A functional ball for a multiple switch bypass system

Abstract

This invention discloses a functional ball for a multiple-switch bypass system, comprising a main ball and a detachable mounting assembly. The mounting assembly includes a main seat and a counterweight mandrel, both locked to the main ball via oppositely helical threads, forming a dynamic self-locking anti-loosening structure during the lowering process. The counterweight mandrel is a hollow, adjustable structure with an internal counterweight column and spring to adapt to different well conditions and density requirements. A segmented locking cover is fitted around the mandrel, with a pre-curved bimetallic strip placed between them. When the ambient temperature reaches a preset value, the bimetallic strip undergoes a sudden change in curvature due to heat, generating radial expansion force, driving the locking cover segments to open. The barbs on its surface pierce the soft metal bushing on the inner wall of the main ball, achieving three-stage mechanical anchoring and sealing at high temperatures. After cooling, the bimetallic strip returns to its original position, and the locking cover retracts and unlocks. This solution combines the advantages of stable lowering, reliable sealing, and multiple reuse with temperature control, significantly improving the operational efficiency and safety of the bypass system.

Description

Technical Field

[0001] This invention belongs to the field of oil drilling and completion engineering technology, and more specifically, relates to a functional ball for a multiple-switch bypass system. Background Technology

[0002] In drilling operations, the repeated activation of the bypass system plays a crucial role and is a core technical means to cope with complex downhole conditions and dynamic construction needs. The main advantage of this system is its ability to intervene in the wellbore environment multiple times without interrupting the drilling process or requiring the drill string to be retrieved. Especially in emergencies such as severe lost circulation, the system can support operators in injecting high-concentration, large-particle plugging materials or performing cementing operations multiple times, thereby efficiently sealing the lost circulation zone and significantly reducing non-productive time (NPT) and operating costs.

[0003] As the core control element of a bypass system that is activated multiple times, the performance of the functional ball (also known as the valve opening ball) directly determines the reliability of the system. The functional ball is typically designed as a sphere with specific geometry and material properties. Its core function is to descend with the drilling fluid to the valve seat position at a predetermined depth, precisely controlling the opening and closing of the bypass channel through a setting action. In existing technologies, the deployment of the functional ball mainly relies on its own gravity to overcome fluid resistance, or on the power of the pumped fluid to push it to the target position. This passive deployment mechanism places extremely high demands on the physical properties of the functional ball.

[0004] However, existing technologies have significant shortcomings in the descent control of functional balls, primarily due to the contradiction between density matching and hydrodynamics. On the one hand, traditional functional balls, limited by their internal structural design, often have a low overall density and insufficient mass. On the other hand, the enormous buoyancy generated by drilling fluids (especially high-density drilling fluids) further offsets the effective weight of the functional ball. This "low mass, high buoyancy" characteristic results in slow speed and unstable trajectory of the functional ball during descent, even causing it to float at a certain point in the wellbore and fail to reach the predetermined setting depth. This problem is particularly prominent in complex wellbore structures or high-viscosity drilling fluid environments, easily leading to the functional ball getting stuck midway, missetting, or failing to set at all. This not only causes bypass system failure, forcing the operation to be interrupted for costly fishing or tripping operations, but may also trigger serious safety accidents such as well control loss and wellbore instability, greatly increasing the risks and uncertainties of drilling operations. Summary of the Invention

[0005] The purpose of this invention is to provide a functional ball for a multiple-switch bypass system, aiming to solve the problems of difficulty in sinking and inaccurate setting of functional balls in the prior art due to their low density and high buoyancy.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A functional ball for a multiple-switch bypass system, comprising:

[0008] The main sphere has a mounting groove; the mounting groove consists of a mounting part and a locking part from top to bottom; the inner wall of the mounting part is provided with a first internal thread.

[0009] The mounting assembly is detachably disposed in a mounting slot; the mounting assembly includes...

[0010] The main body has a first external thread on its side wall, which can be screwed into a first internal thread; the top of the main body has a first internal hexagonal groove.

[0011] A counterweight spindle is located at the bottom of the main body; the side wall of the counterweight spindle is provided with an installation section, and a pre-curled bimetallic strip is provided on the installation section;

[0012] The split-type locking cover is fixedly sleeved on the outside of the counterweight spindle; the pre-curved bimetallic strip is located inside the split-type locking cover. When the ambient temperature reaches the preset activation temperature, the pre-curved bimetallic strip is heated and undergoes a sudden curvature change, generating a radial expansion force, which drives the segments of the split-type locking cover to expand radially outward and abut against the inner wall of the mounting groove.

[0013] Furthermore, the counterweight spindle is rotatably mounted on the main body; a limiting annular groove is provided inside the main body; an annular protrusion is integrally provided on the upper part of the counterweight spindle; the annular protrusion is located in the limiting annular groove.

[0014] Furthermore, the segmented locking cover includes an integrally formed solid part and a segment part; the solid part is fixedly connected to the counterweight spindle.

[0015] Furthermore, the surface of the solid part is provided with a second external thread; the upper inner wall of the locking part is provided with a second internal thread that mates with the second external thread; and the upper end of the counterweight spindle is provided with a second internal hexagonal groove.

[0016] Furthermore, the second external thread has the opposite thread direction to the first external thread.

[0017] Furthermore, a soft metal bushing is fixedly provided on the inner wall of the locking part; and multiple barbed protrusions are provided on the surface of the segmented locking cover.

[0018] Furthermore, the counterweight spindle is configured as a hollow structure with an open bottom and a counterweight cavity inside; a counterweight column is placed inside the counterweight cavity; a cap is threaded to the bottom of the counterweight cavity; and an abutment spring is provided between the cap and the counterweight column.

[0019] Furthermore, the pre-curled bimetallic strip (4) is composed of two layers of metal materials with different coefficients of thermal expansion, including an active layer and a passive layer. The active layer material is a nickel-chromium-manganese high-temperature bimetallic alloy (3J57 or 3J58), and the passive layer material is an Invar alloy or a super Invar alloy. The preset activation temperature ranges from 80°C to 200°C and can be set by adjusting the thickness ratio of the bimetallic strip, the pre-curled radius, and the heat treatment process.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) By setting the counterweight mandrel as a hollow adjustable counterweight structure, it not only supports the selection of integral mandrels of different densities according to needs, but also effectively realizes the rapid replacement mechanism of the counterweight column. Operators can quickly add, remove or replace the internal high-density counterweight column through the bottom cover, and use the buffer spring to absorb the impact, thereby making fine dynamic adjustments to the overall mass of the functional ball. This completely overcomes the obstacle of huge buoyancy, ensuring that the functional ball can rely on its own weight to quickly and stably pass through long-distance wellbore and accurately reach the predetermined valve seat, greatly reducing the well control risk and non-production time caused by delivery failure.

[0022] (2) A reverse "double-helix locking" mechanism is adopted. Before entering the well and during the descent phase, the counterweight mandrel and the main ball are rigidly interlocked through two sets of precisely matched helical thread structures. This double-locking design provides extremely high axial tensile strength and torsional stability, effectively preventing the counterweight mandrel from accidentally loosening or falling out due to fluid scouring, wellbore vibration, or long-term descent. This mechanism ensures that the internal thermal actuation mechanism is always in a safe and complete ready state before reaching the activation depth, laying a solid foundation for the reliability of subsequent actions.

[0023] (3) Through the synergistic effect of the two threaded connections and the mechanical locking of the valve body, the installation stability of the counterweight mandrel under extreme high temperature and high pressure environments is significantly enhanced: the first two locking stages adopt a unique "double helix" thread structure, which double rigidly interlocks the counterweight mandrel and the main ball during the normal temperature placement and transportation stages, effectively preventing the mandrel from loosening due to fluid impact or vibration, and ensuring that the tool reaches the predetermined depth in an intact state; the third locking stage is activated during the high temperature activation stage, using the huge thrust generated by the intense radial expansion of the pre-curved bimetallic strip due to heat to forcefully drive the segmented locking cover to expand outward, so that the barbed structure on its surface is strongly embedded into the soft metal sleeve to form a rigid mechanical engagement. These three mechanisms are interlocked, which not only efficiently transforms the small thermal deformation into a strong radial anchoring force to resist the axial thrust generated by the high pressure difference, but also fundamentally eliminates the risk of slippage of the functional ball under complex working conditions, and comprehensively ensures the sealing safety and structural stability of the bypass system during long-term operation. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a functional sphere structure;

[0025] Figure 2 Exploded view of the functional sphere structure;

[0026] Figure 3 This is an exploded view of the internal structure of the functional sphere.

[0027] Figure 4 This is a schematic diagram of the component structure.

[0028] Figure 5 This is a schematic diagram of the internal structure of the installation components;

[0029] Figure 6 This is a schematic diagram of a pre-curled bimetallic strip structure.

[0030] In the diagram, the correspondence between component names and drawing numbers is as follows:

[0031] Main ball 1, mounting groove 10, mounting part 11, locking part 12, first internal thread 13, mounting assembly 2, main seat 21, first external thread 201, first internal hexagonal groove 2102, counterweight spindle 22, mounting section 2203, pre-curled bimetallic strip 4, split locking cover 23, limiting ring groove 2101, annular protrusion 2201, solid part 2301, flap part 2302, second external thread 202, second internal thread 14, second internal hexagonal groove 2202, soft metal bushing 3, barbed protrusion 2303, counterweight cavity 2200, counterweight column 51, cover 53, abutment spring 52. Detailed Implementation

[0032] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0033] like Figures 1-6 As shown, this invention provides a functional ball for a multiple-switch bypass system, aiming to solve the problems of existing delivery tools having difficulty sinking in high-density drilling fluids, the non-reusability of thermal braking mechanisms, and insufficient locking reliability under high temperature and pressure. The specific structure and working principle of this embodiment are as follows:

[0034] The core carrier of this functional sphere is the main sphere 1, which has an axially oriented mounting groove 10 inside. Structurally, the mounting groove 10 is divided into an upper mounting part 11 and a lower locking part 12. To create the first layer of safety barrier, the inner wall of the mounting part 11 is machined with a first internal thread 13, which serves as the basic interface for subsequent components to be screwed in.

[0035] In this solution, the mounting component 2 is detachably installed in the mounting slot 10. Its core lies in the design of the counterweight spindle 22. This solution provides two implementation modes to adapt to different working conditions:

[0036] Basic Solution: The counterweight mandrel 22 is designed as a series of standardized solid or semi-solid components with different outer diameters, lengths, or material densities. Before field operations, technicians calculate the required buoyancy compensation based on the drilling fluid specific gravity of the target well section and directly select a counterweight mandrel body of matching mass from the spare parts library for installation. This solution has a simple structure, extremely high strength, and is suitable for operational scenarios with relatively uniform well conditions and minimal density variations.

[0037] Preferred Solution: To cope with complex and variable downhole density gradients, the counterweight mandrel 22 is preferably designed as a hollow cavity structure with an open bottom, forming a counterweight cavity 2200 inside. Within the counterweight cavity 2200, operators can flexibly insert different numbers and materials of high-density counterweight columns 51. A cap 53 is threadedly connected to the bottom of the counterweight cavity 2200, enabling rapid access and fine-tuning of the counterweight columns, allowing for continuous mass adjustment without replacing the entire mandrel. Simultaneously, a retaining spring 52 is installed between the cap 53 and the lowest counterweight column 51. When the functional ball is lowered at high speed in the wellbore and impacts the valve seat, the retaining spring 52 effectively absorbs the impact energy, preventing the counterweight column from shifting, deforming, or damaging its internal structure due to severe vibration. This preferred solution eliminates the need to stock a large number of mandrels of different specifications on-site; a single set of mandrels with several counterweight columns is sufficient to cover a wide density range. This ensures that the functional ball can obtain sufficient net weight to overcome buoyancy in drilling fluids of any specific gravity, and quickly and stably reach the predetermined depth, significantly reducing the risk of deployment failure and non-productive time.

[0038] To ensure the absolute stability of the counterweight spindle 22 during the lowering process, this solution adopts a unique "double helix locking" structure, which forms the first two levels of locking defense.

[0039] The first-stage locking mechanism consists of a main body 21 in the mounting assembly 2, whose side wall has a first external thread 201 that engages with the first internal thread 13 of the mounting portion 11 of the main ball 1. The top of the main body 21 has a first internal hexagonal groove 2102 for easy screwing in of tools.

[0040] The second-stage locking mechanism consists of a counterweight spindle 22 that passes through and rotatably mounts on the main body 21. The upper end of the counterweight spindle 22 is provided with a second internal hexagonal groove 2202, and the outer solid part 2301 of the spindle is machined with a second external thread 202, which engages with the second internal thread 14 on the upper part of the locking part 12 of the main ball 1.

[0041] Preferably, the second external thread 202 has the opposite rotation direction to the first external thread 201. This design ensures that in the complex fluid scouring and vibration environment downhole, any rotational torque attempting to loosen one stage of the thread will cause the other stage of the thread to tighten further, thus creating a self-reinforcing interlocking effect.

[0042] In this design, to enable relative rotation between the counterweight spindle 22 and the main body 21, an annular protrusion 2201 is integrally formed on the upper part of the counterweight spindle 22, which is located in the limiting annular groove 2101 inside the main body 21. This structure allows the counterweight spindle 22 to rotate independently relative to the main body 21 to complete the locking of the second-stage thread, while restricting axial movement and eliminating the cumulative effect of frictional torque on the internal precision mechanism during the lowering process. The use of double helical engagement provides extremely high axial tensile strength and torsional resistance, eliminating the risk of the counterweight spindle accidentally loosening and falling out before reaching the activation depth, and ensuring the structural integrity of the tool.

[0043] The third-level locking and core action actuator of this solution is located deep within the locking section 12: specifically, a pre-curled bimetallic strip 4 is fitted onto the mounting section 2203 of the counterweight spindle 22. The pre-curled bimetallic strip 4 is the core driving element of the entire functional ball thermally actuated locking mechanism. Its working principle is based on the difference in thermal expansion coefficients of different metal materials and the geometric amplification effect of the pre-curled structure. This component is made of two layers of metal sheets with completely different physical properties through high-temperature metallurgical composite: one layer is the active layer, which uses a nickel-chromium-manganese high-temperature bimetallic alloy (such as 3J57 or 3J58) with an extremely high thermal expansion coefficient; the other layer is the passive layer, which uses Invar alloy or super Invar alloy, with an extremely low thermal expansion coefficient, even close to zero in a certain temperature range. At room temperature, the bimetallic strip is pre-processed into a tightly curled shape (spiral or C-shaped) and housed in the inner space of the split locking cover 23. At this time, its radial dimension is small and it does not exert external force, ensuring that the flow channel of the functional ball is unobstructed and without interference during the lowering process.

[0044] When the functional sphere enters the high-temperature downhole environment with the drilling fluid, and the surrounding temperature gradually rises to the preset activation temperature range (80℃ to 200℃), the bimetallic strip begins to exhibit a significant thermodynamic response. Because the linear expansion of the active layer material after heating is much greater than that of the passive layer, and the two layers are firmly bonded together and cannot freely expand or contract, this huge difference in expansion will generate enormous internal stress at the material interface. To release this stress, the bimetallic strip will inevitably bend and deform towards the side with the smaller coefficient of expansion (i.e., the passive layer side). For the pre-curled structure in this scheme, this bending deformation manifests as a sharp decrease in the radius of curvature. As the temperature rises, the originally tightly curled bimetallic strip attempts to flatten or expand its curl radius, thereby generating a strong radial expansion force.

[0045] The radial force generated by thermal deformation is transmitted to the external segmented locking cover 23 through direct contact. Due to the high stiffness and large deformation of the bimetallic strip, the thrust it generates is sufficient to overcome the elastic resistance of the locking cover segments, forcibly driving the segments to expand radially outwards significantly. At this time, the barbed protrusions 2303 on the surface of the locking cover, under the action of huge thrust, pierce into the soft metal bushing 3 on the inner wall of the main ball with extremely high pressure, forming a deep plastic deformation engagement, thereby achieving an efficient conversion from "thermal energy" to "mechanical anchoring force". Once the temperature drops, the bimetallic strip contracts and returns to its initial curled state, the radial thrust disappears, the locking cover resets under the action of elastic restoring force, the barbs retract, and the locking is unlocked. By precisely adjusting the thickness ratio of the active layer to the passive layer, the initial radius of the pre-curling, and the heat treatment process, the activation temperature point and output thrust of the bimetallic strip can be precisely set, making it perfectly adaptable to the geothermal gradient at different well depths, ensuring that the functional ball does not malfunction before reaching the predetermined depth, and can be reliably set instantly after reaching the depth.

[0046] The split-type locking cover 23 is fixedly sleeved on the outside of the counterweight spindle 22, and includes an integrally formed solid part 2301 and a petal part 2302. The solid part 2301 is locked to the main ball through the aforementioned second external thread 202. The pre-curved bimetallic strip 4 is located inside the split-type locking cover 23. When the functional ball circulates with the drilling fluid or waits at rest, and the ambient temperature reaches the preset activation temperature, the pre-curved bimetallic strip 4 undergoes a sudden curvature change, generating a huge radial expansion force. This force forcibly pushes the petal part 2302 of the split-type locking cover 23 to expand radially outward.

[0047] To increase the locking force of the valve body 2302, a soft metal bushing 3 is pre-fixed to the inner wall of the locking part 12. When the valve body 2302 expands, multiple barbed protrusions 2303 distributed on its surface forcefully penetrate into the soft metal bushing 3, forming a rigid mechanical engagement.

[0048] The first two stages of threaded locking ensure safe transport and lowering, while the third stage of thermo-mechanical locking achieves ultimate anchoring at high temperatures. The bimetallic strip amplifies minute thermal deformation into powerful radial thrust. Combined with the interference fit between the barbs and the soft metal, it generates a huge radial locking force, sufficient to resist the axial thrust generated by the downhole high pressure differential, fundamentally eliminating the risk of slippage and ensuring long-term sealing safety after the bypass system is opened.

[0049] The operating procedure for this function ball is as follows:

[0050] Ground installation and commissioning

[0051] First, technicians need to collect data on drilling fluid density, geothermal gradient, and pressure at the setting position of the target well section to calculate the net weight required for the functional ball to overcome buoyancy. If the basic scheme is adopted, a solid counterweight mandrel body of the corresponding mass is directly selected; if the preferred hollow adjustable scheme is adopted, the cap at the bottom of the counterweight mandrel is unscrewed, the calculated number of high-density counterweight columns are placed into the counterweight cavity, and the cap is tightened again after the bottom abutment spring provides buffer protection.

[0052] Simultaneously rotate the two internal hexagonal slots. Through the internal hexagonal slot on the top of the main body, screw it into the mounting part of the main ball in the first direction of rotation (e.g., clockwise) to complete the first stage of threaded locking. Then, through the internal hexagonal slot on the top of the counterweight mandrel, rotate the mandrel in the opposite direction of rotation (e.g., counterclockwise) to engage its second external thread with the internal thread of the locking part of the main ball until the preset torque is reached. This reverse thread design ensures that the two stages of locking do not interfere with each other in subsequent operations and create a self-reinforcing effect. After installation, check whether the split locking cover is in the retracted state, confirm that the pre-coiled bimetallic strip is undamaged, and record the total counterweight, torque value, and activation temperature. At this point, the functional ball is ready for well deployment.

[0053] It is worth noting that: when rotating, a hollow hexagonal socket is required to rotate the first internal hexagonal slot; then a hexagonal screw is passed through the hollow hexagonal socket to rotate the second internal hexagonal slot; at this time, it is necessary to rotate in the opposite direction simultaneously to achieve stable screwing of the installation component.

[0054] Underground delivery and lowering process

[0055] After the functional ball is inserted into the wellhead, it enters the lowering stage relying on its own weight and fluid transport. During this stage, the first two stages of mechanical locking mechanisms play a crucial role. Carried by the drilling fluid, the functional ball descends rapidly along the tubing string, enduring severe fluid scouring, tubing vibration, and potential rotational torque. Thanks to the "double-helix reverse locking" structure established during surface assembly, any rotational torque attempting to loosen one thread automatically causes the other thread to tighten further, creating a dynamic self-locking effect and eliminating the risk of the counterweight mandrel accidentally loosening or falling off during lowering. The optimized counterweight system ensures the functional ball has sufficient net weight to overcome the buoyancy resistance of the high-density drilling fluid, allowing it to stably and quickly traverse long wellbore distances and accurately reach the predetermined bypass valve seat. At the moment of placement, the internal springs of the counterweight chamber effectively absorb impact energy, preventing displacement or damage to the internal counterweight column due to severe vibration, ensuring the tool enters the next activation stage in a complete and ready state.

[0056] High-temperature activation and setting / anchoring process

[0057] When the functional ball reaches the predetermined depth and circulates with the drilling fluid or remains stationary, the ambient temperature gradually rises to the preset activation threshold (80℃ to 200℃), triggering the third-stage thermo-actuated locking mechanism. At this time, the pre-coiled bimetallic strip fitted on the counterweight mandrel undergoes a sudden physical change due to heat, violently expanding radially from a coiled state, generating a huge expansion thrust. This thrust acts directly on the inner wall of the segmented locking cover, forcibly driving its segments to expand radially outward, causing the barbs on the surface of the segments to forcefully pierce into the soft metal bushing on the inner wall of the main ball. This process achieves an efficient transformation from thermal deformation to mechanical anchoring, forming an irreversible (or reversible under specific conditions) rigid mechanical engagement. Thus, the functional ball completes the three-stage locking closed loop from "double-threaded anti-loosening" to "thermally actuated radial anchoring," capable of withstanding the axial thrust generated by the huge pressure difference downhole, ensuring no slippage occurs during bypass system opening and subsequent high-pressure operations, and guaranteeing sealing safety.

[0058] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A functional ball for a multiple-switch bypass system, characterized in that, include: The main sphere (1) has an installation groove (10) on it; the installation groove (10) consists of an installation part (11) and a locking part (12) from top to bottom; the inner wall of the installation part (11) is provided with a first internal thread (13). Mounting assembly (2), which is detachably disposed in mounting slot (10); the mounting assembly (2) includes The main body (21) has a first external thread (201) on its side wall, which can be screwed into a first internal thread (13); the top of the main body (21) has a first internal hexagonal groove (2102). A counterweight spindle (22) is provided at the bottom of the main body (21); the side wall of the counterweight spindle (22) is provided with an installation section (2203), and a pre-curved bimetallic strip (4) is provided on the installation section (2203); The split locking cover (23) is fixedly sleeved on the outside of the counterweight spindle (22); the pre-curved bimetallic strip (4) is located inside the split locking cover (23). The pre-curved bimetallic strip (4) is composed of two layers of metal materials with different thermal expansion coefficients. When the ambient temperature reaches the preset activation temperature, the pre-curved bimetallic strip (4) is heated and undergoes a sudden curvature change to generate radial expansion force, which drives the petals of the split locking cover (23) to expand radially outward and abut against the inner wall of the mounting groove (10). The split locking cover (23) includes an integrally formed solid part (2301) and a petal part (2302); the solid part (2301) is fixedly connected to the counterweight spindle (22); The surface of the solid part (2301) is provided with a second external thread (202); the upper inner wall of the locking part (12) is provided with a second internal thread (14) that mates with the second external thread (202); the upper end of the counterweight spindle (22) is provided with a second internal hexagonal groove (2202). The second external thread (202) has the opposite thread direction to the first external thread (201).

2. The functional ball for a multiple-switch bypass system as described in claim 1, characterized in that: The counterweight spindle (22) is rotatably mounted on the main body (21); the main body (21) is provided with a limiting ring groove (2101); the upper part of the counterweight spindle (22) is integrally provided with an annular protrusion (2201); the annular protrusion (2201) is located in the limiting ring groove (2101).

3. The functional ball for a multiple-switch bypass system as described in claim 1, characterized in that: The inner wall of the locking part (12) is fixedly provided with a soft metal bushing (3); the surface of the petal of the split locking cover (23) is provided with multiple barbed protrusions (2303).

4. A functional ball for a multiple-switch bypass system as described in claim 1, characterized in that: The counterweight spindle (22) is a hollow structure with an open bottom and a counterweight cavity (2200) inside; a counterweight column (51) is placed inside the counterweight cavity (2200); a cover (53) is threaded to the bottom of the counterweight cavity (2200); and an abutment spring (52) is provided between the cover (53) and the counterweight column (51).

5. A functional ball for a multiple-switch bypass system as described in claim 1, characterized in that: The pre-curled bimetallic strip (4) includes an active layer and a passive layer. The active layer material is a nickel-chromium-manganese high-temperature bimetallic alloy, and the passive layer material is an Invar alloy or a super Invar alloy. The preset activation temperature ranges from 80°C to 200°C and is set by adjusting the thickness ratio of the bimetallic strip, the pre-curled radius, and the heat treatment process.

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