Duplex check valve

Abstract

The invention relates to the technical field of valves, in particular to a duplex check valve. Comprising a valve body, a circulation opening formed in the valve body, a valve seat arranged on the valve body and located in the circulation opening, a first through hole formed in the valve seat, a sealing valve clack arranged in the valve body in a lifting mode, a guiding piece arranged between the valve seat and the sealing valve clack, and a compression spring arranged between the guiding piece and the sealing valve clack. The auxiliary sleeve is arranged on the valve body and located at the circulation opening, the second through hole is formed in the valve body, the auxiliary valve clack is arranged on the valve body in a lifting mode and located in the circulation opening, the lower end of the auxiliary guide rod is fixedly arranged on the sealing valve clack, the linkage shaft is arranged at the lower end of the sealing valve clack and located in the auxiliary sleeve, and the lower end of the linkage shaft makes contact with the upper end of the auxiliary guide rod. Through the design of the double valve clacks, the double-sealing effect is achieved, the reliability and the sealing performance of the check valve are improved, the linkage shaft structure ensures that the main valve clack and the auxiliary valve clack move synchronously, and response is rapid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of valves, in particular to a double check valve. BACKGROUND

[0002] Check valve refers to a valve with a circular valve disc that blocks the backflow of medium by its own weight and medium pressure. It belongs to automatic valve and is also called non-return valve, one-way valve, backflow valve or isolation valve. The valve disc movement is divided into lifting type and swing type. The lifting check valve is opened by the pressure of the forward flow of medium, and is closed by the pressure of the reverse flow of medium and the weight of the valve disc. Its main function is to prevent the backflow of medium in industrial pipeline and to protect the pump and driving equipment.

[0003] Among various types of check valves, the lifting check valve is widely used due to its simple structure and convenient manufacturing. It mainly includes a valve body, a valve cover and a valve disc arranged on the sealing surface of the valve seat. The valve disc can usually move axially in the guide cylinder of the valve cover. The working principle is as follows: when the medium flows in the forward direction (i.e. the preset allowed flow direction), the pressure of the medium overcomes the weight of the valve disc and the flow resistance, lifts the valve disc, opens the valve, and the medium passes through; when the medium stops flowing or flows in the reverse direction, the valve disc falls back to the sealing surface of the valve seat under the action of its own gravity and the reverse medium pressure, thereby achieving sealing and blocking the backflow of medium.

[0004] The conventional lifting check valve relies on the linear or surface contact between the single valve disc and the single valve seat sealing surface to achieve sealing. Once the single structure of the valve disc or the valve seat sealing surface is blocked by impurities, or the local wear is caused by cavitation and erosion, or the closing action of the single valve disc has corresponding lag, a leakage channel is easily formed on the sealing surface, which leads to sealing failure, cannot effectively prevent the backflow of medium, seriously affects the sealing performance and safety level of the system, and is difficult to improve the sealing reliability and closing response speed of the check valve. SUMMARY

[0005] The present application aims at the defects and deficiencies of the prior art, and provides a double check valve.

[0006] To achieve the above object, the present application adopts the following technical scheme: A double check valve, comprising a valve body, a flow-through opening provided on the valve body for medium flow, a valve seat provided on the valve body in the flow-through opening, a first through hole provided on the valve seat and communicating with the flow-through opening, a sealing valve flap provided on the valve body in the flow-through opening and used for closing the first through hole after descending and opening the first through hole after ascending, a guide provided between the valve seat and the sealing valve flap and used for guiding the ascending and descending directions of the sealing valve flap, a compression spring provided between the guide and the sealing valve flap, a secondary sleeve provided on the valve body in the flow-through opening and below the sealing valve flap, a second through hole provided on the valve body and communicating with the flow-through opening, a secondary valve flap provided on the valve body in the flow-through opening and used for closing the second through hole after descending and opening the second through hole after ascending, a secondary guide rod fixedly provided on the sealing valve flap at the lower end and ascendably provided in the secondary sleeve at the upper end, and a linkage shaft provided on the sealing valve flap at the lower end and in the secondary sleeve and used for pushing the secondary guide rod to drive the secondary valve flap to descend synchronously when the sealing valve flap descends and driving the sealing valve flap to ascend synchronously when the secondary valve flap ascends, wherein the lower end of the linkage shaft is in contact with the upper end of the secondary guide rod.

[0007] The further effect is that when the sealing valve flap descends to close the first through hole, the secondary valve flap can be further compressed in the second through hole through the extrusion of the linkage shaft and the secondary guide rod, and the sealing effect of the secondary valve flap is further improved by the pressure of the medium backflow and the spring driving force of the compression spring on the secondary valve flap.

[0008] Further improvement is that the guide comprises a guide sleeve provided in the flow-through opening above the sealing valve flap, a support rib fixedly provided on the valve body and the circumferential side of the guide sleeve and used for supporting the guide sleeve, a guide rod fixedly provided on the sealing valve flap at the lower end and ascendably provided in the guide sleeve at the upper end and used for guiding the ascending and descending directions of the sealing valve flap, and the compression spring is provided between the guide sleeve and the guide rod or the sealing valve flap.

[0009] The further effect is that the guide rod and the guide sleeve cooperate to ensure that the sealing valve flap keeps vertical movement during the ascending and descending process, reduces the skew and jamming phenomenon, and prolongs the service life; the compression spring provides a reset force to enhance the response speed of the sealing valve flap.

[0010] Further improvement is that the sealing valve flap is fixedly provided on the circumferential side of the guide rod, and the upper end of the linkage shaft is fixedly provided on the lower end of the guide rod.

[0011] The further effect is that the linkage structure is simplified, and the assembly convenience is improved; the fixed connection of the guide rod and the linkage shaft ensures reliable power transmission and reduces the risk of part loosening.

[0012] Further improvement is that the auxiliary sleeve is fixed on the valve body in the flow passage by the connecting rib.

[0013] The further effect is that the auxiliary sleeve is fixed stably and avoids displacement due to medium impact; the connecting rib design allows smooth passage of the medium and reduces flow resistance.

[0014] Further improvement is that the valve seat is provided with a filter screen for filtering impurities in the medium.

[0015] Further improvement is that the valve body includes an upper valve body and a lower valve body, the upper valve body and the lower valve body are fixedly connected by the stud and the nut, the upper end of the lower valve body is provided with a placement slot for placing the valve seat, the guide is arranged on the upper valve body, and the second through hole is arranged on the lower valve body.

[0016] The further effect is that the split detachable arrangement of the upper valve body and the lower valve body can facilitate the assembly and maintenance of the check valve structure.

[0017] Further improvement is that a secondary spring member is arranged between the auxiliary sleeve and the auxiliary valve disc, and the secondary spring member is sleeved on the outer circumferential side of the auxiliary guide rod.

[0018] The further effect is that the secondary spring member can drive the auxiliary valve disc to descend more quickly and effectively when the medium flows in reverse, and press tightly on the second through hole to increase the sealing effect of the second through hole.

[0019] Further improvement is that a reinforcing rib is arranged below the auxiliary valve disc on the valve body, a avoiding through hole is longitudinally arranged at the center end of the reinforcing rib, and the lower end of the auxiliary guide rod passes through the auxiliary valve disc and is located in the avoiding through hole.

[0020] The further effect is that the arrangement of the reinforcing rib can further guide the lifting of the auxiliary guide rod and reduce the tilting phenomenon of the auxiliary guide rod during lifting, thereby increasing the service life of the auxiliary guide rod during use.

[0021] Further improvement is that a lower shaft sleeve for reducing the adhesion of impurities in the avoiding through hole is arranged on the lower end surface of the reinforcing rib, and the lower shaft sleeve is connected to the lower end surface of the reinforcing rib by threads.

[0022] The further effect is that the lower shaft sleeve prevents impurities from entering the avoiding through hole and reduces the jamming of the auxiliary guide rod; the detachable design facilitates cleaning and maintenance.

[0023] After adopting the above technical solution, the beneficial effects of the present invention are as follows: When the medium flows from bottom to top, the medium pushes the secondary valve disc upward, making the second through hole open. During this process, the secondary valve disc drives the secondary guide rod to rise synchronously in the secondary sleeve, pushing the linkage shaft upward to synchronously drive the sealing valve disc to rise. The thrust generated by the upward flow of the medium also keeps the first through hole open, thereby realizing the flow of the medium. When the medium stops flowing upward or flows backward, the sealing valve disc is pushed by the backward flow of the medium and by the elastic potential energy released by the compression spring, causing the sealing valve disc to fall and close the first through hole. During the descent of the sealing valve disc, the linkage shaft pushes the secondary guide rod to synchronously lower the secondary valve disc, thereby closing the second through hole. This linkage structure achieves the technical effects of fast, synchronous and double sealing. Even if one sealing pair fails, the other sealing pair can still serve as a reliable backup barrier, effectively cutting off the backflow of the medium. The double valve disc design achieves a double sealing effect, improving the reliability and sealing performance of the check valve. The linkage shaft structure ensures that the main and secondary valve discs move synchronously and respond quickly. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a front sectional view of the present invention; Figure 2 This is a front sectional view of the valve seat, sealing valve disc, and auxiliary valve disc in this invention; Figure 3 This is a front sectional view of the valve body in this invention; Figure 4 This is a top view of the upper valve body, guide sleeve, and support rib in this invention; Figure 5 This is a bottom view of the lower valve body, reinforcing ribs, and avoidance perforation in this invention.

[0026] Explanation of reference numerals in the attached drawings: 1. Valve body; 2. Flow port; 3. Valve seat; 4. First through hole; 5. Sealing valve disc; 6. Compression spring; 7. Second through hole; 9. Second valve disc; 10. Secondary guide rod; 11. Linkage shaft; 12. Guide sleeve; 13. Support rib; 14. Guide rod; 15. Filter screen; 17. Upper valve body; 18. Lower valve body; 19. Stud; 20. Nut; 21. Placement slot; 22. Secondary spring component; 23. Reinforcing rib; 24. Clearance perforation; 25. Lower bushing; 26. Detailed Implementation

[0027] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0028] See Figures 1 to 5 As shown, the technical solution adopted in this specific embodiment is: a double check valve, including a valve body 1, a flow port 2 opened on the valve body 1 for medium flow, a valve seat 3 disposed on the valve body 1 and located in the flow port 2, a first through hole 4 opened on the valve seat 3 and connected to the flow port 2, a sealing valve disc 5 disposed on the valve body 1 and located in the flow port 2 for closing the first through hole 4 after descending and opening the first through hole 4 after rising, a guide member disposed between the valve seat 3 and the sealing valve disc 5 for guiding the rising and falling direction of the sealing valve disc 5, a compression spring 6 disposed between the guide member and the sealing valve disc 5, and a valve seat 3 disposed on the valve body 1 and located in the flow port 2. The valve body 1 has a secondary sleeve 7 located below the sealing valve disc 5, a second through hole 9 opened on the valve body 1 and connected to the flow port 2, a secondary valve disc 10 located on the valve body 1 and inside the flow port 2 for closing the second through hole 9 after descending and opening the second through hole 9 after rising, a secondary guide rod 11 whose lower end is fixed on the sealing valve disc 5 and whose upper end can be raised and lowered in the secondary sleeve 7, and a linkage shaft 12 located at the lower end of the sealing valve disc 5 and inside the secondary sleeve 7 for pushing the secondary guide rod 11 to drive the secondary valve disc 10 to descend synchronously when the sealing valve disc 5 descends and driving the sealing valve disc 5 to rise synchronously when the secondary valve disc 10 rises. The lower end of the linkage shaft 12 is in contact with the upper end of the secondary guide rod 11.

[0029] The sealing valve disc 5 is located above the valve seat 3, the auxiliary sleeve 7 is located below the sealing valve disc 5, and the auxiliary valve disc 10 is located below the auxiliary sleeve 7. Preferably, a tapered surface is provided on the valve body 1 around the sealing valve disc 5, and the circumference of the sealing valve disc 5 is also provided with a slope for fitting with the tapered surface to obtain better sealing performance. Alternatively, the circumference of the sealing valve disc 5 can be set to a flat state, in which case the diameter of the flow port 2 on the valve body 1 around the sealing valve disc 5 should be smaller than the diameter of the sealing valve disc 5, so that the sealing valve disc 5 can close the flow port 2 after being pressed down and limit the descent space of the sealing valve disc 5. The central axis of the auxiliary sleeve 7 and the auxiliary guide rod 11 corresponds to the central axis of the first through hole 4 and the second through hole 9. To ensure the lower end of the secondary valve disc 10 is contacted when the medium flows upward and contacts its lower surface, the lower end of the secondary valve disc 10 can be designed as an arc surface. This arc surface allows the medium to be dispersed when impacting the secondary valve disc 10, thus uniformly dispersing the thrust exerted by the medium on the secondary valve disc 10 and reducing its vibration, swaying, and movement resistance. When the sealing valve disc 5 and the secondary valve disc 10 are closed at the first through hole 4 and the second through hole 9 respectively, the lower end of the linkage shaft 12 is always in contact with the upper end of the secondary guide rod 11.

[0030] The guide component includes a guide sleeve 13 positioned above the sealing valve disc 5 within the flow port 2; a support rib 14 fixedly disposed around the valve body 1 and the guide sleeve 13 to support the guide sleeve 13; a guide rod 15 fixed at its lower end to the sealing valve disc 5 and raised at its upper end within the guide sleeve 13 to guide the lifting direction of the sealing valve disc 5; and a compression spring 6 disposed between the guide sleeve 13 and the guide rod 15 or the sealing valve disc 5. The support ribs 14 are arranged annularly and equidistantly between the guide sleeve 13 and the valve body 1, forming a space for the medium to pass through in a top view. The support ribs 14 are welded between the guide sleeve 13 and the valve body 1. To facilitate the placement of the compression spring 6, an annular slot for placing the compression spring 6 can be formed at the lower end of the guide sleeve 13. The diameter of this annular slot is larger than the diameter of the center hole of the guide sleeve 13, and its height is smaller than the height of the center hole of the guide sleeve 13.

[0031] The sealing valve disc 5 is fixedly mounted on the periphery of the guide rod 15, and the upper end of the linkage shaft 12 is fixedly mounted on the lower end of the guide rod 15.

[0032] like Figure 2 As shown, the guide rod 15 can be divided into three sections. The diameter of the middle section is larger than that of the upper and lower ends. The lower section passes through the sealing valve disc 5 and is integrally connected to the upper end of the linkage shaft 12 or separately welded. The upper section is raised and lowered inside the guide sleeve 13. At this time, the compression spring 6 is set between the middle section and the guide sleeve 13 and is sleeved on the outer periphery of the upper section.

[0033] In other embodiments, the guide rod 15 can also be configured to have the same diameter, with its upper end rising and falling inside the guide sleeve 13 and its lower end passing through and fixed to the sealing valve disc 5, or its lower end being directly fixed to the upper end of the sealing valve disc 5. The upper end of the linkage shaft 12 can be fixedly set at the lower end of the sealing valve disc 5, or fixedly set on the lower end face of the guide rod 15 passing through the sealing valve disc 5. In this structure, the compression spring 6 is set between the guide sleeve 13 and the upper end face of the sealing valve disc 5.

[0034] The auxiliary sleeve 7 is fixedly installed on the valve body 1 and located inside the flow port 2 by a connecting rib (not shown in the figure).

[0035] The valve seat 3 is equipped with a filter screen 17 for filtering impurities in the medium.

[0036] The filter screen 17 is fixedly connected to the outer periphery of the auxiliary sleeve 7, thereby fixing the position of the auxiliary sleeve 7. When the filter screen 17 is not installed, the auxiliary sleeve 7 is fixedly supported on the lower valve body 19 or the valve seat 3 by a connecting rib (not shown in the figure), and a through hole is opened in the middle of the filter screen 17 so that the filter screen 17 can pass through the auxiliary sleeve 7.

[0037] likeFigure 3 As shown, the valve seat 3 can be configured as a separate structure. A slot for placing the valve seat 3 is opened at the upper end of the lower valve body 19. This slot is clearance-fitted with the valve seat 3. When the upper valve body 18 and the lower valve body 19 are fixedly connected, the upper valve body 18 presses the valve seat 3 tightly onto the lower valve body 19, thereby achieving the effect of fixing the valve seat 3. The filter screen 17 can also be configured as a separate structure from the valve seat 3. A slot for placing the filter screen 17 is opened at the lower end of the valve seat 3. After the valve seat 3 is installed and fixed, the position of the filter screen 17 is restricted and fixed.

[0038] The valve body 1 includes an upper valve body 18 and a lower valve body 19. The upper valve body 18 and the lower valve body 19 are fixedly connected by studs 20 and nuts 21. The upper end of the lower valve body 19 is provided with a placement slot 22 for placing the valve seat 3. A guide is provided on the upper valve body 18, and a second through hole 9 is opened on the lower valve body 19.

[0039] The guide sleeve 13 is mounted on the upper valve body 18 via the support rib 14. The circumference of the auxiliary sleeve 7 is fixedly mounted on the lower valve body 19 by a number of annular equidistant connecting ribs (not shown in the figure). The number of annular equidistant connecting ribs (not shown in the figure) forms a flow space, which allows the medium to pass smoothly and reduce flow resistance.

[0040] A flange is provided at the connection position between the upper valve body 18 and the lower valve body 19. A stud 20 passes through an opening on the flange and is threaded to a nut 21 to fix the upper valve body 18 and the lower valve body 19 together. An annular sealing gasket is provided between the lower end of the upper valve body 18 and the upper end of the lower valve body 19. This annular sealing gasket is used to seal the connection gap between the upper valve body 18 and the lower valve body 19 after they are fixedly connected by the stud 20 and the nut 21, so as to reduce the occurrence of media leakage.

[0041] The stud 20 can be a double-ended stud 20, with a nut 21 provided on each double-ended stud 20 for fixed connection, or the stud 20 can be used as a connecting bolt, with a nut 21 provided on each connecting bolt for fixed connection.

[0042] A secondary spring element 23 is provided between the secondary sleeve 7 and the secondary valve disc 10, and the secondary spring element 23 is sleeved on the outer periphery of the secondary guide rod 11. The secondary spring element 23 is sleeved on the secondary guide rod 11, with one end abutting against the secondary sleeve 7 and the other end abutting against the secondary valve disc 10. The secondary spring element 23 is also a compression spring 6. The provision of the secondary spring element 23 can further improve the downward pushing force on the secondary valve disc 10, thereby increasing the sealing performance of the secondary valve disc 10 to the second through hole 9; alternatively, the secondary spring element 23 can be omitted, and the descent of the secondary valve disc 10 can be driven solely by the downward pressure of the compression spring 6 on the sealing valve disc 5.

[0043] A reinforcing rib 24 is provided on the valve body 1 below the secondary valve disc 10. A clearance hole 25 is longitudinally formed at the center end of the reinforcing rib 24, and the lower end of the secondary guide rod 11 passes through the secondary valve disc 10 and is located in the clearance hole 25. Figure 5 As shown, the middle part of the reinforcing rib 24 is a circular part, and the perforation 25 is opened in the position of the circular part.

[0044] The lower end face of the reinforcing rib 24 is provided with a lower bushing 26 for reducing the adhesion of impurities in the clearance hole 25. The lower bushing 26 is threadedly connected to the lower end face of the reinforcing rib 24.

[0045] A threaded boss is provided on the lower end face of the reinforcing rib 24, and the lower bushing 26 is threadedly connected to the threaded boss through an internal thread. The longitudinal height of the lower bushing 26 only needs to avoid contact with the auxiliary guide rod 11 during lifting and lowering. The lower bushing 26 has a bottle cap-like structure. In the structure of the guide sleeve 13, if the center hole of the guide sleeve 13 is also a through-hole type, a corresponding threaded boss can be provided at the upper end of the guide sleeve 13, and an upper bushing can be threadedly connected to the threaded boss to achieve the same technical effect as the lower bushing 26. The center hole of the guide sleeve 13 does not need to be a through-hole type structure, in which case the upper bushing is not required.

[0046] The working principle of this invention is as follows: When the medium flows from bottom to top, the medium pushes the secondary valve disc 10 upward, causing the second through hole 9 to be in an open state. During this process, the secondary valve disc 10 drives the secondary guide rod 11 to rise synchronously in the secondary sleeve 7, pushing the linkage shaft 12 upward to simultaneously drive the sealing valve disc 5 to rise. The upward flow of the medium also utilizes the thrust generated to keep the first through hole 4 open, thus realizing the flow of the medium. When the medium stops flowing upward or flows in reverse, the sealing valve disc 5 is pushed by the reverse flow of the medium and by the release of elastic potential energy from the compression spring 6, causing the sealing valve disc 5 to descend and close the first through hole 4. During the descent of valve 5, the linkage shaft 12 pushes the auxiliary guide rod 11 to drive the auxiliary valve disc 10 to descend synchronously, thereby closing the second through hole 9. This linkage structure achieves the technical effects of rapid, synchronous and double sealing. Even if one sealing pair fails, the other sealing pair can still serve as a reliable backup barrier, effectively cutting off the backflow of the medium. It eliminates the closing delay caused by inertia or jamming of a single valve, shortens the closing response time, and achieves a double sealing effect through the double valve disc design, improving the reliability and sealing performance of the check valve. The linkage shaft 12 structure ensures that the main and auxiliary valve discs 10 move synchronously and respond quickly. When the sealing valve disc 5 descends to close the first through hole 4, the compression of the linkage shaft 12 and the auxiliary guide rod 11 can further press the auxiliary valve disc 10 into the second through hole 9. The sealing effect of the auxiliary valve disc 10 is further improved by utilizing the pressure of the medium backflow and the spring driving force of the compression spring 6 on the auxiliary valve disc 10. The guide rod 15 and the guide sleeve 13 work together to ensure that the sealing valve disc 5 maintains vertical movement during the lifting and lowering process, reducing skewness and jamming, and extending service life; the compression spring 6 provides the restoring force and enhances the response speed of the sealing valve disc 5. The auxiliary spring element 23 can drive the auxiliary valve disc 10 to descend more quickly and effectively when the medium flows backward, and press it against the second through hole 9 to seal it, thereby increasing the sealing effect of the second through hole 9.

[0047] This invention protects the product's structure; the model numbers of the components are not protected by this invention, as they are common technology. Any component on the market that can achieve the functions described above can be used as a double check valve. Therefore, the model numbers and other parameters of the components are not described in detail in this invention. The contribution of this invention lies in the scientific combination of the various components.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions above are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents. Any aspects not detailed in the present invention are well-known to those skilled in the art.

Claims

1. A double check valve characterized by: The valve body, the flow-through opening, the valve seat, the first through hole, the sealing valve flap, the guide, the compression spring, the auxiliary sleeve, the second through hole, the auxiliary valve flap, the auxiliary guide rod, and the linkage shaft are arranged in the valve body.

2. A double check valve according to claim 1, wherein: The guide includes a guide sleeve, a support rib, a guide rod, and a compression spring.

3. A double check valve according to claim 2, wherein: The sealing valve flap is fixedly arranged on the periphery of the guide rod.

4. A double check valve according to claim 1, wherein: The auxiliary sleeve is fixedly arranged in the flow-through opening of the valve body by a connecting rib.

5. A double check valve according to claim 1, wherein: The valve seat is provided with a filter screen for filtering impurities in the medium.

6. A double check valve according to claim 1, wherein: The valve body includes an upper valve body and a lower valve body, the upper valve body and the lower valve body are fixedly connected by a stud and a nut, the upper end of the lower valve body is provided with a placement slot for placing the valve seat, the guide is arranged on the upper valve body, and the second through hole is arranged on the lower valve body.

7. A double check valve according to claim 1, wherein: The auxiliary sleeve and the auxiliary valve flap are provided with an auxiliary spring member, and the auxiliary spring member is sleeved on the outer periphery of the auxiliary guide rod.

8. A double check valve according to claim 1, wherein: The lower end surface of the reinforcing rib is provided with a lower shaft sleeve for reducing the adhesion of impurities in the avoiding hole.

9. A double check valve according to claim 8, wherein: The lower end surface of the reinforcing rib is provided with a lower shaft sleeve for reducing the adhesion of impurities in the avoiding hole.

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