JP6476405B2 - Sand removal method for sand basin - Google Patents

Description

  The present invention relates to a sand removal method in which earth and sand deposited in a sand basin of a sewage treatment facility are collected together with water in a sand collecting pit, and the collected earth and water are pumped up and removed by a pump.

  Sand collected at the bottom of the sand basin by discharging low pressure water from the nozzle to the bottom of the sand basin while draining the water in the sand basin with a drain pump (draining state) Patent Document 1 discloses a low pressure sand collection type sand removal device that collects sand and sand in the pit, pumps the collected earth and sand together with water by a sand pump installed in the sand collection pit, and transfers it to a sewage settling basin.

  A sand basin that performs low-pressure sand collection by the sand removal device has the following structure. That is, the bottom surface of the sand basin is inclined so that a part thereof, for example, the center is deepest, and a sand collecting pit is formed in a part of the bottom surface, and the bottom part of the sand basin is formed between the side walls on both sides of the sand basin. The trough parallel to the water flow direction in the sand basin (hereinafter referred to as the main trough) is formed so as to be inclined so that the sand collecting pit side is deeper, and the bottom surface of the sand basin is perpendicular to the water flow direction in the sand basin A large number of troughs (hereinafter referred to as small troughs) extending in parallel with each other are formed.

  In order to perform low-pressure sand collection, a number of nozzles are installed as follows. That is, the upper end of the main trough that is inclined so that the sand collecting pit side is deep, the upper end of the inclined surface of the sand collecting pit (hereinafter referred to as the sand collecting pit inclined surface), and the bottom surface of the sand basin are placed in the sand basin. Nozzles are respectively installed on the upper ends of blocks (regions) divided into a plurality of water flow directions. Hereinafter, the nozzles installed on the upper end of the main trough and the sand collecting pit inclined surface may be referred to as trough nozzles. A plurality of nozzles of the block are installed at equal intervals on nozzle headers installed along the side walls of the sand basin in each block. In some cases, a sediment mixing nozzle is installed in the sand collection pit.

  In addition, in order to perform low-pressure sand collection, water from a water supply pump installed in a pump well connected downstream of the sand basin is supplied (flowed) to the trough nozzle and nozzle header. A switching valve group for stopping (water stopping), that is, a trough nozzle switching valve, a switching valve for each nozzle header, or a switching valve for a stirring nozzle is further provided. For example, when the bottom surface of the sand basin is divided into four blocks, there are four nozzle header switching valves. The sand removal apparatus has switching valve control means for switching these nozzle header switching valves in a predetermined order.

  In preparation for the sand removal operation, the dam device installed on the upstream side of the sand basin is kept open and rainwater, sewage and other sewage is flowing into the sand basin and installed in the pump well. The drainage pump is operated and the supernatant water is transferred to the final treatment plant. Then, the dam device is closed to prevent sewage from entering the sand basin. As a result, when the amount of water in the pump well is reduced and the water surface becomes the same height as the upper surface of the weir provided between the sand basin and the pump well, the operation of the drainage pump is stopped. Thereby, the preparation for the sand removal operation is completed.

  Subsequently, when a sand removal operation start command is input to the sand removal device, the automatic operation mode of the sand pump is started. In automatic operation mode, the sand pump will automatically start operation when the water level sensor installed in the sand collection pit detects that the water level in the sand collection pit has exceeded the specified high water level. When the sensor detects that the water level in the sand collecting pit has reached a predetermined low water level, the operation is automatically stopped. That is, the sand pump operates so as to maintain the drainage state in which the water surface in the sand basin is located in the sand collection pit.

  Further, based on the sand removal operation start command input, the switching valve is controlled by the switching valve control means. However, conventionally, the control of the sand pump and the control of the switching valve have been performed independently.

  More specifically, when the automatic operation mode of the sand pump is started, the sand pump is started because the water level in the sand collecting pit is higher than the high water level. As a result, the water level in the sand collecting pit is lowered to a predetermined low water level, so the sand pump is stopped. Following this, the switching valve control means controls the switching valve as follows. Below, the case where the bottom face of a sand basin is divided into 4 blocks is demonstrated to an example.

a) The switching valve control means first opens the trough nozzle switching valve and supplies the water from the water supply pump to the main trough and the trough nozzles on the inclined surface of the sand collection pit, so that water is injected from the trough nozzles. b) After the time Tx necessary for the earth and sand in the main trough to flow into the sand collecting pit has elapsed, the nozzle header switching valve of the first block on the bottom surface of the sand basin is opened for a certain time T1. c) After the lapse of the predetermined time T1, the nozzle header switching valve of the first block is closed and the nozzle header switching valve of the second block is opened for the predetermined time T2. d) After the lapse of the predetermined time T2, the nozzle header switching valve of the second block is closed and the nozzle header switching valve of the third block is opened for the predetermined time T3. e) After the predetermined time T3 has elapsed, the nozzle header switching valve of the third block is closed, and the nozzle header switching valve of the fourth block is opened for a predetermined time T4. f) After the lapse of the predetermined time T4, the nozzle header switching valve of the fourth block is closed and the trough nozzle switching valve is closed.
The fixed times T1 to T4 are times necessary for flowing the sediment accumulation amount of the block.

  After closing the nozzle header switching valve in the 4th block, the water in the sand basin flows into the sand collecting pit and the sand basin is drained, that is, when the water level sensor detects a low water level. The sand pump stops operating. Thereby, a series of sand removal operations is completed. When this series of sand removal operations is completed, the automatic operation mode of the sand pump is canceled.

Japanese Patent No. 3315489

  The opening operation of the nozzle header switching valve in the subsequent block performed after each of the predetermined times T1 to T4 has a slight difference depending on the type of the switching valve, but it is relatively long as 30 seconds to 1 minute. It takes time. For this reason, the water level in the sand collecting pit may be lowered to a predetermined low water level each time the switching valve is switched. Therefore, each time, the sand pump was automatically operated and stopped repeatedly. That is, when the water level in the sand collection pit is at a predetermined high water level, the operation of the sand pump is automatically started, and when the water level is at a predetermined low level, the operation of the sand pump is automatically stopped. In the sand method, since the frequency of start and stop of the sand pump is high, there is a problem that a normal pump has a large load and a short service life. Although it is conceivable to use a pump that takes into account the high frequency of starting and stopping operations, there is a problem that such a pump is expensive.

  In addition, a water supply pump that supplies pressurized water to each nozzle and nozzle header may be repeatedly operated and stopped according to repeated operation and stop associated with changes in the water level of the sand pump. The pump has a problem that the load is large and the service life is short.

  The present invention has been made in view of the above circumstances, and its purpose is to reduce the frequency of start and stop of the operation of the water supply pump and the sand pump as much as possible, and to use a normal inexpensive pump. It is to provide a sand removal method that makes possible.

In order to achieve the above object, the present invention provides a main trough that inclines so that the low pressure water supplied from the water supply pump is deepened on the sand collecting pit side of the sand basin while draining the sand basin. Injecting the low-pressure water in a predetermined order for each block from the nozzle of the nozzle header provided in the block formed by dividing the bottom surface of the sand basin into a plurality of blocks while injecting from the nozzle installed on the inclined surface of the sand pit, The sediment accumulated in the block is poured into the main trough, collected in the sand collection pit, and automatically installed when the water level in the sand collection pit is higher than a predetermined high water level. In the sand removal method for starting and removing the earth and sand with a sand pump that automatically stops operation when the water level in the sand collecting pit reaches a predetermined low water level, The converging said water surface in the sand pit and the high level every time it drops to a predetermined intermediate water level between the low water level, the predetermined time of the water from the nozzle of the inclined surface of said main trough and said current sand pits by pumping by Injecting and subsequent water injection from the nozzle of the nozzle header of the block for a predetermined time are performed , and this process is repeated until the last block.

  Here, the water injection for a predetermined period of time may mean that the water level sensor detects the intermediate water level between the time when the switching valve is closed for the preceding block and the time when the switching valve is opened for the subsequent block. However, it is the water injection of the time set so that a low water level may not be detected.

According to the present invention, every time the water level in the sand collecting pit is lowered to a predetermined intermediate water level between a predetermined high water level and a predetermined low water level by pumping by the sand pump, the inclined surface of the main trough and the sand collecting pit and water injection of a predetermined time from a nozzle installed in performs a predetermined time of the water injection from the nozzles of the nozzle headers of subsequent blocks, so to repeat this process until the last sequence of blocks, the operation of the Agesuna pump And the frequency of outages can be minimized . Therefore, it is possible to use a normal inexpensive pump for the sand pump.

It is a longitudinal cross-sectional view of the rainwater treatment facility including a sand basin. FIG. 2 is a partially omitted plan view of a range of XX in FIG. 1. FIG. 3 is a cross-sectional view taken along line Y1-Y1 of FIG. FIG. 3 is a sectional view taken along line Y2-Y2 of FIG. FIG. 3 is a cross-sectional view taken along line Y3-Y3 of FIG. It is a water supply system diagram. It is a control system diagram which illustrates the control device in one embodiment. It is sectional drawing which shows the detection water level by the water level sensor of a sand collection pit. It is a flowchart of a sand pump control means. It is a flowchart of a switching valve control means.

Next, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a rainwater treatment facility, which includes a sand basin 2 and a pump well 3 formed between side walls Wa and Wb (see FIG. 2). The settling basin 2 is connected to an inflow trough 4 from which sewage such as rainwater and sewage is collected from a sewage pipe not shown. A dam device 5 for allowing or preventing the inflow of sewage from the inflow trough 4 to the sand basin 2 is installed at the downstream end of the inflow trough 4. A contaminant capturing screen 6 is installed immediately before the upstream end of the screen.

  In order to perform low-pressure sand collection, the bottom surface 2a of the sand basin 2 is inclined so that a part thereof, for example, the center becomes the deepest as described above, and the sand collection pit 7 is formed at the bottom center of the sand basin 2. A main trough 8a is formed at the center in the width direction of the bottom of the sand basin so as to be inclined so that the sand collecting pit side becomes deeper. Further, the main trough 8a is formed on the bottom surface of the sand basin from the vicinity of the side walls Wa and Wb. A number of small troughs 8c extending in parallel to each other are formed. When the width of the bottom of the sand basin is small, the main trough 8a may be formed not at the center in the width direction but at a position closer to either one of the side walls Wa and Wb. Reference numeral 8b denotes an inclined surface that is inclined downward from the side walls Wa and Wb to the bottom surface of the sand collecting pit 7 (also referred to as a sand collecting pit inclined surface in this specification).

  In the pump well 3, a drainage pump P <b> 1 described later and a water supply pump P <b> 2 serving also as a staying water pump are installed, and a sand pump P <b> 3 described later is installed in the sand collecting pit 7. F of FIG. 1 is a filter installed at the downstream end of the sand basin 2.

  In addition, a nozzle 9a is 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 is divided into a plurality of sides on both sides of the main trough 8a (in FIG. 2 and FIG. 6, 8 sections). A nozzle 9b is installed at the upper end of the block (area) B. A plurality of nozzles 9b installed in the block B are installed at equal intervals on the nozzle header NH installed in each block in the vicinity of the side walls Wa and Wb. FIG. 5 shows an example in which nozzle headers NH1, NH2,... Formed by attaching a plurality of water supply nozzles 9b to the mother pipe 10 at a predetermined interval are shown. Preferably, a sediment agitation nozzle 9 c is installed in the sand collection pit 7.

  Then, as illustrated in FIG. 6, the water from the water supply pump P <b> 2 of the pump well 3 is supplied to the nozzles 9 a, 9 b and 9 c (water passing), or the supply is stopped (water stopping). Switching valve groups VG1 and VG2 constituted by automatic valves, that is, a trough nozzle switching valve Va, a nozzle header switching valve Vb, and a sediment agitation nozzle switching valve Vc are provided. As illustrated in FIG. 6, when the bottom surface of the sand basin is divided into eight blocks, eight nozzle header switching valves Vb (Vb1 to Vb8) are used.

  A relief circuit 11 is provided via a switching valve Vd in a pipe line connecting the water supply pump P2 and the switching valve groups VG1 and VG2, and the water supply pump when all the switching valves Va, Vb, and Vc are closed. The water from P2 is configured to escape to the sand basin 2. Thus, when all the switching valves Va, Vb, and Vc are closed, the water level in the sand basin can be maintained by supplying water from the water supply pump P2 to the sand basin 13.

  In addition, the soil-mixed water pumped up from the sand collection pit 7 by the sand pump P3 is transferred to the sewage sedimentation basin 13 after the sediment is separated by a known sedimentation separator 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 for carrying out the method of the present invention, and a drain pump control circuit PCON1, A feed water pump control circuit PCON2 and a sand pump control circuit PCON3 are incorporated, and a switching valve control circuit VCON is incorporated.

  As illustrated in FIG. 7 and as will be described later, the switching valve control circuit VCON includes a block order designating unit 102 for sequentially designating the order of blocks to which water should be injected from the nozzle header, and a water level sensor 14 described later. Each time an intermediate water level detection signal is input, a rank determination unit 103 that determines whether or not the block rank designated by the block rank designation unit 102 is in the last order, and the switching valve Vd of the relief circuit are opened and closed. When the determination result of the rank determination unit 103 is not in the last order after the first switching valve control unit 104 that controls the sand removal operation start command or the intermediate water level detection signal from the water level sensor 14 is input, And a second switching valve control unit 105 that opens the nozzle switching valves Va and Vc on the sand collecting pit inclined surface for a predetermined time, and a nozzle header switching valve of a block in which the order is designated and a third switching valve control unit 106 that opens each of b1 to Vb8 for a predetermined time, and gives a control signal for driving the opening or closing operation in a predetermined order to the group of switching valves Va, Vb, Vc, Vd. Is.

  Further, the control device 100 detects and outputs whether the water level at the installation position of the sand collecting pit 7 is higher than the predetermined high water level HWL conceptually shown in FIG. 8, the intermediate water level MWL, or the low water level LWL. A water level sensor 14 (see FIGS. 7 and 8) is electrically connected.

  When the sand pump P3 is operated, it draws the water in the sand basin, lowers the height of the water surface in the sand basin, and exposes the bottom surface of the sand basin from the surface of each nozzle 9a, 9b, 9c. It is used for spraying water and pouring the sediment on the bottom into the sand collecting pit. Based on the signal output when the water level sensor 14 detects the high water level HWL, the sand pump control circuit PCON3 Starts operation of the sand pump P3.

  Where the water level at the position of the sand collecting pit 7 is set as the high water level HWL depends on the water absorption capacity of the sand pump P3 and the size of the sand basin, that is, the volume of the sand basin. The high water level HWL defines an upper water level suitable for initiating low pressure sand collection. In order to prevent the water level from reaching the low water level LWL within a short time from the start of operation of the sand pump P3 when the volume of the sand basin is small compared to the water absorption capacity of the sand pump P3, the main trough It is desirable to set the highest point H1 of 8a (see FIGS. 2 and 8) to the high water level HWL. In addition, when the volume of the sedimentation basin is large compared to the water absorption capacity of the sand pump P3, the time from the start of operation of the sand pump P3 until the water level reaches the low water level LWL is long, so the lowest point of the main trough 8a H3 (see FIGS. 2 and 8) can be set to the high water level HWL, and when the relationship between the water absorption capacity of the sand pump P3 and the volume of the sedimentation basin is in the middle of the above example, the highest point H1 and the lowest During the point H3, for example, the lowest point H2 (see FIGS. 2 and 8) on the bottom of the sand basin can be set to the high water level HWL. FIG. 8 shows an example in which a high water level HWL is set at the lowest point H3 of the main trough 8a.

  Then, the effect | action by the said structure is demonstrated. When the dam device 5 is opened, the sewage flows into the sand basin 2 and further into the pump well 3, and when the water level reaches a predetermined height, the drain pump control circuit of the control device 100 of the sand removal device. The drain pump P1 provided in the pump well 3 is operated by PCON1, and the water in the pump well 3 is pumped up and transferred to a terminal treatment plant or the like outside the figure.

  During the transfer, earth and sand are precipitated from the sewage mixed with the earth and sand flowing into the sand basin 2 and deposited on the bottom surface 2a of the sand basin. When the accumulation amount reaches a predetermined value, the dam device 5 is closed and the sewage flow into the sand basin 2 is prevented. And if the water surface of the sand basin 2 and the pump well 3 falls by the drainage by the drainage pump P1 and reaches a predetermined water level (WL in FIG. 1), the drainage pump control circuit PCON1 stops the operation of the drainage pump P1.

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

  As shown in FIG. 9, the sand pump control circuit PCON3 starts the automatic operation mode of the sand 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 equal to or higher than HWL (S12).

  Further, as shown in FIG. 10, the switching valve control circuit VCON starts a control program based on a sand removal operation start command input from the operation panel 101, and the first switching valve control unit 104 first switches the relief circuit. The valve Vd is opened to prepare for driving the water supply pump P2 (step S21 in FIG. 10). Subsequently, after the second switching valve controller 105 opens the trough nozzle switching valve Va and the earth and sand agitation nozzle switching valve Vc (S22), the first timer (not shown) is started (S23), and The one switching valve control unit 104 closes the switching valve Vd of the relief circuit 11 (S23 ′). When the first timer expires, that is, when water from the water supply pump P2 is sprayed 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 trough nozzle switching valve Va and The switching valve Vc for the earth and sand stirring nozzle is closed (S25). Subsequently, since the block order specifying unit 102 of the switching valve control circuit VCON increments (i + 1) the order (i) (S26), the third switching valve control unit 106 has the order specified by the block order specifying unit 102. In order to open the nozzle header switching valve Vb1 of the block, that is, the first block B1 in this case (S27), water is injected from each nozzle of the nozzle header NH1, and the sediment accumulated in the first block B1 is removed. It flows toward the main trough 8a and further flows into the sand collecting pit 7. Thus, the sewage mixed with the earth and sand collected and stirred in the sand collecting pit 7 is pumped up by the sand pump P3 and transferred to the sewage sand settling basin 13 through the sand settling separator 11.

  When the nozzle header switching valve Vb1 of the first block B1 is opened, a second timer (not shown) is started, and when the time is up by the elapse of a predetermined time set in advance (Y in S29), the first The nozzle header switching valve Vb1 of the block B1 is closed (S210). That is, during the time set in the second timer, water is ejected from the nozzles of the nozzle header of the first block B1.

  Since the discharge amount of the sand pump P3 is designed to be larger than the discharge amount of the water supply pump P2, the water surface in the sand collecting pit 7 rises temporarily due to the inflow of water and earth and sand, but eventually decreases. After that, when the water level sensor 14 detects that the water level in the sand collection pit has reached a predetermined intermediate water level (Y in S211), the rank determining unit 103 of the switching valve control circuit VCON then blocks. It is determined whether or not the order specified in the order specifying unit 102 is the last order (S212).

  If it is not the last order, the process returns to S22, and the second switching valve controller 105 discharges water to the main trough 8a and the sand collecting pit inclined surface 8b for a predetermined time (S22-S25), and then the block order designation unit 102 The next block is designated (S26), and the switching valve control circuit VCON opens the nozzle header switching valve Vb2 of the second block B2 for a predetermined time and then closes it. When it is detected again by the water level sensor 14 that the water level in the sand collecting pit has reached the predetermined intermediate water level, it is then determined whether or not the block order is the last order (S212). That is, until the water injection target block is in the last order, water discharge for a predetermined time (S22-S25) from the nozzle 9a to the main trough 8a and the sand collecting pit inclined surface 8b for the block and water discharge for a predetermined time from the nozzle header ( S27-S210) are repeated. As a result, the earth and sand of all the blocks on the bottom surface of the sand basin are caused to flow along with the water to the main trough 8 a and flow toward the sand collecting pit 7.

  During this time, the sand pump control circuit PCON3 always monitors the detection state of the water level sensor 14 from the start of operation of the sand pump P3 (S13). As described above, water discharge for a predetermined time to the main trough 8a and the sand collecting pit inclined surface 8b and water discharge for a predetermined time from the nozzle header are performed. Further, since the amount of water, earth and sand flowing into the sand collecting pit 7 from the main trough 8a and the sand collecting pit inclined surface 8b is large during the initial fixed time of each sand removal operation, the pumping capacity of the sand pump P3 is high. Therefore, the discharge amount of the sand pump P3 may be less than or equal to the discharge amount of the feed water pump. This is the reason why the water surface in the sand collecting pit 7 temporarily rises due to the inflow of water and soil 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 order, that is, the fourth block B4 (Y in S212), the water level sensor 14 detects that the water level in the sand collection pit has become a predetermined low water level. At (when Y in S213), the first switching valve control unit 104 of the switching valve control circuit VCON performs control to open the switching valve Vd of the relief circuit, and the series of switching valve control is completed. Further, the feed water pump control circuit PCON2 also stops the operation of the feed water pump P2.

  By closing the nozzle header switching valve Vb4 of the fourth block B4, the water level in the sand collecting pit 7 is lowered to the low water level LWL (when Y in S14), so the operation of the sand pump P3 is stopped ( S15). Thereafter, the sand pump control circuit PCON3 checks whether or not the control of the switching valve has been completed (S16). If not completed, the process returns to step S12, and if the water level becomes high (Y in S12). The operation of the sand pump P3 is started again, but after confirming the completion of the switching valve control (Y in S16), the automatic operation mode of the sand pump is canceled (S17).

In summary, when the sand removal operation is started, when the water surface in the sand collection pit 7 at that time is equal to or higher than a predetermined high water level HWL, the operation of the sand pump P3 is started, and the main trough and water from a nozzle placed on the inclined surface of the Atsumarisuna pits are predetermined time injection nozzle header for switching valve of the specified order of the block is opened a predetermined time subsequent to this. And when the water level in the sand collection pit is lowered to a predetermined intermediate water level between a predetermined high water level and a predetermined low water level by pumping by the sand pump, when the order of the designated block is not the last order, Until the water injection for the last block is completed after the water injection for a predetermined time from the nozzle installed on the inclined surface of the main trough and sand collecting pit and the water injection for the predetermined time from the nozzle header switching valve of the next block Repeated. And when the water injection with respect to the last block is complete | finished, control of a switching valve is complete | finished in the state which closed all the switching valves. Since the control of the switching valve is finished with all the switching valves closed, the water level in the sand collecting pit is lowered to a predetermined low water level, and the sand pump is stopped.

  As described above, when the sand pump P3 starts the automatic operation mode, the sand collecting pit 7 is automatically drained when the water level at the sand collecting pit installation position is higher than a predetermined high water level HWL in order to maintain the inside of the sand collecting pit 7 in a drained state. When the water level drops to a predetermined low water level LWL, the operation is automatically stopped. However, in the method of the present invention, water is discharged from the trough nozzle and the earth and sand agitating nozzle for a predetermined time, and water is discharged from the nozzle header of one block for a predetermined time. Each time the water level is lowered, water discharge for a predetermined time from the trough nozzle and the earth and sand stirring nozzle and water discharge for a predetermined time from the nozzle header of the block are repeated until the last block. Therefore, between the switching operation of the switching valve for the preceding block and the switching operation of the switching valve for the succeeding block, the water surface at the sand collecting pit installation position causes water injection by the closing operation of the switching valve for the preceding block. It fluctuates depending on the start of water injection by stopping, pumping up the sand pump, and opening the switching valve for the subsequent block. However, even if the water level sensor may detect the intermediate water level between the closing operation time of the switching valve for the preceding block and the opening operation time of the switching valve for the subsequent block, it should detect the low water level. The opening times of the switching valves Va, Vc, Vb by the second switching valve control unit 105 and the third switching valve control unit 106 are set so that there is no occurrence. The height position of the intermediate water level is set based on the injection amount of each nozzle and each nozzle header, the volume of the sand basin, the discharge amount of the sand pump, and the like.

  If an automatic solenoid valve with a fast switching operation is used as the nozzle header switching valve, the water level in the sand collecting pit from the end of water injection to the previous block to the start of water injection to the next block is reduced. Since the amount of decrease can be reduced, the accuracy in setting the intermediate water level is relaxed. Moreover, since the load of the sand pump is stabilized, the life is extended.

DESCRIPTION OF SYMBOLS 1 Rainwater treatment equipment 2 Settling basin 2a Bottom surface of settling basin 3 Pump well 7 Sand collection pit P1 Drainage pump P2 Water supply pump P3 Sand 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 HWL High water level MWL Intermediate water level LWL Low water level Va, Vb, Vc, Vd selector valve

Claims (1)

In a state where the sand basin is drained, low-pressure water supplied from a water supply pump is injected from a main trough that is inclined so that the sand collecting pit side of the sand basin is deep and nozzles installed on the inclined surface of the sand collecting pit. And spraying the low-pressure water in a predetermined order for each block from a nozzle of a nozzle header provided in a block formed by dividing the bottom surface of the sand basin into a plurality of blocks, and the sediment deposited in the block to the main trough When the water surface in the sand collection pit installed in the sand collection pit is above a predetermined high water level, the operation is automatically started. In the sand removal method, the soil is pumped up and removed by a sand pump that automatically stops operation when the water surface reaches a predetermined low water level.
Each time the water level in the sand collection pit is lowered to a predetermined intermediate water level between the high water level and the low water level by pumping by the sand pump, the main trough and the inclined surface of the sand collection pit from the nozzle of the inclined surface A sand removal method characterized by performing water injection for a predetermined time and water injection for a predetermined time from the nozzle of the nozzle header of the block thereafter, and repeating this step until the last block.

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