Centrifugal pump with wear-resistant layer at water inlet of pump chamber

Abstract

The utility model discloses a centrifugal pump that pump cavity water inlet has wear -resisting layer relates to pump body technical field, wherein centrifugal pump that pump cavity water inlet has wear -resisting layer includes pump shell, drive component and wear -resisting subassembly, and pump shell forms pump cavity, water inlet and mounting hole, water inlet and mounting hole are respectively with pump cavity intercommunication, drive component includes drive motor, pump shaft and impeller, and drive motor is located at pump shell, pump shaft passes through mounting hole and is connected to the output of drive motor, impeller is transmission connection with pump shaft, and is located in pump cavity, wear -resisting subassembly includes wear -resisting layer, and wear -resisting layer is located at the inner wall of pump cavity, and is located at the other side of water inlet relative to impeller, when the liquid containing solid particle enters pump cavity, and impeller rotates and absorbs the liquid from water inlet into pump cavity, and solid particle is thrown to wear -resisting layer in pump cavity, because wear -resisting layer has higher hardness and wear resistance, can effectively resist the impact of solid particle, reduces the loss of pump shell to prolong the service life of centrifugal pump.

Description

Technical Field

[0001] This utility model relates to the field of pump technology, and in particular to a centrifugal pump with a wear-resistant layer at the pump chamber inlet. Background Technology

[0002] Centrifugal pumps work by using the rotation of an impeller to cause water to move in a centrifugal motion. Before starting the pump, the pump casing and suction pipe must be filled with water. Then, the motor is started, and the pump shaft drives the impeller and water to rotate at high speed. The water undergoes centrifugal motion and is thrown towards the outer edge of the impeller, flowing into the pump's discharge pipe through the flow channel of the volute casing.

[0003] In some applications of centrifugal pumps, it may be necessary to handle liquid media containing solid particles. Typically, when the liquid contains solid particles such as debris and gravel, it will cause severe wear to the pump casing during operation. The high-speed impact of the liquid carrying debris, gravel, and other impurities on the pump casing gradually wears down the casing material, and prolonged impact will reduce the service life of the centrifugal pump. Utility Model Content

[0004] The main purpose of this invention is to provide a centrifugal pump with a wear-resistant layer at the pump inlet, aiming to extend the service life of the centrifugal pump.

[0005] To achieve the above objectives, the present invention proposes a centrifugal pump with a wear-resistant layer at the pump chamber inlet, comprising:

[0006] The pump casing forms a pump cavity, a water inlet, and a mounting hole; the water inlet and the mounting hole are respectively connected to the pump cavity;

[0007] A drive assembly, comprising a drive motor, a pump shaft, and an impeller, wherein the drive motor is disposed in the pump housing; the pump shaft passes through the mounting hole and is connected to the output end of the drive motor; the impeller is drively connected to the pump shaft and is located within the pump cavity; and

[0008] A wear-resistant component, comprising a wear-resistant layer disposed on the inner wall of the pump chamber and positioned on the opposite side of the water inlet relative to the impeller.

[0009] In one embodiment, the wear-resistant component further includes an elastic layer disposed on the inner wall of the pump cavity, and the wear-resistant layer is disposed on the side of the elastic layer opposite to the pump cavity.

[0010] In one embodiment, at least a portion of the wear-resistant layer is formed on the inner wall of the housing, extending along the pump axis to the outer edge of the impeller.

[0011] In one embodiment, the wear-resistant layer is made of polyurethane.

[0012] In one embodiment, the wear-resistant component further includes a support ring disposed on the side of the wear-resistant layer opposite to the housing and detachably connected to the housing.

[0013] In one embodiment, the support ring has a plurality of protrusions on the side facing the wear-resistant layer, the wear-resistant layer has through holes corresponding to each of the protrusions, and the inner wall of the housing has grooves corresponding to each of the protrusions; each protrusion passes through a through hole and engages with a groove.

[0014] In one embodiment, the end of the protrusion away from the impeller has a bent portion that bends toward the inlet, and the groove has a bent section adapted to the bent portion, the bent portion being engaged within the bent section.

[0015] In one embodiment, the centrifugal pump with a wear-resistant layer at the pump inlet further includes a filter screen disposed on the peripheral wall of the inlet.

[0016] In one embodiment, the centrifugal pump with a wear-resistant layer at the pump inlet further includes a coupling disposed on the pump casing; the drive motor is connected to the pump shaft via the coupling.

[0017] In one embodiment, the centrifugal pump with a wear-resistant layer at the pump inlet further includes a sealing ring, which is sleeved on the pump shaft, and the outer peripheral wall of the sealing ring abuts against the inner peripheral wall of the mounting hole.

[0018] In the technical solution of this utility model, the centrifugal pump with a wear-resistant layer at the pump inlet includes a pump casing, a drive assembly, and a wear-resistant assembly. The pump casing forms a pump cavity, an inlet, and a mounting hole; the inlet and the mounting hole are respectively connected to the pump cavity; the drive assembly includes a drive motor, a pump shaft, and an impeller; the drive motor is located in the pump casing; the pump shaft passes through the mounting hole and is connected to the output end of the drive motor; the impeller is drively connected to the pump shaft and is located inside the pump cavity; the wear-resistant assembly includes a wear-resistant layer, which is located on the inner wall of the pump cavity and positioned opposite the impeller on the other side of the inlet. In the technical solution of this utility model, by providing a wear-resistant layer on the inner wall of the pump cavity, when liquid containing solid particles enters the pump cavity, the impeller rotates and draws the liquid into the pump cavity from the inlet, while the solid particles in the liquid are thrown towards the inner wall of the pump cavity opposite to the position of the impeller opposite to the inlet; because the wear-resistant layer has high hardness and wear resistance, it can effectively resist the impact of solid particles, thereby reducing the wear of the pump casing, thus extending the service life of the centrifugal pump and reducing maintenance costs. Attached Figure Description

[0019] 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 the structures shown in these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the structure of an embodiment of a centrifugal pump with a wear-resistant layer at the pump chamber inlet provided by this utility model;

[0021] Figure 2 A schematic diagram of the pump casing in a centrifugal pump with a wear-resistant layer at the pump inlet.

[0022] Figure 3 for Figure 2 Sectional view along AA;

[0023] Figure 4 for Figure 3 A magnified view of a section at point B.

[0024] Explanation of icon numbers:

[0025] 1000 Centrifugal pump with wear-resistant layer at pump inlet 23 impeller 1 pump casing 31 wear-resistant layer 1a pump chamber 32 elastic layer 1a1 groove 33 support ring 1a11 Bend section 331 protrusion 1b Inlet 3311 Bending section 1c Mounting holes 4 Filter 21 drive motor 5 Coupling 22 pump shaft 6 sealing ring

[0026] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] 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 scope of protection of the present utility model.

[0028] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0029] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0030] To solve the above problems, this utility model proposes a centrifugal pump 1000 with a wear-resistant layer at the pump chamber inlet. Figures 1 to 4 This is a schematic diagram of an embodiment of the centrifugal pump 1000 with a wear-resistant layer at the pump chamber inlet of this utility model.

[0031] Please refer to Figure 1 , Figure 2 , Figure 3 as well as Figure 4 This utility model proposes a centrifugal pump 1000 with a wear-resistant layer at the pump inlet, including a pump casing 1, a drive assembly, and a wear-resistant assembly. The pump casing 1 forms a pump cavity 1a, an inlet 1b, and a mounting hole 1c. The inlet 1b and the mounting hole 1c are respectively connected to the pump cavity 1a. The drive assembly includes a drive motor 21, a pump shaft 22, and an impeller 23. The drive motor 21 is disposed in the pump casing 1. The pump shaft 22 passes through the mounting hole 1c and is connected to the output end of the drive motor 21. The impeller 23 is drivenly connected to the pump shaft 22 and is located in the pump cavity 1a. The wear-resistant assembly includes a wear-resistant layer 31, which is disposed on the inner wall of the pump cavity 1a and is disposed on the other side of the inlet 1b opposite to the impeller 23.

[0032] The pump casing 1 can be made of materials such as cast iron, stainless steel, or engineering plastics. The internal pump chamber 1a can be volute-shaped or annular. The dimensions of the inlet 1b and mounting hole 1c are designed according to flow requirements. The drive motor 21 can be an asynchronous motor or a permanent magnet synchronous motor. The pump shaft 22 is connected to the motor output end via a key or flange connection for transmission. The impeller 23 can be a closed, semi-open, or open structure. The number of blades in the impeller 23 is designed according to head requirements. The wear-resistant layer 31 can be made of polyurethane, ceramic, or tungsten carbide. The wear-resistant layer 31 can be attached to the inner wall of the pump chamber 1a by bonding, welding, or mechanical fixing.

[0033] In the technical solution of this utility model, by providing a wear-resistant layer 31 on the inner wall of the pump chamber 1a, when liquid containing solid particles enters the pump chamber 1a, the impeller 23 rotates and draws the liquid into the pump chamber 1a from the inlet 1b. The solid particles in the liquid are thrown towards the inner wall of the pump chamber 1a, which is opposite to the position of the impeller 23 relative to the inlet 1b. Since the wear-resistant layer 31 has high hardness and wear resistance, it can effectively resist the impact of solid particles, thereby reducing the wear of the pump casing 1. This extends the service life of the centrifugal pump 1000 with the wear-resistant layer at the pump chamber inlet and reduces maintenance costs. At the same time, the setting position of the wear-resistant layer 31 is optimized, located in the area where the water flow impact is most severe, which can further improve the protection effect.

[0034] In one embodiment of the present invention, the wear-resistant component further includes an elastic layer 32, which is disposed on the inner wall of the pump cavity 1a, and a wear-resistant layer 31 is disposed on the side of the elastic layer 32 away from the pump cavity 1a.

[0035] The elastic layer 32 can be made of elastic materials such as rubber, silicone, or polyurethane foam. The abrasion-resistant layer 31 is fixed to the surface of the elastic layer 32 by adhesive bonding or hot pressing. As a preferred embodiment, the elastic layer 32 can be designed with a corrugated or honeycomb structure to enhance cushioning performance.

[0036] The combined structure of the elastic layer 32 and the wear-resistant layer 31 effectively mitigates the impact of solid particles on the pump casing 1. When liquid containing solid particles impacts the pump chamber 1a, the elastic layer 32 first absorbs part of the impact energy, reducing the impact force transmitted to the pump casing 1. The wear-resistant layer 31 directly bears the friction and impact of the particles, protecting the pump casing 1 from wear. The addition of the elastic layer 32 gives the overall structure better impact resistance without affecting the protective effect of the wear-resistant layer 31. At the same time, the elastic layer 32 can buffer the impact of solid particles, thereby reducing the noise generated when solid particles collide.

[0037] When liquid containing solid particles enters pump chamber 1a, the rotation of impeller 23 causes centrifugal motion of the liquid, and the solid particles are thrown against the inner wall of pump chamber 1a, causing wear on the inner wall of the housing extending from the pump shaft 22 to the outer edge of impeller 23. To solve this problem, in one embodiment of the present invention, at least a portion of the wear-resistant layer 31 is provided on the inner wall of the housing extending from the pump shaft 22 to the outer edge of impeller 23.

[0038] Since the wear-resistant layer 31 is located in the area corresponding to the outer edge of the impeller 23, it can protect the outer edge of the casing peripheral wall of the impeller 23, improve the comprehensiveness of casing protection, and thus further improve the service life of the centrifugal pump 1000 with the wear-resistant layer at the pump inlet.

[0039] It is understood that the wear-resistant layer 31 can be made of polyurethane, ceramic, or tungsten carbide. In one embodiment of this invention, the wear-resistant layer 31 is made of polyurethane.

[0040] Using polyurethane as the wear-resistant layer 31 effectively solves the wear problem caused by the impact of solid particles on the inner wall of the pump cavity 1a. Specifically, when a liquid medium containing solid particles impacts the inner wall of the pump cavity 1a at high speed, the elasticity of the polyurethane material can absorb part of the impact energy, while its excellent wear resistance can significantly reduce the material wear rate. Compared with the traditional metal wear-resistant layer 31, the polyurethane wear-resistant layer 31 not only has better wear resistance, but also reduces noise and vibration during liquid flow. In addition, the polyurethane material has good processing performance and can be precisely molded according to the shape of the pump cavity 1a to ensure a tight fit with the inner wall of the pump cavity 1a.

[0041] In one embodiment of the present invention, the wear-resistant component further includes a support ring 33, which is disposed on the side of the wear-resistant layer 31 away from the housing and is detachably connected to the housing.

[0042] By providing a detachable support ring 33 on the outside of the wear-resistant layer 31, the structural stability of the wear-resistant layer 31 is effectively enhanced. When liquid carrying solid particles impacts the pump casing 1, the support ring 33 can disperse the impact force and prevent the wear-resistant layer 31 from falling off due to excessive local stress.

[0043] It is understood that the detachable connection between the support ring 33 and the housing can be achieved by engaging the protrusion 331 with the groove 1a1, or by a threaded connection. In one embodiment of this utility model, the support ring 33 has a plurality of protrusions 331 on the side facing the wear-resistant layer 31, the wear-resistant layer 31 has a through hole corresponding to each protrusion 331, and the inner wall of the housing has a groove 1a1 corresponding to each protrusion 331; each protrusion 331 passes through a through hole and engages with a groove 1a1.

[0044] Specifically, the protrusion 331 can be cylindrical, prismatic, or conical, with its height matching the thickness of the wear-resistant layer 31 to ensure that the protrusion 331 can pass through the through hole and stably engage with the groove 1a1. The shape of the through hole is consistent with the cross-sectional shape of the protrusion 331, such as circular, square, or polygonal. The depth of the groove 1a1 is slightly greater than the height of the protrusion 331 to allow for assembly tolerances.

[0045] The snap-fit ​​structure between the support ring 33 and the pump housing 1 enables rapid positioning and reliable fixation of the wear-resistant layer 31. Compared with traditional adhesive or bolt fixing methods, this structure avoids the problem of adhesive aging and facilitates the replacement and maintenance of the wear-resistant layer 31. When liquid carrying solid particles impacts the wear-resistant layer 31, the snap-fit ​​structure can effectively disperse the impact force and prevent the wear-resistant layer 31 from falling off locally. Furthermore, the bending design allows the protrusion 331 to generate a self-tightening effect when subjected to centrifugal force, thereby further enhancing the reliability of the connection.

[0046] In one embodiment of the present invention, the end of the protrusion 331 away from the impeller 23 is formed with a bent portion 3311 that bends toward the inlet 1b, and the groove 1a1 is formed with a bent section 1a11 that is adapted to the bent portion 3311, and the bent portion 3311 is engaged in the bent section 1a11.

[0047] Specifically, the mating structure of the bent portion 3311 and the bent section 1a11 effectively prevents the support ring 33 from undergoing axial displacement under the impact of high-speed water flow. As a preferred embodiment, the bent portion 3311 can adopt a bending angle of 30° to 90°, and the curvature of the bent section 1a11 matches it to ensure a tight engagement.

[0048] The interlocking structure between the bending portion 3311 and the bending section 1a11 can significantly improve the connection reliability of the wear-resistant components under high-speed fluid conditions containing particles. When the liquid carrying solid particles impacts the wear-resistant layer 31, the bending structure can offset the axial impact force and prevent the support ring 33 from displacing relative to the housing. Compared with the planar snap-fit ​​structure, this design allows the wear-resistant layer 31 to maintain a more stable fit with the pump housing 1.

[0049] In one embodiment of the present invention, the centrifugal pump 1000 with a wear-resistant layer at the pump inlet also includes a filter screen 4, which is disposed on the peripheral wall of the inlet 1b.

[0050] The filter screen 4 can be made of woven wire mesh, perforated plate, or sintered porous material, and the mesh size is designed according to the particle size distribution of solid particles in the medium. As a preferred embodiment, the filter screen 4 is detachably connected to the peripheral wall of the inlet 1b via a flange structure or a snap-fit ​​structure, facilitating the removal of blockages. Specifically, the filter screen 4 can be designed as an annular structure with a mounting flange on its outer edge, fixed to the flange of the inlet 1b by bolts; alternatively, a quick-release structure can be used, with elastic claws on the edge of the filter screen 4 that engage with the annular groove on the inner wall of the inlet 1b.

[0051] By installing a filter screen 4 at the inlet 1b, solid particles such as debris and gravel in the liquid medium can be effectively intercepted, preventing them from entering the pump chamber 1a and causing wear. The specific working principle is as follows: when liquid containing solid particles flows through the inlet 1b, the filter screen 4 mechanically separates the particles, blocking particles larger than the mesh size on the outside of the filter screen 4, allowing only the purified liquid to enter the pump chamber 1a. This significantly reduces the high-speed impact of solid particles on the inner wall of the pump chamber 1a and the impeller 23, solving the pump body wear problem caused by impurities in the medium. Compared with solutions that directly improve the pump body's wear resistance, this pre-filtration method reduces wear factors at the source, featuring low maintenance costs and strong adaptability.

[0052] In one embodiment of the present invention, the centrifugal pump 1000 with a wear-resistant layer at the pump inlet further includes a coupling 5, which is disposed on the pump casing 1; the drive motor 21 is connected to the pump shaft 22 via the coupling 5.

[0053] The coupling 5, as a transmission component connecting the drive motor 21 and the pump shaft 22, is mainly used to transmit torque and compensate for the relative displacement between the two shafts. The coupling 5 can be a rigid coupling 5 or a flexible coupling 5, with the flexible coupling 5 better absorbing vibration and shock. Specifically, the coupling 5 can be a lamellar coupling 5, a flexible sleeve pin coupling 5, or a diaphragm coupling 5, etc. As a preferred embodiment, the coupling 5 and the pump shaft 22 are connected by a key to achieve reliable transmission, while the coupling 5 and the output shaft of the drive motor 21 are fixed together by a flange connection.

[0054] By installing a coupling 5 between the drive motor 21 and the pump shaft 22, the problems of high alignment accuracy and easy vibration associated with traditional direct connection methods can be effectively solved. The coupling 5 can not only transmit the power of the drive motor 21, but also compensate for installation errors and axial and radial displacements generated during operation, thereby reducing vibration and noise and improving the transmission efficiency and service life of the centrifugal pump 1000 with a wear-resistant layer at the pump inlet.

[0055] In one embodiment of the present invention, the centrifugal pump 1000 with a wear-resistant layer at the pump inlet further includes a sealing ring 6, which is sleeved on the pump shaft 22, and the outer peripheral wall of the sealing ring 6 is in sealing contact with the inner peripheral wall of the mounting hole 1c.

[0056] The sealing ring 6 is made of an elastic material, such as rubber or polytetrafluoroethylene, and its cross-sectional shape can be circular, square, or other polygonal. The inner diameter of the sealing ring 6 is slightly smaller than the outer diameter of the pump shaft 22, and radial sealing is achieved through an interference fit.

[0057] By setting a sealing ring 6 between the pump shaft 22 and the mounting hole 1c, liquid leakage from the pump chamber 1a along the pump shaft 22 is effectively prevented. Specifically, when the pump shaft 22 rotates at high speed, the elastic deformation of the sealing ring 6 can compensate for the assembly gap between the shaft and the hole, while maintaining a stable contact pressure. The sealing ring 6 can not only solve the problem of medium leakage, but also reduce the risk of pump efficiency reduction and bearing corrosion caused by leakage.

[0058] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet, characterized in that, include: Pump housing (1), the pump housing (1) forms a pump chamber (1a), a water inlet (1b) and a mounting hole (1c); the water inlet (1b) and the mounting hole (1c) are respectively connected to the pump chamber (1a); The drive assembly includes a drive motor (21), a pump shaft (22), and an impeller (23). The drive motor (21) is disposed in the pump housing (1). The pump shaft (22) passes through the mounting hole (1c) and is connected to the output end of the drive motor (21). The impeller (23) is drivenly connected to the pump shaft (22) and is located in the pump chamber (1a). as well as The wear-resistant component includes a wear-resistant layer (31) disposed on the inner wall of the pump chamber (1a) and disposed on the other side of the water inlet (1b) opposite to the impeller (23).

2. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 1, characterized in that, The wear-resistant component further includes an elastic layer (32), which is disposed on the inner wall of the pump cavity (1a), and the wear-resistant layer (31) is disposed on the side of the elastic layer (32) away from the pump cavity (1a).

3. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 2, characterized in that, At least a portion of the wear-resistant layer (31) is disposed on the inner wall of the pump casing (1) extending along the pump shaft (22) toward the outer edge of the impeller (23).

4. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 3, characterized in that, The wear-resistant layer (31) is made of polyurethane.

5. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 1, characterized in that, The wear-resistant component also includes a support ring (33), which is located on the side of the wear-resistant layer (31) away from the pump housing (1) and is detachably connected to the pump housing (1).

6. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 5, characterized in that, The support ring (33) has a plurality of protrusions (331) on the side facing the wear-resistant layer (31). The wear-resistant layer (31) has through holes corresponding to each of the protrusions (331). The inner wall of the pump housing (1) has grooves (1a1) corresponding to each of the protrusions (331). Each protrusion (331) passes through a through hole and engages with a groove (1a1).

7. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in claim 6, characterized in that, The protrusion (331) has a bent portion (3311) at one end away from the impeller (23) that bends toward the inlet (1b). The groove (1a1) has a bent section (1a11) that is adapted to the bent portion (3311). The bent portion (3311) is engaged in the bent section (1a11).

8. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in any one of claims 1 to 7, characterized in that, The centrifugal pump (1000) with a wear-resistant layer at the pump inlet also includes a filter screen (4), which is disposed on the peripheral wall of the inlet (1b).

9. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in any one of claims 1 to 7, characterized in that, The centrifugal pump (1000) with a wear-resistant layer at the pump inlet also includes a coupling (5), which is located on the pump casing (1); the drive motor (21) is connected to the pump shaft (22) via the coupling (5).

10. The centrifugal pump (1000) with a wear-resistant layer at the pump chamber inlet as described in any one of claims 1 to 7, characterized in that, The centrifugal pump (1000) with a wear-resistant layer at the pump inlet also includes a sealing ring (6), which is sleeved on the pump shaft (22), and the outer peripheral wall of the sealing ring (6) is in sealing contact with the inner peripheral wall of the mounting hole (1c).

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