Vacuum sampler for volatile organic compounds in underground water

Abstract

The invention discloses a vacuum sampler for volatile organic compounds in underground water, and relates to the technical field of underground water sampling, the vacuum sampler comprises a vacuum sampling assembly, the vacuum sampling assembly at least comprises a ring piece and a U-shaped pipe which are clamped with each other, and a limiting ring is integrally formed in the ring piece; an exhaust seat is arranged at one end, far away from the ring piece, of the U-shaped pipe, and the exhaust seat is communicated with a vacuum generating end of the vacuum pump through an air pipe; the one-way valve assembly is arranged in the ring piece; the piston is arranged in the ring piece and the U-shaped pipe in a sealing and sliding mode, and the upward moving position of the piston is limited by the limiting ring; the self-separation assembly and the pull rope are connected between the one-way valve set and the piston, when the piston moves downwards, the one-way valve assembly can be unblocked through cooperation of the self-separation assembly and the pull rope, the overall stability is high, and the automation degree is high.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater sampling, and specifically to a vacuum sampler for volatile organic compounds in groundwater. Background Art

[0002] Volatile organic compounds (VOCs) in groundwater refer to volatile organic compounds that enter the groundwater environment due to human activities, resulting in the deterioration of groundwater quality. Regarding the definition of VOCs, there are certain differences among different countries or organizations, but generally include the following characteristics: Chemical properties: VOCs are volatile, with boiling points usually between 50°C and 260°C, saturated vapor pressure exceeding 133.32 Pa at room temperature, and existing in the air in the form of vapor at normal temperature.

[0003] Toxicity: VOCs have mobility, persistence, and toxicity, and can enter the human body through the respiratory tract, digestive tract, and skin to cause harm. Their toxicity is mainly manifested in teratogenic, carcinogenic, and mutagenic effects on the human body. When reaching a certain concentration in the body, people will feel headache, nausea, vomiting, fatigue, etc. in a short time. In severe cases, convulsions and coma will occur, and it will damage the liver, kidneys, brain, and nervous system of people, resulting in serious consequences such as memory loss.

[0004] Types: According to chemical structure, volatile organic pollutants in groundwater can be further divided into 8 categories, such as alkanes, aromatics, alkenes, halogenated hydrocarbons, esters, aldehydes, ketones, and other compounds. Common ones include organic compounds such as chloroform, chloromethane, chloroethane, benzene, toluene, xylene (ortho, meta, para), ethylbenzene, and acetone.

[0005] In the current technical field of groundwater sampling, although a variety of sampling methods have been widely used, sampling for volatile organic compounds (VOCs) still faces many challenges. A significant problem is that the degree of automation in the sampling process is relatively low, mainly relying on manual operation to control the start and end of sampling. Although this manual control method has a certain degree of flexibility, it is limited by human factors such as operation proficiency and reaction speed, and it is often difficult to achieve high-precision quantitative sampling.

[0006] In addition, even when the programmed control technology is introduced, a simple timed sampling method is mostly adopted. However, the groundwater environment is complex and changeable, and changes in external factors such as water pressure and water velocity often result in the inability of timed sampling to achieve the effect of quantitative sampling. At the same time, whether it is manual control or program control, a valve body needs to be set at the inlet of the sampling device to control the sampling flow. However, in actual use, this method is very difficult to implement because the valve body occupies a large volume, and the control of the valve body usually requires additional electrical or hydraulic equipment to achieve. In addition, it is difficult to clean this kind of valve body.

[0007] Therefore, it is necessary to provide a vacuum sampler for groundwater volatile organic compounds to solve the above problems. Summary of the Invention

[0008] To solve the above problems, the present invention provides the following technical solutions: A vacuum sampler for groundwater volatile organic compounds, comprising: A winch having a winding and unwinding end, and a winding and unwinding rope is fixed to the winding and unwinding end; A substrate fixed to the free end of the winding and unwinding rope, and a vacuum pump is fixed on the substrate; A plurality of vacuum sampling components distributed below the substrate; Wherein, the vacuum sampling component at least includes: A ring and a U-shaped tube that are snap-connected to each other. Among them, a limiting ring is integrally formed inside the ring; one end of the U-shaped tube away from the ring has an exhaust seat, and the exhaust seat is connected to the vacuum generating end of the vacuum pump through a trachea; A one-way valve assembly disposed in the ring; A piston that is hermetically slidably disposed in the ring and the U-shaped tube, and the upward movement position of the piston is limited by the limiting ring; A self-separating component and a pull rope connected between the one-way valve group and the piston. When the piston moves downward, the one-way valve assembly can be released from the blocked state through the cooperation of the self-separating component and the pull rope.

[0009] Further, preferably, the one-way valve assembly includes: A retaining ring fixedly embedded inside the ring; A conical plug that is slidably disposed inside the ring and can block the retaining ring; A first spring installed between the limiting ring and the conical plug; Wherein, the pull rope is connected to the conical plug.

[0010] Further, preferably, the self-separating component includes: An upper separating member, which has a receiving groove and a first drainage hole communicating with the receiving groove. Two symmetrically arranged limiting blocks are slidably arranged in the receiving groove, and a second spring is further arranged between the limiting block and the receiving groove; A lower separating member, the top of which has a T-shaped head. The T-shaped head can cross over the limiting block and extend into the receiving groove, and a honeycomb block is fixedly embedded in the middle of the lower separating member, and the honeycomb block is filled with expanded sponge; Two symmetrically arranged sliders, which are slidably arranged in the lower separating member. The sliders are connected to the honeycomb block and the sliders correspond to the limiting blocks.

[0011] Further, as a preference, a second drainage hole is opened on the T-shaped head for introducing water into the honeycomb block; The bottom of the limiting block is arc-shaped.

[0012] Further, as a preference, the pull rope is an elastic rope, and the length of the pull rope satisfies that when the one-way valve assembly is in a blocking state, the pull rope is always located inside the ring member in a natural state.

[0013] Further, as a preference, the pull rope is a non-elastic rope, and the length of the pull rope satisfies that when the one-way valve assembly is in a blocking state, the pull rope can extend out of the ring member in a natural state. A magnetic attraction block is embedded in the limiting ring; The piston is made of magnetic attraction material.

[0014] Further, as a preference, a filter screen is installed at one end of the ring member away from the U-shaped tube, and the ring member and the substrate are connected by a positioning frame.

[0015] Further, as a preference, an outer stepped groove and a first clamping groove are also opened on the outer wall of the ring member; An inner stepped groove corresponding to the outer stepped groove is opened on the inner wall of the U-shaped tube, and a second clamping groove is opened on the outer wall of the U-shaped tube; Two symmetrically arranged magnetic attraction arc plates are attached to the outside of the ring member and the U-shaped tube. Both of the two magnetic attraction arc plates have mutually corresponding magnetic attraction columns so that the two magnetic attraction arc plates are magnetically attracted to form a ring, and clamping heads corresponding to the first clamping groove and the second clamping groove are further arranged on the inner wall of the magnetic attraction arc plate.

[0016] Compared with the prior art, the present invention provides a vacuum sampler for groundwater volatile organic compounds, and has the following beneficial effects: In the present invention, through the design of the one-way valve assembly and the self-separation assembly, the backflow of the water sample and the entry of external gas are effectively prevented, ensuring the stability and reliability of sampling. Moreover, the provided piston can effectively prevent water from entering the trachea, ensuring the stable operation of the vacuum pump.

[0017] In the present invention, when the vacuum pump is started and the U-shaped tube is evacuated, a negative pressure environment is formed inside the U-shaped tube. At this time, the piston begins to move downward under the action of the negative pressure, pulling the pull rope and causing the conical plug to leave the retaining ring. The groundwater enters the ring part and the U-shaped tube through the one-way valve assembly, and the overall control is relatively simple and efficient.

[0018] In the present invention, as the water enters the U-shaped tube, the self-separation assembly realizes self-separation, and the tension of the pull rope disappears. At this time, the elastic force of the first spring causes the conical plug to reset and tightly seal the retaining ring, and the one-way valve assembly returns to the closed state again. This process ensures the one-way flow of the water sample and the stability of the sampling system, with a high degree of overall automation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 It is a front view structural schematic diagram of a vacuum sampler for groundwater volatile organic compounds; Figure 2 It is a structural schematic diagram of the vacuum sampling assembly in a vacuum sampler for groundwater volatile organic compounds Figure 1 ; Figure 3 It is a structural schematic diagram of the ring part in a vacuum sampler for groundwater volatile organic compounds; Figure 4 It is a structural schematic diagram of the U-shaped tube in a vacuum sampler for groundwater volatile organic compounds; Figure 5 It is a structural schematic diagram of the magnetic attraction arc plate in a vacuum sampler for groundwater volatile organic compounds; Figure 6 It is Figure 2 The enlarged structural schematic diagram at A of Figure 7 It is a structural schematic diagram of the vacuum sampling assembly in a vacuum sampler for groundwater volatile organic compounds Figure 2 ; Figure 8 It is Figure 7Schematic enlarged structure diagram at position B

[0021] The reference numerals are as follows: 1, winch; 2, winding rope; 3, substrate; 4, vacuum pump; 5, vacuum sampling assembly; 6, air pipe; 51, ring part; 52, U-shaped pipe; 53, magnetic arc plate; 54, one-way valve assembly; 55, filter screen; 56, positioning frame; 57, piston; 58, self-separation assembly; 59, pulling rope; 510, magnetic block; 511, outer stepped groove; 512, first card slot; 513, limiting ring; 521, inner stepped groove; 522, second card slot; 531, chuck; 532, magnetic column; 541, retaining ring; 542, conical plug; 543, first spring; 544, liquid discharge hole; 581, upper separation part; 582, lower separation part; 583, slider; 584, honeycomb block; 585, first drainage hole; 586, second drainage hole; 587, limiting block; 588, second spring. Detailed implementation manners

[0022] The terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances, which is only a way of distinguishing objects with the same attributes when describing the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, so that a process, method, system, product or device including a series of units does not have to be limited to those units, but may include other units not clearly listed or inherent to these processes, methods, products or devices.

[0023] Embodiment 1 Please refer to Figures 1-6 , in the embodiment of the present invention, a vacuum sampler for groundwater volatile organic compounds is provided, including: A winch 1 having a winding and unwinding end, and a winding rope 2 is fixed to the winding and unwinding end; A substrate 3 is fixed to the free end of the winding rope 2, and a vacuum pump 4 is fixed on the substrate 3; A plurality of vacuum sampling assemblies 5 distributed below the substrate 3; Among them, the vacuum sampling assembly 5 at least includes: The mutually clamped ring member 51 and U-shaped tube 52, wherein a limiting ring 513 is integrally formed inside the ring member 51; one end of the U-shaped tube 52 away from the ring member 51 has an exhaust seat, and the exhaust seat is connected to the vacuum generating end of the vacuum pump 4 through an air pipe 6; A one-way valve assembly 54, which is arranged in the ring member 51; A piston 57, which is hermetically and slidably arranged in the ring member 51 and the U-shaped tube 52, and the upward movement position of the piston 57 is limited by the limiting ring 513; A self-separation assembly 58 and a pull rope 59 connected between the one-way valve group 54 and the piston 57. When the piston 57 moves downward, the one-way valve assembly 54 can be released from the blocked state through the cooperation of the self-separation assembly 58 and the pull rope 59.

[0024] During implementation, the following steps are included: Step 1: Utilize the winding and unwinding function of the winch 1 to smoothly lower the substrate 3 and the vacuum sampling assembly 5 below it into the groundwater. During this process, it is necessary to ensure that the sampling assembly 5 can accurately reach the predetermined sampling depth.

[0025] Step 2: Turn on the vacuum pump 4 to perform a vacuum pumping process on the U-shaped tube 52. At this time, a negative pressure environment is formed inside the U-shaped tube 52 to prepare for the subsequent sampling process.

[0026] Step 3: Under the action of negative pressure, the piston 57 begins to move downward and drives the conical plug 542 to move downward together. During this process, the blocked state of the one-way valve assembly 54 is released, allowing groundwater to enter the ring member 51 and the U-shaped tube 52.

[0027] Step 4: After the water body enters the sampling system, self-separation is achieved through the action of the self-separation assembly 58. At this time, the conical plug 542 is reset under the elastic force of the first spring 543, and the one-way valve assembly 54 returns to the blocked state again to prevent the water sample from flowing back and external gas from entering.

[0028] Step 5: After completing the above steps, the water body has been successfully collected and stored in the U-shaped tube 52. At this time, the vacuum pump 4 can be turned off, and the substrate 3 and the vacuum sampling assembly 5 below it can be lifted to the ground through the winch 1 for subsequent water sample analysis.

[0029] The entire sampling process is highly automated, reducing the interference of manual operation and improving the sampling accuracy and efficiency.

[0030] Through the design of the one-way valve assembly 54 and the self-separation assembly 58, the water sample from flowing back and the entry of external gas are effectively prevented, ensuring the stability and reliability of sampling. And the arranged piston 57 can effectively prevent the water body from entering the air pipe 6, ensuring the stable operation of the vacuum pump 4.

[0031] In this embodiment, the one-way valve assembly 54 includes: A retaining ring 541 fixedly embedded inside the ring member 51; A frustum plug 542 slidably disposed inside the ring member 51 and capable of blocking the retaining ring 541. The frustum plug 542 also has a liquid discharge hole 544; A first spring 543 installed between the limit ring 513 and the frustum plug 542; Wherein, the pull rope 59 is connected to the frustum plug 542.

[0032] Then, during the sampling process, when the vacuum pump 4 starts and evacuates the U-shaped tube 52, a negative pressure environment is formed inside the U-shaped tube 52. At this time, the piston 57 starts to move downward under the negative pressure and pulls the pull rope 59. The pulling force of the pull rope 59 causes the frustum plug 542 to leave the retaining ring 541, and the one-way valve assembly 54 is released from the blocked state. Groundwater enters the ring member 51 and the U-shaped tube 52 through the one-way valve assembly 54.

[0033] As the water body enters, the self-separation assembly 58 realizes self-separation, and the pulling force of the pull rope 59 disappears. At this time, the elastic force of the first spring 543 causes the frustum plug 542 to reset and tightly block the retaining ring 541, and the one-way valve assembly 54 returns to the blocked state again. This process ensures the one-way flow of the water sample and the stability of the sampling system.

[0034] In addition, the surface of the frustum plug 542 can be specially treated to ensure good sealing performance and wear resistance.

[0035] In this embodiment, the self-separation assembly 58 includes: An upper separation member 581 having a receiving groove and a first drainage hole 585 communicating with the receiving groove. Two symmetrically arranged limit blocks 587 are slidably disposed in the receiving groove, and a second spring 588 is also disposed between the limit blocks 587 and the receiving groove; A lower separation member 582 having a T-shaped head at the top. The T-shaped head can cross over the limit block 587 and extend into the receiving groove. A honeycomb block 584 is fixedly embedded in the middle of the lower separation member 582, and the honeycomb block 584 is filled with expanded sponge; Two symmetrically arranged sliders 583 slidably disposed in the lower separation member 582. The sliders 583 are connected to the honeycomb block 584 and the sliders 583 correspond to the limit blocks 587.

[0036] When it works, it includes the following steps: Step 1: When installing the upper separating member 581 and the lower separating member 582, align the receiving groove of the upper separating member 581 with the T-shaped head of the lower separating member 582 and push downward.

[0037] Step 2: The T-shaped head will pass over the limiting block 587 and extend into the receiving groove. At this time, the limiting block 587 is pushed by the T-shaped head and resets under the action of the second spring 588, forming a limit to the T-shaped head.

[0038] Step 3: When water enters the honeycomb block 584, the expanding sponge will absorb a certain amount of water and expand. The expanded expanding sponge and the honeycomb block 584 will push the slider 583 to move, and the slider 583 further pushes the limiting block 587. When the limiting block 587 is pushed to a sufficient extent, the limit to the T-shaped head will be released. At this time, the upper separating member 581 and the lower separating member 582 will separate from each other without manual intervention.

[0039] Step 4: After the self-separating assembly 58 separates, the upper separating member 581 will rise along with the pull rope 59 to prevent the water sample from flowing back.

[0040] It is worth mentioning that the self-separating assembly 58 uses an expanding sponge as a triggering element. When the amount of water entering the expanding sponge reaches a sufficient level, the expanding sponge will absorb water and expand, and push the slider 583 to move. This mechanism is automatic and consistent, and is not affected by the underground water flow velocity and pressure.

[0041] Furthermore, a second drainage hole 586 is formed on the T-shaped head for introducing water into the honeycomb block 584; The bottom of the limiting block 587 is arc-shaped.

[0042] In this embodiment, the pull rope 59 is a non-elastic rope, and the length of the pull rope 59 satisfies that when the one-way valve assembly 54 is in a blocked state, the pull rope 59 can extend out of the ring member 51 in a natural state; A magnetic attraction block 510 is embedded in the limiting ring 513; The piston 57 is made of a magnetic attraction material.

[0043] Then, in the stage of installing the upper separating member 581 and the lower separating member 582, since the length of the pull rope 59 satisfies that when the one-way valve assembly 54 is in a blocked state, the pull rope 59 can extend out of the ring member 51 in a natural state, therefore, the upper separating member 581 and the lower separating member 582 can be mutually clamped outside the ring member 51. After that, attach the piston 57 below the limiting ring 513, and use the magnetic attraction block 510 to realize the positioning and adsorption of the piston 57. Finally, the ring member 51 and the U-shaped tube 52 can be mutually clamped.

[0044] In this embodiment, a filter screen 55 is installed at one end of the ring member 51 away from the U-shaped tube 52, and the ring member 51 is connected to the substrate 3 by a positioning bracket 56.

[0045] In this embodiment, an outer stepped groove 511 and a first clamping groove 512 are further formed on the outer wall of the ring member 51; An inner stepped groove 521 corresponding to the outer stepped groove 511 is formed on the inner wall of the U-shaped tube 52, and a second clamping groove 522 is formed on the outer wall of the U-shaped tube 52; Two magnetically attractive arc plates 53 are symmetrically attached to the outside of the ring member 51 and the U-shaped tube 52. Both of the two magnetically attractive arc plates 53 have magnetically attractive columns 532 corresponding to each other, so that the two magnetically attractive arc plates 53 are magnetically attracted to each other to form a ring. A clamping head 531 corresponding to the first clamping groove 512 and the second clamping groove 522 is further provided on the inner wall of the magnetically attractive arc plate 53.

[0046] By clamping the ring member 51 and the U-shaped tube 52 with each other, rapid extraction of the sample in the U-shaped tube 52 can be achieved, as well as rapid cleaning and assembly of the self-separation component 58. After the ring member 51 and the U-shaped tube 52 are clamped with each other, the axial directions of the two can be restricted by the two magnetically attractive arc plates 53 to ensure the clamping effect of the two.

[0047] Embodiment 2 Please refer to Figure 7 and Figure 8 , the difference from Embodiment 1 is that: the pull rope 59 is an elastic rope, and the length of the pull rope 59 satisfies that when the one-way valve assembly 54 is in a blocked state, the pull rope 59 is always located inside the ring member 51 in a natural state.

[0048] Then, in the stage of installing the upper separation member 581 and the lower separation member 582, since the pull rope 59 is an elastic rope, and the length of the pull rope 59 satisfies that when the one-way valve assembly 54 is in a blocked state, the pull rope 59 is always located inside the ring member 51 in a natural state. Therefore, the pull rope 59 can be stretched, so that the upper separation member 581 and the lower separation member 582 are clamped with each other outside the ring member 51. Then, the piston 57 naturally adheres to the lower side of the limit ring 513 under the pulling action of the pull rope 59. Finally, the ring member 51 and the U-shaped tube 52 are clamped with each other.

[0049] Compared with the solution in Embodiment 1, in this solution, the material requirements for the piston 57 are reduced, and the installation of the magnetic attraction block 510 is reduced, but the replacement frequency of the pull rope 59 may be increased.

[0050] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A vacuum sampler for volatile organic compounds in groundwater, characterized in that: include: A winch (1) having a retractable end, to which a retractable rope (2) is fixed; A base plate (3) fixed to the free end of the retractable rope (2), and a vacuum pump (4) fixed on the base plate (3); A plurality of vacuum sampling components (5) distributed below the substrate (3); Wherein, the vacuum sampling assembly (5) comprises at least: A ring member (51) and a U-shaped tube (52) that are clamped together, wherein a limiting ring (513) is integrally formed inside the ring member (51); an end of the U-shaped tube (52) away from the ring member (51) has an exhaust seat, and the exhaust seat is connected to a vacuum generating end of the vacuum pump (4) via an air pipe (6); a one-way valve assembly (54) disposed in the ring member (51); a piston (57) which is sealingly slidably disposed in the ring member (51) and the U-shaped tube (52), and the upward movement position of the piston (57) is limited by the limiting ring (513); A self-separating component (58) and a pull rope (59) are connected between the one-way valve assembly (54) and the piston (57). When the piston (57) moves downward, the one-way valve assembly (54) can be released from the blocked state through the cooperation of the self-separating component (58) and the pull rope (59).

2. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: The one-way valve assembly (54) comprises: A retaining ring (541) fixedly embedded in the ring member (51); A truncated cone plug (542) which is slidably disposed inside the ring member (51) and is capable of sealing the retaining ring (541); A first spring (543) installed between the limiting ring (513) and the truncated cone plug (542); Wherein, the pull rope (59) is connected to the truncated cone plug (542).

3. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: The self-separating component (58) comprises: An upper separation member (581) having a receiving groove and a first drainage hole (585) penetrating the receiving groove, wherein two symmetrically arranged limit blocks (587) are slidably arranged in the receiving groove, and a second spring (588) is further arranged between the limit blocks (587) and the receiving groove; A lower separation piece (582) having a T-shaped head at the top, the T-shaped head being able to pass over the limiting block (587) and extend into the accommodating groove, and a honeycomb block (584) being fixedly embedded in the middle of the lower separation piece (582), the honeycomb block (584) being filled with an expansion sponge; Two symmetrically arranged sliding blocks (583) are slidably arranged in the lower separation member (582); the sliding blocks (583) are connected to the honeycomb block (584), and the sliding blocks (583) correspond to the limiting blocks (587).

4. A vacuum sampler for volatile organic compounds in groundwater according to claim 3, characterized in that: The T-shaped head is provided with a second drainage hole (586) for introducing water into the honeycomb block (584); The bottom of the limiting block (587) is arc-shaped.

5. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: The pull rope (59) is an elastic rope, and the length of the pull rope (59) satisfies that: when the one-way valve assembly (54) is in a blocked state, the pull rope (59) is always located inside the ring member (51) in a natural state.

6. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: The pull rope (59) is a non-elastic rope, and the length of the pull rope (59) satisfies that: when the one-way valve assembly (54) is in a blocked state, the pull rope (59) can extend out of the ring member (51) in a natural state; A magnetic attraction block (510) is embedded in the limiting ring (513); The piston (57) is made of magnetic material.

7. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: A filter screen (55) is installed at one end of the ring member (51) away from the U-shaped tube (52), and the ring member (51) and the base plate (3) are connected by a positioning frame (56).

8. A vacuum sampler for volatile organic compounds in groundwater according to claim 1, characterized in that: The outer wall of the ring member (51) is also provided with an outer step groove (511) and a first clamping groove (512); An inner wall of the U-shaped tube (52) is provided with an inner step groove (521) corresponding to the outer step groove (511), and an outer wall of the U-shaped tube (52) is provided with a second clamping groove (522); Two symmetrically arranged magnetic arc-attracting plates (53) are attached to the outside of the ring member (51) and the U-shaped tube (52); the two magnetic arc-attracting plates (53) are provided with magnetic attraction columns (532) corresponding to each other, so that the two magnetic arc-attracting plates (53) are magnetically attracted to each other and form a ring shape; the inner walls of the magnetic arc-attracting plates (53) are also provided with clamping heads (531) corresponding to the first clamping groove (512) and the second clamping groove (522), respectively.

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