Sewage treatment tank and its dissolved oxygen control system

Abstract

This invention relates to a wastewater treatment tank and its dissolved oxygen control system. The wastewater treatment tank includes a tank body and a dissolved oxygen control system. The dissolved oxygen control system includes a blower air supply device. A first aeration system and a second aeration system are installed at the bottom of the tank body. The first aeration system includes multiple first aeration pipes, each with multiple aeration micropores distributed on its wall. The second aeration system includes multiple second aeration pipes, each with multiple aeration pipe perforations distributed on its wall. The diameter of the aeration pipe perforations is larger than the diameter of the aeration micropores. The blower air supply device is connected to a first air supply pipe supplying air to the first aeration system and a second air supply pipe supplying air to the second aeration system. A first switching valve is installed on the first air supply pipe, and a second switching valve is installed on the second air supply pipe. This invention solves the technical problem in the prior art where the adjustment range of dissolved oxygen value is limited by relying solely on controlling the air supply volume.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more particularly to a wastewater treatment tank and its dissolved oxygen control system. Background Technology

[0002] In existing technologies, aeration is required in biological treatment tanks to provide dissolved oxygen for aerobic microorganisms to "respire." This is because the activated sludge in biological treatment tanks is a community of billions of microorganisms, among which aerobic bacteria are dominant. They consume large amounts of oxygen when degrading organic matter (COD, BOD) in wastewater and when carrying out nitrification (converting ammonia nitrogen into nitrate).

[0003] In the existing technology, an aeration pipe is installed at the bottom of the sewage treatment tank. Aeration micropores are opened on the pipe wall. When in use, a blower sends gas into the aeration pipe, which aerates the sewage treatment tank through the aeration micropores, thereby increasing the dissolved oxygen in the biological treatment tank.

[0004] The problem with existing technology is that a reasonable dissolved oxygen level needs to be maintained in the aeration tank, for example, the dissolved oxygen value needs to be controlled between 0.5-0.8 mg / L. When the dissolved oxygen is higher than this level, it needs to be reduced, and when the dissolved oxygen is lower than this level, it needs to be increased. In existing technology, the increase or decrease of dissolved oxygen depends entirely on the air volume of the blower, and its adjustment range and efficiency are very limited. For example, when the dissolved oxygen is higher than the set value, the air volume of the blower is reduced to lower the dissolved oxygen value in the aeration tank. If the dissolved oxygen in the biological tank is still higher than the set upper limit when the blower is reduced to the minimum operating frequency, then there is no other way. If the blower is forcibly shut down, the dissolved oxygen value will drop rapidly below the set value, which is not conducive to the survival of microorganisms. Summary of the Invention

[0005] The purpose of this invention is to provide a dissolved oxygen control system to solve the technical problem that the adjustment range of dissolved oxygen value is limited by relying solely on controlling the air supply volume in the prior art.

[0006] The technical solution for the wastewater treatment tank in this invention is as follows:

[0007] A wastewater treatment system includes a tank and a dissolved oxygen control system. The dissolved oxygen control system includes a blower air supply device. The system is characterized in that: a first aeration system and a second aeration system are provided at the bottom of the tank; the first aeration system includes multiple first aeration pipes, each with multiple aeration micropores distributed on its wall; the second aeration system includes multiple second aeration pipes, each with multiple aeration pipe perforations distributed on its wall, the perforations having a larger diameter than the micropores; the blower air supply device is connected to a first air supply pipe supplying air to the first aeration system and a second air supply pipe supplying air to the second aeration system; a first switching valve is provided on the first air supply pipe, and a second switching valve is provided on the second air supply pipe.

[0008] Furthermore, both the first and second switching valves are electric valves.

[0009] Furthermore, the dissolved oxygen control system also includes a pressure tank. The inner cavity of the pressure tank is divided into a first chamber and a second chamber arranged on the left and right by a partition. A first air inlet connected to the first chamber is provided at the left end of the pressure tank. The first air inlet is connected to a first air supply pipe through a first air inlet pipe. A first air inlet check valve is provided on the first air inlet pipe. The pressure tank is also provided with a first air outlet connected to the first chamber. The first air outlet is connected to the second air supply pipe through a first air outlet pipe. A first pressure valve is provided on the first air outlet pipe.

[0010] Furthermore, the feature is that: a second air inlet connected to the second chamber is provided at the right end of the pressure tank, the second air inlet is connected to the second air supply pipe through the second air inlet pipe, a second air inlet check valve is provided on the second air inlet pipe, the pressure tank is also provided with a second air outlet connected to the second chamber, the second air outlet is connected to the first air supply pipe through the second air outlet pipe, and a second pressure valve is provided on the second air outlet pipe.

[0011] Furthermore, the baffle is slidably fitted into the inner cavity of the pressure tank in the left-right direction. The inner wall of the pressure tank is provided with a left limiting structure and a right limiting structure to limit the left-right movement of the baffle. When the baffle moves to the point where it is blocked by the left limiting structure, the baffle is in the left limit position that blocks the first air outlet and avoids it. When the baffle moves to the point where it is blocked by the right limiting structure, the baffle is in the right limit position that blocks the second air outlet.

[0012] The technical solution of the dissolved oxygen control system in this invention is as follows:

[0013] The dissolved oxygen control system includes a blower air supply device, and also includes a first aeration system and a second aeration system installed at the bottom of the tank. The first aeration system includes multiple first aeration pipes, and multiple aeration micropores are distributed on the pipe walls of the first aeration pipes. The second aeration system includes multiple second aeration pipes, and multiple aeration pipe perforations are distributed on the pipe walls of the second aeration pipes. The diameter of the aeration pipe perforations is larger than the diameter of the aeration micropores. The blower air supply device is connected to a first air supply pipe that supplies air to the first aeration system and a second air supply pipe that supplies air to the second aeration system. A first switching valve is installed on the first air supply pipe, and a second switching valve is installed on the second air supply pipe.

[0014] Furthermore, both the first and second switching valves are electric valves.

[0015] Furthermore, the dissolved oxygen control system also includes a pressure tank. The inner cavity of the pressure tank is divided into a first chamber and a second chamber arranged on the left and right by a partition. A first air inlet connected to the first chamber is provided at the left end of the pressure tank. The first air inlet is connected to a first air supply pipe through a first air inlet pipe. A first air inlet check valve is provided on the first air inlet pipe. The pressure tank is also provided with a first air outlet connected to the first chamber. The first air outlet is connected to the second air supply pipe through a first air outlet pipe. A first pressure valve is provided on the first air outlet pipe.

[0016] Furthermore, a second air inlet connected to the second chamber is provided at the right end of the pressure tank. The second air inlet is connected to the second air supply pipe through the second air inlet pipe. A second air inlet check valve is provided on the second air inlet pipe. The pressure tank is also provided with a second air outlet connected to the second chamber. The second air outlet is connected to the first air supply pipe through the second air outlet pipe. A second pressure valve is provided on the second air outlet pipe.

[0017] Furthermore, the baffle is slidably fitted into the inner cavity of the pressure tank in the left-right direction. The inner wall of the pressure tank is provided with a left limiting structure and a right limiting structure to limit the left-right movement of the baffle. When the baffle moves to the point where it is blocked by the left limiting structure, the baffle is in the left limit position that blocks the first air outlet and avoids it. When the baffle moves to the point where it is blocked by the right limiting structure, the baffle is in the right limit position that blocks the second air outlet.

[0018] The beneficial effects of this application are as follows: In this invention, the aperture of the aeration tube perforation on the second aeration tube is larger than the aperture of the aeration micropore on the first aeration tube. Therefore, under the same air supply standard, the oxygenation efficiency of the second aeration tube is lower than that of the first aeration tube. During normal use, the first aeration pipe aerates the tank. When the dissolved oxygen level in the tank is higher than the set value, the blower air supply device adjusts the blower frequency to reduce the air supply of the first aeration pipe, thereby lowering the dissolved oxygen level in the tank. If the dissolved oxygen level in the tank is still higher than the upper limit of the dissolved oxygen set value when the blower is reduced to the lowest operating frequency, the air supply of the first aeration pipe is turned off, and the air supply of the second aeration pipe is turned on to further reduce the oxygenation efficiency. When the dissolved oxygen level in the tank is lower than the lower limit of the dissolved oxygen set value, the blower air supply device adjusts the blower frequency to increase, thereby increasing the air supply of the second aeration pipe. If the dissolved oxygen level in the tank is still lower than the lower limit of the dissolved oxygen set value when the blower is increased to the highest operating frequency, the air supply of the first aeration pipe is turned on, the air supply of the second aeration pipe is turned off, and the system switches to high-efficiency air supply from the first aeration system.

[0019] Furthermore, when the first aeration pipe supplies air but the second aeration pipe does not supply air for an extended period, the aeration perforations of the second aeration pipe are easily clogged by sludge; conversely, when the second aeration pipe supplies air but the first aeration pipe does not supply air for an extended period, the aeration micropores of the first aeration pipe are easily clogged by sludge. To address this problem, this invention innovatively utilizes a pressure tank. For example, when the first aeration pipe supplies air, it supplies air to the first chamber of the pressure tank through the first air inlet. The baffle moves to its rightmost extreme position, at which point the second air outlet is blocked by the baffle. As the first chamber continues to be filled with air, the pressure in the first chamber gradually increases. When the pressure exceeds the set pressure of the first pressure valve, the gas in the first chamber flows through the first air outlet to the second air supply pipe, flushing the second aeration pipe with gas. The gas is then discharged through the aeration pipe perforations, washing away the sludge inside the perforations. This allows for periodic flushing of the aeration pipe perforations, preventing sludge blockage.

[0020] Similarly, when the second aeration pipe supplies air, it supplies air to the second chamber of the pressure tank through the second air inlet. The baffle moves to the left to its left limit position. At this time, the first air outlet is blocked by the baffle. As the second chamber is filled with air, the pressure in the second chamber gradually increases. When the pressure is greater than the set pressure of the second pressure valve, the gas in the second chamber flows to the first air supply pipe through the second air outlet. The gas is then flushed into the first aeration pipe and discharged through the aeration micropores, washing away the sludge in the aeration micropores. In this way, the aeration micropores can be flushed at certain time intervals to prevent them from being blocked by sludge. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a specific embodiment of a sewage treatment tank according to the present invention;

[0022] Figure 2 for Figure 1 Schematic diagram of the structure of the medium-pressure tank;

[0023] In the diagram: 1. Dissolved oxygen control system; 2. Main gas circuit electric valve; 3. Control line; 4. Second gas supply pipe; 5. First gas supply pipe; 6. Second switching valve; 7. First switching valve; 8. Pressure tank; 9. First air inlet pipe; 10. First check valve; 11. Second air inlet pipe; 12. Second check valve; 13. First air outlet pipe; 14. First pressure valve; 15. Second air outlet pipe; 16. Second pressure valve; 17. First aeration pipe; 18. Second aeration pipe; 19. Tank body; 20. Liquid surface; 21. First chamber; 22. Second chamber; 23. Baffle; 24. Left side limiting structure; 25. Right side limiting structure; 26. First air inlet; 27. Second air inlet; 28. First air outlet; 29. ​​Second air outlet. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0026] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0027] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0028] A specific embodiment of a sewage treatment tank in this invention is as follows: Figures 1-2 As shown,

[0029] It includes a pool body 19 and a dissolved oxygen control system 1. The dissolved oxygen control system 1 includes a blower supply device, which includes a frequency-adjustable blower and a controller that can control the adjustment of the blower frequency.

[0030] In Figure 1, item 20 represents the liquid level of the sewage in pool 19.

[0031] The dissolved oxygen control system 1 includes a first aeration system and a second aeration system installed at the bottom of the tank 19. The first aeration system includes multiple first aeration pipes 17, and multiple aeration micropores are distributed on the pipe wall of the first aeration pipe 17. The second aeration system includes multiple second aeration pipes 18, and multiple aeration pipe perforations are distributed on the pipe wall of the second aeration pipe 18. The individual first aeration pipe 17 and the individual second aeration pipe 18 are both existing technologies. The pore size of the aeration micropores is about 1 mm, for example, 0.7~1.2 mm, and the pore size of the aeration perforations is 3–8 mm.

[0032] The blower air supply device is connected to a first air supply pipe 5 that supplies air to each of the first aeration pipes 17 in the first aeration system and a second air supply pipe 4 that supplies air to each of the second aeration pipes 18 in the second aeration system. A first switching valve 7 is installed on the first air supply pipe 5, and a second switching valve 6 is installed on the second air supply pipe 4. The first air supply pipe 5 and the second air supply pipe 4 are connected in parallel to the main air supply pipe. Item 2 in the figure represents the main air circuit electric valve on the main air supply pipe; item 3 represents the control line that realizes the control connection between the controller and the first and second switching valves.

[0033] In this embodiment, both the first switching valve 7 and the second switching valve 6 are electric valves. To avoid the problem of sludge clogging the aeration perforations when the first aeration pipe 17 is working and the second aeration pipe 18 is not working for a long time, and the problem of sludge clogging the aeration micropores when the second aeration pipe 18 is working and the first aeration pipe 17 is not working for a long time, the dissolved oxygen control system 1 in this invention also includes a pressure tank 8; the inner cavity of the pressure tank 8 is divided into a first chamber 21 and a second chamber 22 arranged on the left and right by a partition 23.

[0034] The left end of the pressure tank 8 is provided with a first air inlet 26 connected to the first chamber 21. The first air inlet 26 is connected to the first air supply pipe 5 through a first air inlet pipe 9. A first air inlet check valve 10 is provided on the first air inlet pipe 9. The pressure tank 8 is also provided with a first air outlet 28 connected to the first chamber 21. The first air outlet 28 is connected to the second air supply pipe 4 through a first air outlet pipe 13. A first pressure valve 14 is provided on the first air outlet pipe 13.

[0035] The right end of the pressure tank 8 is provided with a second air inlet 27 connected to the second chamber 22. The second air inlet 27 is connected to the second air supply pipe 4 through a second air inlet pipe 11. A second air inlet check valve 12 is provided on the second air inlet pipe 11. The pressure tank 8 is also provided with a second air outlet 29 connected to the second chamber 22. The second air outlet 29 is connected to the first air supply pipe 5 through a second air outlet pipe 15. A second pressure valve 16 is provided on the second air outlet pipe 15.

[0036] The first pressure valve 14 and the second pressure valve 16 are existing technologies. They are pressure valves that only open the corresponding air pipe when the set pressure is reached and remain closed when the set pressure is not reached. Their valve cores can be designed as ball cores that float by a spring. When the pressure in the corresponding chamber does not reach the set value, the gas pressure is insufficient to overcome the spring force, and the valve core and valve seat remain sealed. When the chamber pressure reaches the set value, the gas pressure overcomes the spring force, the valve core and valve seat separate, and the corresponding air pipe is opened.

[0037] In this embodiment, the partition 23 is slidably fitted into the inner cavity of the pressure tank 8 in a left-right direction. The inner wall of the pressure tank 8 is provided with a left-side limiting structure 24 and a right-side limiting structure 25 to restrict the left-right movement limits of the partition 23. The left-side limiting structure 24 and the right-side limiting structure 25 are retaining ring structures fixed to the inner wall of the pressure tank 8. When the partition 23 moves to the point where it is stopped by the left-side limiting structure 24, it is at the left-side limit position, blocking the first air outlet 28 and avoiding the second air outlet 29. When the partition 23 moves to the point where it is stopped by the right-side limiting structure 25, it is at the right-side limit position, blocking the second air outlet 29 and avoiding the first air outlet 28.

[0038] In this invention, the perforation diameter of the aeration pipe on the second aeration pipe 18 is larger than the aeration micropore diameter on the first aeration pipe 17. Therefore, under the same air supply, the oxygenation efficiency of the second aeration pipe 18 is lower than that of the first aeration pipe 17. During normal operation, the first aeration pipe 17 is used first for aeration. When the dissolved oxygen value in the pool is higher than the set value, the blower air supply device adjusts the blower frequency to reduce the air supply of the first aeration pipe 17 and reduce the dissolved oxygen value in the pool. If the dissolved oxygen in the pool is still higher than the set upper limit after the blower is reduced to the lowest operating frequency, the first switch valve 7 is closed to cut off the air supply of the first aeration pipe 17, and the second switch valve 6 is opened to start the air supply of the second aeration pipe 18, using the low oxygenation efficiency of the second aeration pipe 18 to further reduce the dissolved oxygen.

[0039] When the dissolved oxygen level in the pool is lower than the set lower limit, the blower air supply device increases the blower frequency to increase the air supply of the second aeration pipe 18; if the dissolved oxygen level in the pool is still lower than the set lower limit after the blower is raised to the highest operating frequency, the second switch valve 6 is closed to cut off the air supply of the second aeration pipe 18, and at the same time the first switch valve 7 is opened to start the air supply of the first aeration pipe 17, switching to the first aeration system for high-efficiency oxygen supply.

[0040] Furthermore, when the first aeration pipe 17 is supplied with air and the second aeration pipe 18 is shut down for a long period, its aeration perforations are easily blocked by sludge; conversely, when the second aeration pipe 18 is supplied with air and the first aeration pipe 17 is shut down for a long period, its aeration micropores are easily blocked by sludge. This invention achieves automatic backflushing and anti-clogging through the pressure tank 8: when the first aeration pipe 17 is working, the first air supply pipe 5 fills the first chamber 21 of the pressure tank 8 with air through the first air inlet pipe 9 and the first air inlet 26. The partition 23 moves to the right to the right limit structure 25, blocking the second air outlet 29. As the air filling proceeds, the pressure in the first chamber 21 gradually increases. When the pressure exceeds the set value of the first pressure valve 14, the gas flows into the second air supply pipe 4 through the first air outlet 28 and the first air outlet pipe 13, flows back into the second aeration pipe 18, and is discharged from the aeration perforations, flushing the sludge in the holes, thus achieving periodic automatic backflushing and anti-clogging.

[0041] Similarly, when the second aeration pipe 18 is working, the second air supply pipe 4 fills the second chamber 22 of the pressure tank 8 with air through the second air inlet pipe 11 and the second air inlet 27. The partition 23 moves to the left to the left limiting structure 24, blocking the first air outlet 28. As the filling proceeds, the pressure in the second chamber 22 gradually increases. When the pressure exceeds the set value of the second pressure valve 16, the gas flows into the first air supply pipe 5 through the second air outlet 29 and the second air outlet pipe 15, and flows back into the first aeration pipe 17, and is discharged from the aeration micropores to flush the sludge in the holes and prevent the micropores from becoming blocked.

[0042] Implementation of dissolved oxygen control systems, for example Figures 1-2 As shown, the specific structure of the dissolved oxygen control system is the same as that of the dissolved oxygen control system described in the above-mentioned wastewater treatment pond embodiments, and will not be described in detail here.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A wastewater treatment system, comprising a tank and a dissolved oxygen control system, wherein the dissolved oxygen control system includes a blower supply device, characterized in that: The bottom of the pool is equipped with a first aeration system and a second aeration system. The first aeration system includes multiple first aeration pipes, and the pipe walls of the first aeration pipes are distributed with multiple aeration micropores. The second aeration system includes multiple second aeration pipes, and the pipe walls of the second aeration pipes are distributed with multiple aeration pipe perforations. The diameter of the aeration pipe perforations is larger than the diameter of the aeration micropores. A blower air supply device is connected to a first air supply pipe that supplies air to the first aeration system and a second air supply pipe that supplies air to the second aeration system. A first switch valve is installed on the first air supply pipe and a second switch valve is installed on the second air supply pipe.

2. The sewage treatment tank according to claim 1, characterized in that: Both the first and second switching valves are electric valves.

3. The wastewater treatment tank according to claim 1 or 2, characterized in that: The dissolved oxygen control system also includes a pressure tank. The inner cavity of the pressure tank is divided into a first chamber and a second chamber, arranged on the left and right sides, by a partition. A first air inlet connected to the first chamber is located at the left end of the pressure tank. The first air inlet is connected to a first air supply pipe via a first air inlet pipe. A first air inlet check valve is installed on the first air inlet pipe. The pressure tank also has a first air outlet connected to the first chamber. The first air outlet is connected to the second air supply pipe via a first air outlet... The air pipe is connected, and a first pressure valve is installed on the first air outlet pipe.

4. The wastewater treatment tank according to claim 3, characterized in that: The right end of the pressure tank is provided with a second air inlet connected to the second chamber. The second air inlet is connected to the second air supply pipe through the second air inlet pipe. The second air inlet pipe is provided with a second air inlet check valve. The pressure tank is also provided with a second air outlet connected to the second chamber. The second air outlet is connected to the first air supply pipe through the second air outlet pipe. The second air outlet pipe is provided with a second pressure valve.

5. The sewage treatment tank according to claim 4, characterized in that: The baffle is slidably fitted into the inner cavity of the pressure tank in a left-right direction. The inner wall of the pressure tank is provided with a left limiting structure and a right limiting structure to limit the left-right movement of the baffle. When the baffle moves to the point where it is blocked by the left limiting structure, the baffle is in the left limit position that blocks the first air outlet and avoids it. When the baffle moves to the point where it is blocked by the right limiting structure, the baffle is in the right limit position that blocks the second air outlet.

6. A dissolved oxygen control system, including a fan supply device, characterized in that: It also includes a first aeration system and a second aeration system for installation at the bottom of the pool. The first aeration system includes multiple first aeration pipes, and multiple aeration micropores are distributed on the pipe walls of the first aeration pipes. The second aeration system includes multiple second aeration pipes, and multiple aeration pipe perforations are distributed on the pipe walls of the second aeration pipes. The diameter of the aeration pipe perforations is larger than the diameter of the aeration micropores. A blower air supply device is connected to a first air supply pipe that supplies air to the first aeration system and a second air supply pipe that supplies air to the second aeration system. A first switch valve is installed on the first air supply pipe and a second switch valve is installed on the second air supply pipe.

7. The dissolved oxygen control system according to claim 6, characterized in that: Both the first and second switching valves are electric valves.

8. The dissolved oxygen control system according to claim 6 or 7, characterized in that: The dissolved oxygen control system also includes a pressure tank. The inner cavity of the pressure tank is divided into a first chamber and a second chamber, arranged on the left and right sides, by a partition. A first air inlet connected to the first chamber is located at the left end of the pressure tank. The first air inlet is connected to a first air supply pipe via a first air inlet pipe. A first air inlet check valve is installed on the first air inlet pipe. The pressure tank also has a first air outlet connected to the first chamber. The first air outlet is connected to the second air supply pipe via a first air outlet... The air pipe is connected, and a first pressure valve is installed on the first air outlet pipe.

9. The dissolved oxygen control system according to claim 8, characterized in that: The right end of the pressure tank is provided with a second air inlet connected to the second chamber. The second air inlet is connected to the second air supply pipe through the second air inlet pipe. The second air inlet pipe is provided with a second air inlet check valve. The pressure tank is also provided with a second air outlet connected to the second chamber. The second air outlet is connected to the first air supply pipe through the second air outlet pipe. The second air outlet pipe is provided with a second pressure valve.

10. The dissolved oxygen control system according to claim 9, characterized in that: The baffle is slidably fitted into the inner cavity of the pressure tank in a left-right direction. The inner wall of the pressure tank is provided with a left limiting structure and a right limiting structure to limit the left-right movement of the baffle. When the baffle moves to the point where it is blocked by the left limiting structure, the baffle is in the left limit position that blocks the first air outlet and avoids it. When the baffle moves to the point where it is blocked by the right limiting structure, the baffle is in the right limit position that blocks the second air outlet.

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