A helical twin-rotor flowmeter

Abstract

The application discloses a spiral double-rotor flowmeter, and belongs to the technical field of measurement, which comprises a flowmeter main body, the side of the flowmeter main body is provided with symmetrically arranged through holes, one of the through holes is connected with an output pipe, the other through hole is connected with an input pipe, and the end of the input pipe is provided with a filtering assembly, characterized in that the filtering assembly comprises a sleeve and a filtering basket, the diameter of the filtering basket is smaller than that of the sleeve, the end of the sleeve is connected with the end of the input pipe, the filtering basket is rotationally connected in the sleeve, the front end of the sleeve is threadedly connected with a connecting cover, the front surface of the connecting cover is connected with a connecting pipe, the connecting pipe is connected with a backflushing pipe, and the other end of the backflushing pipe penetrates through the tail of the sleeve. In the application, the liquid inputted by the backflushing pipe impacts a turbine to drive the filtering basket to rotate, so that the filter screen of the filtering basket is contacted with the backflushing water flow in all directions, compared with the design that the static filter screen can only flush one side, impurities adhered to each part of the filter screen can be completely removed, and the problem of increased fluid flow resistance caused by local blockage can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of metering technology, and specifically relates to a spiral dual rotor flow meter. Background Technology

[0002] With its core advantages of high metering accuracy, low pressure loss, and wide applicability to a wide range of media, the spiral twin rotor flowmeter has become a key device for fluid metering in industries such as petroleum, chemical, and gas. In this process, the meshing accuracy of the spiral rotor, the internal sealing performance of the flowmeter, and the cleanliness of the flowing fluid directly determine the accuracy of the metering results and the long-term service life of the equipment. If solid particulate impurities in the fluid enter the flowmeter body, they can easily cause rotor wear, jamming of the meshing structure, and even bearing damage, seriously affecting the normal operation of the equipment. Therefore, it is common practice in the industry to install a filter assembly at the front end of the flowmeter's inlet pipe to intercept impurities in the fluid and ensure the safety of the flowmeter's core components.

[0003] To address the cleaning and maintenance issues of filter components, relevant technologies have undergone targeted improvements. For example, Chinese utility model patent CN221325567U discloses a spiral dual rotor flow meter, which achieves filter plate flushing and cleaning by setting a rotatable filter plate inside the connecting pipe and switching two solenoid valves: during normal operation, the fluid enters the flow meter after being filtered by the filter plate; when cleaning is required, the filter plate is rotated by a motor so that the side with attached impurities faces the flushing water flow, and the impurities are discharged by switching the solenoid valves.

[0004] While existing technologies simplify cleaning operations to some extent, they still have significant shortcomings: First, the rotation of the filter plate relies on an independent motor drive, which not only increases the structural complexity and manufacturing cost of the equipment but also requires additional power and control modules. Second, the filter plate can only rotate 180°, and the rinsing water flow can only act on one side of the filter plate. This makes it difficult to thoroughly remove stubborn impurities attached to the edges, back, and inner walls of the filter holes, easily leading to localized clogging of the filter screen. Long-term use will still increase fluid flow resistance and affect measurement stability. Third, this solution does not optimize the fluid action path and sealing structure of the flow meter. The compatibility between the fluid inlet / outlet direction and the rotor meshing surface is insufficient, which can easily lead to uneven force on the rotor. At the same time, the single rubber-bonded seal has limited anti-leakage effect under high-pressure conditions and cannot meet the stringent requirements of industrial fields.

[0005] In addition, existing flow meters with filtration functions generally have common problems: some backwashing filter components use a static filter design, which does not clean impurities thoroughly and requires shutdown for disassembly and maintenance, affecting continuous production; some self-cleaning structures have high rotational resistance, which can easily cause component wear and shorten the service life of the filter components. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] To address the problems mentioned in the background section, the present invention adopts the following technical solution.

[0008] A spiral dual rotor flow meter includes a flow meter body with symmetrical through holes on its side. One through hole is connected to an output pipe, and the other through hole is connected to an input pipe. A filter assembly is fitted to the end of the input pipe. The filter assembly includes an outer jacket and a filter basket. The diameter of the filter basket is smaller than that of the outer jacket. The end of the outer jacket is connected to the end of the input pipe. The filter basket is rotatably connected inside the outer jacket. A connecting cap is threaded to the front end of the outer jacket. A connecting pipe is connected to the front surface of the connecting cap. A backflush pipe is connected to the connecting pipe. The other end of the backflush pipe passes through the tail of the outer jacket. Liquid enters the outer jacket through the backflush pipe to flush the filter basket.

[0009] Preferably, a second valve is installed on the connecting pipe and located between the backflushing pipe and the connecting cover. When backflushing is performed, the second valve is closed, allowing the liquid to flow into the backflushing pipe.

[0010] Preferably, a circular hole is provided at the center of the end of the outer casing, and a short pipe is connected to the outer diameter of the circular hole. The end of the short pipe is connected to the input pipe with a flange. A third valve is installed on the short pipe. When backwashing is performed, the third valve is closed to prevent the flushing water from flowing into the flow meter body.

[0011] Preferably, a first valve is installed on the backflush pipe. When the flow meter body is working normally, the backflush pipe is closed through the first valve, so that the liquid can flow normally into the flow meter body.

[0012] Preferably, a perforated piece is fixedly provided in the round hole at the end of the outer jacket, and a bearing is centrally embedded in the perforated piece. A short column is centrally provided at the tail of the filter basket, and the short column is fixedly inserted into the bearing. A turbine is fixedly sleeved on the short column. When liquid enters the outer jacket through the backflush pipe, the liquid impacts the turbine, causing the filter basket to rotate, so that the filter basket is flushed by the liquid while rotating, thus achieving self-cleaning.

[0013] Preferably, a limiting ring is provided inside the outer jacket at the waist position, the limiting ring has a groove, and a corresponding protruding ring is provided on the filter basket, and the protruding ring is adapted to the groove of the limiting ring.

[0014] Preferably, a support ring is provided inside the outer jacket near its end. When the filter basket is assembled inside the outer jacket, the front surface of the filter basket is flush with the front surface of the support ring. The front surface of the filter basket is integrally connected with a flange, and the flange fits against the support ring. Annular grooves are provided at the contact points between the convex ring and the limiting ring, as well as at the contact points between the flange and the support ring, and ball bearings are placed in the grooves.

[0015] Preferably, a drain pipe is provided on the lower surface of the connecting pipe, and the drain pipe is located between the second valve and the connecting cover, and a ball valve is installed on the drain pipe.

[0016] Preferably, a pair of helical rotors are rotatably connected inside the flow meter body, the pair of helical rotors mesh, and the line connecting the centers of the input pipe and the output pipe is perpendicular to the meshing surface between the helical rotors.

[0017] Preferably, stepped grooves are provided on the inner walls of both the upper and lower ends of the flow meter body, and a sealing groove is provided on the upper surface of the lowest point of the stepped groove. A rubber ring is embedded in the sealing groove. A sealing sheet, a pressure plate, and an end cap are arranged sequentially from top to bottom in the stepped groove. The lower surface of the sealing sheet is provided with a groove to fit the rubber ring, and screw holes are provided in the middle of the pressure plate and the stepped groove. The pressure plate is fixed in the stepped groove by screws. A bolt hole is provided between the end cap and the uppermost end of the stepped groove for fastening with bolts.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, the liquid impact turbine input by the backwash pipe drives the filter basket to rotate, so that the filter screen surface of the filter basket can come into full contact with the backwash water flow. Compared with the design of a static filter screen that can only be rinsed on one side, it can thoroughly remove the impurities attached to all parts of the filter screen and avoid the problem of increased fluid flow resistance caused by local blockage. At the same time, the filter basket rotates through the ball joint between the convex ring, the flange and the limiting ring and the support ring, which transforms the sliding friction into rolling friction, greatly reducing the rotation resistance and component wear, and extending the service life of the filter assembly. Moreover, this self-cleaning process does not require disassembling the filter basket. With the help of the drain pipe, the flushing impurities can be quickly discharged, achieving non-stop cleaning and ensuring the continuous and stable operation of the flow meter.

[0019] (2) In this invention, the line connecting the center of the input pipe and the output pipe is perpendicular to the meshing surface of the spiral rotor, so that the fluid acts perpendicularly on the rotor tooth surface, ensuring smooth meshing transmission of the dual rotors and reducing the measurement error caused by uneven fluid impact; the filter component can effectively intercept solid particles in the fluid, preventing particles from entering the flow meter body and wearing the rotor, increasing the meshing gap, and further maintaining the stability of measurement accuracy.

[0020] (3) In this invention, the sealing sheet and the rubber ring in the sealing groove are tightly fitted in the stepped groove at the upper and lower ends of the flow meter body. The double fastening structure of the pressure plate and the end cover can effectively enhance the sealing effect and is suitable for high-pressure fluid metering scenarios. The outer sleeve and the input pipe are connected by a flange, and the connection part has good sealing performance, which can prevent fluid leakage.

[0021] (4) The linkage design of the first, second and third valves in this invention can quickly realize the switching between "normal metering" and "backwashing" modes: during normal operation, the first valve is closed and the second and third valves are opened, and the fluid flows into the flow meter after filtration; during backwashing, the second and third valves are closed and the first valve is opened to prevent the flushing water from entering the main body of the flow meter. The operation process is simple and no complex control device is required. Attached Figure Description

[0022] Figure 1 The assembly of the spiral dual rotor flowmeter in this invention Figure 1 .

[0023] Figure 2 This is an exploded view of the spiral dual rotor flowmeter of the present invention.

[0024] Figure 3 This is a front view of the spiral dual rotor flowmeter of the present invention.

[0025] Figure 4 The assembly of the spiral dual rotor flowmeter in this invention Figure 2 .

[0026] Figure 5 This is an exploded cross-sectional view of the spiral dual rotor flowmeter of the present invention.

[0027] Figure 6 The explosion of the filter assembly of the spiral dual rotor flowmeter in this invention Figure 1 .

[0028] Figure 7 The explosion of the filter assembly of the spiral dual rotor flowmeter in this invention Figure 2 .

[0029] Figure 8 A cross-sectional view of the filter assembly of the spiral dual rotor flowmeter in this invention. Figure 1 .

[0030] Figure 9 A cross-sectional view of the filter assembly of the spiral dual rotor flowmeter in this invention. Figure 2 .

[0031] The correspondence between the labels and component names in the attached figures is as follows: 100. Flowmeter body; 100a. Stepped groove; 100b. Sealing groove; 101. Spiral rotor; 102. Sealing plate; 103. Pressing plate; 104. End cap; 105. Output pipe; 106. Input pipe; 200. Filter assembly; 201. Outer jacket; 201a. Limiting ring; 201b. Support ring; 202. Turbine; 203. Filter basket; 203a. Convex ring; 203b. Flanged edge; 204. Connecting cover; 205. Connecting pipe; 206. Backflush pipe; 206a. First valve; 207. Second valve; 208. Third valve. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments. The present invention provides the following embodiments.

[0035] See Figure 1 and Figure 2This is a structural diagram of a spiral dual-rotor flowmeter in this embodiment. The flowmeter includes a flowmeter body 100, which is a hollow cavity structure. Two identical through holes are symmetrically opened radially on the side of the flowmeter body 100. Internal threads are machined on the inner walls of the through holes. An output pipe 105 is fixed to one through hole via a threaded connection and welding reinforcement. An input pipe 106 is fixed to the other through hole via the same connection method. The input pipe 106 and the output pipe 105 have the same diameter, and their axes are on the same straight line. A filter assembly 200 is assembled at the end of the input pipe 106 away from the flowmeter body 100. The filter assembly 200 includes an outer sleeve 201 and a filter basket 203. The outer sleeve 201 is a cylindrical structure open at both ends, and the filter basket 203 is a cage-type filter structure. The outer diameter of the filter basket 203 is smaller than the inner diameter of the outer sleeve 201, forming an annular gap between the outer wall of the filter basket 203 and the inner wall of the outer sleeve 201. This gap allows for smooth fluid flow. The outer sleeve 201 is close to the input... The end of pipe 106 is connected to the end of input pipe 106. Filter basket 203 is rotatably connected inside outer sleeve 201. The inner wall of the front end of outer sleeve 201 away from input pipe 106 is machined with internal threads, and the outer wall of connecting cover 204 is correspondingly machined with external threads. Outer sleeve 201 and connecting cover 204 are sealed together by a threaded structure, and PTFE tape is wrapped around the threaded connection to further improve sealing performance. A connecting pipe 205 is integrally formed on the front surface of connecting cover 204. The inner wall of connecting pipe 205 and connecting cover 204 are connected by... The cavity is connected, and a backflush pipe 206 is welded to the side wall of the connecting pipe 205. The diameter of the backflush pipe 206 is smaller than that of the connecting pipe 205. The other end of the backflush pipe 206 passes through the tail side wall of the outer jacket 201 and extends into the inner part of the outer jacket 201 near the filter basket 203. The penetration between the backflush pipe 206 and the outer jacket 201 is sealed by welding to prevent fluid leakage. Liquid can enter the outer jacket 201 through the backflush pipe 206 to rinse the filter screen surface of the filter basket 203 in all directions.

[0036] See Figure 2 , Figure 6 as well as Figure 7In this embodiment, a second valve 207 is installed on the connecting pipe 205 and between the backflushing pipe 206 and the connecting cover 204. When its valve core is fully open, it can ensure unobstructed flow of fluid. When backflushing is performed, the second valve 207 is closed to cut off the forward flow path of the connecting pipe 205, so that the liquid can flow into the backflushing pipe 206. A circular hole is centrally located at the end of the outer casing 201 near the input pipe 106. The inner diameter of the circular hole matches the outer diameter of the short pipe. The short pipe is fixed to the outer diameter of the circular hole by welding. Flanges are welded to both the end of the short pipe away from the outer casing 201 and the end of the input pipe 106 away from the flowmeter body 100. The two flanges are of the same specification and are fastened together by bolts and nuts. A sealing gasket is sandwiched between the flanges to effectively ensure the sealing of the connection. A third valve 208 is installed on the short pipe. The third valve 208 is a gate valve, and its valve plate can completely block the fluid passage. When backflushing is performed, the third valve 208 is closed, which can effectively prevent flushing water from flowing into the flowmeter body 100 and avoid flushing impurities from contaminating the internal components of the flowmeter. A first valve 206a is installed on the backflush pipe 206. The first valve 206a is a ball valve. When the flow meter body 100 is working normally, the passage of the backflush pipe 206 is cut off by closing the first valve 206a, so that the liquid can flow into the connecting cover 204 through the connecting pipe 205, and then flow into the flow meter body 100 normally after being filtered by the filter basket 203.

[0037] See Figure 8 and Figure 9In this embodiment, a perforated plate is welded and fixed inside the circular hole at the end of the outer jacket 201. Multiple evenly distributed circular flow holes are formed on the perforated plate. The diameter of the flow holes is larger than the mesh diameter of the filter basket 203, ensuring smooth fluid flow. A bearing is centrally embedded in the perforated plate, with its outer ring interlocked with the mounting hole on the perforated plate. A cylindrical short column is integrally formed at the center of the tail of the filter basket 203. The outer diameter of the short column matches the inner ring of the bearing, and the short column is fixedly inserted into the inner ring of the bearing via an interference fit. A turbine 202 is fixedly sleeved on the short column via a flat key. The blades of the turbine 202 have an arc-shaped structure, providing excellent fluid guiding performance and efficiently converting the impact force of the fluid into rotational power. When liquid enters the outer jacket 201 through the backwash pipe 206, the liquid impacts the blades of the turbine 202 at high speed, causing the filter basket 203 to rotate at high speed around the axis of the short column. This allows the filter basket 203 to be thoroughly flushed by the liquid during rotation, achieving efficient self-cleaning. An integrally formed limiting ring 201a is located at the waist position inside the outer casing 201. The limiting ring 201a has an annular groove on the side facing the filter basket 203. A corresponding integrally formed protruding ring 203a is formed on the outer wall of the filter basket 203, and the protruding ring 203a is adapted to the groove of the limiting ring 201a. The protruding ring 203a can be embedded in the groove to effectively limit the axial displacement of the filter basket 203 and prevent the filter basket 203 from axially moving during rotation. An integrally formed support ring 201b is located inside the outer casing 201 near its front end. The inner diameter of the support ring 201b matches the outer diameter of the front end of the filter basket 203. When the filter basket 203 is assembled inside the outer casing 201, the front surface of the filter basket 203 is flush with the front surface of the support ring 201b. An annular flange 203b is integrally connected to the front surface of the filter basket 203. The outer diameter of the flange 203b is the same as the outer diameter of the support ring 201b, and the flange 203b and the support ring 201b fit tightly together. Annular grooves are provided at the contact points between the convex ring 203a and the limiting ring 201a, as well as at the contact points between the flange 203b and the support ring 201b. Several ball bearings are placed in the grooves, which can convert the sliding friction between the filter basket 203 and the outer casing 201 into rolling friction, greatly reducing rotational resistance and component wear.

[0038] See Figure 3 and Figure 4In this embodiment, a drain pipe 205a is welded to the lower surface of the connecting pipe 205. The diameter of the drain pipe 205a is smaller than that of the connecting pipe 205, and the drain pipe 205a is located between the second valve 207 and the connecting cover 204. A ball valve is installed on the drain pipe 205a. When the ball valve is closed, it ensures the normal flow of the connecting pipe 205. When it is open, it can quickly discharge the impurities and sewage after rinsing, preventing impurities from accumulating inside the filter assembly 200. A pair of spiral rotors 101 are rotatably connected inside the flow meter body 100. The spiral teeth of the pair of spiral rotors 101 mesh with each other. The line connecting the centers of the input pipe 106 and the output pipe 105 is perpendicular to the meshing surface between the spiral rotors 101, so that the fluid can act perpendicularly on the tooth surface of the spiral rotors 101 after entering the flow meter body 100, improving the stability of the rotor rotation. The inner walls of both the upper and lower ends of the flow meter body 100 are provided with stepped grooves 100a. The stepped grooves 100a have a multi-level coaxial cylindrical groove structure, and an annular sealing groove 100b is formed on the upper surface of the lowest point of the stepped groove 100a. A rubber ring is embedded in the sealing groove 100b. From top to bottom, a sealing plate 102, a pressure plate 103, and an end cap 104 are arranged sequentially within the stepped groove 100a. An annular groove adapted to the rubber ring is formed on the lower surface of the sealing plate 102, allowing the rubber ring to be embedded in the groove, thus enhancing the sealing effect. Both the pressure plate 103 and the stepped groove 100a have corresponding matching screw holes in their middle parts. The pressure plate 103 is fixed in the stepped groove 100a by screws. The pressure plate 103 can press and fix the sealing sheet 102 to prevent the sealing sheet 102 from displacing under fluid pressure. The end cap 104 and the uppermost end of the stepped groove 100a have corresponding matching bolt holes. Bolts are used for fastening. The lower surface of the end cap 104 can fit tightly with the upper surface of the pressure plate 103, further enhancing the stability of the sealing structure.

[0039] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A spiral dual rotor flow meter, comprising a flow meter body (100), wherein the flow meter body (100) has symmetrically arranged through holes on its side, one through hole is connected to an output pipe (105), and the other through hole is connected to an input pipe (106), wherein a filter assembly (200) is assembled at the end of the input pipe (106), characterized in that: The filter assembly (200) includes an outer casing (201) and a filter basket (203). The diameter of the filter basket (203) is smaller than that of the outer casing (201). The end of the outer casing (201) is connected to the end of the inlet pipe (106). The filter basket (203) is rotatably connected inside the outer casing (201). The front end of the outer casing (201) is threaded with a connecting cap (204). The front surface of the connecting cap (204) is connected to a connecting pipe (205). A backflushing pipe (206) is connected to the connecting pipe (205). The other end of the backflushing pipe (206) passes through the tail of the outer casing (201). Liquid enters the outer casing (201) through the backflushing pipe (206) to rinse the filter basket (203).

2. The spiral dual-rotor flowmeter according to claim 1, characterized in that: A second valve (207) is installed on the connecting pipe (205) and between the backflushing pipe (206) and the connecting cover (204). When backflushing is performed, the second valve (207) is closed, so that the liquid flows into the backflushing pipe (206).

3. The spiral dual rotor flowmeter according to claim 1, characterized in that: The outer casing (201) has a centrally located circular hole at one end. A short pipe is connected to the outer diameter of the circular hole. The short pipe is connected to the end of the input pipe (106) by a flange. A third valve (208) is installed on the short pipe. When backwashing is performed, the third valve (208) is closed to prevent the flushing water from flowing into the flow meter body (100).

4. The spiral dual-rotor flowmeter according to claim 1, characterized in that: A first valve (206a) is installed on the backflush pipe (206). When the flow meter body (100) is working normally, the backflush pipe (206) is closed through the first valve (206a), so that the liquid can flow normally into the flow meter body (100).

5. The spiral dual-rotor flowmeter according to claim 3, characterized in that: A perforated piece is fixedly installed in the round hole at the end of the outer casing (201), and a bearing is centrally embedded in the perforated piece. A short column is centrally installed at the tail of the filter basket (203), and the short column is fixedly inserted into the bearing. A turbine (202) is fixedly sleeved on the short column. When liquid enters the outer casing (201) through the backwash pipe (206), the liquid impacts the turbine (202), causing the filter basket (203) to rotate, so that the filter basket (203) is flushed by the liquid while rotating, thus achieving self-cleaning.

6. The spiral dual-rotor flowmeter according to claim 1, characterized in that: The outer casing (201) is provided with a limiting ring (201a) at the waist position. The limiting ring (201a) has a groove. The filter basket (203) is provided with a corresponding protruding ring (203a), and the protruding ring (203a) is adapted to the groove of the limiting ring (201a).

7. The spiral dual-rotor flowmeter according to claim 6, characterized in that: A support ring (201b) is provided inside the outer casing (201) near its end. When the filter basket (203) is assembled inside the outer casing (201), the front surface of the filter basket (203) is flush with the front surface of the support ring (201b). The front surface of the filter basket (203) is integrally connected with a flange (203b), and the flange (203b) fits against the support ring (201b). Annular grooves are provided at the contact points between the convex ring (203a) and the limiting ring (201a) and between the flange (203b) and the support ring (201b), and ball bearings are placed in the grooves.

8. The spiral dual rotor flowmeter according to claim 1, characterized in that: The lower surface of the connecting pipe (205) is provided with a drain pipe (205a), and the drain pipe (205a) is located between the second valve (207) and the connecting cover (204). A ball valve is installed on the drain pipe (205a).

9. The spiral dual rotor flowmeter according to claim 1, characterized in that: A pair of spiral rotors (101) are rotatably connected inside the flow meter body (100). The pair of spiral rotors (101) mesh with each other. The line connecting the centers of the input pipe (106) and the output pipe (105) is perpendicular to the meshing surface between the spiral rotors (101).

10. The spiral dual-rotor flowmeter according to claim 1, characterized in that: The inner walls of the upper and lower ends of the flow meter body (100) are provided with stepped grooves (100a), and a sealing groove (100b) is provided on the upper surface of the lowest point of the stepped groove (100a). A rubber ring is embedded in the sealing groove (100b). A sealing plate (102), a pressure plate (103), and an end cap (104) are arranged sequentially from top to bottom in the stepped groove (100a). The lower surface of the sealing plate (102) is provided with a groove to fit the rubber ring. A screw hole is provided in the middle of the pressure plate (103) and the stepped groove (100a). The pressure plate (103) is fixed in the stepped groove (100a) by screws. A bolt hole is provided between the end cap (104) and the uppermost end of the stepped groove (100a) for fastening with bolts.

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