Float valve pulse generator

Abstract

The present application relates to the technical fields of downhole operation, and discloses a float valve type pulse generator, which comprises a throttle valve, an upper joint, a transition nipple, a connecting neck, a throttle sleeve, a valve head, a valve rod, a valve sheath, an outer sheath and a magneto-rheological fluid assembly, the inner side of the upper end of the upper joint is fixedly provided with the throttle valve, the inner side of the upper part of the upper joint is provided with a first limiting ring table, the inner side of the lower end of the upper joint is fixedly provided with the transition nipple, and the central part of the transition nipple is provided with an installation hole which penetrates upward and downward. The present application has reasonable and compact structure, and is convenient to use. By setting a throttle curved surface and cooperating with the valve head at different positions, the flow area between the valve head and the throttle sleeve is changed, so that the mud flow channel generates a pulse. By turning on and off the power of the magnetic field generator, the state of the magneto-rheological fluid is changed, the flow area is changed according to a rule, so that the mud flow channel generates a regular pulse, and the present application has the characteristics of stability, reliability and fast response.

Description

Technical Field

[0001] This invention relates to the field of downhole operation technology and is a floating valve type pulse generator. Background Technology

[0002] Logging while drilling (LoWW) in oilfields uses instruments installed inside the drill collar to measure drilling and formation parameters. Based on these parameters, the drill bit trajectory is adjusted in real time to guide drilling along the target formation. Because the formation parameters obtained from LoWW are closest to the original state of the formation, they are more beneficial for evaluating the oil and gas content of complex formations. LoWW instruments are placed inside non-magnetic drill collars and can measure directional parameters (inclination, azimuth, tool face angle), formation parameters (gamma, resistivity, sound velocity, neutron porosity, density, etc.), and drilling parameters (bit pressure, torque, rotational speed, annular pressure, etc.). LoWW signal transmission methods are divided into wired and wireless. Wired transmission includes cable transmission, special drill pipe transmission, and fiber optic transmission, while wireless transmission includes mud pulses, electromagnetic waves, and acoustic waves. Mud pulses can be used in deep wells and have lower development costs, making them the most widely used transmission method currently.

[0003] Currently, the communication between the surface and the well is generally achieved by using a pulse generator to control the mud delivery pipeline. The principle is to set up a pulse generator in the mud channel, and the pulse generator opens / blocks (in actual applications, it does not completely block, but usually reduces the diameter of the channel) the mud channel according to a certain pattern, thereby generating regular pulses in the mud channel. Surface personnel detect and decode these pulses to obtain detection data.

[0004] Chinese patent document CN 105626940 B discloses a downhole pulse generator control valve, including a valve port, a drain hole, a plug, a push rod, and an electromagnetic drive device. The valve port is connected to the drain hole. The electromagnetic drive device drives the push rod to move towards the valve port according to a received control signal, so that the push rod drives the plug to seal the valve port. The valve is characterized by further including a return spring, one end of which is connected to the push rod and the other end to the plug. The push rod deforms the return spring, thereby driving the plug to seal the valve port. When the plug seals the valve port, the force exerted by the return spring on the push rod and the plug is greater than the pressure of the fluid on the valve port plug. This downhole pulse generator control valve suffers from slow pulse generator response and difficulty in controlling the valve head.

[0005] Magnetorheological fluids (MR fluids) are a novel type of fluid with controllable flowability. They exhibit low-viscosity Newtonian fluid characteristics in the absence of an external magnetic field, but become high-viscosity, low-flowability Bingham fluids under an applied magnetic field. MR fluids are special suspension systems formed by uniformly dispersing micron-sized magnetizable particles in a specific carrier mother liquor and additives. Under the influence of an external magnetic field, they exhibit non-Newtonian fluid characteristics, transforming from a freely flowing liquid to a semi-solid or even a solid within milliseconds. They display strong controllable rheological properties, characterized by low conversion energy consumption, ease of control, and rapid response. Summary of the Invention

[0006] This invention provides a floating valve type pulse generator that overcomes the shortcomings of the prior art and can effectively solve the problems of slow response and difficult valve head control in existing pulse generators.

[0007] The technical solution of this invention is achieved through the following measures: A floating valve type pulse generator includes a throttle valve, an upper connector, a transition short section, a connecting neck, a throttle sleeve, a valve head, a valve stem, a valve sleeve, an outer protective sleeve, and a magnetorheological fluid assembly. A throttle valve is fixedly installed on the inner side of the upper end of the upper connector. A first limiting ring platform is provided on the inner side of the upper part of the upper connector. A transition short section is fixedly installed on the inner side of the lower end of the upper connector. A vertically penetrating mounting hole is provided in the center of the transition short section. At least one vertically penetrating first flow passage hole is provided on the transition short section corresponding to the outer position of the mounting hole. A connecting neck is provided on the lower side of the transition short section at the orifice position. A throttling sleeve is installed in the upper connector corresponding to the position between the first limiting ring platform and the transition short section. A valve head is provided on the upper inner side of the throttling sleeve. A valve stem with its lower end located below the throttling sleeve is provided at the lower end of the valve head. A throttling curved surface is provided on the inner side of the throttling sleeve corresponding to the valve head position. A valve sleeve is provided on the outer side of the middle part of the valve stem. The lower end of the valve sleeve is fixedly installed on the inner side of the transition short section. An outer casing is fixedly installed on the outer side of the lower part of the connecting neck. A magnetorheological fluid assembly capable of adjusting the flow area of ​​drilling fluid at the valve head and the throttling curved surface is provided inside the outer casing.

[0008] The following are further optimizations and / or improvements to the above-mentioned technical solution: The aforementioned magnetorheological fluid assembly may include a top cap, a non-magnetic spring, a bottom cap, a magnetic field generator, and a support sleeve. The lower end of the valve stem is fixedly installed together with the upper end of the top cap. A bottom cap is provided on the inner side of the upper part of the outer casing corresponding to the position below the top cap. The bottom cap has a second through-hole that runs vertically through the top and bottom caps. A non-magnetic spring is provided between the top cap and the bottom cap. A second limiting ring platform is provided on the inner side of the middle part of the outer casing. Magnetorheological fluid is provided inside the outer casing corresponding to the position between the top cap and the second limiting ring platform. A magnetic field generator that can change the state of the magnetorheological fluid is provided on the second limiting ring platform. A third through-hole is provided on the magnetic field generator. A support sleeve is provided between the upper end of the magnetic field generator and the lower end of the bottom cap.

[0009] The aforementioned magnetic field generator may include a generator body, a magnetic flux tube, an iron core, and a coil. An upper outer ring platform is provided on the outer side of the upper end of the generator body, and a lower outer ring platform is provided on the outer side of the lower end of the generator body. At least two vertically penetrating upper magnetic flux holes are provided on the upper outer ring platform at circumferential intervals. A vertically penetrating lower magnetic flux hole is provided on the lower outer ring platform corresponding to the position of each upper magnetic flux hole. A magnetic flux tube is fixedly installed between each pair of corresponding upper and lower magnetic flux holes, and a third flow hole is provided on the magnetic flux tube. An iron core is provided on the outer side of the generator body at the position between the upper and lower outer ring platforms, and a coil is wound on the outer side of the iron core.

[0010] The above-mentioned throttling sleeve may be provided with an upper flow passage, a middle flow passage, and a lower flow passage connected sequentially from top to bottom. The middle flow passage has a throttling curved surface that is narrow at the top and wide at the bottom; the upper end of the valve head has a conical surface that is small at the top and large at the bottom.

[0011] The valve head at the corresponding valve sleeve position can be provided with a sleeve ring groove, and the upper end of the valve sleeve can enter the sleeve ring groove when the valve head moves downward relative to it.

[0012] The above may also include O-rings, with an O-ring provided between the top cap and the connecting neck, and an O-ring provided between the top cap and the outer casing.

[0013] The top cap may have a downward-opening upper blind hole at its lower end, and the bottom cap may have a upward-opening lower blind hole at its upper end. The upper end of the non-magnetic spring is located in the upper blind hole, and the lower end of the non-magnetic spring is located in the lower blind hole.

[0014] This invention has a reasonable and compact structure and is easy to use. By setting a throttling surface and cooperating with valve heads at different positions, the flow area between the valve head and the throttling sleeve changes, thereby generating pulses in the mud flow channel. By switching the magnetic field generator on and off, the state of the magnetorheological fluid is changed, causing the flow area to change in a regular manner, thereby generating regular pulses in the mud flow channel. It has the characteristics of stability, reliability and fast response. Attached Figure Description

[0015] Appendix Figure 1 These are schematic diagrams of the main cross-sectional structure of embodiments 1 to 7 of the present invention.

[0016] Appendix Figure 2 For the appendix Figure 1 A three-dimensional structural diagram of a throttle valve.

[0017] Appendix Figure 3 For the appendix Figure 1 A three-dimensional structural diagram of the intermediate transition section and connecting neck.

[0018] Appendix Figure 4 For the appendix Figure 1 A three-dimensional structural diagram of the valve head and valve stem.

[0019] Appendix Figure 5 For the appendix Figure 1 A three-dimensional structural diagram of a medium magnetic field generator.

[0020] Appendix Figure 6 A schematic diagram of drilling fluid pressure changes Figure 1 .

[0021] Appendix Figure 7 A schematic diagram of drilling fluid pressure changes Figure 2 .

[0022] The codes in the attached diagram are as follows: 1 is the upper connector, 2 is the transition section, 3 is the connecting neck, 4 is the throttling sleeve, 5 is the valve head, 6 is the valve stem, 7 is the valve sleeve, 8 is the outer sleeve, 9 is the throttling valve, 10 is the top cap, 11 is the non-magnetic spring, 12 is the bottom cap, 13 is the support sleeve, 14 is the generator body, 15 is the magnetorheological tube, 16 is the iron core, 17 is the coil, 18 is the magnetorheological fluid, 19 is the upper flow hole, 20 is the throttling surface, 21 is the lower flow hole, 22 is the O-ring seal, 23 is the sleeve annular groove, 24 is the upper blind hole, 25 is the lower blind hole, 26 is the first limiting ring platform, 27 is the second limiting ring platform, 28 is the first flow hole, and 29 is the second flow hole. Detailed Implementation

[0023] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0024] In this invention, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as front, back, top, bottom, left, right, etc. The positional relationships are determined based on the layout direction of the attached diagram in the instruction manual.

[0025] The present invention will be further described below with reference to embodiments and accompanying drawings: Example 1: As shown in the attached document Figure 1 , 2As shown in Figures 3, 4, 5, 6, and 7, the floating valve type pulse generator includes a throttle valve 9, an upper connector 1, a transition short section 2, a connecting neck 3, a throttle sleeve 4, a valve head 5, a valve stem 6, a valve sleeve 7, an outer protective sleeve 8, and a magnetorheological fluid 18 assembly. The throttle valve 9 is fixedly installed on the inner side of the upper end of the upper connector 1. A first limiting ring platform 26 is provided on the inner side of the upper part of the upper connector 1. The transition short section 2 is fixedly installed on the inner side of the lower end of the upper connector 1. The transition short section 2 has a vertically penetrating mounting hole in its center. At least one vertically penetrating first flow passage 28 is provided on the transition short section 2 at the position corresponding to the outer side of the mounting hole. Section 2 has a connecting neck 3 on its lower side. A throttling sleeve 4 is installed in the upper connector 1 corresponding to the position between the first limiting ring platform 26 and the transition short section 2. A valve head 5 is provided on the upper inner side of the throttling sleeve 4. A valve stem 6 with its lower end located below the throttling sleeve 4 is provided at the lower end of the valve head 5. A throttling curved surface 20 is provided on the inner side of the throttling sleeve 4 corresponding to the position of the valve head 5. A valve sleeve 7 is provided on the outer side of the middle part of the valve stem 6. The lower end of the valve sleeve 7 is fixedly installed on the inner side of the transition short section 2. An outer casing 8 is fixedly installed on the outer side of the lower part of the connecting neck 3. A magnetorheological fluid 18 assembly that can adjust the flow area of ​​drilling fluid at the valve head 5 and the throttling curved surface 20 is provided inside the outer casing 8.

[0026] This invention has a reasonable and compact structure and is easy to use. By setting a throttling surface 20, which cooperates with the valve head 5 at different positions after movement, the flow area between the valve head 5 and the throttling sleeve 4 changes, thereby generating pulses in the mud flow channel. By setting a magnetorheological fluid 18 component, the state of the magnetorheological fluid 18 is changed, making it impossible for the valve head 5 to retract or rebound. Consequently, the flow area between the valve head 5 and the throttling sleeve 4 cannot be changed, thereby generating regular pulses in the mud flow channel. It has the characteristics of stability, reliability and fast response.

[0027] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention uses magnetorheological fluid 18 to control the extension and retraction of valve head 5. Since the solid-liquid conversion speed of magnetorheological fluid 18 is in the millisecond range, the present invention has the advantages of low delay and fast response in controlling the pulse generator; (2) The device of the present invention is placed inside the drill collar, without continuous high-frequency moving parts or high-speed dynamic seals, which can avoid the situation of heat generation caused by friction between drill string and well wall and friction between drill bit and formation. The fluid flowing through the device can play a cooling role. Therefore, the device is suitable for high temperature and high pressure drilling environment.

[0028] The above-mentioned floating valve type pulse generator can be further optimized and / or improved according to actual needs: Example 2: As shown in the attached document Figure 1 , 5As shown, the magnetorheological fluid 18 assembly includes a top cap 10, a non-magnetic spring 11, a bottom cap 12, a magnetic field generator, and a support sleeve 13. The lower end of the valve stem 6 is fixedly installed together with the upper end of the top cap 10. The bottom cap 12 is provided on the inner side of the upper part of the outer casing 8 corresponding to the position below the top cap 10. The bottom cap 12 is provided with a second through hole 29 that runs vertically through the top and bottom. The non-magnetic spring 11 is provided between the top cap 10 and the bottom cap 12. The inner side of the middle part of the outer casing 8 is provided with a second limiting ring platform 27. The magnetorheological fluid 18 is provided in the outer casing 8 corresponding to the position between the top cap 10 and the second limiting ring platform 27. The second limiting ring platform 27 is provided with a magnetic field generator that can change the state of the magnetorheological fluid 18. The magnetic field generator is provided with a third through hole. The support sleeve 13 is provided between the upper end of the magnetic field generator and the lower end of the bottom cap 12. During use, the magnetic field generator generates a magnetic field, which can turn the magnetorheological fluid 18 into a solid, so that the valve head 5 cannot move downward under the action of the drilling fluid, thus keeping the flow area constant; when the magnetic field generator does not generate a magnetic field, the magnetorheological fluid 18 can turn into a liquid, so that the valve head 5 moves downward under the action of the drilling fluid and compresses the non-magnetic spring 11. With this setting, the flow area can be adjusted to the set flow area by the time interval between the generation and non-generation of the magnetic field by the magnetic field generator, so that the mud flow channel generates regular pulses.

[0029] Example 3: As shown in the attached document Figure 1 , 5 As shown, the magnetic field generator includes a generator body 14, a magnetorheological tube 15, an iron core 16, and a coil 17. An upper outer ring platform is located on the outer side of the upper end of the generator body 14, and a lower outer ring platform is located on the outer side of the lower end of the generator body 14. At least two vertically penetrating upper magnetorheological holes are spaced along the circumference of the upper outer ring platform. A vertically penetrating lower magnetorheological hole is located on the lower outer ring platform corresponding to each upper magnetorheological hole. A magnetorheological tube 15 is fixedly installed between every two corresponding upper and lower magnetorheological holes, and the magnetorheological tube 15 has a third flow hole. An iron core 16 is located on the outer side of the generator body 14 at a position between the upper and lower outer ring platforms, and a coil 17 is wound around the outer side of the iron core 16. This arrangement facilitates the control of power supply to and from the magnetic field generator during use; energizing the coil 17 generates magnetism, changing the state of the magnetorheological fluid 18.

[0030] Example 4: As shown in the appendix Figure 1 As shown, the throttling sleeve 4 has an upper flow hole 19, a middle flow hole, and a lower flow hole 21 connected sequentially from top to bottom in the middle part. The middle flow hole has a throttling curved surface 20 that is narrow at the top and wide at the bottom; the upper end of the valve head 5 has a conical surface that is small at the top and large at the bottom. During use, this arrangement makes the throttling sleeve 4 and the valve head 5 form a throttling unit. When the valve head 5 moves, the flow area between the valve head 5 and the throttling sleeve 4 changes, thereby generating pulses in the mud flow channel.

[0031] Example 5: As shown in the attached document Figure 1 , 4As shown, a sleeve annular groove 23 is provided on the lower side of the valve head 5 corresponding to the position of the valve sleeve 7, and the upper end of the valve sleeve 7 can enter the sleeve annular groove 23 when the valve head 5 moves downward relative to it. During use, this setting increases the length of the valve sleeve 7 and enhances the stability of the valve head 5 after it is pressed down.

[0032] Example 6: As shown in the appendix Figure 1 As shown, it also includes O-ring seals 22. O-ring seals 22 are provided between the top cap 10 and the connecting neck 3, and between the top cap 10 and the outer protective sleeve 8. This arrangement ensures the sealing between the components during use.

[0033] Example 7: As attached Figure 1 As shown, the top cap 10 has a downward-opening upper blind hole 24 at its lower end, and the bottom cap 12 has an upward-opening lower blind hole 25 at its upper end. The upper end of the non-magnetic spring 11 is located inside the upper blind hole 24, and the lower end of the non-magnetic spring 11 is located inside the lower blind hole 25. This design facilitates the compression of the non-magnetic spring 11 and its return to its original position during use.

[0034] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0035] The specific implementation of this invention is as follows, taking the well logging inclination angle as an example: (1) The present invention is used in conjunction with existing known mud pumps, ground pressure gauges, lower-level machines, upper-level machines and measuring subs, etc. The present invention and the measuring subs are installed in the middle of the oil and gas well drill string. The measuring subs is equipped with a vibration sensor, a tilt sensor and a data processor. During normal drilling, the magnetic field generator is de-energized and the magnetorheological fluid 18 is in a liquid state. The mud pump is turned on, the drilling fluid in the drill string circulates, and the valve head 5 moves downward under the action of the drilling fluid and compresses the non-magnetic spring 11. (2) When it is necessary to measure the well inclination angle data, the mud pump is turned off. The vibration sensor detects that the drill string vibration signal is rapidly attenuated. The data processor determines that the signal is the trigger signal to start the well inclination angle measurement. The magnetic field generator is powered on and the magnetorheological fluid 18 is in a solid state. At the same time, the inclination sensor measures the well inclination angle data and transmits it to the data processor. The data processor processes the well inclination angle data. (3) The well inclination angle data is assigned and stored in the data processor using a timer interrupt function; (4) By delaying the start of the mud pump and intermittently cutting off the power to the magnetic field generator twice, the well inclination angle data is transmitted to the surface in the form of drilling fluid pressure pulses; (5) After the pressure pulse signal is transmitted, the magnetic field generator is powered off and the magnetorheological fluid 18 is in a liquid state by controlling the data processor; (6) The ground pressure gauge receives the well deviation signal. When the drilling fluid pressure pulse signal returns to the ground with the drilling fluid, the ground pressure gauge receives the drilling fluid pressure pulse signal and transmits it to the lower computer. (7) After the lower-level machine receives the drilling fluid pressure pulse signal, it decodes it according to the encoding rules to obtain the value of the well inclination angle; (8) Output the value of the well inclination angle to the host computer for staff to view. When the value of the well inclination angle exceeds the threshold, an alarm is issued, and the drilling operation is interrupted or the well trajectory is corrected.

[0036] After the control magnetic field generator is de-energized twice, the valve head 5 retracts, causing a change in the throttling area, which in turn generates a drilling fluid pressure pulse. The surface pressure gauge receives this pulse as the drilling fluid returns to the surface. Figure 6 After the drilling fluid pressure pulse shown, there are two falling edges. When the GPIO port of the lower computer captures the first falling edge, it triggers the advanced timer to start counting. When the second falling edge is captured, the advanced timer stops counting. The counting time is Δt, and the value corresponding to Δt is the measured well inclination angle data.

[0037] Furthermore, such as Figure 7 As shown, when the lower-level machine's GPIO port captures the first falling edge, the corresponding time is t=13s, triggering the advanced timer to start counting. When the second falling edge is captured, the corresponding time is t=14.5s, and the advanced timer stops counting. The counting time is Δt=1.5s, and its specific value is 1.5. Therefore, 1.5 is the measured well inclination angle data, that is, the measured well inclination angle is 1.5 degrees.

Claims

1. A floating valve type pulse generator, characterized in that... The system includes a throttle valve, an upper connector, a transition section, a connecting neck, a throttle sleeve, a valve head, a valve stem, a valve sleeve, an outer casing, and a magnetorheological fluid assembly. A throttle valve is fixedly installed on the inner side of the upper end of the upper connector. A first limiting ring is provided on the inner side of the upper part of the upper connector. A transition section is fixedly installed on the inner side of the lower end of the upper connector. A vertically penetrating mounting hole is provided in the center of the transition section. At least one vertically penetrating first flow hole is provided on the transition section corresponding to the outer position of the mounting hole. A connecting neck is provided on the lower side of the transition section corresponding to the mounting hole. A connection is provided between the first limiting ring and the transition section. A throttling sleeve is installed inside the upper connector at the position; a valve head is provided on the inner side of the upper part of the throttling sleeve, and a valve stem with its lower end located below the throttling sleeve is provided at the lower end of the valve head. A throttling curved surface is provided on the inner side of the throttling sleeve corresponding to the valve head position. A valve sleeve is provided on the outer side of the middle part of the valve stem. The lower end of the valve sleeve is fixedly installed on the inner side of the transition short section. An outer casing is fixedly installed on the outer side of the lower part of the connecting neck. A magnetorheological fluid assembly is provided inside the outer casing, which can adjust the flow area of ​​drilling fluid at the valve head and the throttling curved surface. The magnetorheological fluid assembly includes a top cap, a non-magnetic spring, a bottom cap, a magnetic field generator, and a support sleeve. The lower end of the valve stem... A bottom cap is fixedly installed on the upper part of the outer casing, corresponding to the position below the top cap. The bottom cap has a second through-hole. A non-magnetic spring is installed between the top cap and the bottom cap. A second limiting ring is located on the inner side of the middle of the outer casing. Magnetorheological fluid is placed inside the outer casing at the position between the top cap and the second limiting ring. A magnetic field generator capable of changing the state of the magnetorheological fluid is located on the second limiting ring. The magnetic field generator has a third through-hole. A support sleeve is provided between the upper end of the magnetic field generator and the lower end of the bottom cap. The magnetic field generator includes a generator... The generator consists of a main body, a magnetoresistive tube, an iron core, and a coil. The upper outer ring platform is located on the outer side of the upper end of the generator body, and the lower outer ring platform is located on the outer side of the lower end of the generator body. At least two vertically penetrating upper magnetoresistive holes are spaced along the circumference of the upper outer ring platform. A vertically penetrating lower magnetoresistive hole is located on the lower outer ring platform corresponding to the position of each upper magnetoresistive hole. A magnetoresistive tube is fixedly installed between each pair of corresponding upper and lower magnetoresistive holes. The magnetoresistive tube has a third flow hole. An iron core is located on the outer side of the generator body at the position between the upper and lower outer ring platforms, and a coil is wound around the outer side of the iron core.

2. The floating valve type pulse generator according to claim 1, characterized in that... The throttling sleeve has an upper flow passage, a middle flow passage, and a lower flow passage connected sequentially from top to bottom. The middle flow passage has a throttling curved surface that is narrow at the top and wide at the bottom. The upper end of the valve head has a conical surface that is small at the top and large at the bottom.

3. The floating valve type pulse generator according to claim 1 or 2, characterized in that... A sleeve annular groove is provided on the lower side of the valve head corresponding to the valve sleeve position, and the upper end of the valve sleeve can enter the sleeve annular groove when the valve head moves downward relative to it.

4. The floating valve type pulse generator according to claim 1 or 2, characterized in that... It also includes O-rings, with an O-ring between the top cap and the connecting neck, and an O-ring between the top cap and the outer casing.

5. The floating valve type pulse generator according to claim 3, characterized in that... It also includes O-rings, with an O-ring between the top cap and the connecting neck, and an O-ring between the top cap and the outer casing.

6. The floating valve type pulse generator according to claim 1, 2, or 5, characterized in that... The top cap has a downward-opening upper blind hole at the bottom, and the bottom cap has an upward-opening lower blind hole at the top. The upper end of the non-magnetic spring is located in the upper blind hole, and the lower end of the non-magnetic spring is located in the lower blind hole.

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