Valve rod assembly and fixed ball valve adopting same

Abstract

The utility model relates to the technical field of valves, in particular to a valve rod assembly and a fixed ball valve with the valve rod assembly, the valve rod assembly comprises a valve rod, a thrust bearing, an outer triangular filler, an inner triangular filler and a first pressing ring, and the outer triangular filler and the inner triangular filler are both annular; the thrust bearing is arranged on the valve rod in a sleeving mode and comprises a first shaft sleeve and a second shaft sleeve, the first shaft sleeve abuts against the valve rod, the outer triangular filler and the inner triangular filler are arranged on the second shaft sleeve, a V-shaped groove is formed between the outer triangular filler and the inner triangular filler, and the first pressing ring is arranged in the V-shaped groove. The first pressing ring extrudes the outer triangular filler and the inner triangular filler; and in the direction from the thrust bearing to the first pressing ring, the extrusion degree of the outer triangular filler and the inner triangular filler by the first pressing ring is gradually increased. According to the valve rod assembly and the fixed ball valve adopting the valve rod assembly, the risk that a medium leaks from the valve rod can be reduced, and the sealing reliability of the packing to the valve rod is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of valves, and particularly relates to a valve stem assembly and a fixed ball valve adopting the assembly. Background Art

[0002] As a core component of a fluid control system, the fixed ball valve is widely used in fields such as petrochemical industry, electric power, nuclear energy and municipal engineering. Among them, the valve stem is a key transmission component for driving the movement of the valve core.

[0003] However, during the operation of the fixed ball valve, leakage often occurs at the valve stem. For example, frequent opening and closing of the valve causes wear of the packing, or the pre-tightening force on the packing is insufficient, which increases the probability that the packing is not in close contact with the inner wall of the valve body or the outer wall of the valve stem, thereby increasing the risk of medium leakage from the valve stem.

[0004] Therefore, how to improve the reliability of the packing seal for the valve stem is a technical problem that needs to be solved urgently at present. Summary of the Utility Model

[0005] The purpose of the utility model is to provide a valve stem assembly and a fixed ball valve adopting the assembly to improve the reliability of the packing seal for the valve stem in view of the above-mentioned deficiencies of the current fixed ball valve.

[0006] In order to achieve the above-mentioned utility model purpose, the utility model provides the following technical solutions:

[0007] A valve stem assembly includes a valve stem, a thrust bearing, an outer triangular packing, an inner triangular packing and a first compression ring, and both the outer triangular packing and the inner triangular packing are annular;

[0008] The thrust bearing is sleeved on the valve stem. The thrust bearing includes a first shaft sleeve and a second shaft sleeve. The first shaft sleeve abuts against the valve stem. The outer triangular packing and the inner triangular packing are arranged on the second shaft sleeve. A V-shaped groove is formed between the outer triangular packing and the inner triangular packing. The first compression ring is placed in the V-shaped groove, and the first compression ring squeezes the outer triangular packing and the inner triangular packing, so that the outer wall of the outer triangular packing abuts against the inner wall of the valve body, and the inner wall of the inner triangular packing abuts against the outer wall of the valve stem;

[0009] And in the direction from the thrust bearing to the first compression ring, the degree of being squeezed by the first compression ring on the outer triangular packing and the inner triangular packing gradually increases.

[0010] As a preferred technical solution of the present application, the first compression ring is a V-shaped compression ring. The first compression ring includes a first compression surface and a second compression surface. The first compression surface and the second compression surface cooperate to form a V-shaped structure. The first compression surface is used to abut against the inner wall of the outer triangular packing, and the second compression surface is used to abut against the outer wall of the inner triangular packing.

[0011] As a preferred technical solution of the present application, on the basis that the plane perpendicular to the central axis of the first compression ring is used as the first reference plane, the included angle between the first compression surface and the first reference plane is α, and the included angle between the second compression surface and the first reference plane is β. Among them, the included angle α > 45°, and the included angle β > 45°.

[0012] As a preferred technical solution of the present application, the valve stem assembly further includes a second compression ring. The second compression ring is used to be stuck on the valve body. When the second compression ring is stuck on the valve body, the second compression ring abuts against the first compression ring to limit the first compression ring.

[0013] The second compression ring is a three-piece ring.

[0014] As a preferred technical solution of the present application, a sealing assembly is provided on the second shaft sleeve. The sealing assembly includes a first sealing ring and a second sealing ring. The first sealing ring is located on the outer wall of the second shaft sleeve and is used to abut against the inner wall of the valve seat. The second sealing ring is located on the inner wall of the second shaft sleeve and is used to abut against the outer wall of the valve stem.

[0015] As a preferred technical solution of the present application, a plurality of sealing assemblies are provided on the second shaft sleeve, and the plurality of sealing assemblies are distributed along the length direction of the second shaft sleeve.

[0016] As a preferred technical solution of the present application, a first channel and a second channel are provided on the second shaft sleeve. The first channel communicates the inner wall and the outer wall of the second shaft sleeve. The second channel communicates with the first channel. The second channel extends to the end face of the second shaft sleeve that abuts against the outer triangular packing or the inner triangular packing. A piston is provided in the second channel, and the piston can move relative to the second channel so that the piston exposes or retracts into the second shaft sleeve; the piston has an initial state, and when the piston is in the initial state, the piston does not expose from the second shaft sleeve.

[0017] As a preferred technical solution of the present application, when the piston is in the initial state, the end face of the piston is flush with the end face of the second shaft sleeve.

[0018] As a preferred technical solution of the present application, the first channel divides the second shaft sleeve into a first part of the shaft sleeve and a second part of the shaft sleeve, and at least one sealing assembly is provided on each of the first part of the shaft sleeve and the second part of the shaft sleeve.

[0019] The present utility model also provides a fixed ball valve, which includes the valve stem assembly as described above.

[0020] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0021] 1. In the solution of the present application, by providing an outer triangular packing, an inner triangular packing, and a first pressing ring, the first pressing ring squeezes the outer triangular packing and the inner triangular packing, and in the direction from the thrust bearing to the first pressing ring, the degree of squeezing of the outer triangular packing and the inner triangular packing by the first pressing ring gradually increases. In this way, the outer triangular packing, the inner triangular packing, and the first pressing ring cooperate to seal the gap between the valve body and the valve stem. And in the sealing area, the higher the pressure on the area of the corresponding outer triangular packing and the inner triangular packing away from the valve core, the closer the contact between the outer triangular packing and the inner wall of the valve body and the first pressing ring can be further improved, and the closer the contact between the inner triangular packing and the outer wall of the valve stem and the first pressing ring can be improved, thereby reducing the risk of medium leakage from the valve stem. The higher deformation amount of the outer triangular packing and the inner triangular packing can increase the pre-tightening force received by the packing to further improve the tightness of the contact between the packing and the inner wall of the valve body and the outer wall of the valve stem; and by providing a thrust bearing, when the valve stem rotates, the second shaft sleeve on the thrust bearing can be stationary relative to the valve body, and further the second shaft sleeve can be stationary relative to the outer triangular packing and the inner triangular packing, thereby reducing the wear of the outer triangular packing and the inner triangular packing, further reducing the risk of medium leakage from the valve stem, and improving the reliability of the packing for sealing the valve stem; at the same time, the packing of the present application includes an outer triangular packing and an inner triangular packing, and both the outer triangular packing and the inner triangular packing are independent individuals. When the sealing performance of a single outer triangular packing or inner triangular packing fails, the corresponding outer triangular packing or inner triangular packing can be replaced, thereby reducing the use cost and improving the economic effect;

[0022] 2. Further, by setting the first pressing ring as a V-shaped pressing ring, the first pressing surface abuts against the inner wall of the outer triangular packing, and the second pressing surface abuts against the outer wall of the inner triangular packing. When the outer triangular packing and the inner triangular packing are squeezed by the first pressing ring and the second shaft sleeve, the inclined first pressing surface and the second pressing surface can play a guiding role to further improve the squeezing effect between the outer triangular packing and the inner wall of the valve body, and further improve the squeezing effect between the inner triangular packing and the outer wall of the valve stem, and further improve the sealing effect of the packing for sealing the valve stem;

[0023] 3. Further, by providing the first channel and the second channel, when the ball valve is under high-pressure working conditions, there will be a situation where the medium flows towards the gap between the valve body and the valve stem. When the high-pressure medium flows to the first channel, part of the high-pressure medium can flow through the first channel to the second channel and push the piston in the second channel, causing the piston to move relative to the second channel and gradually expose from the second bushing, thereby pushing against the bottom of the corresponding external triangular packing or internal triangular packing, which can further improve the tightness of the contact between the corresponding external triangular packing and the inner wall of the valve body, and / or further improve the tightness of the contact between the corresponding internal triangular packing and the outer wall of the valve stem; and after the piston is pushed, the space for the medium to flow in the second channel increases, which can reduce the impact of the medium on the valve body, valve stem and packing, thereby further improving the reliability of the packing for sealing the valve stem. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of one embodiment of a valve stem assembly of the present application;

[0025] Figure 2 is a valve stem assembly of the present application Figure 1 and is an enlarged structural diagram of part A therein;

[0026] Figure 3 is a schematic partial structural diagram of one embodiment of a valve stem assembly of the present application;

[0027] Figure 4 is a schematic structural diagram of one embodiment of a fixed ball valve of the present application;

[0028] In the figure: 1-valve stem, 2-thrust bearing, 3-external triangular packing, 4-internal triangular packing, 5-first compression ring, 6-first bushing, 7-second bushing, 8-first pressure surface, 9-second pressure surface, 10-second compression ring, 11-sealing assembly, 12-first sealing ring, 13-second sealing ring, 14-first channel, 15-second channel, 16-piston. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present utility model.

[0030] Therefore, the following detailed description of the embodiments of the present utility model is not intended to limit the scope of the present utility model claimed, but merely represents some embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without making creative efforts fall within the scope of protection of the present utility model.

[0031] It should be noted that, without conflict, the embodiments and the features and technical solutions in the embodiments in the present utility model can be combined with each other.

[0032] It should be noted that: Similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0033] In the description of the present utility model, it should be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present utility model is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. Such terms are only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present utility model. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0034] Embodiment 1: A valve stem assembly provided in this embodiment, see Figure 1 and Figure 2 as shown, including a valve stem 1, a thrust bearing 2, an external triangular packing 3, an internal triangular packing 4, and a first compression ring 5. Both the external triangular packing 3 and the internal triangular packing 4 are annular;

[0035] The thrust bearing 2 is sleeved on the valve stem 1. The thrust bearing 2 includes a first shaft sleeve 6 and a second shaft sleeve 7. The first shaft sleeve 6 abuts against the valve stem 1. The external triangular packing 3 and the internal triangular packing 4 are arranged on the second shaft sleeve 7. A V-shaped groove is formed between the external triangular packing 3 and the internal triangular packing 4. The first compression ring 5 is placed in the V-shaped groove, and the first compression ring 5 squeezes the external triangular packing 3 and the internal triangular packing 4, so that the outer wall of the external triangular packing 3 abuts against the inner wall of the valve body, and the inner wall of the internal triangular packing 4 abuts against the outer wall of the valve stem 1;

[0036] And in the direction from the thrust bearing 2 pointing to the first compression ring 5, the degree of being squeezed by the first compression ring 5 on the external triangular packing 3 and the internal triangular packing 4 gradually increases.

[0037] In the present application, by providing the outer triangular packing 3, the inner triangular packing 4, and the first compression ring 5, the first compression ring 5 squeezes the outer triangular packing 3 and the inner triangular packing 4. And along the direction from the thrust bearing 2 towards the first compression ring 5, the degree of squeezing of the outer triangular packing 3 and the inner triangular packing 4 by the first compression ring 5 gradually increases. Thus, the outer triangular packing 3, the inner triangular packing 4, and the first compression ring 5 cooperate to seal the gap between the valve body and the valve stem 1. And in the sealing area, the higher the pressure on the areas of the outer triangular packing 3 and the inner triangular packing 4 away from the valve core, the closer the contact between the outer triangular packing 3 and the inner wall of the valve body and the first compression ring 5 can be further improved, and the closer the contact between the inner triangular packing 4 and the outer wall of the valve stem 1 and the first compression ring 5 can be improved, thereby reducing the risk of medium leakage from the valve stem 1. The higher deformation amount of the outer triangular packing 3 and the inner triangular packing 4 can increase the pre-tightening force received by the packing to further improve the tightness of the contact between the packing and the inner wall of the valve body and the outer wall of the valve stem 1. And by providing the thrust bearing 2, when the valve stem 1 rotates, the second shaft sleeve 7 on the thrust bearing 2 can be stationary relative to the valve body, and further the second shaft sleeve 7 can be stationary relative to the outer triangular packing 3 and the inner triangular packing 4, thereby reducing the wear of the outer triangular packing 3 and the inner triangular packing 4 and further reducing the risk of medium leakage from the valve stem 1, and improving the reliability of the packing's seal for the valve stem 1. At the same time, the packing of the present application includes the outer triangular packing 3 and the inner triangular packing 4, and the outer triangular packing 3 and the inner triangular packing 4 are both independent individuals. When the sealing performance of a single outer triangular packing 3 or inner triangular packing 4 fails, the corresponding outer triangular packing 3 or inner triangular packing 4 can be replaced, thereby reducing the use cost and improving the economic effect.

[0038] As a preferred embodiment, on the basis of the above method, further, the first compression ring 5 is a V-shaped compression ring. The first compression ring 5 includes a first pressing surface 8 and a second pressing surface 9. The first pressing surface 8 and the second pressing surface 9 cooperate to form a V-shaped structure. The first pressing surface 8 is used to abut against the inner wall of the outer triangular packing 3, and the second pressing surface 9 is used to abut against the outer wall of the inner triangular packing 4.

[0039] Further, by setting the first compression ring 5 as a V-shaped compression ring, the first pressing surface 8 abuts against the inner wall of the outer triangular packing 3, and the second pressing surface 9 abuts against the outer wall of the inner triangular packing 4. When the outer triangular packing 3 and the inner triangular packing 4 are squeezed by the first compression ring 5 and the second shaft sleeve 7, the inclined first pressing surface 8 and the second pressing surface 9 can play a guiding role to further improve the squeezing effect between the outer triangular packing 3 and the inner wall of the valve body, and further improve the squeezing effect between the inner triangular packing 4 and the outer wall of the valve stem 1, and further improve the sealing effect of the packing for sealing the valve stem 1.

[0040] As a preferred embodiment, on the basis of the above method, further, on the basis of taking the plane perpendicular to the central axis of the first pressing ring 5 as the first reference plane, the included angle between the first pressing surface 8 and the first reference plane is α, and the included angle between the second pressing surface 9 and the first reference plane is β, where the included angle α > 45°, and the included angle β > 45°.

[0041] Further, by making the included angle α > 45° and the included angle β > 45°, when the first pressing ring 5 and the second shaft sleeve 7 cooperate to extrude the outer triangular packing 3 and the inner triangular packing 4, the tightness of the contact between the inner triangular packing 4 and the outer wall of the valve stem 1 can be further improved, and the tightness of the contact between the outer triangular packing 3 and the inner wall of the valve body can be improved.

[0042] As a preferred embodiment, on the basis of the above method, further, the valve stem assembly further includes a second pressing ring 10, and the second pressing ring 10 is used to be stuck on the valve body. When the second pressing ring 10 is stuck on the valve body, the second pressing ring 10 abuts against the first pressing ring 5 to limit the first pressing ring 5;

[0043] The second pressing ring 10 is a three-opening ring.

[0044] Further, by providing the second pressing ring 10 and making the second pressing ring 10 a three-opening ring, the three-opening ring structure improves the convenience of installing the second pressing ring 10. After the second pressing ring 10 is stuck on the valve body, it is convenient to limit the first pressing ring 5, thereby improving the stability of the extrusion of the outer triangular packing 3 and the inner triangular packing 4.

[0045] Embodiment 2: On the basis of the technical solution of Embodiment 1, further, as shown in Figures 1-3 A sealing assembly 11 is provided on the second shaft sleeve 7. The sealing assembly 11 includes a first sealing ring 12 and a second sealing ring 13. The first sealing ring 12 is located on the outer wall of the second shaft sleeve 7, and the first sealing ring 12 is used to abut against the inner wall of the valve seat. The second sealing ring 13 is located on the inner wall of the second shaft sleeve 7, and the second sealing ring 13 is used to abut against the outer wall of the valve stem 1.

[0046] Further, by providing the first sealing ring 12 and the second sealing ring 13, so that the first sealing ring 12 abuts against the inner wall of the valve seat and the second sealing ring 13 abuts against the inner wall of the valve stem 1, to further improve the sealing effect of the valve stem 1, thereby further reducing the probability of medium leakage from the valve stem 1; in this application, the first sealing ring 12 and the second sealing ring 13 are O-shaped sealing rings, and the O-shaped sealing rings are equipped with retaining rings.

[0047] As a preferred embodiment, on the basis of the above method, further, a plurality of sealing assemblies 11 are provided on the second shaft sleeve 7, and the plurality of sealing assemblies 11 are distributed along the length direction of the second shaft sleeve 7.

[0048] As a preferred technical solution of the present application, a first channel 14 and a second channel 15 are provided on the second bushing 7. The first channel 14 communicates with the inner wall and the outer wall of the second bushing 7. The second channel 15 communicates with the first channel 14. The second channel 15 extends to an end face of the second bushing 7 for abutting against the outer triangular packing 3 or the inner triangular packing 4. A piston 16 is arranged in the second channel 15. The piston 16 can move relative to the second channel 15 so that the piston 16 is exposed or retracted into the second bushing 7. The piston 16 has an initial state. When the piston 16 is in the initial state, the piston 16 is not exposed from the second bushing 7.

[0049] Furthermore, by providing the first channel 14 and the second channel 15, when the ball valve is under high-pressure working conditions, there will be a situation where the medium flows towards the gap between the valve body and the valve stem 1. When the high-pressure medium flows to the first channel 14, part of the high-pressure medium can flow through the first channel 14 to the second channel 15 and push the piston 16 in the second channel 15, causing the piston 16 to move relative to the second channel 15 and gradually exposing the piston 16 from the second bushing 7, so as to push against the bottom of the corresponding outer triangular packing 3 or inner triangular packing 4, thereby further improving the tightness of the contact between the corresponding outer triangular packing 3 and the inner wall of the valve body, and / or further improving the tightness of the contact between the corresponding inner triangular packing 4 and the outer wall of the valve stem 1. And after the piston 16 is pushed, the space for the medium to flow in the second channel 15 increases, which can reduce the impact of the medium on the valve body, the valve stem 1 and the packing, thereby further improving the reliability of the packing for sealing the valve stem 1.

[0050] As a preferred implementation manner, on the basis of the above manner, further, when the piston 16 is in the initial state, the end face of the piston 16 is flush with the end face of the second bushing 7.

[0051] Furthermore, when the piston 16 is in the initial state, the end face of the piston 16 is flush with the end face of the second bushing 7. In this way, during the installation of the outer triangular packing 3, the inner triangular packing 4 and the first compression ring 5, when the first compression ring 5 and the second bushing 7 squeeze the outer triangular packing 3 and the inner triangular packing 4, it is convenient to make the end face of the second bushing 7 for contacting the outer triangular packing 3 and the inner triangular packing 4 flat, so as to further improve the squeezing effect of the first compression ring 5 and the second bushing 7 on the packing.

[0052] As a preferred implementation manner, on the basis of the above manner, further, the first channel 14 divides the second bushing 7 into a first bushing part and a second bushing part, and at least one sealing component 11 is provided on each of the first bushing part and the second bushing part.

[0053] Further, by providing at least one sealing assembly 11 on the first sleeve part and the second sleeve part, before the high-pressure medium flows to the first channel 14, at least one sealing assembly 11 can block the medium to prevent it from flowing towards the first channel 14. At the same time, after the high-pressure medium flows towards the first channel 14, at least one sealing assembly 11 can block the medium to prevent it from flowing towards the packing, thereby forming multiple layers of protection and further improving the sealing effect of the valve stem 1.

[0054] Embodiment 3: A fixed ball valve provided in this embodiment, see Figure 4 as shown, including the valve stem assembly as described above.

[0055] In this application, by providing the above valve stem assembly in the fixed ball valve, the probability of medium leakage from the valve stem 1 can be further reduced, and the reliability of the packing in sealing the valve stem 1 can be further improved.

[0056] The above embodiments are only used to illustrate the present invention and not to limit the technical solutions described in the present invention. Although this specification has described the present invention in detail with reference to the above embodiments, the present invention is not limited to the above specific embodiments. Therefore, any modification or equivalent replacement of the present invention; and all technical solutions and their improvements that do not depart from the spirit and scope of the present invention are covered by the scope of the claims of the present invention.

Claims

1. A valve stem assembly, characterized in that: It includes a valve stem, a thrust bearing, an outer triangular packing, an inner triangular packing and a first pressure ring, wherein the outer triangular packing and the inner triangular packing are both annular; The thrust bearing sleeve is arranged on the valve stem, and the thrust bearing comprises a first sleeve and a second sleeve, the first sleeve abuts against the valve stem, the outer triangular packing and the inner triangular packing are arranged on the second sleeve, a V-shaped groove is formed between the outer triangular packing and the inner triangular packing, the first pressure ring is placed in the V-shaped groove, and the first pressure ring squeezes the outer triangular packing and the inner triangular packing, so that the outer wall of the outer triangular packing abuts against the inner wall of the valve body, and the inner wall of the inner triangular packing abuts against the outer wall of the valve stem; In addition, along the direction from the thrust bearing to the first pressure ring, the degree to which the outer triangular filler and the inner triangular filler are squeezed by the first pressure ring gradually increases.

2. A valve stem assembly according to claim 1, characterized in that: The first pressure ring is a V-shaped pressure ring, which includes a first pressure surface and a second pressure surface. The first pressure surface and the second pressure surface cooperate to form a V-shaped structure. The first pressure surface is used to abut against the inner wall of the outer triangular filler, and the second pressure surface is used to abut against the outer wall of the inner triangular filler.

3. A valve stem assembly according to claim 2, characterized in that: On the basis of taking the plane perpendicular to the central axis of the first pressure ring as the first reference plane, the angle between the first pressure surface and the first reference plane is α, and the angle between the second pressure surface and the first reference plane is β, wherein the angle α>45°, and the angle β>45°.

4. A valve stem assembly according to claim 3, characterized in that: The valve stem assembly further includes a second pressing ring, which is used to be clamped on the valve body. When the second pressing ring is clamped on the valve body, the second pressing ring abuts against the first pressing ring to limit the position of the first pressing ring. The second pressure ring is a three-open ring.

5. A valve stem assembly according to claim 4, characterized in that: A sealing assembly is provided on the second sleeve, and the sealing assembly includes a first sealing ring and a second sealing ring. The first sealing ring is located on the outer wall of the second sleeve, and the first sealing ring is used to abut against the inner wall of the valve seat. The second sealing ring is located on the inner wall of the second sleeve, and the second sealing ring is used to abut against the outer wall of the valve stem.

6. A valve stem assembly according to claim 5, characterized in that: The second shaft sleeve is provided with a plurality of sealing components, and the plurality of sealing components are distributed along the length direction of the second shaft sleeve.

7. A valve stem assembly according to claim 6, characterized in that: The second sleeve is provided with a first channel and a second channel, the first channel is connected to the inner wall and the outer wall of the second sleeve, the second channel is connected to the first channel, the second channel extends to the end surface of the second sleeve for abutting against the outer triangular filler or the inner triangular filler, a piston is provided in the second channel, the piston can move relative to the second channel so that the piston is exposed or retracted to the second sleeve; the piston has an initial state, and when the piston is in the initial state, the piston is not exposed from the second sleeve.

8. A valve stem assembly according to claim 7, characterized in that: When the piston is in an initial state, the end surface of the piston is flush with the end surface of the second sleeve.

9. A valve stem assembly according to claim 8, characterized in that: The first channel divides the second sleeve into a sleeve part 1 and a sleeve part 2, and at least one sealing component is disposed on each of the sleeve part 1 and the sleeve part 2.

10. A fixed ball valve, characterized in that: A valve stem assembly comprising any one of claims 1-9.

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