A mechanical device for replacing wellhead master valve under pressure

Abstract

The utility model relates to the technical field of oil and natural gas exploration and exploitation, especially to a kind of device of mechanical type replacement wellhead master control valve under pressure, including pull rod, locking screw, sending-in rod, plug, pull rod nut, expansion seal rubber tube and anti-rotation limiting piece;Pull rod one end is equipped with accommodating cavity, the other end is connected with plug;Locking screw two ends are respectively with the inner wall of sending-in rod, the inner wall of accommodating cavity thread cooperation connection, and the rotation direction of locking screw two ends thread is opposite;Anti-rotation limiting piece is used to limit the axial movement of sending-in rod and prevent sending-in rod from circumferential rotation;The end of sending-in rod away from anti-rotation limiting piece is connected with the inner wall of pull rod nut and the outer wall of accommodating cavity simultaneously, and can limit pull rod circumferential rotation;The inner wall of pull rod nut and the outer wall of accommodating cavity form sliding sealing cooperation connection between them. Through the device, the accurate adjustment and stable maintenance of sealing pressure can be realized under high pressure working condition, and the expansion seal structure is reliable and convenient to operate.

Description

Technical Field

[0001] This utility model relates to the field of oil and gas exploration and development technology, and in particular to a mechanical device for replacing the wellhead main control valve under pressure. Background Technology

[0002] After an oil and gas well is put into production, the integrity and operational flexibility of the wellhead gate valves at the production tree are prerequisites and key factors for ensuring safe oil and gas production. If the wellhead gate valves at the production tree have hidden dangers such as poor sealing or leakage, and these cannot be eliminated in a timely and effective manner, it can easily lead to dangerous situations that are difficult to handle. If such hidden dangers exist in sulfur-containing wells, they will have a huge impact. In recent years, hidden dangers at the production tree wellhead have become increasingly prominent. After years of production and exploitation in various oil and gas fields, many production wells, old wells, and shut-in wells have experienced hidden dangers such as corrosion, leakage, and poor sealing at their production tree gate valves. A large number of old wells that do not have production capacity have been shut in for a long time, with gate valves that have not been activated for many years, are severely corroded, and cannot be opened or closed. The pressure inside the well is unknown, posing a significant safety and environmental risk. It is necessary to replace wellhead gate valves with hidden dangers in a timely manner.

[0003] In existing technologies, hydraulic expansion sealing is generally used. A hydraulic device is used to deliver the plug to the predetermined blocking position. The hydraulic device is then activated to inject hydraulic oil or other fluid into the plug, causing it to expand and seal. This seals the well passage, isolating the pressure inside the well and allowing replacement of the potentially hazardous main control valve. However, this type of sealing structure mostly involves hydraulic insertion and hydraulic expansion sealing, which carries risks such as hydraulic passage blockage and hydraulic control failure. If hydraulic passage blockage or hydraulic control failure occurs during the gate valve replacement process, it is highly likely that the plug will not expand properly or will suddenly unseal, creating a dangerous situation that is difficult to handle.

[0004] In the prior art, a Chinese invention patent document with publication number CN111878020A and publication date of November 3, 2020 has been proposed. The technical solution disclosed in this patent document is as follows: a pressure-operated valve changing tool and method, including a column assembly connected to a large four-way flange at the wellhead, a plugging rod connected to the upper part of the column assembly through a straightening beam, the plugging rod being inserted into a hydraulic cylinder assembly, the plugging rod including a plug, the upper part of the plug being connected to a movable connecting assembly through a plug upper connector, a piston rod being connected to the upper part of the movable connecting assembly, a central rod being inserted through the central hole of the upper part of the plug, the central hole of the plug upper connector, the central hole of the movable connecting assembly and the central hole of the piston rod, the free end of the central rod passing through the end of the piston rod, and the end of the piston rod being fixed to the central rod by a fixing nut and a central rod pressure cap.

[0005] In practical use, the above-mentioned technical solution uses the linear movement of the central rod to drive the plug to move synchronously, ultimately applying axial pressure to the sealing sleeve to achieve a seal. This method has the following problems: the central rod needs to overcome the reaction force between the wellhead medium pressure and the sealing sleeve. If manual operation is relied upon, the operator's workload is extremely high; if hydraulic drive is relied upon, the matching relationship between the "hydraulic system output pressure" and the "wellhead pressure" needs to be precisely coordinated through the hydraulic control console—ensuring that the driving force is sufficient to push the central rod to complete the seal, while preventing sudden pressure increases that could overload the equipment or damage the sealing structure. Under high-pressure conditions, pressure control becomes significantly more difficult, and the force transmission path is long, with high losses and low transmission efficiency. Summary of the Invention

[0006] To solve the above-mentioned technical problems, this utility model proposes a mechanical device for replacing the wellhead main control valve under pressure, which can achieve precise adjustment and stable maintenance of sealing pressure under high pressure conditions. The expansion seal structure is reliable and easy to operate.

[0007] This utility model is achieved by adopting the following technical solution: A mechanical device for replacing a wellhead main control valve under pressure includes a pull rod, a locking screw, an insert rod, a plug, a pull rod nut, an expansion seal sleeve, and an anti-rotation limiting component. The locking screw is disposed inside the insert rod. One end of the pull rod has a receiving cavity, and the other end is connected to the plug. Both ends of the locking screw are threadedly connected to the inner wall of the insert rod and the inner wall of the receiving cavity, respectively, and the threads at both ends of the locking screw have opposite directions of rotation. The anti-rotation limiting component is used to limit the axial movement of the insert rod and prevent the insert rod from rotating circumferentially. The end of the insert rod away from the anti-rotation limiting component is connected to both the inner wall of the pull rod nut and the outer wall of the receiving cavity, and the connection between the insert rod and the outer wall of the receiving cavity restricts the circumferential rotation of the pull rod. The inner wall of the pull rod nut and the outer wall of the receiving cavity form a sliding seal connection. When the locking screw is rotated, under the constraint of the anti-rotation limiting component, the axial movement and rotational movement of the locking screw itself can exert a dual force on the plug.

[0008] It also includes a vent flange for connection to the flange of the valve to be replaced, the vent flange being connected to the feed rod via a hollow sealing sleeve.

[0009] The sealing sleeve is connected to the vent flange by a thread.

[0010] A sealing ring is also provided between the sealing sleeve and the vent flange.

[0011] The sealing sleeve and the feed rod are connected by a sliding sealing fit.

[0012] A pressure gauge is also installed on the vent flange.

[0013] The pull rod nut and the feed rod are connected by threads.

[0014] A sealing ring is also provided between the pull rod nut and the feed rod.

[0015] The plug and the pull rod are connected by threads.

[0016] The end face of the plug is provided with a screw hole for slab-slab connection.

[0017] Compared with the prior art, the beneficial effects of this utility model are as follows: 1. In this utility model, the locking screw forms a dual tension through "rotation driving the pull rod to move axially + its own axial movement to apply tension". Based on a reliable and simple mechanical structure, it can solve the problems existing in the technical solution of using the linear movement of the central rod to drive the plug to apply pressure and seal.

[0018] Specifically, this invention utilizes threaded transmission to generate greater axial compressive force under the same operating conditions, enabling the expansion sealing sleeve to achieve a greater radial expansion, thus meeting the sealing requirements of high-pressure wellheads (such as deep and ultra-deep wells). The dual tension is based on rigid coupling of mechanical transmission; the rotation angle of the locking screw forms a strict proportional relationship with its own axial displacement and the axial displacement of the pull rod (determined by the thread parameters). The output of the compressive force exhibits a "linear and stable" characteristic: for every fixed rotation angle, the superposition increment of the dual tension is constant, the compressive force on the expansion sealing sleeve increases uniformly without instantaneous fluctuations, resulting in a more stable compressive effect. Furthermore, it can precisely match the expansion amount required by the expansion sealing sleeve under different wellhead pressures, avoiding overpressure or underpressure.

[0019] Furthermore, this invention utilizes the static friction between the threads to prevent reverse rotation, thus maintaining continuous pressure on the expansion seal cylinder. Through the "deceleration and force amplification" principle of the threads, the operator's rotational force (or the rotational torque of a small drive device) can be converted into a greater axial compressive force, significantly reducing the operational difficulty and labor intensity in high-pressure scenarios.

[0020] 2. In this utility model, the vent flange facilitates better installation of the device.

[0021] 3. The sealing sleeve and the vent flange, as well as the tie rod nut and the feed rod, are all connected by threaded sealing rings. The sealing sleeve and the feed rod, as well as the inner wall of the tie rod nut and the outer wall of the receiving cavity, are connected by sliding sealing fits. This enables multiple seals, provides a high safety factor, and the sealing pressure rating can reach 70MPa.

[0022] 4. A pressure gauge is also provided on the vent flange to facilitate intuitive judgment of whether pressure has been raised.

[0023] 5. The end face of the plug is also provided with a screw hole for sliding across the seam, which can serve to limit the position and prevent the screw from coming off. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a schematic diagram of the sealing tool in this utility model; Figure 2 This is a schematic diagram of the operating state of the pressure-changing valve equipment in this utility model. Figure 1 ; Figure 3 This is a schematic diagram of the operating state of the pressure-changing valve equipment in this utility model. Figure 2 ; Marked in the image: 1. Plug, 2. Expansion sealing sleeve, 3. Tie rod, 4. Tie rod nut, 5. Vent flange, 6. Feed rod, 7. Sealing sleeve, 8. Locking screw, 9. Anti-rotation limiter, 10. Fixed beam, 11. Fixed screw, 12. Anti-push screw, 13. Locking nut, 14. Anti-push beam, 15. Locking nut, 16. Sealing ring. Detailed Implementation

[0025] Example 1 As a basic embodiment of this utility model, this utility model includes a mechanical device for replacing the main control valve of a wellhead under pressure, comprising a pull rod 3, a locking screw 8, an insertion rod 6, a plug 1, an anti-rotation limiting component 9, a pull rod nut 4, and an expansion sealing sleeve 2. The locking screw 8 is disposed inside the insertion rod 6. One end of the pull rod 3 has a receiving cavity, and the other end is connected to the plug 1. Both ends of the locking screw 8 are threadedly connected to the inner wall of the insertion rod 6 and the inner wall of the receiving cavity, respectively, and the threads at both ends of the locking screw 8 have opposite directions of rotation. The anti-rotation limiting component 9 is used to limit the axial movement of the insertion rod 6 and prevent the insertion rod 6 from rotating circumferentially. The end of the insertion rod 6 away from the anti-rotation limiting component 9 is connected to both the inner wall of the pull rod nut 4 and the outer wall of the receiving cavity, and the connection between the insertion rod 6 and the outer wall of the receiving cavity restricts the pull rod 3 from rotating circumferentially. The inner wall of the pull rod nut 4 and the outer wall of the receiving cavity form a sliding seal connection.

[0026] When the locking screw 8 is rotated, under the constraint of the anti-rotation limiting member 9, the locking screw 8 moves axially away from the end of the plug 1. The axial linear motion of the locking screw 8 is transmitted to the plug 1 through the pull rod 3. At the same time, due to the threaded engagement between the locking screw 8 and the receiving cavity, the rotational motion of the locking screw 8 is converted into the linear motion of the plug 1 axially toward the expansion sealing cylinder 2 through the pull rod 3. Through the double pulling force on the plug 1, the plug 1 applies a better axial compressive force to the expansion sealing cylinder 2.

[0027] Example 2 In a preferred embodiment of this utility model, the present utility model includes a mechanical device for replacing the wellhead main control valve under pressure, comprising a pull rod 3, a locking screw 8, an insertion rod 6, a plug 1, an anti-rotation limiting component 9, a pull rod nut 4, an expansion sealing sleeve 2, and a vent flange 5. The vent flange 5 and the insertion rod 6 are connected by a hollow sealing sleeve 7. Specifically, the sealing sleeve 7 and the vent flange 5 are connected by threads, and the sealing sleeve 7 and the insertion rod 6 are connected by a sliding sealing fit. The locking screw 8 is disposed inside the insertion rod 6.

[0028] One end of the pull rod 3 has a receiving cavity, and the other end is connected to the plug 1. The two ends of the locking screw 8 are threadedly connected to the inner wall of the feeding rod 6 and the inner wall of the receiving cavity, respectively, with the threads at both ends of the locking screw 8 rotating in opposite directions. The anti-rotation limiting member 9 is used to limit the axial movement of the feeding rod 6 and prevent circumferential rotation of the feeding rod 6. The end of the feeding rod 6 away from the anti-rotation limiting member 9 is simultaneously connected to the inner wall of the pull rod nut 4 and the outer wall of the receiving cavity, and the connection between the feeding rod 6 and the outer wall of the receiving cavity restricts circumferential rotation of the pull rod 3. The inner wall of the pull rod nut 4 and the outer wall of the receiving cavity form a sliding seal connection.

[0029] When the locking screw 8 is rotated, under the constraint of the anti-rotation limiting member 9, the locking screw 8 moves axially away from the end of the plug 1. The axial linear motion of the locking screw 8 is transmitted to the plug 1 through the pull rod 3. At the same time, due to the threaded engagement between the locking screw 8 and the receiving cavity, the rotational motion of the locking screw 8 is converted into the linear motion of the plug 1 axially toward the expansion sealing cylinder 2 through the pull rod 3. Through the double pulling force on the plug 1, the plug 1 applies a better axial compressive force to the expansion sealing cylinder 2.

[0030] Example 3 In another preferred embodiment of this utility model, the utility model includes a mechanical device for replacing the wellhead main control valve under pressure, comprising a pull rod 3, a locking screw 8, an insertion rod 6, a plug 1, an anti-rotation limiting component 9, a pull rod nut 4, and an expansion sealing sleeve 2. The locking screw 8 is disposed inside the insertion rod 6. One end of the pull rod 3 has a receiving cavity, and the other end is connected to the plug 1. Specifically, the plug 1 and the pull rod 3 are connected by threads, and the end face of the plug 1 has a threaded screw hole.

[0031] The locking screw 8 has two ends threadedly connected to the inner wall of the feeding rod 6 and the inner wall of the receiving cavity, respectively, with the threads at both ends of the locking screw 8 rotating in opposite directions. The anti-rotation limiting member 9 is used to limit the axial movement of the feeding rod 6 and prevent the feeding rod 6 from rotating circumferentially. The end of the feeding rod 6 away from the anti-rotation limiting member 9 is connected to both the inner wall of the pull rod nut 4 and the outer wall of the receiving cavity, and the connection between the feeding rod 6 and the outer wall of the receiving cavity restricts the circumferential rotation of the pull rod 3. Specifically, the pull rod nut 4 and the feeding rod 6 are threadedly connected, and a sealing ring 16 is provided between the pull rod nut 4 and the feeding rod 6. The inner wall of the pull rod nut 4 and the outer wall of the receiving cavity form a sliding sealing fit connection.

[0032] When the locking screw 8 is rotated, under the constraint of the anti-rotation limiting member 9, the locking screw 8 moves axially away from the end of the plug 1. The axial linear motion of the locking screw 8 is transmitted to the plug 1 through the pull rod 3. At the same time, due to the threaded engagement between the locking screw 8 and the receiving cavity, the rotational motion of the locking screw 8 is converted into the linear motion of the plug 1 axially toward the expansion sealing cylinder 2 through the pull rod 3. Through the double pulling force on the plug 1, the plug 1 applies a better axial compressive force to the expansion sealing cylinder 2.

[0033] Example 4 As another preferred embodiment of this utility model, this utility model includes a mechanical device for replacing the wellhead main control valve under pressure, as described in the attached specification. Figure 1 The sealing tool includes a pull rod 3, an insertion rod 6, a pull rod nut 4, a plug 1, an expansion sealing tube 2, a locking screw 8, a venting flange 5, and an anti-rotation limiting component 9. The end of the insertion rod 6 near the anti-rotation limiting component 9 has two symmetrical keyways, and one end of the anti-rotation limiting component 9 has two symmetrical internal keys for engaging with the keyways. This structural design allows the anti-rotation limiting component 9 to restrict the axial movement of the insertion rod 6 and prevent circumferential rotation of the insertion rod 6.

[0034] The vent flange 5 is connected to the flange of the valve to be replaced by double-ended bolts, and is connected to the feed rod 6 by a hollow sealing sleeve 7. Specifically, the sealing sleeve 7 and the vent flange 5 are connected by threads and sealed by O-rings 16. The sealing sleeve 7 and the feed rod 6 are connected by a sliding seal. More specifically, two O-rings 16 are provided between the sealing sleeve 7 and the feed rod 6 to achieve a sliding seal. The vent flange 5 is also equipped with a pressure gauge to better determine whether the setting is successful.

[0035] The end of the pull rod 3 furthest from the plug 1 has an axially extending receiving cavity, and the other end is threadedly connected to the plug 1. Furthermore, the end face of the plug 1 has a threaded screw hole. This threaded screw hole is located at the midpoint of the threaded engagement between the plug 1 and the pull rod 3. Screwing in the threaded screw is equivalent to installing a key between the plug 1 and the pull rod 3, preventing relative rotation and thus achieving a limiting and anti-retrofit function.

[0036] The feed rod 6 has a hollow structure, which reduces the weight of structural components and allows for quick installation and disassembly while meeting strength requirements, thus improving operational efficiency. The end of the feed rod 6 furthest from the anti-rotation limiting component 9 is hexagonal in shape and connects to both the outer wall of the receiving cavity and the inner wall of the tie rod nut 4. Specifically, the tie rod nut 4 has a hollow structure, and the feed rod 6 is threaded to the inner wall of the tie rod nut 4, sealed by an O-ring 16. The outer wall of the receiving cavity is machined with an outer hexagonal shape, connecting to the inner hexagonal shape of the feed rod 6. This connection method prevents the tie rod 3 from rotating circumferentially after it is inserted into the feed rod 6. The inner wall of the tie rod nut 4 and the outer wall of the receiving cavity are also sealed by two O-rings 16, providing a sliding seal that not only seals but also prevents the tie rod 3 from being pushed out under wellhead pressure.

[0037] The expansion-sealing rubber sleeve 2 is a hollow structure, fitted around the outer periphery of the pull rod 3 to achieve position locking, and its axial ends respectively abut against the plug 1 and the pull rod nut 4. The locking screw 8 has threads at both ends that engage with the inner wall of the feeding rod 6 and the inner wall of the receiving cavity, respectively, and the threads at both ends of the locking screw 8 have opposite directions of rotation. Specifically, the inner wall of the feeding rod 6 has a left-hand internal thread, and the inner wall of the receiving cavity has a right-hand internal thread. The right end of the locking screw 8 has a left-hand external thread, and the left end of the locking screw 8 has a right-hand external thread.

[0038] When the locking screw 8 is rotated, under the constraint of the anti-rotation limiting member 9, the locking screw 8 moves axially away from the end of the plug 1. The axial linear motion of the locking screw 8 is transmitted to the plug 1 through the pull rod 3. At the same time, due to the threaded engagement between the locking screw 8 and the receiving cavity, the rotational motion of the locking screw 8 is converted into the axial linear motion of the plug 1 towards the expansion sealing cylinder 2 through the pull rod 3. Through the double pulling force on the plug 1, the plug 1 applies axial compressive force to the expansion sealing cylinder 2.

[0039] In use, the other end of the anti-rotation limiting component 9 is connected to a fixed frame installed on the wellhead four-way flange. The fixed frame includes a fixed frame body and a locking component connected to the fixed frame body. The fixed frame body includes a fixed crossbeam 10, a fixed screw 11, an anti-overhead screw 12, and an anti-overhead crossbeam 14. The anti-overhead screw 12 is threadedly connected to the fixed crossbeam 10, and the fixed crossbeam 10 is secured to the wellhead four-way flange by the fixed screw 11. This installation method avoids the need to disassemble the threaded flange, pipelines, and other structures on the outer end of the valve opposite the valve to be replaced, which do not need to be replaced, required by conventional frame installation. Furthermore, if both valves on both sides of the four-way flange need to be replaced, it is only necessary to remove the anti-overhead screw 12 and install it on the fixed crossbeam 10 on the other side. The anti-rotation limiting component 9 can be connected to the middle of the anti-overhead crossbeam 14 by two pins, and through cooperation with the locking component, it can position and fix the installation position of the sealing tool.

[0040] The anti-top beam 14 is connected to two anti-top screws 12 at both ends. The locking components include a locking nut 13 and a tightening nut 15 respectively mounted on the anti-top screws 12. Along the axial direction, the locking nut 13 and tightening nut 15 are located at both ends of the anti-top beam 14. The locking nut 13 restricts the movement of the anti-top beam 14 towards the plug 1, and the tightening nut 15 withstands the upward force generated by well pressure. Specifically, the anti-top beam 14 has a two-part structure, which is bolted together during installation. After assembly, an elongated hole is formed at the connection point with the anti-top screws 12 for connection, and the elongated hole structure can accommodate different center distances between the two anti-top screws 12. With this two-part structure, during installation and disassembly, it is not necessary to completely unscrew the tightening nut 15 from the anti-top screw 12; only a few millimeters of backscrewing are needed to install or remove the anti-top beam 14.

[0041] Based on the above device, valve replacement under pressure can be completed, specifically including the following steps: Step S1. Install the fixing bracket on the wellhead four-way connector. Specifically, install the fixing beam 10 on the wellhead four-way connector, adjust the angle and position of the fixing beam 10, and tighten the nut on the fixing screw 11. Install the anti-jacking screw 12 on the fixing beam 10 and tighten it in place.

[0042] Step S2. Connect the sealing tool to the outer valve of the valve to be replaced through the vent flange 5, tighten the connecting bolts, and test the seal at the connection.

[0043] Step S3. Open the valve to be replaced and the outer valve to the fully open position, and connect the sealing tool to the fixing frame. Specifically, connect the anti-rotation limiter 9 of the sealing tool to the anti-top beam 14 of the fixing frame, move the anti-top beam 14 and the sealing tool together, and send the sealing tool and the anti-top beam 14 into the sealing head expansion position. Tighten the locking nut 13 and the locking nut 15, as detailed in the attached instruction manual. Figure 2 Included with instruction manual Figure 3 As shown.

[0044] Step S4. Rotate the locking screw 8 clockwise. Under the rotational and linear motion of the locking screw 8, the plug 1 is driven to move backward and press against the expansion sealing cylinder 2, causing the expansion sealing cylinder 2 to be squeezed and deformed to fill the gap, thus sealing the pressure inside the well within the four-way valve.

[0045] Step S5. Release the pressure at the rear end of the expansion seal, close the pressure relief port and observe for 15 minutes. Check if the pressure gauge on the vent flange 5 rises again to determine if the setting seal is successful.

[0046] Step S6. If no pressure is applied, the setting is successful. Remove the connecting nut between the valve to be replaced and the four-way valve, move the valve to be replaced, install the anti-overhead crescent flange, and tighten the connecting nut. The anti-overhead crescent flange is used to transfer the upward force generated by well pressure during valve replacement to the threaded bolts in the side hole of the four-way valve. Tighten the threaded bolts so that the anti-overhead crescent flange bears the upward force, while the rear anti-overhead beam 14 is not stressed.

[0047] Step S7. Loosen the locking nut 15, remove the anti-top beam 14, remove the anti-rotation limiter 9, and remove the old valve from the rear end of the sealing tool.

[0048] Step S8. Insert the new valve through the end of the sealing tool to a distance of about 220mm from the four-way valve, reinstall the anti-overturning beam 14, and tighten the locking nut 15. Remove the anti-overturning crescent flange, insert the new valve, and tighten the connecting nut.

[0049] Step S9. Pressure test at vent flange 5, check the connection seal between the new valve and the four-way valve, and then release the pressure.

[0050] Step S 10 Rotate the locking screw 8 counterclockwise to move the plug 1 and pull rod 3 forward, restoring the expansion sealing tube 2 to its pre-expansion state and releasing the seal.

[0051] Step S 11 Release the locking nut 15, retract the sealing tool and anti-top beam 14, so that the sealing tool retracts past the new valve, close the new valve, and relieve the pressure after the new valve.

[0052] Step S 12 Dismantle the live valve replacement equipment to complete the entire live valve replacement work.

[0053] In summary, any other corresponding modifications made by those skilled in the art based on the technical solution and concept of this utility model without creative mental effort after reading this utility model document are all within the scope of protection of this utility model.

Claims

1. A mechanical device for replacing a wellhead main control valve under pressure, comprising a pull rod (3), a locking screw (8), an insertion rod (6), a plug (1), a pull rod nut (4), and an expansion sealing sleeve (2); wherein the locking screw (8) is disposed inside the insertion rod (6); characterized in that: It also includes an anti-rotation limiting component (9); one end of the pull rod (3) is provided with a receiving cavity, and the other end is connected to the plug (1); the two ends of the locking screw (8) are respectively threadedly connected to the inner wall of the feeding rod (6) and the inner wall of the receiving cavity, and the threads at both ends of the locking screw (8) are opposite in direction; the anti-rotation limiting component (9) is used to limit the axial movement of the feeding rod (6) and prevent the feeding rod (6) from rotating circumferentially; the end of the feeding rod (6) away from the anti-rotation limiting component (9) is simultaneously connected to the inner wall of the pull rod nut (4) and the outer wall of the receiving cavity, and the connection between the feeding rod (6) and the outer wall of the receiving cavity can limit the circumferential rotation of the pull rod (3); the inner wall of the pull rod nut (4) and the outer wall of the receiving cavity form a sliding seal connection; when the locking screw (8) is rotated, under the constraint of the anti-rotation limiting component (9), the axial movement and rotation of the locking screw (8) itself can exert a dual force on the plug (1).

2. The device for mechanically replacing the wellhead main control valve under pressure according to claim 1, characterized in that: It also includes a vent flange (5) for connection to the flange of the valve to be replaced, the vent flange (5) being connected to the feed rod (6) via a hollow sealing sleeve (7).

3. The device for mechanically replacing the wellhead main control valve under pressure according to claim 2, characterized in that: The sealing sleeve (7) is connected to the vent flange (5) by a thread.

4. The device for mechanically replacing the wellhead main control valve under pressure according to claim 3, characterized in that: A sealing ring (16) is also provided between the sealing sleeve (7) and the vent flange (5).

5. A device for mechanically replacing the wellhead main control valve under pressure according to claim 2 or 4, characterized in that: The sealing sleeve (7) and the feeding rod (6) are connected by a sliding sealing fit.

6. The device for mechanically replacing the wellhead main control valve under pressure according to claim 2, characterized in that: A pressure gauge is also provided on the vent flange (5).

7. The device for mechanically replacing the wellhead main control valve under pressure according to claim 1, characterized in that: The pull rod nut (4) and the feed rod (6) are connected by threads.

8. The device for mechanically replacing the wellhead main control valve under pressure according to claim 7, characterized in that: A sealing ring (16) is also provided between the pull rod nut (4) and the feed rod (6).

9. The device for mechanically replacing the wellhead main control valve under pressure according to claim 1, characterized in that: The plug (1) and the pull rod (3) are connected by threads.

10. The device for mechanically replacing the wellhead main control valve under pressure according to claim 9, characterized in that: The end face of the plug (1) is provided with a screw hole for slab thread.

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