A device and method for detecting the airtightness of the back seal of the main valve of the oil wellhead.

Abstract

This invention relates to a device and method for testing the airtightness of the back seal of a main valve in an oil well, belonging to the field of testing technology for oil and gas extraction equipment. It includes: a sealing assembly comprising a sealing seat, an inner sealing ring, and an outer sealing ring. The sealing seat is fitted over the valve stem, with its inner wall surface spaced apart from the outer wall surface of the valve stem. The inner sealing ring is fixedly disposed on the inner wall surface of the sealing seat and abuts against the outer wall surface of the valve stem. The outer sealing ring is fixedly disposed on the end face of the sealing seat facing the valve cover and abuts against the valve cover. A testing chamber is formed between the sealing seat, valve stem, valve cover, and back seal structure. A pressure testing assembly includes a pressure connector, a pressure pump, and a pressure gauge. The pressure connector is fixed to the sealing seat and communicates with the testing chamber. The pressure connector is connected to the pressure pump. The pressure gauge detects the pressure in the testing chamber, simplifying the testing process and eliminating the need to disassemble the valve cover.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction equipment testing technology, and in particular to a device and method for testing the airtightness of the back seal of the main valve of the wellhead. Background Technology

[0002] The main valve of the wellhead is a key control component of the oil and gas wellhead production system, used to control the opening and closing of wellhead fluids. Its sealing performance directly affects the safety of oil production operations. The back seal structure is an important safety structure of the main valve of the wellhead. It is located between the valve stem and the valve cover. When it is necessary to replace the valve stem packing under pressure, the back seal structure can achieve sealing isolation, preventing high-pressure fluid in the well from leaking from the valve stem, and ensuring the safety of maintenance operations.

[0003] The airtightness of the back seal structure directly determines the safety of pressurized maintenance operations. Therefore, airtightness testing of the back seal structure is required before valve installation, after maintenance, and during regular maintenance. Existing back seal airtightness testing methods mostly employ disassembly-based testing, which requires removing the valve cover from the valve body and then fixing the back seal component with a special clamp before pressurization testing. This method has several drawbacks: firstly, disassembling the valve cover is complex, time-consuming, and labor-intensive, especially during wellhead operations, requiring a large number of tools and manpower, affecting work efficiency; secondly, the disassembly and reinstallation of the valve cover can easily damage the back seal structure, leading to a decrease in valve sealing performance after testing and even the risk of leakage; furthermore, existing testing tooling has poor versatility, requiring different specifications of the main wellhead valves to be equipped with corresponding testing tooling, increasing testing costs.

[0004] To address the aforementioned issues, some existing technologies have attempted non-disassembly-based testing solutions. However, these solutions suffer from complex fixture structures, poor sealing reliability, inability to achieve precise pressurization and leak detection, and low testing accuracy, failing to meet on-site testing requirements. Therefore, developing a portable, versatile, and valve cover-free inverted seal airtightness testing fixture and method has become a crucial need in the field of wellhead maintenance and testing. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the existing detection device being complex in structure and requiring the valve cover to be disassembled, thereby providing a device and method for detecting the airtightness of the back seal of the main valve of the oil well tree.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A device for testing the airtightness of the back seal of a main valve in an oil wellhead, used to test the airtightness of the back seal structure between the valve stem and the valve cover, comprising: A sealing assembly includes a sealing seat, an inner sealing ring, and an outer sealing ring. The sealing seat is sleeved on the outside of the valve stem, and the inner wall surface of the sealing seat is spaced apart from the outer wall surface of the valve stem. The inner sealing ring is fixedly disposed on the inner wall surface of the sealing seat and abuts against the outer wall surface of the valve stem. The outer sealing ring is fixedly disposed on the end face of the sealing seat facing the valve cover and abuts against the valve cover. A detection cavity is formed between the sealing seat, the valve stem, the valve cover, and the inverted sealing structure. The pressure testing assembly includes a pressure connector, a pressure pump, and a pressure gauge. The pressure connector is fixed to the sealing seat and communicates with the testing chamber. The pressure connector is connected to the pressure pump, and the pressure gauge detects the pressure in the testing chamber.

[0007] Preferably, the sealing seat has an inner groove on its inner side, the inner sealing ring is fixed in the inner groove, the sealing seat has an outer groove on its end face facing the valve cover, the outer sealing ring is fixed in the outer groove, and a detection cavity is formed between the valve stem, the sealing seat, the inner sealing ring, the valve cover, the outer sealing ring, and the inverted sealing structure.

[0008] Preferably, it further includes a tee connector, the pressure connector is connected to one end of the tee connector, and the pressure pump and the pressure gauge are respectively connected to the other two ends of the tee connector; Alternatively, it may include a tee fitting and a connecting pipe, wherein the pressure fitting is connected to one end of the tee fitting, and the connecting pipe and the pressure gauge are respectively connected to the other two ends of the tee fitting.

[0009] Preferably, the device further includes an arc-shaped clamp, a bolt, and a nut. There are two arc-shaped clamps. At least part of the inner side of the arc-shaped clamp abuts against the outer side of the sealing seat. The bolt passes through the lower end of the arc-shaped clamp and abuts against the outer side of the valve cover. The nut passes through the upper end of the arc-shaped clamp and abuts against the outer side of the sealing seat.

[0010] Preferably, both of the arc-shaped clamps have an arc-shaped sealing part on their inner sides, the lower end face of the valve cover at least partially abuts against the upper end face of the sealing part, and the inner ring surface of the sealing part abuts against the outer side surface of the valve cover.

[0011] Preferably, the device further includes a fastener, which includes a fastening portion and a lower limiting portion integrally formed with the fastening portion. Both the fastening portion and the lower limiting portion are annular, and the diameter of the fastening portion is smaller than the diameter of the lower limiting portion. The fastening portion is fixed to the valve cover, and the lower limiting portion faces the sealing seat.

[0012] Preferably, both of the arc-shaped clamps have an upper limit portion protruding from their inner sides, the upper limit portion facing the lower limit portion, and the lower limit portion being able to engage with the upper limit portion.

[0013] A method for testing the airtightness of the back seal of the main valve of the wellhead includes the following steps: S1, the sealing seat is sleeved on the valve stem, and the lower end face of the sealing seat is in contact with the upper end face of the valve cover. Two arc-shaped clamps are fixedly connected to the valve cover and the sealing seat. A detection cavity is provided between the sealing seat, the valve stem, the valve cover, and the inverted sealing structure. S2, one end of the tee is connected to the pressure fitting fixed on the sealing seat, and the pressure pump and pressure gauge are respectively connected to the other two ends of the tee; S3, start the pressurization pump, slowly pressurize the detection chamber to the preset pressure value, stop pressurizing, and maintain the pressure for 5 minutes; In step S4, if the pressure drop is within the allowable range, the pressurizing pump continues to slowly pressurize the detection chamber until it reaches 1.2-1.5 times the valve's rated working pressure, then stops pressurizing and maintains the pressure for 30 minutes; if the pressure drop exceeds the allowable range, then the leak point is checked and the valve is reinstalled. S5. If the pressure drop is within the preset allowable range within 30 minutes and there are no obvious signs of leakage, the back seal is qualified for air tightness. If the pressure drop exceeds the allowable range, or if bubbles or fluid leakage are observed at the seal, the back seal is leaking and needs to be repaired or replaced.

[0014] Preferably, in step S1, the inner sealing ring is fixed to the inner groove, and the valve stem is in contact with the inner sealing ring; the outer sealing ring is fixed to the outer groove, and one end face of the outer sealing ring is in contact with the upper end face of the valve cover; a detection cavity is provided between the valve stem, the sealing seat, the inner sealing ring, the valve cover, the outer sealing ring, and the inverted sealing structure.

[0015] Preferably, the procedure further includes step S6: after the test is completed, open the pressure relief valve of the pressurizing pump to slowly release the pressure in the test chamber. After the pressure drops to normal pressure, disassemble the pressurizing pump and pressure gauge, remove the sealing seat, and complete the test operation.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The aforementioned technical solution provides a back seal airtightness testing device for the main valve of the production tree. This device includes a sealing assembly and a pressurized testing assembly. A sealing seat is fitted outside the valve stem. An inner sealing ring, fixed to the inner wall of the sealing seat and abutting against the valve stem, and an outer sealing ring, fixed to the end face of the sealing seat and abutting against the valve cover, together with the valve stem, valve cover, and back seal structure, form an independent testing chamber. A pressurized connector is fixed to the sealing seat and communicates with the testing chamber, connecting a pressurized pump and a pressure gauge. The inner and outer sealing rings construct a closed testing chamber. The pressurized pump injects media into the chamber through the connector, and the pressure gauge monitors pressure changes. The testing fixture is directly installed outside the valve cover, eliminating the need to disassemble the valve cover, thus avoiding damage to the valve during disassembly, simplifying the testing process, significantly improving testing efficiency, and reducing the difficulty of on-site operations. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A schematic diagram of an oil well main valve back seal airtightness testing device provided for an embodiment of the present invention; Figure 2 A cross-sectional view of a back seal airtightness testing device for the main valve of the oil wellhead provided in an embodiment of the present invention; Figure 3 A schematic diagram of a sealing seat provided for an embodiment of the present invention; Figure 4 A cross-sectional view of a sealing seat provided for an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Sealing assembly; 11. Sealing seat; 111. Inner groove; 112. Outer groove; 12. Inner sealing ring; 13. Outer sealing ring; 2. Pressure detection assembly; 21. Pressure fitting; 22. Pressure pump; 23. Pressure gauge; 3. Valve stem; 4. Valve cover; 5. Detection chamber; 6. T-joint; 7. Connecting pipe; 8. Arc-shaped clamp; 81. Sealing part; 82. Upper limit part; 9. Fastener; 91. Fastening part; 92. Lower limit part; 10. Inverted sealing structure. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Please read carefully. Figures 1 to 4This invention provides a device for testing the airtightness of the back seal of a main valve in a production tree. The device is used to test the airtightness of the back seal structure 10 between the valve stem 3 and the valve cover 4. The back seal structure 10 is located radially between the valve stem 3 and the valve cover 4 and includes: a sealing assembly 1 and a pressure testing assembly 2. Specifically, it includes a sealing seat 11, an inner sealing ring 12, and an outer sealing ring 13. The outer surface of the sealing seat 11 is cylindrical, and the upper end face of the sealing seat 11 has a through hole with a diameter smaller than the diameter of the valve stem 3. The sealing seat 11 is fitted over the valve stem 3, and the inner wall of the sealing seat 11 is flush with the outer wall of the valve stem 3. The sealing seat 11 and valve stem 3 are spaced apart to ensure that a cavity can be formed between them. The inner sealing ring 12 is fixedly set on the inner wall surface of the sealing seat 11 and abuts against the outer wall surface of the valve stem 3, filling the gap between the inner wall surface of the sealing seat 11 and the outer wall surface of the valve stem 3, ensuring the sealing performance at the connection between the sealing seat 11 and the valve stem 3. The outer sealing ring 13 is fixedly set on the end face of the sealing seat 11 facing the valve cover 4 and abuts against the valve cover 4, ensuring the sealing performance at the connection between the sealing seat 11 and the valve cover 4. A detection cavity 5 is provided between the sealing seat 11, valve stem 3, valve cover 4, and inverted sealing structure 10. The pressure testing assembly 2 includes a pressure connector 21, a pressure pump 22, and a pressure gauge 23. The pressure connector 21 is fixed to the sealing seat 11 and is connected to the testing chamber 5. The pressure connector 21 is connected to the pressure pump 22. The pressure gauge 23 detects the pressure in the testing chamber 5. The pressure pump 22 inflates the testing chamber 5 to ensure the sealing of each connection. The airtightness of the reverse sealing structure 10 can be tested by detecting the pressure in the testing chamber 5.

[0024] The inner wall of the sealing seat 11 is provided with an inner groove 111, and the inner sealing ring 12 is fixed in the inner groove 111. The inner sealing ring 12 is tightly fitted with the outer wall of the valve stem 3. The end face of the sealing seat 11 facing the valve cover 4 is provided with an outer groove 112, and the outer sealing ring 13 is fixed in the outer groove 112. The outer sealing ring 13 is tightly fitted with the upper end face of the valve cover 4 to ensure that all connections are sealed. A detection chamber 5 is provided between the valve stem 3, the sealing seat 11, the inner sealing ring 12, the valve cover 4, the outer sealing ring 13, and the inverted sealing structure 10. If the pressure gauge 23 detects that the pressure drop exceeds the predetermined range and all connections are sealed, then there is a leak in the inverted sealing structure 10.

[0025] The main valve back seal airtightness testing device for the wellhead also includes a tee connector 6, with a pressure connector 21 connected to one end of the tee connector 6. The detection chamber 5 is connected to the pressure connector 21, ensuring that the pressure inside the detection chamber 5 is transmitted to the pressure sensing element without damage. This provides a standard and stable pressure tapping point, avoiding pressure reading deviations caused by irregular shapes at the connection points. The pressure pump 22 and pressure gauge 23 are respectively connected to the other two ends of the tee connector 6. The pressure sensor can be installed inside the sealing seat 11 to visually display the pressure value of the detection chamber 5. The pressure sensor and pressure gauge 23 are connected in parallel to collect pressure data in real time and transmit the data to a portable display terminal for accurate monitoring of pressure changes and determination of whether a leak exists. Alternatively, the device includes a tee connector 6 and a connecting pipe 7, with the pressure connector 21 connected to one end of the tee connector 6, and the connecting pipe 7 and pressure gauge 23 respectively connected to the other two ends of the tee connector 6. The remaining structure is the same as the above scheme.

[0026] The back seal airtightness testing device for the main valve of the oil well site also includes an arc-shaped clamp 8, bolts, and nuts. Two arc-shaped clamps 8 are provided. At least part of the inner surface of the arc-shaped clamp 8 abuts against the outer surface of the sealing seat 11. Bolts pass through the lower end of the arc-shaped clamp 8 and abut against the outer surface of the valve cover 4. Nuts pass through the upper end of the arc-shaped clamp 8 and abut against the outer surface of the sealing seat 11, fixing the sealing seat 11 to the valve cover 4. This ensures that the sealing seat 11 does not shift during pressure testing, guaranteeing testing stability. The arc-shaped clamps 8 of the fixing component can be adapted to valve covers 4 of different diameters by adjusting the bolt spacing, improving the tooling versatility. Both arc-shaped clamps 8 have arc-shaped sealing parts 81 protruding from their inner sides. The lower end face of the valve cover 4 at least partially abuts against the upper end face of the sealing part 81, and the inner ring surface of the sealing part 81 abuts against the outer side surface of the valve cover 4. The connection between the sealing seat 11 and the valve cover 4 is provided with a double sealing structure. The first sealing structure is set at the abutment between the lower end face of the sealing seat 11 and the upper end face of the valve cover 4 to ensure that the gas in the detection chamber 5 will not leak outward. The second sealing structure is set at the connection between the sealing seat 11 and the outer peripheral surface of the valve cover 4 to enhance the sealing performance of the connection and ensure that the gas will not leak outward.

[0027] Additionally, it includes a fastener 9, which comprises a fastening portion 91 and a lower limiting portion 92 integrally formed with the fastening portion 91. Both the fastening portion 91 and the lower limiting portion 92 are annular. The fastening portion 91 has a rough inner annular surface, and the inner annular surface of the fastening portion 91 abuts against the outer surface of the valve cover 4, increasing the friction of the contact surface and thus improving the stability of the fastener 9. The diameter of the fastening portion 91 is smaller than the diameter of the lower limiting portion 92, and the cross-section of the fastener 9 is L-shaped. The fastening portion 91 is fixed to... The valve cover 4 can be fixed by a threaded connection, and the fixing method is not limited. The lower limit part 92 faces the sealing seat 11. The inner sides of the two arc-shaped clamps 8 are provided with upper limit parts 82, which have an L-shaped cross-section. The lower limit part 92 can be engaged with the upper limit part 82. The fastener 9 is fixed to the valve cover 4. The arc-shaped clamps 8 are engaged with the fastener 9 to improve the stability of the arc-shaped clamps 8 during pressurization, thereby ensuring the sealing of the detection chamber 5 and improving the accuracy of detecting the airtightness of the reverse sealing structure 10.

[0028] This invention also provides a method for detecting the airtightness of the back seal of the main valve of the wellhead, comprising the following steps: S1, the sealing seat 11 is sleeved on the valve stem 3, and the lower end face of the sealing seat 11 is in contact with the upper end face of the valve cover 4. Two arc-shaped clamps 8 are fixedly connected to the valve cover 4 and the sealing seat 11. A detection cavity 5 is provided between the sealing seat 11, the valve stem 3, the valve cover 4, and the inverted sealing structure 10. S2, one end of the three-way connector 6 is connected to the pressure connector 21 fixed on the sealing seat 11, and the pressure pump 22 and pressure gauge 23 are respectively connected to the other two ends of the three-way connector 6; S3, start the pressurization pump 22, slowly pressurize the detection chamber 5 to the preset pressure value, stop pressurizing, and maintain the pressure for 5 minutes; In step S4, if the pressure drop is within the allowable range, the pressurizing pump 22 continues to slowly pressurize the detection chamber 5 until it reaches 1.2-1.5 times the valve's rated working pressure, then stop pressurizing and maintain the pressure for 30 minutes; if the pressure drop exceeds the allowable range, check for leaks and reinstall the valve. S5. If the pressure drop is within the preset allowable range within 30 minutes and there are no obvious signs of leakage, the back seal is qualified for air tightness. If the pressure drop exceeds the allowable range, or if bubbles or fluid leakage are observed at the seal, the back seal is leaking and needs to be repaired or replaced.

[0029] In step S3, the preset pressure value is usually 50% of the detection pressure; in step S5, the preset allowable value range is usually 2% of the detection pressure.

[0030] In step S1, the inner sealing ring 12 is fixed to the inner groove 111, and the valve stem 3 is in contact with the inner sealing ring 12. The outer sealing ring 13 is fixed to the outer groove 112, and one end face of the outer sealing ring 13 is in contact with the upper end face of the valve cover 4. A detection cavity 5 is provided between the valve stem 3, the sealing seat 11, the inner sealing ring 12, the valve cover 4, the outer sealing ring 13, and the reverse sealing structure 10.

[0031] The test also includes step S6, after which the pressure relief valve of the pressure pump 22 is opened to slowly release the pressure in the test chamber 5. After the pressure drops to normal pressure, the pressure pump 22 and pressure gauge 23 are disassembled, and the sealing seat 11 is removed to complete the test.

[0032] This testing method constructs a sealed environment by testing the valve stem 3, valve cover 4, sealing seat 11, inverted sealing structure 10, and inner and outer sealing rings 13. A pressure gauge 23 monitors the pressure of the medium introduced through the pressurization connector 21 to determine the airtightness of the inverted sealing structure 10. Specifically, the inverted sealing structure 10 is positioned between the testing valve stem 3 and the valve cover 4. The sealing seat 11, together with the testing valve stem 3 and valve cover 4, forms the testing chamber 5. Regarding the sealing structure, the inner sealing ring 12 is fixedly mounted on the inner wall of the sealing seat 11 and abuts against the outer wall of the testing valve stem 3; the outer sealing ring 13 is fixedly positioned on the end face of the sealing seat 11 facing the valve cover 4 and abuts against the valve cover 4, thus ensuring the sealing performance of each connection point. In terms of the detection circuit, the pressure connector 21 is connected to the detection chamber 5 and connected to the pressure pump 22. The pressure pump 22 pressurizes the detection chamber 5, and the pressure inside the detection chamber 5 is monitored by the pressure gauge 23, thereby realizing the detection of the airtightness of the reverse sealing structure 10. The detection fixture is directly installed on the outside of the valve cover 4 without disassembling the valve cover 4, avoiding damage to the valve during the disassembly process, simplifying the detection process, greatly improving detection efficiency, and reducing the difficulty of on-site operation.

[0033] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A device for testing the airtightness of the back seal of a main valve in a production tree, used to test the airtightness of the back seal structure (10) between the valve stem (3) and the valve cover (4), characterized in that, include: The sealing assembly (1) includes a sealing seat (11), an inner sealing ring (12), and an outer sealing ring (13). The sealing seat (11) is sleeved on the valve stem (3), and the inner wall surface of the sealing seat (11) is spaced apart from the outer wall surface of the valve stem (3). The inner sealing ring (12) is fixedly disposed on the inner wall surface of the sealing seat (11), and the inner sealing ring (12) abuts against the outer wall surface of the valve stem (3). The outer sealing ring (13) is fixedly disposed on the end face of the sealing seat (11) facing the valve cover (4), and the outer sealing ring (13) abuts against the valve cover (4). A detection cavity (5) is provided between the sealing seat (11), the valve stem (3), the valve cover (4), and the inverted sealing structure (10). The pressure testing assembly (2) includes a pressure connector (21), a pressure pump (22), and a pressure gauge (23). The pressure connector (21) is fixed to the sealing seat (11) and is connected to the testing chamber (5). The pressure connector (21) is connected to the pressure pump (22), and the pressure gauge (23) detects the pressure of the testing chamber (5).

2. The oil well main valve back seal airtightness testing device according to claim 1, characterized in that, The sealing seat (11) has an inner groove (111) on its inner side, and the inner sealing ring (12) is fixed in the inner groove (111). The sealing seat (11) has an outer groove (112) on its end face facing the valve cover (4), and the outer sealing ring (13) is fixed in the outer groove (112). A detection cavity (5) is formed between the valve stem (3), the sealing seat (11), the inner sealing ring (12), the valve cover (4), the outer sealing ring (13), and the inverted sealing structure (10).

3. The oil well main valve back seal airtightness testing device according to claim 1, characterized in that, It also includes a three-way connector (6), the pressure connector (21) is connected to one end of the three-way connector (6), and the pressure pump (22) and the pressure gauge (23) are respectively connected to the other two ends of the three-way connector (6); Alternatively, it may include a tee connector (6) and a connecting pipe (7), wherein the pressure fitting (21) is connected to one end of the tee connector (6), and the connecting pipe (7) and the pressure gauge (23) are respectively connected to the other two ends of the tee connector (6).

4. The oil well main valve back seal airtightness testing device according to claim 1, characterized in that, It also includes an arc-shaped clamp (8), bolts and nuts. There are two arc-shaped clamps (8). The inner side of the arc-shaped clamp (8) at least partially abuts against the outer side of the sealing seat (11). The bolt passes through the lower end of the arc-shaped clamp (8) and abuts against the outer side of the valve cover (4). The nut passes through the upper end of the arc-shaped clamp (8) and abuts against the outer side of the sealing seat (11).

5. The oil well main valve back seal airtightness testing device according to claim 4, characterized in that, Both of the arc-shaped clamps (8) have an arc-shaped sealing part (81) on their inner sides. The lower end face of the valve cover (4) is at least partially in contact with the upper end face of the sealing part (81), and the inner ring surface of the sealing part (81) is in contact with the outer side of the valve cover (4).

6. The oil well main valve back seal airtightness testing device according to claim 5, characterized in that, It also includes a fastener (9), which includes a fastening part (91) and a lower limiting part (92) integrally formed with the fastening part (91). The fastening part (91) and the lower limiting part (92) are both annular, and the diameter of the fastening part (91) is smaller than the diameter of the lower limiting part (92). The fastening part (91) is fixed to the valve cover (4), and the lower limiting part (92) faces the sealing seat (11).

7. The oil well trunk main valve back seal airtightness testing device according to claim 6, characterized in that, Both of the arc-shaped clamps (8) have an upper limit part (82) protruding from their inner sides. The upper limit part (82) faces the lower limit part (92), and the lower limit part (92) can engage with the upper limit part (82).

8. A method for testing the airtightness of the back seal of the main valve of the oil wellhead, characterized in that, The method of using the back seal airtightness testing device for the main valve of the wellhead as described in any one of claims 1-7 includes the following steps: S1, the sealing seat (11) is sleeved on the valve stem (3), and the lower end face of the sealing seat (11) is in contact with the upper end face of the valve cover (4). Two arc-shaped clamps (8) are fixedly connected to the valve cover (4) and the sealing seat (11). A detection cavity (5) is provided between the sealing seat (11), the valve stem (3), the valve cover (4), and the inverted sealing structure (10). S2, one end of the three-way connector (6) is connected to the pressure connector (21) fixed on the sealing seat (11), and the pressure pump (22) and pressure gauge (23) are respectively connected to the other two ends of the three-way connector (6); S3, start the pressurization pump (22) and slowly pressurize the detection chamber (5) to the preset pressure value, stop pressurizing, and maintain the pressure for 5 minutes; In step S4, if the pressure drop is within the allowable range, the pressurizing pump (22) continues to slowly pressurize the detection chamber (5) until it reaches 1.2-1.5 times the rated working pressure of the valve, then the pressurization is stopped and the pressure is maintained for 30 minutes; if the pressure drop exceeds the allowable range, the leak point is checked and the valve is reinstalled. S5. If the pressure drop is within the preset allowable range within 30 minutes and there are no obvious signs of leakage, the back seal is qualified for air tightness. If the pressure drop exceeds the allowable range, or if bubbles or fluid leakage are observed at the seal, the back seal is leaking and needs to be repaired or replaced.

9. The method for detecting the airtightness of the back seal of the main valve of the wellhead as described in claim 8, characterized in that, In step S1, the inner sealing ring (12) is fixed to the inner groove (111), and the valve stem (3) is in contact with the inner sealing ring (12). The outer sealing ring (13) is fixed to the outer groove (112), and one end face of the outer sealing ring (13) is in contact with the upper end face of the valve cover (4). A detection cavity (5) is provided between the valve stem (3), the sealing seat (11), the inner sealing ring (12), the valve cover (4), the outer sealing ring (13), and the inverted sealing structure (10).

10. The method for detecting the airtightness of the back seal of the main valve of the wellhead as described in claim 8, characterized in that, The test also includes step S6. After the test is completed, the pressure relief valve of the pressurizing pump (22) is opened to slowly release the pressure in the test chamber (5). After the pressure drops to normal pressure, the pressurizing pump (22) and pressure gauge (23) are disassembled, and the sealing seat (11) is removed to complete the test.

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