) on the bottom surface of the sand basin 2 and can be set in the sand collection pit 7. Further, when the volume of the sand basin is large compared to the water absorption capacity of the sand pump P3, it takes a long time from the start of operation of the sand basin P3 until the water level reaches the low water level LWL, so that the lowest point of the main trough 8a If H3 (see FIGS. 8A and 8B) can be set to a high water level HWL and the relationship between the water absorption capacity of the sand pump P3 and the volume of the sand basin is in the middle of the above example, the highest point H1 of the main trough 8a Between and the lowest point H3, for example, the lowest point H2 (see FIGS. 8A, 8B) at the bottom of the sand basin can be set to a high water level HWL. FIG. 8A shows an example in which a high water level HWL is set at the lowest point H3 of the main trough 8a. In addition, in FIG. 8B, the small trough 8c on the bottom surface of the sand basin of FIG. 2 is omitted.

Subsequently, the operation of the above configuration will be described. When the dam device 5 is opened, the sewage flows into the sand sink 2 and further flows into the pump well 3, and when the water level reaches a predetermined height, the drainage pump control circuit of the control device 100 of the sand removal device 100. The drainage pump P1 provided in the pump well 3 is operated by the PCON 1, and the water in the pump well 3 is pumped up and transferred to a terminal treatment plant or the like (not shown).

During the transfer, sediment is settled from the sewage mixed with sediment that has flowed into the sand basin 2 and is deposited on the bottom surface 2a of the sand basin 2. When the accumulated amount reaches a predetermined value, the dam device 5 is closed to prevent the inflow of sewage into the sand basin 2. Then, when the water levels of the sand basin 2 and the pump well 3 are lowered by the drainage by the drainage pump P1 and reach a predetermined water level (WL in FIG. 1), the operation of the drainage pump P1 is stopped by the drainage pump control circuit PCON1.

When it is detected that the water surface of the pump well 3 has reached a predetermined water level (WL in FIG. 1), the control device 100 activates the water supply pump control circuit PCON2, the sand lifting pump control circuit PCON3, and the switching valve control circuit VCON.

As shown in FIG. 9, the sand-lifting pump control circuit PCON3 starts the automatic operation mode of the sand-lifting pump P3 (S11), and the water level in the sand collecting pit 7 is set to a predetermined high water level by the detection signal from the water level sensor 14. It is checked whether or not it is HWL or higher (S12), and when the water level is higher than HWL, the operation of the sand lifting pump P3 is started (S13).

Further, as shown in FIG. 10, the switching valve control circuit VCON activates the control program based on the input of the sand removal operation start command signal from the operation panel 101, and the first switching valve control unit 104 first releases the relief circuit. The switching valve Vd of the above is opened (step S21 of FIG. 10, at the time of t1 in FIG. 11). As a result, the drive of the water supply pump P2 is prepared.

Subsequently, the second switching valve control unit 105 opens the switching valve Va for the trough nozzle and the switching valve Vc for the nozzle for agitating earth and sand (S22, at the time of t2 in FIG. 11). At the same time, the first timer (not shown) is started (S23), and the first switching valve control unit 104 closes the switching valve Vd of the relief circuit 11 (S23'). When the time of the first timer is up (at the time of t3 in FIG. 11), that is, when the water from the water supply pump P2 is ejected from the nozzle 9a to the main trough 8a and the sand collecting pit inclined surface 8b for a predetermined time (Y in S24). ), The second switching valve control unit 105 closes the switching valve Va for the trough nozzle and the switching valve Vc for the nozzle for stirring earth and sand (S25).

Next, the switching valve control circuit VCON monitors whether or not the water level sensor 14 outputs an intermediate water level detection signal (S26). It is designed to open the switching valve Vd of the relief circuit 11 (S27) when the intermediate water level (MWL) or lower is detected, and to close the switching valve Vd (S29) when a certain time elapses (Y in S28). ing. The switching valve control circuit VCON corresponds to a water supply control means for supplying water to the sand basin for a certain period of time by a water supply means other than the nozzle when the water level sensor 14 detects an intermediate water level (MWL) or less.

When the intermediate water level (MWL) or lower is not detected in S26, the sand collection order designation unit 102 of the switching valve control circuit VCON increments (i + 1) the order (i) (S210). The third switching valve control unit 106 opens the nozzle header switching valve Vb1 in the region of the order designated by the sand collection order designating unit 102, that is, in this case, the first region B1 (S211; t3 in FIG. 11). At the time.). Therefore, water is jetted from each nozzle 9b of the nozzle header NH1, and the earth and sand accumulated in the first region B1 is flowed toward the main trough 8a and further flows into the sand collecting pit 7. In this way, the sewage mixed with earth and sand collected in the sand collection pit 7 is pumped up by the sand lifting pump P3 and transferred to the sewage sedimentation basin 13 via the sand sedimentation separator 11.

When the nozzle header switching valve Vb1 in the first region B1 is opened, the second timer T2 is started (S212). The switching valve control circuit VCON checks whether or not the switching valve Vb is fully opened within the predetermined time set in the second timer T2 (S213), and if it is not fully opened within the predetermined time, returns to step S210. And advance the sand collection order to the next. That is, it is considered that the switching valve Vb is defective, and the switching valve Vb in the next order is opened.

When the switching valve Vb is fully opened within the predetermined time in S213, the switching valve Vb is closed when the second timer T2 is timed up (when it is Y in S214) (S215, at the time of t4 in FIG. 11). Then, it is examined whether or not the intermediate water level (MWL) or lower is detected again (S216).

Since the discharge amount of the sand lifting pump P3 is designed to be larger than the discharge amount of the water supply pump P2, the water level in the sand collecting pit 7 initially temporarily rises due to the inflow of water and earth and sand, but eventually decreases. Then, when the water level sensor 14 detects that the water level in the sand basin is below the predetermined intermediate water level MWL (at Y in S216; at t5 in FIG. 11), first, the switching valve control circuit VCON The first switching valve control unit 104 opens the switching valve Vd of the relief circuit 11 for a predetermined time (S217; t5-t6 in FIG. 11). As a result, the pressurized water from the water supply pump P2 is discharged to the main trough 8a.

Further, when the water level sensor 14 detects that the water level has fallen below the intermediate water level, the order determination unit 103 of the switching valve control circuit VCON determines whether or not the sand collection order designated by the sand collection order designation unit 102 at that time is the last. Is determined (S218).

If it is not determined to be the last (in the case of N in S218), the process returns to S22. Therefore, until the sand collection in the last region is completed, water is discharged from the nozzle 9b to the main trough 8a and the inclined surface of the sand collection pit 8b for a predetermined time, water is discharged from the nozzle header for a predetermined time, and the intermediate water level is detected. Water supply from the relief circuit 11 to the sand basin is repeated. As a result, the earth and sand in the entire area of the bottom surface of the sand basin is flushed to the main trough 8a together with water, and is flushed toward the sand collecting pit 7.

During this period, the sand lifting pump control circuit PCON3 constantly monitors the detection state of the water level sensor 14 from the start of operation (S13) of the sand lifting pump P3. Then, as described above, water is discharged from the main trough 8a and the inclined surface of the sand collecting pit 8b for a predetermined time and from the nozzle header for a predetermined time. Further, during the initial fixed time of each sand removal operation, the amount of water, earth and sand, etc. flowing into the sand collection pit 7 from the main trough 8a and the inclined surface 8b of the sand collection pit is large, so that the sand pump P3 has a pumping capacity. Since it is suppressed, the discharge amount of the sand lifting pump P3 may be less than or equal to the discharge amount of the water supply pump. This is the reason why the water level in the sand collecting pit 7 initially temporarily rises due to the inflow of water and earth and sand during the sand removal operation described above, but eventually falls to a predetermined intermediate water level.

When the rank determination unit 103 determines the last region, that is, the fourth region B4 (when Y in S213), the switching valve control circuit VCON has a predetermined time from the nozzle header with respect to the last region (fourth region). When the intermediate water level is detected after the water is discharged, the series of switching valve control is terminated later. Further, when the water level sensor 14 detects that the water surface in the sand collection pit has reached a predetermined low water level LWL (at t17 in FIG. 11), the water supply pump control circuit PCON2 also stops the operation of the water supply pump P2.

As described above, the nozzle header switching valve Vb4 in the fourth region B4 is closed, the water surface in the sand collecting pit 7 is lowered to the intermediate water level MWL, and the first switching valve control unit 104 is the switching valve Vd of the relief circuit 11. After opening for a certain period of time, the water level in the sand collecting pit 7 eventually drops to the low water level LWL (when Y in S219), so that the sand lifting pump control circuit PCON3 stops the operation of the sand lifting pump P3 (when it is Y in S219). S15).

After that, the sand lifting pump control circuit PCON3 checks whether or not the control of the switching valve is completed (S16), returns to step S12 if it is not completed, and if the water level becomes high (when Y in S12), The operation of the sand lifting pump P3 is started again. However, after confirming the completion of the switching valve control (when Y in S16), the automatic operation mode of the sand lifting pump is released (S17).

In addition, if the amount of sediment that has flowed into the sand basin and accumulated due to the large amount of rainfall is large and the sediment on the bottom of the sand basin cannot be completely removed by one sand removal operation, sand removal is started again. The same sand removal operation may be performed continuously by operating the button.

To summarize the above, the switching valve Vd is opened for a certain period of time when all the switching valves Va, Vb, and Vc are closed at the beginning of sand collection and at the end of sand collection, and mainly pressurized water from the water supply pump P2. It is discharged to the upper end of the trough 8a. This prevents an excessive load from being applied to the water supply pump P2 when all the switching valves Va, Vb, and Vc are closed. In addition, since the sediment accumulated in the main trough 8a at the beginning of sand collection is washed away before the full-scale sand collection starts, it flows down from the bottom of the sand basin to the main trough 8a when the full-scale sand collection starts. The sediment can smoothly flow down the main trough 8a to the sand collection pit.

When it is detected that the height of the water surface of the sand basin is below the intermediate water level and the sand collection target area is changed without supplying water to the sand basin from the relief circuit, MWL to LWL in FIG. As shown by the dotted line extending diagonally downward in the direction, the water level of the sand basin may drop to the low water level (LWL). However, in the present embodiment, when it is detected that the height of the water surface of the sand basin reaches the intermediate water level every time the sand collection target area is changed, the switching valve of the relief circuit is opened for a certain period of time. Since water is supplied to the sand basin (main trough), it is possible to prevent the water level of the sand basin from becoming low while the sand collection target area is replaced. Therefore, the operation of the sand lifting pump is not stopped before the sand collection from the entire area is completed.

In the above embodiment, water is supplied to the main trough 8a from the relief circuit 11 connected to the pipeline of the water supply pump P2, but water may be supplied to a sand basin other than the main trough 8a. Further, as another embodiment, water may be supplied from the pump well into the sand basin via a pump other than the water supply pump P2, or water outside the sand basin such as a river or lake near the sand basin may be used. ..

In addition, (a) the distribution of sediment accumulation in the sand basin is generally the largest on the inflow side of the sand basin and decreases toward the downstream side. When the sand collection pit where the sand pump is installed is located in the center of the front and back of the sand basin, the upstream side is about 60 to 70% and the downstream side is about 30 to 40%. When the upstream side is divided into two regions in the front and back, the upstream side of these two regions is about 50-60% and the downstream side is about 40-50%. Further, (b) the flow rate of earth and sand to the sand collection pit is large for each region and immediately after the start of sand collection, and decreases with the passage of time. Then, (c) the ratio of the amount of jet water to the amount of earth and sand at the time of sand collection is generally said to be that the water transfers sand at a sand content of 5% as a fluid transfer capacity. This is an average value, but it is also considered to be about 5% even when removing sand from a sand basin. However, since a certain amount of sand lumps flow down at the initial stage of sand collection, it is about 10% at first, about 5% after a while, and after that, a small amount of sand is washed away with almost water.

Since the range of change in water level due to the amount of sand is relatively small, if the water injection time and intermediate water level in each region are set appropriately, the water level will not easily drop to a low level even when the amount of sand is small. It is possible. Further, when water is replenished from the water supply pump to the sand basin when the intermediate water level is detected, the accuracy of setting the intermediate water level is further relaxed.

1 Rainwater treatment equipment 2 Sand basin 2a Bottom of sand basin 3 Pump well 7 Sand collection pit P1 Drainage pump P2 Water supply pump P3 Sand lifting pump 8a Main trough 8b Inclined surface of sand collection pit 8c Small trough 9a, 9b, 9c Nozzle NH1 NH8 Nozzle header 14 Water level sensor (water level detection means)
HWL High water level MWL Intermediate water level LWL Low water level Va, Vb, Vc, Vd switching valve 11 Relief circuit 11, Vd Water supply means other than nozzle VCON switching valve control circuit (water supply control means)

Claims (1)

When the water level in the sand basin rises above a predetermined high level, the sand lifting pump provided in the sand collection pit is started to operate, and while keeping the sand basin in a drainage state, low pressure is applied to the bottom surface of the sand basin by a nozzle. Water is sprayed to flow the sediment accumulated on the bottom of the sand basin to the main trough, and then collected in the sand collection pit, and the collected sand is pumped up with water by the sand lifting pump, and the water level in the sand basin is at a predetermined low level. In the sand removal device of the sand basin, which stops the operation of the sand lifting pump when the water level is reached.
A water level detecting means for detecting that the water level in the sand basin is below the intermediate water level between the high water level and the low water level, and a water supply means other than the nozzle for supplying water to the sand basin from the outside of the sand basin. A water supply control means for supplying water to the sand basin for a certain period of time by a water supply means other than the nozzle when the water level detecting means detects that the water level has fallen below the intermediate water level.
Previous SL predetermined high water level, in accordance with the magnitude of the volume of the water uptake capacity and the settling basin of the Agesuna pump, that has been set between the lowest point of the main trough and the highest point of the bottom of the settling basin A featured sand removal device for sand basins.

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