Anti-back pressure mechanism for mechanical seal

Abstract

The application relates to a back pressure prevention mechanism for mechanical seal, which is applied to a mechanical seal comprising a gland, a sealing cavity and a medium side static ring, and is characterized in that a sealing liquid communication hole is arranged on the sealing cavity, the back pressure prevention mechanism comprises a balance sleeve, a balance pin, a sealing washer and a spring A, the balance sleeve is sleeved between the medium side static ring and the gland, the balance sleeve is in sliding type cooperation with the medium side static ring and the gland, a balance cavity is formed among the balance sleeve, the gland, the sealing cavity and the medium side static ring, the balance pin is provided with a large end and a small end, the spring A is arranged between the large end and the small end of the balance pin in a stepped structure, and one end of the spring A is blocked outside the balance sleeve; under the action of the spring A, the balance pin is closed, and the sealing washer closes the sealing liquid communication hole; when the medium pressure is in an abnormal state, the balance pin cuts off the communication between the sealing liquid communication hole and the balance cavity, the balance cavity is closed, the balance sleeve moves to press the balance cavity, the pressure of the balance cavity is increased, and the closing force of the seal is increased.

Description

[0001] The original basis for this divisional application is patent application No. 202410273800.4, filed on March 11, 2024, entitled "Anti-backpressure mechanical seal device for a sand mill". Technical Field

[0002] This invention relates to the field of mechanical seal structure technology, and in particular to an anti-backpressure mechanism for mechanical seals. Background Technology

[0003] Sand mills are wet ultrafine grinding equipment, widely used in industries such as building materials, coatings, and lithium batteries. Their main principle is to rotate the cylinder or shaft and use zirconia beads and other particles to grind the media into fine particles. Then, pumps and other equipment are used to transport the finished particles to the next process. Due to the high content of media particles, the conveying pipelines and pumps are often blocked, causing the pressure inside the sand mill to rise.

[0004] Common sand mill seals are double-end mechanical seals, consisting of two sets of seals with pressurized sealing fluid flowing between them for lubrication and cooling. The sealing fluid pressure is 0.2–0.3 MPa higher than the medium pressure. When downstream pipelines or pumps become blocked, the pressure inside the sand mill increases, causing the medium pressure to exceed the sealing fluid pressure, resulting in back pressure on the seal and often leading to seal failure. Increasing the sealing fluid pressure to accommodate the blockage will exacerbate seal wear under normal conditions and increase leakage. Furthermore, many users lack the on-site facilities to increase the sealing fluid pressure.

[0005] In summary, there is a need for a seal that can adapt to back pressure conditions when the pressure inside the sand mill increases.

[0006] Therefore, this patent application is filed. Summary of the Invention

[0007] The purpose of this invention is to provide a back pressure prevention mechanical seal device for a sand mill. By utilizing the mobility of the balance sleeve and balance pin, when the medium pressure is high and in an abnormal state, the balance pin cuts off the connection between the sealing fluid communication hole and the balance chamber, causing the balance chamber to close. Meanwhile, the balance sleeve moves and squeezes the balance chamber, increasing the pressure in the balance chamber and increasing the sealing closing force to prevent seal failure, thereby adapting to back pressure conditions.

[0008] This invention is achieved through the following technical solution: The present invention aims to provide an anti-backpressure mechanical seal device for a sand mill, comprising a gland, a sealing cavity, a medium-side stationary ring, and an anti-backpressure mechanism. The anti-backpressure mechanism includes a balance sleeve, a balance pin, and a sealing gasket. The balance sleeve is fitted between the medium-side stationary ring and the gland, and the balance sleeve, the medium-side stationary ring, and the gland are in a sliding fit. One end of the balance pin is fixedly fitted with the sealing gasket, and the other end is slidably connected to the balance sleeve. The balance sleeve, the gland, the sealing cavity, and the medium-side stationary ring form a balance cavity. The sealing cavity is provided with a sealing fluid communication hole. When the pressure of the sealing fluid is greater than the medium pressure, the balance sleeve and the balance pin move, and the sealing fluid communication hole communicates with the balance cavity. When the pressure of the sealing fluid is less than the medium pressure, the balance sleeve and the balance pin move in the opposite direction until the pressure in the balance cavity equals the medium pressure, and the sealing gasket closes the sealing fluid communication hole, thereby disconnecting the sealing fluid communication hole from the balance cavity.

[0009] In an optional embodiment, the end face of the balancing sleeve is provided with a groove, and the end of the balancing pin is inserted into the groove and slidably engaged with the groove.

[0010] In an optional embodiment, a sixth O-ring is provided between the contact surfaces of the balance sleeve and the gland, and a seventh O-ring is provided between the contact surfaces of the balance sleeve and the medium-side stationary ring.

[0011] In an optional embodiment, the balance pin has a large end and a small end, forming a stepped structure. The small end of the balance pin is slidably connected to the balance sleeve. A sealing washer is fitted on the large end of the balance pin. A spring A is provided between the large end and the small end of the balance pin. One end of the spring A is held outside the balance sleeve.

[0012] In an optional embodiment, a spring B is provided between the medium-side stationary ring and the sealing cavity, and a medium-side moving ring is provided on one side of the medium-side stationary ring. The medium-side moving ring is assembled on the bushing by a second anti-rotation pin, and the bushing is sleeved on the rotating shaft.

[0013] In an optional embodiment, a first O-ring is fitted on the inner hole of the bushing, and an eighth O-ring is provided between the bushing and the medium-side moving ring.

[0014] In an optional embodiment, a rotating ring seat is fixedly provided on the bushing, a third O-ring is provided between the rotating ring seat and the bushing, an atmospheric rotating ring is provided at the end of the rotating ring seat facing the medium side, an atmospheric stationary ring is installed in the sealing cavity, the atmospheric stationary ring is located on one side of the atmospheric rotating ring, a ninth O-ring is provided between the atmospheric rotating ring and the rotating ring seat, and a push ring is provided at the end of the atmospheric stationary ring away from the atmospheric rotating ring; the atmospheric rotating ring, the atmospheric stationary ring, the medium-side rotating ring, the medium-side stationary ring and the bushing form a sealed cavity for the flow of sealing fluid, and the sealed cavity is provided with a sealing fluid inlet and a sealing fluid outlet.

[0015] In an optional embodiment, a spring B is provided between the push ring and the sealing cavity.

[0016] In an optional embodiment, one end of the bushing is provided with a locking nut, which presses the bushing onto the rotating shaft.

[0017] In an optional embodiment, the gland and the sealing cavity are fastened together by a cylindrical head screw.

[0018] The advantages and beneficial effects of this invention compared to the prior art are: (1) The anti-back pressure mechanical seal device for a sand mill provided in the embodiments of the present invention utilizes the mobility of the balance pin: when the sealing fluid is introduced, the balance pin opens under the pressure of the sealing fluid, and the sealing fluid enters the balance chamber. At this time, the pressure of the balance chamber is the same as the pressure of the sealing fluid. Utilizing the mobility of the balance sleeve: when the medium pressure is high, the balance sleeve moves to squeeze the balance chamber, thereby increasing the pressure of the balance chamber, increasing the sealing closing force, preventing seal failure, adapting to back pressure conditions, achieving good sealing without increasing the pressure of the sealing fluid, not aggravating seal wear, and not causing seal leakage.

[0019] (2) The anti-back pressure mechanical seal device for a sand mill provided in the embodiment of the present invention has a balance sleeve and a medium-side stationary ring outer diameter fit without any step dead angle, etc., and there is no space for particles to accumulate, ensuring good floating of the medium-side stationary ring, adapting to particle working conditions, and ensuring the service life of the seal. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1This is a schematic diagram of the overall structure of an anti-backpressure mechanical seal device for a sand mill, provided as an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of a back pressure prevention mechanical seal device for a sand mill under normal operating conditions, showing the cooperation of the balance sleeve, balance pin, balance chamber, and sealing fluid communication hole.

[0022] Figure 3 This is a schematic diagram of the structure of a back pressure prevention mechanical seal device for a sand mill provided in an embodiment of the present invention, showing the cooperation of the balance sleeve, balance pin, balance chamber and sealing fluid communication hole under abnormal back pressure conditions.

[0023] Figure 4 This is a schematic diagram showing the forces acting on the balance sleeve and balance pin.

[0024] Figure 5 This is a schematic diagram of the flow direction of the sealing fluid in an anti-backpressure mechanical seal device for a sand mill, provided as an embodiment of the present invention.

[0025] The markings and the components they represent in the attached diagram are as follows: 1. Bushing; 2. First O-ring; 3. Medium-side moving ring; 4. Compression nut; 5. Balance sleeve; 6. Spring A; 7. Medium-side stationary ring; 8. Balance pin; 9. Sealing washer; 10. Gland; 11. Spring B; 12. Sealing cavity; 13. Push ring; 14. Atmospheric-side stationary ring; 15. Second O-ring; 16. Atmospheric-side moving ring; 17. Ninth O-ring; 18. Moving ring seat; 19. Locking nut; 20. Set screw; 21. Third O-ring; 22. First anti-rotation pin; 23. Cylindrical head screw; 24. Fourth O-ring; 25. Fifth O-ring; 26. Sixth O-ring; 27. Seventh O-ring; 28. Eighth O-ring; 29. ​​Second anti-rotation pin; 30. Balance cavity; 31. Sealing fluid communication hole. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0027] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0028] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] In the description of this invention, the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0030] like Figures 1-5 As shown, a backpressure prevention mechanical seal device for a sand mill includes a gland 10, a sealing cavity 12, a medium-side stationary ring 7, and a backpressure prevention mechanism.

[0031] The gland 10 and the sealing cavity 12 are fastened together by a cylindrical head screw 23. An anti-backpressure mechanism is installed between the gland 10, the sealing cavity 12, and the medium-side stationary ring 7. This mechanism includes a balance sleeve 5, a balance pin 8, and a sealing washer 9. The balance sleeve 5 is fitted between the medium-side stationary ring 7 and the gland 10. The inner side of the balance sleeve 5 is in contact with the medium-side stationary ring 7, and the outer side of the balance sleeve 5 is in contact with the gland 10. The balance sleeve 5 has a sliding fit with both the medium-side stationary ring 7 and the gland 10, allowing it to move between them. One end of the balance pin 8 is fixedly fitted with the sealing washer 9, and the other end is slidably connected to the balance sleeve 5. The balance pin 8 can move relative to the balance sleeve 5 without disengaging. The sealing washer 9 is positioned along the side closest to the sealing cavity 12. The balance sleeve 5 has a cavity between the gland 10, the sealing cavity 12, and the medium-side stationary ring 7 to form a balance cavity 30. A sealing fluid communication hole 31 is provided on the sealing cavity 12. The balance cavity 30 and the sealing fluid communication hole 31 are connected, and the sealing fluid can be introduced into the balance cavity 30 through the sealing fluid communication hole 31.

[0032] like Figure 4As shown, during the sealing process, when the balance pin 8 is subjected to the pressure of the sealing fluid, the direction of the pressure is to open the balance pin 8, so that the balance cavity 30 and the sealing fluid communication hole 31 are connected. When the balance sleeve 5 is subjected to the pressure of the medium on the medium side, the direction of the pressure is to squeeze the balance cavity 30 to the right. At the same time, the balance cavity 30 contains sealing fluid. When the balance sleeve 5 is subjected to the pressure of the sealing fluid in the balance cavity 30, the direction of the pressure is opposite to the direction of the medium pressure.

[0033] like Figure 2 As shown, when the pressure of the sealing fluid is greater than the pressure of the medium, the seal works normally. The sealing fluid is introduced into the sealing fluid communication hole 31. The sealing fluid acts on the balance pin 8, causing the balance pin 8 to move to the left and be in the open state. At this time, the balance chamber 30 is connected to the sealing fluid communication hole 31. The sealing fluid enters the balance chamber 30. The closing force on the medium side stationary ring 7 is the sealing fluid pressure, which is greater than the medium pressure. At this time, the medium side stationary ring 7 is in the closed state.

[0034] like Figure 3 As shown, when the medium pressure is greater than the sealing fluid pressure, an abnormal state occurs. Under the action of the medium pressure, the balance sleeve 5 moves to the right, squeezing the balance pin 8, causing the end sealing gasket 9 to fit against the sealing cavity 12. At this time, the balance cavity 30 is in a sealed state, and the sealing gasket 9 blocks the sealing fluid connection hole 31, disconnecting the connection between the sealing fluid connection hole 31 and the balance cavity 30. Under the action of the medium pressure, the balance sleeve 5 will continue to move to the right, the volume of the balance cavity 30 will decrease, and the pressure will increase until the pressure inside the balance cavity 30 is the same as the medium pressure. The pressure on both sides of the balance sleeve 5 will reach equilibrium. At this time, the force on the medium-side stationary ring 7 is the same as the medium pressure, and the medium-side stationary ring 7 remains in a closed state. In this way, regardless of whether the seal is in a normal working state or in an abnormal state of blockage in the pipeline or pump, the sealing end face is always in a closed state, and the seal is always in a normal state. Good sealing can be achieved without increasing the sealing fluid pressure, without aggravating seal wear, and without the problem of seal leakage.

[0035] Therefore, in this embodiment of the invention, by utilizing the mobility of the balance sleeve 5 and the balance pin 8, when the medium pressure is high and in an abnormal state, the balance pin 8 cuts off the connection between the sealing fluid communication hole 31 and the balance cavity 30, causing the balance cavity 30 to close, while the balance sleeve 5 moves to squeeze the balance cavity 30, causing the pressure in the balance cavity 30 to increase, increasing the sealing closing force, and preventing seal failure.

[0036] Furthermore, a groove is provided on the end face of the balance sleeve 5, and the end of the balance pin 8 is inserted into the groove and slides in the groove to ensure the movement of the balance pin 8.

[0037] To improve sealing, a sixth O-ring 26 is provided between the contact surfaces of the balance sleeve 5 and the gland 10, and a seventh O-ring 27 is provided between the contact surfaces of the balance sleeve 5 and the medium-side stationary ring 7. This ensures that the balance sleeve 5 is always in a good sealing state with the gland 10 and the medium-side stationary ring 7 during movement, thus avoiding sealing failure.

[0038] Furthermore, the balance pin 8 has a large end and a small end, forming a stepped structure. The small end of the balance pin 8 is inserted into the groove of the balance sleeve 5, and is slidably connected to the balance sleeve 5. A sealing washer 9 is fitted onto the large end of the balance pin 8. A spring A6 is provided between the large end and the small end of the balance pin 8, with one end of the spring A6 blocking the outside of the balance sleeve 5. By setting the spring A6, the balance pin 8 is subjected to the force of the spring A6, and the direction of the force is to close the balance pin 8 and seal the sealing washer 9 to close the sealing fluid communication hole 31. In the initial state, the balance pin 8 is closed under the action of the spring A6, and the sealing washer 9 closes the sealing fluid communication hole 31, as shown. Figure 4 As shown, when the sealing fluid pressure is greater than the medium pressure, the sealing fluid pressure overcomes the spring force on the balance pin 8, and the balance pin 8 moves to the left and is in the open state. At this time, the sealing fluid enters the balance chamber 30, and the closing force on the back of the medium-side stationary ring 7 is the sealing fluid pressure, which is greater than the medium pressure. At this time, the medium-side stationary ring 7 is in the closed state.

[0039] Furthermore, a spring B11 is provided between the medium-side stationary ring 7 and the sealing cavity 12. The spring B11 is connected to the rear end of the medium-side stationary ring 7. A medium-side moving ring 3 is provided on one side of the medium-side stationary ring 7. The spring B11 ensures that the medium-side stationary ring 7 is always in contact with the medium-side moving ring 3 in the initial state. The medium-side moving ring 3 is assembled onto the bushing 1 by the second anti-rotation pin 29, which ensures that the medium-side moving ring 3 can rotate with the bushing 1. At the same time, the clamping nut 4 is used to press the medium-side moving ring 3 onto the bushing 1. The bushing 1 is fitted onto the rotating shaft.

[0040] To improve sealing performance, a first O-ring 2 is fitted onto the inner bore of the bushing 1 to prevent media leakage along the gap between the bushing 1 and the shaft. An eighth O-ring 28 is provided between the bushing 1 and the media-side moving ring 3 to prevent media leakage from the gap between the bushing 1 and the media-side moving ring 3.

[0041] A rotating ring seat 18 is fixed to the bushing 1 by a set screw 20. A third O-ring 21 is provided between the rotating ring seat 18 and the bushing 1 to prevent the sealing fluid from leaking between the rotating ring seat 18 and the bushing 1. An atmospheric rotating ring 16 is provided at the end of the rotating ring seat 18 facing the medium. A ninth O-ring 17 is provided between the atmospheric rotating ring 16 and the rotating ring seat 18. One end of the first anti-rotation pin 22 is fixed to the rotating ring seat 18, and the other end extends into the corresponding pin groove of the atmospheric rotating ring 16 to ensure that the atmospheric rotating ring 16 can rotate with the rotating shaft.

[0042] An atmospheric side stationary ring 14 is installed inside the sealing cavity 12. The atmospheric side stationary ring 14 is located on one side of the atmospheric side moving ring 16, and a push ring 13 is provided at the end of the atmospheric side stationary ring 14 away from the atmospheric side moving ring 16. A second O-ring 15 is fitted between the atmospheric side stationary ring 14 and the sealing cavity 12.

[0043] like Figure 5 As shown, the atmospheric side moving ring 16, the atmospheric side stationary ring 14, the medium side moving ring 3, the medium side stationary ring 7, the bushing 1, and the related auxiliary O-rings form a sealed cavity for the flow of sealing fluid. The sealed cavity is provided with a sealing fluid inlet and a sealing fluid outlet, which can carry away the heat generated by the wear of the sealing end face.

[0044] A spring B11 is provided between the push ring 13 and the sealing cavity 12, so that the atmospheric side stationary ring 14 is always in contact with the atmospheric side moving ring 16 in the initial state.

[0045] Furthermore, the bushing 1 is fitted onto the rotating shaft, with one end of the bushing 1 abutting against the shaft shoulder and the other end provided with a locking nut 19. The bushing 1 is pressed onto the rotating shaft by the locking nut 19, thereby realizing the rotation of the bushing 1.

[0046] More preferably, a fourth O-ring 24 is also fitted on the gland 10, and a fifth O-ring 25 is also fitted on the outside of the medium-side stationary ring 7 to achieve a better sealing effect.

[0047] In this embodiment of the invention, the anti-backpressure mechanical seal device uses a double-end face cartridge structure, with no dead angles at the positions of the dynamic and static rings on the medium side and the inner pressure cover 10. Particulate media are not easy to accumulate at the sealing position, so that the seal always maintains good floating properties, adapts to particulate working conditions, and ensures the service life of the seal.

[0048] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A backpressure prevention mechanism for a mechanical seal, applied to a mechanical seal comprising a gland (10), a sealing cavity (12), and a medium-side stationary ring (7), wherein the sealing cavity (12) is provided with a sealing fluid communication hole (31), characterized in that, The anti-backpressure mechanism includes a balance sleeve (5), a balance pin (8), a sealing washer (9), and a spring A (6): The balance sleeve (5) is fitted between the medium-side stationary ring (7) and the pressure cap (10). The balance sleeve (5) is in sliding fit with the medium-side stationary ring (7) and the pressure cap (10). The balance sleeve (5) forms a balance cavity (30) with the pressure cap (10), the sealing cavity (12), and the medium-side stationary ring (7). The balance pin (8) has a large end and a small end, forming a stepped structure. The spring A (6) is located between the large end and the small end of the balance pin (8). One end of the spring A (6) is held against the outside of the balance sleeve (5). Under the action of the spring A (6), the balance pin (8) closes, and the sealing gasket (9) seals the sealing fluid communication hole (31). When the medium pressure is high and in an abnormal state, the balance pin (8) cuts off the communication between the sealing fluid communication hole (31) and the balance chamber (30), causing the balance chamber (30) to close, while the balance sleeve (5) moves and squeezes the balance chamber (30), causing the pressure in the balance chamber (30) to increase and increase the sealing closing force.

2. The anti-backpressure mechanism according to claim 1, characterized in that, The end face of the balance sleeve (5) is provided with a hole groove; The small end of the balance pin (8) is inserted into the groove and slides with the groove, and the large end of the balance pin (8) is fitted with the sealing gasket (9).

3. The anti-backpressure mechanism according to claim 1 or 2, characterized in that, A sixth O-ring (26) is provided between the contact surface of the balance sleeve (5) and the pressure cap (10), and a seventh O-ring (27) is provided between the contact surface of the balance sleeve (5) and the medium-side stationary ring (7).

4. The anti-backpressure mechanism according to any one of claims 1 to 3, characterized in that, A fourth O-ring (24) is also fitted on the gland (10), and a fifth O-ring (25) is also fitted on the outside of the medium-side stationary ring (7).

5. The anti-backpressure mechanism according to any one of claims 1 to 4, characterized in that, A spring B (11) is provided between the medium-side stationary ring (7) and the sealing cavity (12). A medium-side moving ring (3) is provided on one side of the medium-side stationary ring (7). The medium-side moving ring (3) is assembled on the bushing (1) by the second anti-rotation pin (29), and the medium-side moving ring (3) is pressed on the bushing (1) by the clamping nut (4). The bushing (1) is sleeved on the rotating shaft.

6. The anti-backpressure mechanism according to claim 5, characterized in that, The inner hole of the bushing (1) is fitted with a first O-ring (2), and an eighth O-ring (28) is provided between the bushing (1) and the medium-side moving ring (3).

7. The anti-backpressure mechanism according to claim 5 or 6, characterized in that, A rotating ring seat (18) is fixedly provided on the bushing (1). A third O-ring (21) is provided between the rotating ring seat (18) and the bushing (1). An atmospheric rotating ring (16) is provided at one end of the rotating ring seat (18) facing the medium side. A ninth O-ring (17) is provided between the atmospheric rotating ring (16) and the rotating ring seat (18). One end of the first anti-rotation pin (22) is fixed on the rotating ring seat (18), and the other end extends into the corresponding pin groove of the atmospheric rotating ring (16). The atmospheric rotating ring (16) can rotate together with the rotating shaft.

8. The anti-backpressure mechanism according to claim 7, characterized in that, The sealed cavity (12) is equipped with an atmospheric side stationary ring (14), which is located on one side of the atmospheric side moving ring (16). The end of the atmospheric side stationary ring (14) away from the atmospheric side moving ring (16) is provided with a push ring (13). The atmospheric side moving ring (16), atmospheric side stationary ring (14), medium side moving ring (3), medium side stationary ring (7) and the bushing (1) form a sealed cavity for the flow of sealing fluid. The sealed cavity is provided with a sealing fluid inlet and a sealing fluid outlet.

9. The anti-backpressure mechanism according to claim 8, characterized in that, A spring B (11) is provided between the push ring (13) and the sealing cavity (12), and a second O-ring (15) is sleeved between the atmospheric side static ring (14) and the sealing cavity (12).

10. The anti-backpressure mechanism according to any one of claims 5 to 9, characterized in that, One end of the bushing (1) is provided with a locking nut (19), which presses the bushing (1) onto the rotating shaft.

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