An experimental device for simulating water-salt interaction in estuaries with salinity measurement function

Abstract

This invention discloses a water-salt interaction simulation experimental device for estuaries with salinity measurement function, belonging to the field of hydraulic physical models. It includes a water-sand tank with two water level tanks symmetrically arranged on its left and right sides. A water-blocking gate is installed between the water-sand tank and the water level tanks. The water-sand tank is filled with a porous media simulation material, and a salinity measuring device and a perforated pipe are installed inside the tank. A water level control device is installed inside each water level tank. This invention can simulate the water-salt interaction process of heterogeneous aquifers in estuaries and their upstream surface-groundwater systems, conveniently and stably measuring salinity at any location within the aquifer. The device has a simple structure and low measurement cost.

Description

Technical Field

[0001] This utility model relates to an experimental device for simulating water-salt interaction in estuaries with salinity measurement function, belonging to the field of hydraulic physical model technology. Background Technology

[0002] In estuaries and their upstream areas, the water-salt interaction process between surface water and groundwater has a significant impact on regional water resource quality, ecosystem stability, and agricultural water security. Especially under the combined effects of factors such as excessive groundwater extraction, frequent river sand mining, increased extreme weather events, and sea-level rise, the upstream intrusion of saltwater is becoming increasingly severe, exacerbating the salinization of coastal groundwater and becoming a major environmental problem restricting regional sustainable development.

[0003] The main methods for studying surface-groundwater salinity interactions in estuaries and their upstream areas include physical models, numerical simulations, statistical models, and field observations. Compared to field observations and numerical simulations, physical models offer advantages such as more controllable influencing factors, clearer experimental conditions, and higher reliability of results.

[0004] Currently, most physical models used to simulate surface-groundwater salinity interactions in estuaries and their upstream regions are simplified two-dimensional models, typically ignoring aquifer heterogeneity, and most lack real-time monitoring capabilities for salinity changes. Researchers can add specialized salinity measurement devices to these physical models; however, on the one hand, some devices can only obtain data by sampling and measuring salinity in a laboratory setting, lacking the ability to measure salinity in situ, making it difficult to quickly measure salinity at different locations within the physical models of surface-groundwater salinity interactions in estuaries and their upstream regions. On the other hand, while some high-precision sensors can achieve online, rapid salinity measurements, they are costly, complex to install, require strict experimental environments, are difficult to deploy within porous media, are unsuitable for physical models, and are easily affected by water flow disturbances, resulting in poor measurement stability and data repeatability. These difficulties limit a deeper understanding of the water-salt interaction mechanism.

[0005] In the study of surface-groundwater salinity interaction in estuaries and their upstream areas, especially under the condition of three-dimensional heterogeneous aquifers, how to accurately obtain salinity variation information at different depths and spatial locations within the aquifer through physical models is a key challenge currently faced in physical model experiments. Utility Model Content

[0006] The purpose of this invention is to provide an experimental device for simulating water-salt interaction in estuaries with salinity measurement function. This device can simulate the water-salt interaction of heterogeneous aquifers in estuaries and their upstream surface-groundwater under complex conditions. It can also measure the salinity of any cross section inside the aquifer using a salinity measurement device in a three-dimensional experimental device. The device has a simple structure and low measurement cost.

[0007] To achieve the above objectives / to solve the above technical problems, this utility model adopts the following technical solution:

[0008] This utility model provides a water-salt interaction simulation experimental device for estuary areas with salinity measurement function, including a water-sand tank, two water level tanks symmetrically arranged on the left and right sides of the water-sand tank, and a water-blocking gate between the water-sand tank and the water level tanks; the water-sand tank is filled with porous media simulation material, and a salinity measuring device and a perforated pipe are installed in the water-sand tank; a water level control device is installed inside each water level tank.

[0009] Preferably, the water-sand trough is a lidless transparent acrylic box, and the outer edges of the water-sand trough are reinforced with angle steel; the water level tank is a lidless transparent acrylic box without a panel on one side, and the side of the water level tank without a panel is connected to the water-sand trough.

[0010] Preferably, the water-sand trough has evenly distributed circular openings on both side walls near the water level tank, and the side walls are lined with fine screens.

[0011] Preferably, the perforated tube is closed at both ends, and the surface of the tube body is provided with uniformly distributed perforations. The perforation diameter is smaller than the minimum particle size of the porous media simulation material, and a water injection hole is provided at the top of one end of the perforated tube.

[0012] Preferably, the perforated tube is installed against the long side wall of the water-sand tank, and the top of the perforated tube is flush with the upper surface of the porous media simulation material filled in the water-sand tank.

[0013] Preferably, a slot is provided at the connection between the water level tank and the water-sand trough, the water-blocking gate is installed in the slot, and there is a certain distance between the water-blocking gate and the side wall of the water-sand trough.

[0014] Preferably, the salinity measuring device includes a drawer-type support frame, a water-blocking plate, a salinity test paper fixing net, and salinity test paper fixed on the salinity test paper fixing net; the drawer-type support frame includes a base plate and a support keel vertically fixed on the base plate, forming a drawer-type space with an open top between the base plate and the support keel; the water-blocking plate and the salinity test paper fixing net are inserted between the support keel and the base plate of the drawer-type support frame, and the water-blocking plate is located between the support keel and the salinity test paper fixing net, with the side of the salinity test paper fixing net that fixes the salinity test paper facing the base plate of the drawer-type support frame.

[0015] Preferably, the bottom of the drawer-type support frame has a V-shaped structure.

[0016] Preferably, the drawer-type support frame includes a base plate and multiple support keels, which are fixed vertically and at equal intervals to the base plate.

[0017] Preferably, the water level control device includes a screw jack and an overflow plate. The screw jack is fixed to the top of the water level tank, and the overflow plate is fixed to the lifting platform of the screw jack by an extension rod and extends into the water level tank. The overflow plate is provided with an overflow hole, which is connected to the outside of the water level tank through an overflow pipe.

[0018] Compared with the prior art, the beneficial effects achieved by this utility model are as follows:

[0019] This invention proposes a water-salt interaction simulation experimental device for estuaries with salinity measurement function. A porous media simulation material filled in a water-sand tank simulates the heterogeneous aquifer in the estuary and its upstream areas. Combined with a perforated pipe and a water level control device, it can efficiently and accurately simulate the water-salt interaction process between surface water and groundwater in the estuary and its upstream areas. The device incorporates a salinity measuring device installed in a three-dimensional water-salt interaction simulation experimental device for estuaries. This device can be inserted at any cross-sectional position within the aquifer inside the water-sand tank. With the salinity test paper inside the device, the salinity at any location within the water-sand tank can be measured quickly and accurately.

[0020] This utility model device has a simple overall structure, convenient operation for salinity measurement, low measurement cost, and good measurement stability, which greatly increases the usability of the experiment. It is of great significance for improving the research level of water-salt interaction processes in estuaries and their upstream areas, and also has broad application prospects. Attached Figure Description

[0021] Figure 1 The diagram shown is a structural schematic of a water-salt interaction simulation experimental device for estuary areas with salinity measurement function provided in an embodiment of this utility model.

[0022] Figure 2 The figure shown is a partial structural cross-sectional view of the water-salt interaction simulation experimental device in the estuary area in this embodiment of the present invention.

[0023] Figure 3 The diagram shown is a structural schematic of the salinity measuring device in an embodiment of this utility model.

[0024] Figure 4 The diagram shown is an exploded view of the salinity measuring device in an embodiment of this utility model.

[0025] In the diagram, 1 is a water-sand trough, 2 is a salinity measuring device, 2-1 is a drawer-type support frame, 2-2 is a water baffle, 2-3 is a salinity test paper fixing net, 2-4 is a salinity test paper, 3 is a perforated pipe, 4 is a water gate, 5 is a water level tank, 6 is a water level control device, 6-1 is a screw jack, 6-2 is an overflow plate, 6-3 is an extension rod, 7 is an overflow pipe, 8 is a porous media simulation material, 9 is a sand washing drainage hole, and 10 is a partition. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features therein are detailed descriptions of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features therein can be combined with each other.

[0027] This utility model embodiment introduces an experimental device for simulating water-salt interaction in estuaries with salinity measurement function, such as... Figures 1-4 As shown, the main body of the device is a water-sand tank 1. Two water level tanks 5 are symmetrically arranged on the left and right sides of the water-sand tank 1. A water-blocking gate 4 is set between the water-sand tank 1 and the water level tanks 5. A salinity measuring device 2 and a perforated pipe 3 are installed in the water-sand tank 1. A water level control device 6 is installed inside each water level tank 5.

[0028] The water-sand tank 1 is an open, transparent acrylic box. The outer edges of the tank are reinforced with angle steel to prevent deformation. The water-sand tank 1 is filled with porous media simulation material 8, such as quartz sand and glass microspheres. Different particle sizes of quartz sand and glass microspheres are filled in layers to simulate stratified heterogeneous aquifers in estuaries, or different particle sizes of quartz sand are filled in different areas of the same layer to simulate random heterogeneous aquifers in estuaries.

[0029] When filling the porous media simulation material 8, the water in the water-sand tank 1 should always be kept above the porous media simulation material 8, and the filling speed should not be too fast to avoid air bubbles being incorporated into the porous media simulation material 8, which would affect the experimental results. When simulating a stratified heterogeneous aquifer in a river mouth, the thickness of each layer and the form of the interlayer contact surface should be determined according to the experimental requirements, such as a plane or a random irregular curved surface. When simulating a random heterogeneous aquifer in a river mouth, the water-sand tank can be divided into several regular or random irregular units using vertical partitions. Then, porous media simulation material 8 with the corresponding particle size can be filled into different units. After filling, the partitions can be removed.

[0030] The side walls of the water-sand tank 1 near the water level tank 5 have evenly distributed circular openings, typically with a diameter of 5mm, which can be adjusted according to experimental requirements. The side walls of the water-sand tank 1 are lined with fine mesh to prevent the aquifer simulation material from entering the water level tanks 5 and affecting the experimental results.

[0031] The water level tank 5 is a transparent acrylic tank without a lid and without a panel on one side. The panelless side of the water level tank 5 is connected to the sand trough 1. The sand trough 1 and the water level tank 5 can be fixedly connected together or movably connected together through a slot or other means. When a movable connection is used, a sealing strip or similar material must be used to ensure a proper seal.

[0032] Two water level tanks 5 on either side of the water-sand tank 1 are used to simulate the saltwater interaction process: one is a freshwater tank (containing freshwater), and the other is a seawater tank (containing seawater). At least two sand washing and drainage holes 9 are provided at the bottom of the water-sand tank 1, symmetrically distributed near the two water level tanks 5. These holes are used to rinse the salt in the porous media simulation material 8 filling the water-sand tank 1 after the experiment, restoring the experimental setup to its initial state.

[0033] A baffle 10 can be installed in the water level tank 5 to separate the surface water in the tank and reduce water surface fluctuations in the tank 5, so as to measure the water level and improve the accuracy of experimental parameter measurement.

[0034] The perforated tube 3 is a thin-walled tubular structure made of stainless steel, specifically a cubic tube. Its length is the same as that of the water-sand tank 1, while its height and width are determined according to experimental requirements. The perforated tube 3 is closed at both ends, and each surface has uniformly distributed perforations. The diameter of these perforations is smaller than the minimum particle size of the porous media simulation material 8 filled in the water-sand tank 1, preventing the porous media simulation material 8 from entering the perforated tube 3 and causing blockage, thus affecting the experimental results. For example, the dimensions of the perforated tube 3 could be set as 2 m × 0.01 m × 0.05 m, with a perforation diameter of 0.5 mm and a perforation spacing of 1 mm. A water injection hole is provided at the top of one end of the perforated tube 3. The diameter of this water injection hole should be larger than that of a typical water injection pipe to facilitate the insertion of a water injection pipe, for example, 8 mm.

[0035] The perforated pipe 3 is installed against the long side wall of the water-sand tank 1, and the top surface of the perforated pipe 3 should be flush with the upper surface of the porous medium simulation material 8 filled in the water-sand tank 1. In the experiment simulating the water-salt interaction in the estuary, seawater flows to the freshwater tank through the perforated pipe 3. The high concentration of seawater in the perforated pipe 3 infiltrates into the interior of the water-sand tank 1 to simulate the upstream intrusion of saltwater in the estuary.

[0036] The water-retaining gate 4 is a flat acrylic plate gate. Slots are provided at the connection points between the two side water level tanks 5 and the water-sand trough 1. The water-retaining gate 4 is detachably installed in these slots, allowing the water-sand trough 1 to be separated from the two side water level tanks 5 when needed. There is a certain distance between the water-retaining gate 4 and the side walls of the water-sand trough 1. The specific distance can be determined based on experimental requirements and experience. When the water-retaining gate 4 is closed, an external peristaltic pump is used to inject water into the space between the water-retaining gate 4 and the porous side walls of the water-sand trough 1. By adjusting the peristaltic pump, the flow boundary conditions of this physical model can be controlled.

[0037] When the water gate 4 is opened, the water level tanks 5 on both sides of the water-sand trough 1 can be connected to the water-sand trough 1 through the openings on both sides of the water-sand trough 1, and together with the water level control device 6 inside the water level tank 5, the water level in the experimental device can be controlled.

[0038] The water level control device 6 includes a screw jack 6-1 and an overflow plate 6-2. The screw jack 6-1 is fixed to the top of the water level tank 5, and the overflow plate 6-2 is fixed to the lifting platform of the screw jack 6-1 via an extension rod 6-3 and extends into the water level tank 5. The overflow plate 6-2 has an overflow hole, which is connected to the outside of the water level tank 5 via an overflow pipe 7. By controlling the lifting and lowering of the screw jack 6-1, the height of the overflow plate 6-2 inside the water level tank 5 can be controlled. Water exceeding the height of the overflow hole will overflow through the overflow pipe 7, thereby controlling the water level inside the water level tank 5 and achieving the purpose of controlling the experimental head boundary.

[0039] The salinity measuring device 2 is used to measure the salinity of the internal cross-section of the water-sand tank 1. It includes a thin drawer-type support frame 2-1, a water-retaining plate 2-2, a salinity test paper fixing net 2-3, and salinity test papers 2-4 fixed on the salinity test paper fixing net. The drawer-type support frame 2-1 is an integrated structure of a base plate and a frame. One side of the base plate is a thin iron sheet, and the other side is a support keel vertically fixed on the thin iron sheet. The support keel is made of high-strength metal material, and a drawer-type space with an open top is formed between the base plate and the support keel. The water-retaining plate 2-2 is generally made of metal or plastic. The dimensions of the water-retaining plate 2-2 and the salinity test paper fixing net 2-3 are similar to the dimensions of the drawer-type support frame 2-1, and they can be inserted between the support keel and the base plate of the drawer-type support frame 2-1.

[0040] Multiple salinity test papers 2-4 are fixed on the salinity test paper fixing net 2-3. Before using this utility model device to measure salinity, the accuracy of the salinity of the cross section to be measured, the number of measuring points and the position of the measuring points can be determined according to the experimental requirements. Then, different types of salinity test papers 2-4 are selected, and the salinity test papers 2-4 are fixed at the corresponding positions on the salinity test paper fixing net 2-3 according to the position of the measuring points. The water-blocking plate 2-2 and the salinity test paper fixing net 2-3, which fixes the salinity test paper 2-4, are installed together between the support keel and the bottom plate of the drawer-type support frame 2-1. The water-blocking plate 2-2 is located between the support keel and the salinity test paper fixing net 2-3. The side of the salinity test paper fixing net 2-3 that fixes the salinity test paper 2-4 is set back from the side where the support keel is located. That is, the side of the salinity test paper fixing net 2-3 that fixes the salinity test paper 2-4 faces the bottom plate of the drawer-type support frame 2-1. This design can prevent the salinity test paper 2-4 from being pulled out of the salinity test paper fixing net 2-3 when the water-blocking plate 2-2 is pulled out.

[0041] In salinity testing experiments, the salinity measuring device 2 is simply inserted into the porous media simulation material 8 to measure the salinity at any location on that cross-section. Specifically, the salinity measuring device 2 is inserted into the porous media simulation material 8 within the water-sand tank 1. Supported by the porous media simulation material 8, the salinity measuring device remains vertical and stationary. The supporting frame supports the water-blocking plate 2-2, preventing the salinity test paper 2-4 from prematurely contacting the water during insertion, thus reducing interference with the accuracy of salinity measurement. This also ensures that the entire salinity measuring device 2 can be smoothly inserted into the water-sand tank 1 without unexpected deformation. After the salinity measuring device 2 is inserted to the designated position, the water-blocking plate 2-2 is removed. The salinity test paper 2-4 on the salinity test paper fixing net 2-3 then comes into contact with the water inside the water-sand tank 1. After a reaction, the salinity test paper 2-4 displays a color corresponding to the salinity level. Experimenters can determine the salinity value at different locations in the water by observing the color of the salinity test paper 2-4.

[0042] Preferably, the bottom of the drawer-type support frame 2-1 can be designed as a V-shaped structure, which facilitates the insertion of the salinity measuring device 2 into the porous medium in the water-sand tank.

[0043] The working principle of this utility model device is as follows:

[0044] Before conducting the experiment using this experimental setup, insert the water-blocking gate 4 and inject an appropriate amount of water into the water-sand tank 1. Then, fill the water-sand tank 1 with the required clean and saturated porous media simulation material 8, such as quartz sand or glass microspheres. During the sand filling process, the water in the water-sand tank 1 must always be submerged above the porous media simulation material 8 to ensure that the aquifer material is completely saturated. Depending on the experimental requirements, fill the porous media simulation material 8 to the target height using a layered heterogeneous or random heterogeneous filling method, and then level it. Next, place the perforated pipe 3 on the front panel of the water-sand tank 1 to simulate a river. Finally, fill the remaining part of the water-sand tank 1 completely, ensuring that the upper surface of the perforated pipe 3 is flush with the top of the filled porous media simulation material 8. For example, first fill with 15cm of saturated quartz sand, level the surface, place the perforated pipe 3 near the front panel, and continue filling with quartz sand until it is flush with the top of the perforated pipe 3.

[0045] When conducting experiments using a physical experimental model: If a water head boundary is required, first insert the water-retaining gate 4 between the water-sand trough 1 and the water level tank 5. Then, adjust the water level in the water level tanks 5 on both sides of the water-sand trough 1 to the target height. Finally, pull the water-retaining gate 4 out of the slot to connect the water-sand trough 1 with the water level tanks 5 on both sides. Select whether to activate the water level control motor according to actual needs to achieve the boundary conditions of dynamic water head and constant water head. If a flow rate boundary is required, keep the water-retaining gate 4 in the closed state and supply water between the side wall of the water-sand trough 1 and the water-retaining gate 4 through an external peristaltic pump. By adjusting the power of the peristaltic pump, the boundary conditions of variable flow rate and constant flow rate can be achieved. If it is necessary to simulate inland water inflow, connect the water injection hole of the perforated pipe 3 to the peristaltic pump through a rubber hose, and then inject water into the water-sand trough through the water injection hole on the perforated pipe 3 to simulate inland water inflow.

[0046] During the experiment, the prepared salinity measuring device 2 is inserted into the porous medium simulation material 8 at the cross-section to be measured in the water-sand tank 1, and the water-blocking plate 2-2 is quickly pulled out. After a period of time, once the salinity test paper 2-4 has completed the measurement, the salinity measuring device 2 can be pulled out to complete the salinity measurement.

[0047] After the experiment is completed, when it is necessary to rinse the porous media simulation material 8, simply close the water-blocking gate 4 on the side of the water level tank 5 (which serves as the seawater tank) and open the water-blocking gate 4 on the side of the water level tank 5 (which serves as the freshwater tank). At the same time, open the sand washing and drainage hole 9 on the side of the seawater tank and continuously inject fresh water into the water-sand tank 1. After waiting for a period of time, the in-situ rinsing of the porous media simulation material 8 can be completed. There is no need to dig it out of the water-sand tank 1 for rinsing and then refill it, which can greatly reduce the labor intensity of the experimenter.

[0048] This invention uses a porous medium filled in a water-sand tank to simulate the heterogeneous aquifer in the estuary and its upstream areas. Combined with perforated pipes and water level control devices, it can efficiently and accurately simulate the water-salt interaction process between surface water and groundwater in the estuary and its upstream areas. This invention also includes a salinity measuring device installed in a three-dimensional water-salt interaction simulation experimental device in the estuary area. The salinity measuring device can be inserted at any cross-sectional position in the aquifer inside the water-sand tank. With the salinity test paper inside the salinity measuring device, the salinity at any location in the water-sand tank can be measured quickly and accurately.

[0049] This novel device can simulate heterogeneous aquifers in estuaries and the water-salt interaction between surface and groundwater upstream, conducting indoor experiments on three-dimensional groundwater dynamics and solute transport processes. It explores the hydrodynamic and solute transport characteristics of surface water-groundwater interaction during saline intrusion under three-dimensional conditions. This device can simultaneously realize different experimental environments, including constant and variable flow boundaries, constant and variable head boundaries, and dynamic inland water inflow in coastal and inland areas. It can also conveniently measure salinity information at any depth and spatial location within the aquifer during the experiment.

[0050] This utility model device has a simple overall structure, convenient operation for salinity measurement, low measurement cost, and good measurement stability, which greatly increases the usability of the experiment. It is of great significance for improving the research level of water-salt interaction processes in estuaries and their upstream areas, and also has broad application prospects.

[0051] The embodiments of the present utility model have been described above with reference to the accompanying drawings. However, the present utility model is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present utility model without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present utility model.

Claims

1. An estuary water salinity interaction simulation experiment device with salinity measurement function, characterized in that, It includes a water-sand tank, with two water level tanks symmetrically arranged on the left and right sides of the water-sand tank, and a water-blocking gate between the water-sand tank and the water level tank; the water-sand tank is filled with porous media simulation material, and a salinity measuring device and a perforated pipe are installed in the water-sand tank; a water level control device is installed inside each water level tank.

2. The estuary water-salt interaction simulation experiment device according to claim 1, characterized in that, The water-sand trough is a lidless transparent acrylic box, and the outer edges of the water-sand trough are reinforced with angle steel. The water level tank is a lidless transparent acrylic box without a panel on one side, and the side of the water level tank without a panel is connected to the water-sand trough.

3. The estuary water-salt interaction simulation experiment device according to claim 1, characterized in that, The water-sand trough has evenly distributed circular openings on both sides of the side wall near the water level tank, and the side walls are lined with fine screens.

4. The estuary water-salt interaction simulation experiment device according to claim 1, characterized in that, The perforated tube is closed at both ends, and the surface of the tube body is provided with uniformly distributed perforations. The perforation diameter is smaller than the minimum particle size of the porous media simulation material, and a water injection hole is provided at the top of one end of the perforated tube.

5. The estuary water-salt interaction simulation experiment device according to claim 4, characterized in that, The perforated tube is installed against the long side wall of the water-sand tank, and the top of the perforated tube is flush with the upper surface of the porous media simulation material filled in the water-sand tank.

6. The estuary water-salt interaction simulation experiment device according to claim 1, characterized in that, A slot is provided at the connection between the water level tank and the water-sand trough, and a water-blocking gate is installed in the slot, with a certain distance between the water-blocking gate and the side wall of the water-sand trough.

7. The estuary water-salt interaction simulation experiment device according to claim 1, characterized in that, The salinity measuring device includes a drawer-type support frame, a water-blocking plate, a salinity test paper fixing net, and salinity test paper fixed on the salinity test paper fixing net. The drawer-type support frame includes a base plate and a vertically fixed support keel on the base plate, forming a drawer-type space with an open top between the base plate and the support keel. The water-blocking plate and the salinity test paper fixing net are inserted between the support keel and the base plate of the drawer-type support frame, with the water-blocking plate located between the support keel and the salinity test paper fixing net. The side of the salinity test paper fixing net that fixes the salinity test paper faces the base plate of the drawer-type support frame.

8. The estuary water-salt interaction simulation experiment device according to claim 7, characterized in that, The bottom of the drawer-type support frame has a V-shaped structure.

9. The estuary water-salt interaction simulation experiment device according to claim 7, characterized in that, The drawer-type support frame includes a base plate and multiple support keels, which are fixed vertically and at equal intervals to the base plate.

10. The experimental device for simulating water-salt interaction in estuary regions according to claim 1, characterized in that, The water level control device includes a screw jack and an overflow plate. The screw jack is fixed to the top of the water level tank, and the overflow plate is fixed to the lifting platform of the screw jack by an extension rod and extends into the water level tank. The overflow plate is provided with an overflow hole, which is connected to the outside of the water level tank through an overflow pipe.

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