Special valve bonnet device with filtering function and its manufacturing method

Abstract

The present invention relates to a special valve bonnet device with a filtering function and a manufacturing method thereof. It includes a bonnet, a filtering device, and a fixing device. The filtering device is installed at the inlet end of the bonnet through the fixing device. The beneficial effects are as follows: Two layers of coarse filter meshes sandwich a layer of fine filter mesh in the middle and are integrated into the bonnet through a resistance welding process, eliminating the disadvantages of general bonnets without a filtering device or being unable to withstand high-intensity impact in both forward and reverse directions. It not only effectively prevents the risk of excess material flowing into the valve at the front end of the bonnet, improves the safety and stability of valve use, but also provides a practical and effective method for the prevention and control design and production of excess materials in aerospace valves.

Description

Technical Field

[0001] This application belongs to the technical field of aerospace cryogenic high-pressure valves, and particularly relates to a special valve bonnet device with a filtering function and a manufacturing method thereof. Background Art

[0002] With the rapid development of the commercial aerospace industry, more valves are applied in the pipeline systems of aerospace high-tech aircraft. The valves play important roles such as controlling switches and attitude adjustment, and they play a decisive role in the normal operation and accurate flight of aerospace aircraft. In the pipe valve system of aerospace products, the actual working environment of valves is usually very harsh, often with cryogenic and high-pressure working conditions, and there are extremely high requirements for the prevention and control of foreign matters. It not only needs to meet the functional technical requirements but also the safety indicators, with extremely high requirements for aerospace valve technology. The bonnet is the core component of aerospace valves, mainly used for connecting or supporting the actuator, so the bonnet is the key to the design and production of aerospace valves.

[0003] Generally speaking, the bonnet has two functions. One is to position the valve stem to ensure the normal transmission and switching of the valve stem; the other is the sealing function. The bonnet has a certain strength, and it forms a sealed and pressure-bearing cavity with the valve body to prevent the internal fluid from flowing out, and there are no other functions. However, aerospace valves have extremely high requirements for the prevention and control of foreign matters. To prevent foreign matters from flowing into the valve, a foreign matter prevention and control device needs to be set in front of the valve, and it also needs to withstand the forward high-pressure impact force when the medium flows in quickly and the backward pulling force when the medium flows out urgently. Otherwise, impurities and foreign matters in the pipeline system will break into the valve. In the lightest case, it will cause slight leakage of the valve, resulting in the risk of harmful medium leakage. In the worst case, it will directly cause the valve to be stuck or damaged, and the valve cannot be opened and closed normally, making the system unable to execute according to the normal procedure, resulting in the failure of the launch mission. Therefore, in order to meet the requirements, during the flight test of spacecraft, a filter is generally installed in the pipeline system. To meet the requirements of the flow channel and interface, the volume and weight of the external filter will be relatively large, increasing the burden on the flight system. Moreover, because there is a part of the pipeline at the front end where the medium of the bonnet flows in, the risk of foreign matters in front of the valve cannot be completely eliminated. Before the flight test of the spacecraft, it is necessary to repeatedly check for foreign matters, which also directly increases the labor cost of cleaning and inspecting foreign matters.

[0004] Therefore, it is of great significance to develop a valve bonnet filtering device that meets the performance requirements, integrates foreign matter protection, and is configured for internal use in the valve. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a special valve bonnet device with a filtering function and a manufacturing method thereof. The filtering layer is integrated into the bonnet by resistance welding, which overcomes the drawbacks that the general bonnet has no filtering device or cannot withstand high-intensity impact in both directions. It not only effectively prevents the risk of excess material flowing into the valve at the front end of the bonnet, improves the safety and stability of valve use, but also provides a practical and effective method for the design and production of the prevention and control of excess materials in aerospace valves.

[0006] To achieve the above object, the present application provides the following technical solutions:

[0007] A special valve bonnet device with a filtering function, comprising a bonnet, a filtering device, and a fixing device. The filtering device is installed at the inlet end of the bonnet through the fixing device.

[0008] Preferably, the filtering device includes a filtering layer and two retaining rings. The filtering layer is welded between the two retaining rings by resistance welding.

[0009] Preferably, the filtering layer includes one layer of fine filter mesh and two layers of coarse filter mesh, and one layer of fine filter mesh is arranged between the two layers of coarse filter mesh.

[0010] Preferably, the mesh size of the coarse filter mesh is 8 - 15 times that of the fine filter mesh.

[0011] Preferably, the fixing device is a shaft snap ring, and the shaft snap ring is installed on the clamping groove of the bonnet to fix the filtering device.

[0012] Preferably, the fine filter mesh and the coarse filter mesh are made of high-strength and low-temperature-resistant stainless steel material.

[0013] The present application also provides a manufacturing method of a special valve bonnet device with a filtering function, comprising the following steps:

[0014] S1. Use a pulverizer to pulverize the raw materials for making the powder, and then use a sieve with a mesh size smaller than that of the fine filter mesh to screen out the formed powder;

[0015] S2. Use laser cutting to cut the whole filter mesh into a formed filter mesh;

[0016] S3. Uniformly fill the formed powder into the formed filter mesh;

[0017] S4. Use resistance welding to weld multiple formed filter meshes together to form a filtering layer;

[0018] S5. Press the filtering layer tightly with two retaining rings from above and below, and use resistance welding for welding;

[0019] S6. Fix and install the filter device formed by welding with a shaft retaining ring at the inlet end of the valve cover to form a valve cover filter device.

[0020] Preferably, when cutting the filter screen in step S2, fix the filter screen on a special tool for cutting to ensure that the filter screen does not warp or move.

[0021] Preferably, when using resistance welding, the shape and size of the welding electrode of the resistance welding are the same as those of the end face of the pressing ring to ensure that the heating and deformation amounts of the workpieces during welding are consistent.

[0022] Generally speaking, the beneficial effects of the above technical solutions conceived by the present invention are as follows:

[0023] 1. The filter layer of this device consists of three layers of filter screens. Two layers of coarse filter screens sandwich one layer of fine filter screen in the middle. The coarse filter screens play a role of skeleton support to ensure that the fine filter screen does not deform, break or fall off when subjected to huge impact forces; the filter screen and the upper and lower pressing rings are fixed together by the resistance welding method, solving the common problem of poor weldability of the multi-layer filter screen hollow structure, enabling this filter device to meet the forward high-pressure impact force when the medium flows in quickly, and also meeting the backward pulling force when the medium is urgently discharged, realizing the disadvantages of general valve covers without filter devices or unable to withstand positive and negative high-intensity impacts, providing ideas for the design and manufacture of aerospace valve covers;

[0024] 2. The filter device of this device is fixed on the valve cover by a snap ring. When installing or disassembling, only need to remove the snap ring to realize the replacement of the filter device. The operation is simple and convenient for later maintenance work;

[0025] 3. This device can be directly used in aerospace valves. Because it has a built-in filtering function, there is no need to install an external filter, which is more convenient when used in the integrated pipe valve system; because there is no need to additionally install a sub-pipe for the external filter in front of the valve, the risk of foreign objects generating redundant objects is reduced, the workload of cleaning foreign object redundant objects is reduced, and the system safety is improved; also because there is no need to install an external filter and supporting sub-pipe parts, this will greatly reduce the volume and weight of the pipe valve system, save physical space for the pipe valve system, and reduce the load burden for spacecraft flight tests;

[0026] 4. This device integrates a filter device on the aerospace valve cover, effectively preventing the risk of redundant substances flowing into the valve from the front end of the valve, and improving the service life and stability of the valve; the structure of this device is ingeniously designed and the manufacturing method is simple, and the volume of the filter device can be controlled within a few millimeters. The advantage of directly integrating the filter device on the valve cover without additionally increasing the outer contour volume of the valve provides more possibilities for the limited space of spacecraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a flowchart of a method for manufacturing a valve cover filter screen provided in an embodiment of the present invention;

[0028] Figure 2 It is a schematic structural diagram of a valve cover provided in an embodiment of the present invention;

[0029] Figure 3 It is a sectional view of the structure of a valve cover provided in an embodiment of the present invention;

[0030] Figure 4 It is a partial sectional view of a filtering device provided in an embodiment of the present invention;

[0031] Figure 5 It is a schematic structural diagram of a filter screen provided in an embodiment of the present invention;

[0032] Figure 6 It is a schematic structural diagram of a shaft retaining ring provided in an embodiment of the present invention;

[0033] Figure 7 It is a schematic structural diagram of a special tooling provided in an embodiment of the present invention.

[0034] In all the drawings, the same reference numerals are used to represent the same elements or structures, where:

[0035] 1 - valve cover, 11 - valve cover inlet, 12 - flow channel, 13 - inner cavity, 2 - clamping groove, 3 - pressing ring, 4 - filter layer, 41 - fine filter screen, 42 - coarse filter screen, 5 - shaft retaining ring, 6 - special tooling, 61 - lifting member, 62 - fixing member, 63 - filter screen. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention; in addition, in the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0038] AsFigures 2 - 7 As shown in Figures 2 - 7 , a special valve bonnet device with a filtering function provided by the present invention includes a valve bonnet, a filtering device, and a fixing device. The valve bonnet is divided into three parts: a valve bonnet inlet, a flow channel, and an inner cavity. The filtering device is installed at the inlet end of the valve bonnet, that is, the front end of the valve bonnet flow channel, through the fixing device, so that when the fluid passes through the valve bonnet, it sequentially passes through the valve bonnet inlet, the filtering device, the flow channel, and the inner cavity. The filtering device can prevent redundant substances from flowing into the inner cavity of the valve bonnet and damaging the sealing surface and guiding surface of the inner cavity. Among them, the filtering device is composed of a filtering layer and a pressing ring. The filtering layer is a three-layer filter screen welded together by resistance welding. The middle layer of the three-layer filter screen is a fine filter screen, and the upper and lower layers are coarse filter screens. The mesh size of the coarse filter screen is 8-15 times that of the fine filter screen. In this embodiment, the mesh size of the fine filter screen is selected as 0.04 mm, and the mesh size of the coarse filter screen is 0.4 mm. The fine filter screen and the coarse filter screen are made of high-strength and low-temperature-resistant stainless steel material. In this embodiment, the stainless steel of the 022Cr17Ni12Mo2 grade is selected. There are two pressing rings, which are respectively welded to both side surfaces of the filtering layer by resistance welding. A shaft retaining ring is installed in the matching card slot on the valve bonnet to fix the above-mentioned filtering device.

[0039] As Figure 1 shown in Figure 1 , the present application also provides a manufacturing method of a special valve bonnet device with a filtering function, including the following steps:

[0040] S1. Use a crusher to crush the raw materials for making the powder, and then use a sieve with a mesh size smaller than that of the fine filter screen to screen out the formed powder. The raw materials are made of the same material as the filter screen, which is high-strength and low-temperature-resistant stainless steel;

[0041] S2. Use fiber laser cutting to cut the whole filter screen into a formed filter screen. Because the filter screen is thin and fine, when cutting by hand with scissors, there are deviations in the size of the cut filter screen, and the filter screen is extremely easy to deform. The originally circular filter screen that was supposed to fit the size of the pressing ring easily becomes oval, resulting in the filter screen not being able to fit tightly and causing false soldering.

[0042] The specific steps of using laser cutting are as follows:

[0043] (1) Design the cutting size and cutting pattern of the filter screen. Draw the outer contour size of the filter screen in Auto CAD. The outer contour size of the filter screen is the same as the outer contour shape and size of the pressing ring to ensure that the heating and deformation amounts of the two workpieces are the same. In this case, the cutting shape of the outer contour of the filter screen is O-shaped;

[0044] (2) Import the designed graphics into the control software of the fiber laser cutting machine. In this embodiment, a HG-V20 laser cutting machine from Huagong Laser is used, which comes with its own control software. Open the control software of the fiber laser cutting machine and import the designed cutting contour map into the control software of the fiber laser machine at a 1:1 scale; in the control software, the cutting graphics can be arrayed according to the required number of filter meshes and the size of the filter mesh raw material (the arrayed graphics do not exceed the boundary of the filter mesh), that is, multiple cuts can be made on one filter mesh on one operation interface to improve the cutting efficiency;

[0045] (3) Set the cutting parameters.

[0046] The cutting heat Q1 of the fiber laser = n * P * t (1)

[0047] In the formula, Q1 is the cutting heat (J), P is the cutting power (w), t is the cutting time (s), and n is the number of cuts. The determination of the number of cuts n: A laser sensor is set on the cutting head of the fiber laser cutting machine. When preparing to cut, when the laser recognizes the filter mesh on the cutting platform, the cutting command is started, and the laser cutting machine starts to execute the cutting task; when the filter mesh cutting is completed, if the laser sensor does not recognize the filter mesh on the cutting platform, the cutting stop signal is fed back to the operation software, and the operation software executes the stop cutting command, that is, 1 filter mesh cutting task is completed.

[0048] The cutting power, time, and number of cycles can be set on the control software of the fiber laser cutting machine, and the three can be matched with each other within the range set by the control software; in this embodiment, the power for cutting a single filter mesh is 30W, the cutting time is 3s, and the number of cycles is 1 to complete the operation;

[0049] (4) Use a special tooling to place the filter mesh to be cut. The special tooling includes a lifting part and a fixing part. The size of the special tooling can be designed according to the size of the filter mesh. Lift the filter mesh flat to a certain height from all around and place it flat on the lifting part, then fix the fixing part and the lifting part with bolts (or a fixing part with magnetism can be used to suck the lifting part) to fix the four sides of the filter mesh to be cut, and then fix the special tooling on the fiber laser cutting machine platform with bolts; because the filter mesh is not easy to be flattened, it is easy to warp or move. Otherwise, the cut filter mesh deviates from the required shape, and it is not the required O-shaped, resulting in the filter mesh not being able to fit completely with the pressure ring during welding, and it is easy to produce false welding and affect the welding strength, so it cannot meet the technical requirements. Therefore, using the special tooling can avoid this problem.

[0050] (5) Laser cutting of the filter mesh. Click the cutting command on the control software of the fiber laser cutting machine to carry out the filter mesh cutting work.

[0051] S3. Uniformly fill the formed powder into the formed filter mesh;

[0052] S4. Weld the formed filter screen by resistance welding to form a filter layer;

[0053] S5. Clamp the filter layer with upper and lower pressure rings and weld it by resistance welding; the upper and lower two electrodes used for resistance welding are customized electrodes, which are the same in shape and size as the pressure rings; during welding, place the workpiece to be welded between the two specific electrodes, apply a certain pressure to compact the welded part, so that the workpiece to be welded is firmly clamped between the upper and lower electrodes, and then set the corresponding welding current and welding time according to the thickness of the workpiece to be welded, so that the welding position is fully penetrated to ensure the welding quality is firm and reliable.

[0054] Among them, the heat generated by welding can be calculated by the following formula:

[0055] Q2 = I 2 Rt (2)

[0056] In the formula, Q2 is the heat generated by welding (J), I is the welding current (A), R is the resistance between the electrodes (Ω), and t is the welding time (s).

[0057] The resistance welding process is as follows:

[0058] (1) Design of welding electrodes: The welding electrodes are the same in shape and size as the outer contour of the workpiece end face to ensure the same heating and deformation of the workpiece.

[0059] (2) Cleaning before welding: The surface to be welded should be flat and smooth. Before welding, the surface to be welded should be cleaned to remove oil, oxides and other inclusions. Otherwise, it will affect the surface quality of the welded part, the size and shape of the fusion zone and the stability of the welding strength. For example, too deep oxides and stains will produce a high resistance coefficient and prevent the current from conducting, resulting in incomplete penetration of the product; if the surface of the product is uneven due to tiny debris, the part can only become a contact point at the local rough surface, affecting the uniformity of the welding current. The reduction of the current path will increase the resistance at the contact point, causing local welding breakdown of the product, forming large sparks and splashes. In this embodiment, the workpiece to be welded is first placed in hydrofluoric acid (HF specific gravity 1.1) for cleaning for 20 - 30 minutes, then cleaned with anhydrous ethanol, then cleaned with deionized water, then dried with compressed air (or nitrogen) at 0.3 - 0.5 MPa, and finally vacuum dried in a vacuum dryer at 60 - 80 °C for 2 h; the waste liquid from the last cleaning is inspected with a particle size detector, and it is required that there are no particles larger than 30 μm.

[0060] (3) Welding current: Set a suitable welding current. Set appropriate welding parameters during welding. If the welding current is too strong, it is not easy to heat evenly, the heating area is narrow, and it is difficult to deform, and it is easy to produce incomplete penetration defects; if the welding current is too weak, the joint surface will be severely oxidized, the grains in the joint area will be coarse, affecting the mechanical properties of the welded joint. Therefore, it is crucial to select appropriate welding parameters. In this embodiment, the welding current is 20 A and the welding time is 10 s.

[0061] Among them, the current is calculated to obtain the minimum value through the above formula (2), and then the corresponding current value is selected on the welding machine;

[0062] The heat Q3 required when the material melts can be calculated by the following formula:

[0063] Q3 = C * M * ΔT (3)

[0064] In the formula: Q3 is the heat value (J) required for material melting, C is the specific heat capacity of the melt KJ / (kg·°C), M is the mass of the melt (KG), and ΔT is the temperature change value (°C) of the object when it melts.

[0065] (4) Welding time: Set the appropriate welding time t. Welding current and welding time are two important parameters that determine the heat generation of the workpiece, and the two can be matched with each other within a certain range. The welding resistance is related to the welding material, and the welding resistance can be confirmed when the welding material is confirmed. When the welding current and welding material are determined, the welding time can be confirmed through the above formula (2). Generally, when welding with a large current, the welding time is short; when welding with a small current, the welding time is long. In this embodiment, the welding time is 10s.

[0066] (5) Welding displacement: Set the welding displacement in the welding machine. During the actual welding process, the welded part undergoes thermal deformation, and the welded part will shorten under the extrusion of the welding pressure, that is, the offset displacement of the welding electrode. In this embodiment, the welding displacement is set to 0.1mm;

[0067] Among them, the displacement can be set according to the following empirical formula:

[0068] ΔL = (0.05 - 0.1)h (4)

[0069] In the formula, h is the thickness of the welded part (mm), and ΔL is the displacement amount (mm).

[0070] (6) Welding pressure: The formula for pressure and resistance is as follows,

[0071]

[0072] In the formula: k is the stiffness coefficient, ΔL is the displacement amount, ρ is the resistivity of the conductor (Ω·m), and R is the resistance of the conductor (Ω);

[0073] The resistance calculation formula is: R = ρ × L / S (6)

[0074] Among them, ρ is the resistivity of the conductor (Ω·m), L is the length of the conductor (m), and S is the cross-sectional area of the conductor (㎡);

[0075] The above formula

[0076] In the formula, Q3 is the heat value (J) required for material melting, I is the welding current (A), ρ is the conductor resistivity (Ω·m), L is the conductor length (m), and t is the welding time (s);

[0077] The welding pressure is calculated by the above formula (5). The welding pressure is perpendicular to the direction of the surface to be welded. A suitable welding pressure makes the welding surfaces fit closely in contact, fully utilizing the heat generation due to the concentrated resistance between the welded parts. Otherwise, it will affect the heat generation intensity of the contact surface; it can be seen from the above formula (6) that the resistance is inversely proportional to the welding area. If the welding pressure is too low and the welded parts are not in good contact, the welding contact area will become smaller, resulting in a sudden increase in the welding resistance and rapid generation of strong heat at local positions, which is likely to cause uneven welding; if the welding pressure is too low, it will also increase the oxidation of the joint surface, easily causing looseness near the interface and affecting the welding quality. Therefore, using a suitable welding pressure is beneficial for achieving high-quality bonding of the welded parts. In this embodiment, the welding pressure is 5 N.

[0078] (7) Post-weld cleaning: After welding, the parts are ground to remove burrs and pickled to clean up the excess materials.

[0079] (8) Welding quality inspection: In this embodiment, radiographic inspection is selected because radiographic inspection can more accurately judge the nature, quantity, size, and location of defects, and is particularly suitable for the detection of defects in the resistance welding joints in this case.

[0080] Common welding inspection methods include magnetic particle inspection, penetrant inspection, eddy current inspection, etc. However, there are limitations in using these methods. For example, when using magnetic particle inspection, it is required that the inspected material has ferromagnetic properties. If this method is used for the inspection of austenitic stainless steel, it cannot meet the requirements, and it can only inspect the surface and near-surface of the inspected object, and it is impossible to accurately judge the internal defects of the material; another example is that penetrant inspection is based on capillary action. After a certain period of time, the penetrant can penetrate into the surface open defects to detect the morphology and distribution state of the defects, but it is impossible to judge the internal defects of the material; another example is that eddy current inspection uses the principle of electromagnetic induction. The material itself must have conductivity, and it can only detect the defects on the surface and near-surface of the conductive material, and it is impossible to judge the internal defects of the material. Therefore, the radiographic inspection method is selected here to detect the welding quality.

[0081] (9) Welding strength inspection: After the welding quality inspection is qualified, the welded parts are installed in the designed special fixture for strength and corresponding life tests to ensure that the welding strength absolutely meets the requirements and conforms to the quality requirements of aerospace products.

[0082] S6. Fix and install the filter device formed by welding to one side of the valve cover with a shaft retaining ring to form a valve cover filter device.

[0083] In summary, the device has a simple structure and an ingenious design. The filter layer is directly integrated into the valve cover through a flexible fixing method, which is convenient for later maintenance operations. In the manufacturing method of a special valve cover device with a filtering function proposed in this application, laser cutting is used to avoid the size deviation caused by manually cutting the filter screen with scissors. The filter screen is thin and fine and is very easy to deform. If the circular filter screen that was originally intended to fit the same size as the pressure ring is cut, it is very easy to be deformed into an elliptical shape, resulting in the filter screen being unable to fit tightly and causing a cold weld in the subsequent welding process. Replacing welding methods such as argon arc welding and laser welding with resistance welding can ensure that the welding quality is firm and reliable, so that the filter device can better withstand the positive high-pressure impact force when the medium quickly flows into the valve and the reverse high-intensity impact during emergency discharge. This device has both a filtering function and can withstand positive and reverse high-intensity impacts. It is light in weight and small in size. There is no additional increase in the outer contour volume of the valve, saving valuable physical space for the pipe valve system.

[0084] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A manufacturing method of a special valve bonnet device with a filtering function, characterized in that It includes the following steps: S1. Crush the raw materials for making powder with a crusher, and then screen out the formed powder with a sieve whose mesh size is smaller than that of the fine filter screen; S2. Use laser cutting to cut the whole filter screen into a formed filter screen. When cutting the filter screen, fix the filter screen on a special tooling for cutting to ensure that the filter screen does not warp or shift; S3. Uniformly fill the formed powder into the formed filter screen; S4. Use resistance welding to weld multiple formed filter screens together to form a filter layer; S5. Press the filter layer tightly from above and below with two pressing rings and use resistance welding. When using resistance welding, the shape and size of the welding electrode of the resistance welding are the same as those of the end face of the pressing ring to ensure that the heating and deformation amount of the welded parts are the same during welding; S6. Fix and install the filter device formed by welding to the inlet end of the valve cover with a shaft retaining ring to form a valve cover filter device.

2. The manufacturing method of the special valve bonnet device with a filtering function according to claim 1, characterized in that: The filter layer includes one layer of fine filter screen and two layers of coarse filter screens, and one layer of fine filter screen is arranged between the two layers of coarse filter screens.

3. The manufacturing method of the special valve bonnet device with a filtering function according to claim 2, characterized in that: The mesh size of the coarse filter screen is 8 - 15 times that of the fine filter screen.

4. The manufacturing method of the special valve bonnet device with a filtering function according to claim 2, characterized in that: The fine filter screen and the coarse filter screen are made of high-strength low-temperature-resistant stainless steel material.

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