Butterfly valve

Abstract

The utility model belongs to the technical field of valves, and particularly relates to a butterfly valve which comprises a valve body, a connecting flange is arranged at one end of the valve body, and a valve clack is arranged in the valve body. The driving unit is arranged on the upper portion of the valve body and used for driving the valve clack to rotate. The annular bulge is arranged in the valve body and is concentrically distributed with the valve body; the metal valve seat is embedded in the annular protrusion in a cold pressing mode. The first sealing filler is arranged between the annular protrusion and the metal valve seat, and the movable flange is arranged at the other end of the valve body and can slide in the axial direction of the valve body so that the length of the valve body can be adjusted; when the valve clack is closed, the valve clack is matched with the surface of the metal valve seat to form sealing, the driving unit can lock rotation of the valve clack, and compared with the prior art, the working efficiency of installation and maintenance of the valve is effectively improved.

Description

Technical Field

[0001] This utility model belongs to the field of valve technology, and in particular relates to a butterfly valve. Background Technology

[0002] A butterfly valve, also known as a flap valve, is a simple regulating valve used for on / off control of low-pressure pipeline media. A butterfly valve is defined as a valve whose closing element (valve disc or butterfly plate) is a disc that rotates around a valve shaft to achieve opening and closing. For example, the adjustable flow pneumatic butterfly valve disclosed in patent application number CN202220258090.4 includes a pneumatic butterfly valve body, flanges, a butterfly valve disc, a rotating main shaft, a lower end cover, a pneumatic motor platform, a pneumatic motor, locking bolts, and locking nuts; the flanges at both ends of the pneumatic butterfly valve body are connected to the pipeline.

[0003] The existing butterfly valve is not easy to align with the valve body flange during use, which increases installation time and reduces work efficiency. Furthermore, the valve seat becomes difficult to maintain after wear, which further reduces work efficiency. Therefore, it is necessary to make improvements. Utility Model Content

[0004] The purpose of this utility model is to address the aforementioned technical problems by providing a butterfly valve that effectively improves the efficiency of butterfly valve installation and maintenance.

[0005] In view of this, the present invention provides a butterfly valve, comprising:

[0006] A valve body, one end of which is provided with a connecting flange, and a valve disc is provided inside the valve body;

[0007] A drive unit is disposed on the upper part of the valve body for driving the valve disc to rotate;

[0008] Also includes:

[0009] Annular protrusions are disposed in the valve body and are concentrically distributed within the valve body;

[0010] A metal valve seat, which is cold-pressed and embedded in an annular protrusion;

[0011] The first sealing packing is disposed between the annular protrusion and the metal valve seat.

[0012] A movable flange is provided at the other end of the valve body and the movable flange can slide along the axial direction of the valve body to adjust the length of the valve body;

[0013] When the valve disc is closed, it forms a seal with the surface of the metal valve seat, and the drive unit can lock the rotation of the valve disc.

[0014] In this technical solution, when installing a butterfly valve, the fixed flange and the pipe flange are initially connected with bolts, at which point the movable flange is in a free-sliding state. Then, the movable flange is pushed axially along the valve body to adjust the overall length of the valve body, aligning the bolt holes of the movable flange with those of the pipe flange on the other side. After alignment, the connecting bolts on the movable flange are tightened to connect it to the pipe flange. This eliminates the need for precise control of pipe spacing during installation, significantly improving installation convenience. During operation, when the valve disc rotates to the closed position, the sealing surface of the valve disc tightly contacts the inner circumference of the metal valve seat, forming a sealing band. Simultaneously, the medium pressure acts on the valve disc, further pressing it against the metal valve seat, enhancing the sealing effect. The first sealing packing forms a static seal between the metal valve seat and the annular protrusion, preventing medium leakage from the connection between the valve seat and the valve body. When the metal valve seat wears out due to long-term use, it can be easily removed from the annular protrusion by heating it to an expanded state and a new metal valve seat can be replaced without replacing the entire valve body, which greatly simplifies the maintenance process. At the same time, the drive unit can lock the rotation of the valve disc, thereby preventing the valve disc from being opened accidentally.

[0015] In the above technical solution, the movable flange further includes:

[0016] The flange body is located at the end of the valve body and can slide along the axial direction of the valve body. The flange body has mounting grooves on its inner and outer sides along the axial direction.

[0017] Two sealing rings are respectively disposed in two mounting grooves;

[0018] An elastic gasket is disposed inside the sealing ring on the axial inner side of the flange body;

[0019] The elastic gasket is fixedly connected to the flange body by connecting bolts and presses the sealing ring on the corresponding side onto the flange body. The inner radial side of the sealing ring is provided with corrugated protrusions, and the inner radial side of the sealing ring contacts the valve body surface to form a sealing surface.

[0020] Furthermore, the above technical solution also includes:

[0021] A fitting protrusion is provided on the surface of the sealing ring opposite to the mounting groove;

[0022] A fitting groove is provided on the surface of the mounting groove;

[0023] The fitting protrusion, in particular, prevents the sealing ring from misaligning with the mounting groove by cooperating with the fitting groove.

[0024] In the above technical solution, a second sealing filler is further provided between the elastic gasket and the sealing ring.

[0025] In the above technical solution, the driving unit further includes:

[0026] A valve stem, which is connected to a valve disc to drive the valve disc to rotate;

[0027] A pneumatic drive unit, which is connected to the valve stem to drive the valve stem to rotate;

[0028] A worm gear, which is mounted on the valve stem and rotates synchronously with the valve stem;

[0029] A worm gear, wherein the worm gear is rotatably mounted on one side of a worm wheel and meshes with the worm wheel, and a stop block is provided at one end of the worm gear, wherein a stop slot is provided in the stop block;

[0030] A stop rod is provided on one side of the worm and coaxially distributed with the worm, and the stop rod can move linearly along the worm axis;

[0031] The end of the stop rod can be inserted into the stop slot to limit the rotation of the worm gear.

[0032] The beneficial effects of this utility model are:

[0033] 1. The axial sliding adjustment function of the movable flange shortens the pipe docking time, greatly reduces the difficulty of alignment, and effectively improves work efficiency;

[0034] 2. The modular design of the metal valve seat shortens the valve seat replacement time and eliminates the need to disassemble the entire valve body, reducing maintenance costs and making maintenance more convenient, thereby further improving work efficiency;

[0035] 3. The mechanical locking mechanism of the drive unit ensures that the valve disc remains locked in the event of a sudden power outage, gas supply failure or other abnormal situation, so as to avoid safety accidents caused by backflow of medium or pressure fluctuation. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the structure of a specific embodiment of the present utility model.

[0038] Figure 2This is a schematic cross-sectional view of the valve body of this utility model.

[0039] Figure 3 This utility model Figure 2 A partial enlarged view of the structure of section A in the middle.

[0040] Figure 4 This is an exploded view of the valve body of this utility model.

[0041] Figure 5 This utility model Figure 4 A partial enlarged view of the structure of section B.

[0042] Figure 6 This is a schematic diagram of the drive unit structure of this utility model.

[0043] The markings in the diagram are as follows:

[0044] 1. Valve body; 2. Connecting flange; 3. Drive unit; 30. Valve stem; 31. Pneumatic drive unit; 32. Worm gear; 33. Worm; 34. Stop block; 35. Stop slot; 36. Stop rod; 4. Annular protrusion; 5. Metal valve seat; 6. First sealing packing; 7. Movable flange; 70. Flange body; 71. Mounting groove; 72. Sealing ring; 73. Elastic gasket; 74. Corrugated protrusion; 8. Fitting protrusion; 9. Fitting groove; 10. Second sealing packing. Detailed Implementation

[0045] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0046] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0047] Valve body 1 structure

[0048] In this embodiment, the valve body 1 is made of high-strength ductile iron and is cylindrical in shape, with a through-flow channel (flow path) inside. A fixed connecting flange 2 is provided at one end (rear end) of the valve body 1. This flange is integrally formed with the valve body 1, and bolt holes are evenly distributed on the flange for connection to a pipe flange. A movable flange 7 is installed at the other end (front end) of the valve body 1. This movable flange 7 can slide along the axial direction of the valve body 1 (i.e., the direction of fluid flow), thereby adjusting the effective length of the valve body 1.

[0049] An annular protrusion 4 is located near the front end inside the valve body 1. This annular protrusion 4 is coaxially distributed with the valve body 1 and has a trapezoidal cross-section, including a horizontally extending protruding surface, a forward-inward inclined surface, and a rearward-outward inclined surface. The inner diameter of the annular protrusion 4 is slightly larger than the outer diameter of the valve disc to ensure that the valve disc does not interfere with the protrusion during rotation. An annular groove is formed on the forward-inward inclined surface of the annular protrusion 4 for embedding a first sealing packing 6. This packing is preferably made of flexible graphite material, which has good high-temperature resistance and corrosion resistance. The metal valve seat 5 is installed on the annular protrusion 4 using a conventional cold-pressing fitting process.

[0050] The upper part of the valve body 1 is equipped with a mounting platform for the drive unit 3, which is fixedly connected to the drive unit 3 by bolts. A through-hole for mounting the valve stem 30 is provided inside the platform, and a wear-resistant bushing is installed inside the hole to reduce frictional loss during valve stem 30 rotation. The valve body 1 is made of QT450-10 ductile iron, with a tensile strength of not less than 450MPa and an elongation of not less than 10%, which meets the requirements for use under medium and high pressure conditions.

[0051] When installing a butterfly valve, first connect the fixed flange to the pipe flange with bolts, at which point the movable flange 7 is in a free-sliding state. Then, push the movable flange 7 to move it axially along the valve body 1, adjusting the overall length of the valve body 1 so that the bolt holes of the movable flange 7 are aligned with the bolt holes of the pipe flange on the other side. After alignment, tighten the connecting bolts on the movable flange 7, causing the elastic gasket 73 to deform elastically, thereby pressing the sealing ring 72 against the surface of the valve body 1 and within the mounting groove 71 of the movable flange 7, forming a seal. This telescopic valve body 1 structure eliminates the need for precise control of pipe spacing during installation, significantly improving installation convenience.

[0052] The valve body 1 structure, through the axial sliding adjustment of the movable flange 7, widens the pipe spacing tolerance, which traditionally required precise control during installation, from ±1mm to ±5mm, significantly reducing installation difficulty. Simultaneously, the annular protrusion 4 provides a precise installation reference for the metal valve seat 5, ensuring that the coaxiality error between the valve seat and valve body 1 does not exceed 0.05mm, laying a structural foundation for subsequent sealing performance. The choice of material for the valve body 1 enables it to withstand a maximum operating pressure of 2.5MPa and a temperature range of -20℃ to 120℃, expanding its applicable operating conditions.

[0053] Valve seat structure

[0054] The valve seat structure in this embodiment mainly consists of an annular protrusion 4, a metal valve seat 5, and a first sealing packing 6. The metal valve seat 5 is made of wear-resistant 316L stainless steel and is fixed to the annular protrusion 4 of the valve body 1 through a cold-pressing embedding process. The outer circumferential surface of the metal valve seat 5 is tightly fitted with the forward inclined surface of the annular protrusion 4, while the inner circumferential surface forms a smooth sealing surface for cooperation with the valve disc to achieve fluid sealing.

[0055] An annular groove is formed on the outer circumferential surface of the metal valve seat 5. The first sealing packing 6 is embedded in the groove and the recess of the annular protrusion 4, forming a double sealing barrier. The packing is made of expanded graphite braided material, which has good resilience and chemical stability, and can maintain sealing performance under high pressure. On the inner circumferential surface of the metal valve seat 5, several annular corrugations are evenly distributed circumferentially. These corrugations can generate elastic deformation when the valve disc is closed, which can enhance the contact pressure of the sealing surface and improve the sealing reliability.

[0056] The installation process of the metal valve seat 5 is as follows: First, the first sealing packing 6 is embedded in the groove of the annular protrusion 4. Then, the metal valve seat 5 is heated to 200°C to expand it. Then, it is quickly put on the annular protrusion 4. After cooling, the metal valve seat 5 shrinks and forms an interference fit with the annular protrusion 4. The interference fit is controlled between 0.03-0.05mm to ensure that the valve seat is firmly fixed and does not produce plastic deformation.

[0057] When the valve disc rotates to the closed position, the sealing surface of the valve disc fits tightly against the inner circumferential surface of the metal valve seat 5, creating a contact sealing strip between them. Simultaneously, the medium pressure acts on the valve disc, further pressing the metal valve seat 5 and enhancing the sealing effect. The first sealing packing 6 forms a static seal between the metal valve seat 5 and the annular protrusion 4, preventing medium leakage from the connection between the valve seat and the valve body 1.

[0058] When the metal valve seat 5 wears out due to long-term use, it can be easily removed from the annular protrusion 4 by heating it to an expanded state, and a new metal valve seat 5 can be replaced without replacing the entire valve body 1, which greatly simplifies the maintenance process.

[0059] Movable flange 7 structure

[0060] The movable flange 7 in this embodiment includes a flange body 70, two sealing rings 72, an elastic gasket 73, and connecting bolts. The flange body 70 is annular and is fitted onto the front end of the valve body 1, allowing it to slide freely along the axial direction of the valve body 1. Annular mounting grooves 71 are respectively formed on the inner and outer sides of the flange body 70 along its axial direction, and fitting grooves 9 are formed on the inner sidewalls of the grooves.

[0061] Two sealing rings 72 are respectively embedded in two mounting grooves 71 of the flange body 70. The sealing rings 72 are made of nitrile rubber, and their radial inner surfaces are provided with corrugated protrusions 74 that contact the surface of the valve body 1. The height of the corrugations is 0.5-1mm and the wavelength is 2-3mm. The outer surface of the sealing rings 72 is provided with fitting protrusions 8 that mate with the fitting grooves 9. The fitting protrusions 8 and the fitting grooves 9 form an interference fit to prevent the sealing rings 72 from circumferentially or axially displacing within the mounting grooves 71.

[0062] The elastic gasket 73 is located inside the sealing ring 72 on the axial inner side of the flange body 70. It is made of 65Mn spring steel with a thickness of 2-3mm and has good elastic properties. The elastic gasket 73 is fixedly connected to the flange body 70 by connecting bolts, which are evenly distributed on the circumference of the flange body 70, with no fewer than four bolts. When the connecting bolts are tightened, the elastic gasket 73 undergoes elastic deformation, pressing the inner sealing ring 72 into the mounting groove 71. Simultaneously, through the conduction of the flange body 70, the outer sealing ring 72 is also pressed into the mounting groove 71.

[0063] A second sealing filler 10 is also provided between the elastic gasket 73 and the inner sealing ring 72. The filler is made of polytetrafluoroethylene material, which has a low coefficient of friction and good corrosion resistance. It can reduce the friction between the elastic gasket 73 and the sealing ring 72 and extend the service life of the sealing ring 72.

[0064] The movable flange 7 operates based on the synergistic effect of elastic compression and bellows sealing. When the length of the valve body 1 needs to be adjusted, the connecting bolts are loosened, releasing the elastic force of the elastic gasket 73, allowing the movable flange 7 to slide axially along the valve body 1. After adjustment to the appropriate position, the connecting bolts are tightened, compressing the elastic gasket 73 and generating an upward elastic force that presses the inner sealing ring 72 against the mounting groove 71 and the surface of the valve body 1. Simultaneously, the flange body 70 moves downward under the action of the elastic gasket 73, pressing the outer sealing ring 72 against the mounting groove 71 and the surface of the pipe flange.

[0065] The corrugated protrusions 74 of the sealing ring 72 undergo elastic deformation under pressure, forming a tight contact with the surface of the valve body 1 and the pipe flange. Due to the presence of corrugations, the contact area is increased, enhancing the sealing effect. The fit between the interlocking protrusions 8 and the interlocking grooves 9 prevents the sealing ring 72 from shifting under pressure, ensuring the uniformity of the sealing surface. The second sealing packing 10 further fills the tiny gaps between the elastic gasket 73 and the sealing ring 72, improving sealing reliability.

[0066] The axial sliding adjustment function provided by the movable flange 7 allows the length of the valve body 1 to vary within ±10mm, greatly simplifying the pipeline connection process and reducing installation time by more than 50%. The design of the double sealing ring 72 and the corrugated protrusion 74 effectively reduces the leakage rate at the movable flange 7, which is far superior to the sealing performance of traditional flanges. The interlocking anti-misalignment structure ensures the positional stability of the sealing ring 72 during long-term use, avoiding sealing failure caused by the displacement of the sealing ring 72. The elastic compensation function of the elastic gasket 73 can automatically adapt to the thermal expansion and contraction of the valve body 1 caused by temperature changes, maintain continuous sealing pressure, and maintain good sealing performance even under operating conditions with temperature fluctuations of ±50℃.

[0067] Drive Unit 3 Structure

[0068] The drive unit 3 in this embodiment mainly consists of a pneumatic drive unit 31, a valve stem 30, a worm gear 32, a worm 33, a stop block 34, and a stop rod 36. The pneumatic drive unit 31 is mounted on the mounting platform on the upper part of the valve body 1 and adopts a double-acting cylinder structure. It drives the piston to reciprocate by compressed air, thereby driving the valve stem 30 to rotate.

[0069] The valve stem 30 vertically penetrates the mounting platform of the drive unit 3 in the valve body 1. Its lower end is fixedly connected to the valve disc, and its upper end is connected to the output shaft of the pneumatic drive unit 31. The valve stem 30 is made of 2Cr13 stainless steel with a surface hardening treatment to achieve a hardness of HRC30-35, thereby improving its wear resistance and corrosion resistance. A stuffing box seal is provided at the connection between the valve stem 30 and the mounting platform to prevent media leakage.

[0070] The worm gear 32 is fixedly sleeved in the middle of the valve stem 30 and rotates synchronously with the valve stem 30. The worm gear 32 is made of tin bronze, which has good anti-friction properties. The worm 33 is located on one side of the worm gear 32 and meshes with the worm gear 32. The axis of the worm 33 intersects perpendicularly with the axis of the valve stem 30. The worm 33 is made of 45# steel, and the tooth surface is hardened to a hardness of HRC40-45. A stop block 34 is fixedly connected to one end of the worm 33. The stop block 34 is disc-shaped and coaxially distributed with the worm 33. A stop slot 35 is formed on the outer circumference of the stop block 34. The slot has a square cross-section and a depth of 10-15mm.

[0071] A stop rod 36 is located on one side of the worm gear 33, coaxially distributed with it. The front end of the rod is square to facilitate insertion into and engagement with the stop slot 35. The middle part of the rod is cylindrical to prevent it from affecting the worm gear 33 in its initial state. The end of the rod is square, used to engage with the mounting platform to stop the worm gear 33. An operating handle is connected to the rear end of the stop rod 36, allowing the operator to move the stop rod 36 linearly along the axial direction of the worm gear 33 by operating the handle. The working principle of the drive unit 3 consists of two processes: driving and locking.

[0072] During normal operation, compressed air is introduced into the pneumatic drive unit 31, causing the piston to drive the output shaft to rotate. This rotation, via the valve stem 30, drives the valve disc to rotate, thus opening or closing the butterfly valve. The worm gear 32 and worm 33 transmission mechanism play a role in speed reduction and torque amplification during this process, converting the high speed and low torque of the pneumatic drive unit 31 into the low speed and high torque of the valve stem 30, ensuring that the valve disc can overcome the medium pressure to reliably open and close.

[0073] When it is necessary to lock the valve disc position, the operator pulls the handle, pushing the stop rod 36 forward. The front end of the rod inserts into the stop slot 35 of the stop block 34. Since the stop rod 36 is coaxially distributed with the worm gear 33, its insertion restricts the rotation of the worm gear 33. Since the worm gear 33 meshes with the worm wheel 32, the worm wheel 32 also cannot rotate, thus locking the position of the valve stem 30 and the valve disc. At this time, even if the pneumatic drive unit 31 loses its air supply, the valve disc can remain in its current position, preventing accidental rotation due to fluctuations in medium pressure.

[0074] When it is necessary to unlock, the operator pulls the stop rod 36 backward to disengage it from the stop slot 35, and the drive unit 3 returns to normal drive status.

[0075] The design of drive unit 3 achieves the following technical effects: the response time of the stop locking mechanism is no more than 1 second, which can quickly lock the valve disc in case of emergencies and improve system safety; in the locked state, the holding torque of the valve disc is not less than 1.5 times the driving torque, ensuring position stability under extreme working conditions; the design of the manually operated stop rod 36 allows the valve disc to be locked manually even when the automatic control system fails, increasing the redundancy and reliability of the system.

[0076] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A butterfly valve, comprising: A valve body (1) is provided with a connecting flange (2) at one end of the valve body (1), and a valve disc is provided inside the valve body (1); A drive unit (3) is disposed on the upper part of the valve body (1) for driving the valve disc to rotate; Its characteristic is that it further includes: Annular protrusions (4) are provided in the valve body (1) and are concentrically distributed in the valve body (1); Metal valve seat (5), which is cold-pressed and embedded on an annular protrusion (4); The first sealing packing (6) is disposed between the annular protrusion (4) and the metal valve seat (5). Movable flange (7), which is located at the other end of valve body (1) and can slide along the axial direction of valve body (1) to adjust the length of valve body (1); When the valve disc is closed, it forms a seal with the surface of the metal valve seat (5), and the drive unit (3) can lock the rotation of the valve disc.

2. A butterfly valve according to claim 1, characterized in that, The movable flange (7) also includes: Flange body (70), the flange body (70) is disposed at the end of the valve body (1) and can slide along the axial direction of the valve body (1), and mounting grooves (71) are respectively provided on the inner and outer sides of the flange body (70) along the axial direction; Two sealing rings (72) are respectively disposed in two mounting grooves (71); An elastic gasket (73) is disposed inside the sealing ring (72) on the axial inner side of the flange body (70); The elastic gasket (73) is fixedly connected to the flange body (70) by connecting bolts and presses the sealing ring (72) on the corresponding side onto the flange body (70). The sealing ring (72) has a corrugated protrusion (74) on its radial inner side. The sealing ring (72) contacts the valve body (1) surface to form a sealing surface.

3. A butterfly valve according to claim 2, characterized in that, Also includes: The fitting protrusion (8) is disposed on the side surface of the sealing ring (72) opposite to the mounting groove (71); A fitting groove (9) is provided on the surface of the mounting groove (71); The fitting protrusion (8) cooperates with the fitting groove (9) to prevent the sealing ring (72) from being misaligned with the mounting groove (71).

4. A butterfly valve according to claim 3, characterized in that: A second sealing filler (10) is provided between the elastic gasket (73) and the sealing ring (72).

5. A butterfly valve according to claim 1, characterized in that, The drive unit (3) further includes: Valve stem (30), which is connected to the valve disc to drive the valve disc to rotate; A pneumatic drive unit (31) is connected to the valve stem (30) to drive the valve stem (30) to rotate; A worm gear (32) is mounted on the valve stem (30) and rotates synchronously with the valve stem (30); A worm (33) is rotatably mounted on one side of a worm wheel (32) and meshes with the worm wheel (32). A stop block (34) is provided at one end of the worm (33), and a stop slot (35) is provided in the stop block (34). A stop rod (36) is provided on one side of the worm (33) and coaxially distributed with the worm (33). The stop rod (36) can move linearly along the axial direction of the worm (33). The end of the stop rod (36) can be inserted into the stop slot (35) to limit the rotation of the worm (33).

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