Explosion-proof high-temperature and high-pressure electromagnetic valve

Abstract

The application discloses an explosion-proof high-temperature and high-pressure electromagnetic valve and relates to the technical field of electromagnetic valves.The explosion-proof high-temperature and high-pressure electromagnetic valve comprises a valve assembly, an execution module fixedly installed on the valve assembly and an induction module installed on the execution module.The valve assembly comprises a valve body, opposite flanges arranged at the two ends of the valve body, a heat insulation support fixedly installed at the upper end of the valve body, ventilation openings formed around the heat insulation support, a valve sleeve threadedly installed on the valve body, a valve core slidingly installed in the valve sleeve, a valve rod fixedly installed on the valve core, and a first spring arranged in the valve sleeve.The execution module comprises an explosion-proof shell fixedly installed at the upper end of the heat insulation support.The explosion-proof high-temperature and high-pressure electromagnetic valve can prevent high-temperature medium heat from being transmitted to the execution module, reduce the working temperature of the execution module, delay the aging of internal components, improve the service life and reliability of the equipment in a high-temperature environment and effectively isolate internal electrical elements from an external flammable and explosive environment.

Description

Technical Field

[0001] This invention relates to the field of solenoid valve technology, specifically an explosion-proof high-temperature and high-pressure solenoid valve. Background Technology

[0002] A solenoid valve is a basic automated component that uses electromagnetic force to control the flow, direction, or volume of fluid. Its core working principle is that when an internal electromagnetic coil is energized, it generates magnetic force, driving the valve core to overcome the spring force and move, thereby changing the connectivity of the various channels in the valve body and switching the flow path. When the power is off, the magnetic force disappears, and the valve core returns to its initial state under the action of the spring. Due to its advantages of rapid action, sensitive response, ease of electrical automation control, and high reliability, solenoid valves are widely used in industrial automation, automotive, medical equipment, home appliances, and water treatment.

[0003] Solenoid valves typically consist of three parts: the valve body, the actuator module, and the sensing module. Each of these components performs its specific function, working together to ensure the overall normal operation of the solenoid valve. In chemical production applications, the temperature of the process medium inside the flow pipeline often reaches as high as 200 degrees Celsius. As the medium continuously flows through the valve body, the heat carried by the medium is easily conducted along the valve body structure to the actuator module, ultimately causing a significant increase in the overall temperature of the actuator module. Prolonged exposure to excessively high temperatures can easily lead to aging, failure, and other malfunctions in the internal components of the actuator module, resulting in solenoid valve malfunction, sealing failure, or even complete failure, seriously affecting the normal operation of the solenoid valve and the safety of the entire production system. Furthermore, chemical sites often contain flammable and explosive gases or dust. The electrical sparks or high-temperature surfaces generated during the operation of ordinary solenoid valves may ignite explosive mixtures in the environment, posing a serious safety hazard. Therefore, an explosion-proof high-temperature and high-pressure solenoid valve is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide an explosion-proof high-temperature and high-pressure solenoid valve to solve the problems in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an explosion-proof high-temperature and high-pressure solenoid valve, comprising a valve assembly, an execution module fixedly mounted on the valve assembly, a sensing module mounted on the execution module, the valve assembly comprising a valve body, the valve body having mating flanges at both ends, a heat insulation bracket fixedly mounted on the upper end of the valve body, and ventilation openings around the heat insulation bracket, a valve sleeve threadedly mounted on the valve body, a valve core slidably mounted inside the valve sleeve, a valve stem fixedly mounted on the valve core, and a first spring provided inside the valve sleeve.

[0006] Preferably, the execution module includes an explosion-proof housing fixedly installed on the upper end of the heat insulation bracket. End caps are fixedly installed at both the upper and lower ends of the explosion-proof housing. A terminal block is fixedly installed on the surface of the explosion-proof housing. A protective sleeve is fixedly installed on the terminal block. A sealing cap is threaded onto the end of the protective sleeve. A wire hole is provided on the side wall of the protective sleeve.

[0007] Preferably, an electromagnetic coil is fixedly installed inside the explosion-proof housing. An upper magnetic plate is provided at the upper end of the electromagnetic coil, and a lower magnetic plate is provided at the lower end of the electromagnetic coil. A fixed iron core is fixedly installed inside the electromagnetic coil, and a moving iron core is slidably installed inside the electromagnetic coil. A PEEK guide sleeve is fitted on the outer wall of the moving iron core. A connecting rod is fixedly installed at the lower end of the moving iron core, and a pin is provided at the lower end of the connecting rod. An installation groove is opened on the moving iron core, and a second spring is provided in the installation groove. A push rod is slidably installed in the installation groove.

[0008] Preferably, the sensing module includes a component housing fixedly installed on the upper end of the explosion-proof housing. A cover is installed on one side of the component housing. Two sensing switches are fixedly installed on one side of the component housing and are aligned vertically. A linkage rod is fixedly installed on the upper end of the moving iron core and extends into the component housing. Two sensing blocks are connected to the linkage rod. Adjusting nuts are provided on the upper and lower sides of the sensing blocks. A limit pin is provided at the lower end of the linkage rod.

[0009] Preferably, the upper end of the valve sleeve is provided with a Y-shaped sealing ring, a sealing gasket is provided between the contact end face of the valve sleeve and the valve body, an O-ring is provided on the valve stem and the outer wall of the valve sleeve, and bolts are connected to the four corners of the bottom of the heat insulation bracket, and the heat insulation bracket is fixedly installed on the valve body by bolts.

[0010] Preferably, one end of the first spring is connected to the top of the valve sleeve, and the other end of the first spring is connected to the valve core.

[0011] Preferably, an explosion-proof gasket is provided at the connection between the end cap and the explosion-proof housing, the connecting rod is connected to the valve stem by a pin, the sheath is threaded, and the sealing cap is threaded to the sheath.

[0012] Preferably, the push rod is slidably mounted on the moving iron core through the mounting groove, one end of the second spring is connected to the bottom of the mounting groove, and the other end of the second spring is connected to the push rod.

[0013] Preferably, screws are connected to the four corners of the shell cover, and the shell cover is fixedly installed on the component housing by the screws. A through hole is opened in the middle of the fixed iron core, and the linkage rod passes through the through hole through the fixed iron core.

[0014] Preferably, the sensing block is fixed to the linkage rod by an adjusting nut, the lower end of the linkage rod is fixed to the moving iron core by a countersunk nut, and the limiting pin can restrict the circumferential rotation of the linkage rod.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This application provides a heat-insulating bracket with ventilation openings between the valve body and the actuator module. On the one hand, it elevates the actuator module, extending the heat conduction path and reducing heat transfer. On the other hand, the ventilation openings allow air circulation, forming a convection heat exchange channel to carry away the heat from the valve stem. This prevents the high-temperature medium from transferring heat to the actuator module through both conduction and heat dissipation, thereby reducing the operating temperature of the actuator module, delaying the aging of internal components, and improving the service life and reliability of the equipment in high-temperature environments.

[0016] 2. This application, by configuring an explosion-proof housing and installing explosion-proof gaskets at the connection between the end cap and the explosion-proof housing, can form a closed explosion-proof chamber. When an electrical fault occurs inside the equipment and sparks are generated, the explosion-proof housing can withstand the explosion pressure inside the chamber. At the same time, the flame-extinguishing effect of the gasket gaps prevents the flame from spreading outward, effectively isolating internal electrical components from the external flammable and explosive environment. This meets the safety requirements for use in flammable and explosive environments such as chemical and petroleum industries, and expands the application scenarios of solenoid valves.

[0017] 3. At the sliding fit between the valve sleeve and the valve stem, this application employs a multi-stage combination seal of Y-rings and O-rings. The Y-rings improve sealing performance with increasing medium pressure, and together with the static seal of the O-rings, form a sealing barrier to prevent leakage of high-pressure media. A PEEK guide sleeve is fitted onto the outer wall of the moving iron core. The self-lubricating properties of PEEK material reduce the coefficient of friction between the moving iron core and the inner wall of the housing, reducing motion wear, ensuring flexible movement of the moving iron core, maintaining dimensional accuracy for long-term use, and extending the overall lifespan of the solenoid valve. A threaded sheath and sealing cap are provided. Wiring can be performed by unscrewing the sealing cap without disassembling other components, making wiring convenient. After wiring, tightening the sealing cap restores protection, simplifying the wiring process and improving on-site installation and maintenance efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the valve assembly of the present invention; Figure 3 This is a cross-sectional view of the valve assembly of the present invention; Figure 4 This is a schematic diagram of the execution module of the present invention; Figure 5 For the present invention Figure 4 Enlarged view of point A in the middle; Figure 6This is a cross-sectional view of the execution module of the present invention; Figure 7 This is a cross-sectional view of the electromagnetic coil of the present invention; Figure 8 This is a cross-sectional view of the moving iron core of the present invention; Figure 9 This is a schematic diagram of the sensing module of the present invention.

[0019] Markings in the diagram: 1. Valve assembly; 101. Valve body; 102. Flange; 103. Insulation bracket; 104. Valve sleeve; 105. Valve stem; 106. Y-ring seal; 107. O-ring seal; 108. First spring; 109. Valve core; 2. Actuation module; 201. Explosion-proof housing; 202. End cap; 203. Terminal block; 204. Sheath; 205. Sealing cap; 206. Wire hole; 207. Upper magnetic guide plate 208. Electromagnetic coil; 209. Lower magnetic plate; 210. Connecting rod; 211. Fixed iron core; 212. Moving iron core; 213. PEEK guide sleeve; 214. Second spring; 215. Top rod; 216. Mounting slot; 217. Pin; 3. Induction module; 301. Component housing; 302. Induction switch; 303. Adjusting nut; 304. Linkage rod; 305. Limit pin; 306. Housing cover; 307. Induction block. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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] Please see Figure 1 This invention provides an explosion-proof high-temperature and high-pressure solenoid valve, comprising a valve assembly 1, an actuation module 2, and a sensing module 3. The valve assembly 1 is the part that directly contacts the process medium, the actuation module 2 is the driving part, and the sensing module 3 is the signal feedback part. The three are assembled sequentially from bottom to top to form a compact whole.

[0022] Please see Figure 2 and Figure 3The valve assembly 1 includes a valve body 101, which has an internal channel for media flow. Flanges 102 are located at both ends for connection to the conveying pipeline. During installation, the flanges 102 are bolted to the pipeline flanges, and a sealing gasket is placed between them to ensure a tight seal at the connection. A heat insulation bracket 103 is bolted to the upper end of the valve body 101. This heat insulation bracket 103 has a cage-like or column-like structure, with bolts at its four corners for fixing to the valve body 101. Ventilation openings are provided around the heat insulation bracket 103; these openings can be grid-like, round, or elongated, and their number and size should ensure smooth natural air convection. A valve sleeve 104 is threadedly installed on the valve body 101. A valve core 109 is slidably installed inside the valve sleeve 104. A valve stem 105 is fixedly installed on the valve core 109. The upper end of the valve stem 105 extends upward and passes through the top of the valve sleeve 104, and is connected to the connecting rod 210 of the actuator module 2 via a pin 217. A first spring 108 is provided inside the valve sleeve 104. The first spring 108 is sleeved on the outside of the valve stem 105. Its upper end is connected to the top of the valve sleeve 104, and its lower end is connected to the upper end face of the valve core 109. It always applies a downward closing force to the valve core 109. A Y-shaped sealing ring 106 is provided at the upper end of the valve sleeve 104. The sealing ring is embedded in the annular groove at the top of the valve sleeve 104. Its lip faces the medium side. Under the action of medium pressure, the lip will further open and tightly seal the cover. The higher the pressure, the better the sealing effect. A sealing gasket is provided between the contact end faces of the valve sleeve 104 and the valve body 101 to prevent media leakage from the threaded connection. O-rings 107 are fitted between the sliding mating surfaces of the valve stem 105 and the valve sleeve 104, and between the outer wall of the valve sleeve 104 and the mounting hole of the valve body 101, to achieve reliable static and dynamic sealing. The combination of double O-rings and Y-rings provides redundant sealing and ensures zero leakage during operation. The valve sleeve 104 uses a combination of O-rings and high-temperature PTFE gaskets for sealing, and the valve core uses FFKM seals. This redundant sealing design ensures zero leakage during operation.

[0023] Please see Figure 4 The execution module 2 includes an explosion-proof housing 201, which is bolted to the upper end of the heat insulation bracket 103. The explosion-proof housing 201 is made of metal and has sufficient mechanical strength to withstand the internal explosion pressure without permanent deformation or rupture. End caps 202 are bolted or threaded to both the upper and lower ends of the explosion-proof housing 201. An explosion-proof gasket is provided at the connection between the end cap 202 and the explosion-proof housing 201. This explosion-proof gasket is typically made of materials such as copper, stainless steel, or flame-retardant rubber, and its function is to prevent flame propagation by intermittent flame extinguishing and cooling products in the event of an internal explosion.

[0024] Please see Figure 4 and Figure 5A terminal block 203 is fixedly mounted on the surface of the explosion-proof housing 201. The terminal block 203 has wiring holes and locking screws. A sheath 204 is fixedly mounted on the terminal block 203, and a sealing cap 205 is threaded onto the end of the sheath 204. A wire hole 206 is provided on the side wall of the sheath 204. When wiring is required, the sealing cap 205 is unscrewed to expose the wiring hole on the terminal block 203. The wire is then passed through the wire hole 206 into the sheath 204 and inserted into the wiring hole. Tightening the screw on the wiring hole allows for quick wire installation. After wiring is complete, the sealing cap 205 is tightened back onto the end of the sheath 204 to seal the wiring cavity. The sheath 204 has threads, and the sealing cap 205 is connected to the sheath 204 through these threads, resulting in a simple structure and reliable sealing. The sealing cap 205 is hand-tightened, and the electrical interface is compatible with explosion-proof glands, providing a high protection level and convenient and quick wiring and wire replacement.

[0025] Please see Figure 6 and Figure 7 An electromagnetic coil 208 is fixedly installed inside the explosion-proof housing 201. The frame of the electromagnetic coil 208 is made of high-temperature resistant engineering plastic, and the winding is made of high-temperature resistant enameled wire. An upper magnetic guide plate 207 is provided at the upper end of the electromagnetic coil 208, and a lower magnetic guide plate 209 is provided at the lower end. Both magnetic guide plates are made of soft magnetic material with high magnetic permeability, used to guide and constrain magnetic lines of force, improving the utilization efficiency of electromagnetic force. A fixed iron core 211 is fixedly installed inside the electromagnetic coil 208. The fixed iron core 211 is cylindrical and centrally fixed in the inner hole of the electromagnetic coil 208. A moving iron core 212 is slidably installed inside the electromagnetic coil 208, located below the fixed iron core 211, with a working air gap between them. A PEEK guide sleeve 213 is fitted on the outer wall of the moving iron core 212. This guide sleeve is interference-fitted with the moving iron core 212 or fixed by a retaining ring, and moves with the moving iron core 212, serving both guiding and friction-reducing functions. A connecting rod 210 is fixedly installed at the lower end of the moving iron core 212. A pin 217 is provided at the lower end of the connecting rod 210. The connecting rod 210 is connected to the insertion hole at the upper end of the valve stem 105 through the pin 217, thereby realizing the linkage between the moving iron core 212 and the valve core 109. A mounting groove 216 is opened on the upper end face of the moving iron core 212. The mounting groove 216 is a blind hole structure, which contains a second spring 214 and a push rod 215. One end of the second spring 214 is connected to the bottom of the mounting groove 216, and the other end is connected to the push rod 215. The push rod 215 is slidably installed on the moving iron core 212 through the mounting groove 216 and can extend out of the upper end face of the moving iron core 212. In the power-off state, the push rod 215 abuts against the lower end face of the fixed iron core 211, and pushes the moving iron core 212 downward through the reaction force.

[0026] Specifically, when the electromagnetic coil 208 is not energized, the solenoid valve is in the closed state. At this time, the elastic force of the second spring 214 pushes the push rod 215 upward beyond the moving iron core 212. The upper end of the push rod 215 presses against the lower end face of the fixed iron core 211. Since the fixed iron core 211 is fixed, the reaction force of the push rod 215 pushes the moving iron core 212 downward. When the moving iron core 212 moves downward, it drives the valve stem 105 and the valve core 109 downward through the connecting rod 210. At the same time, the elastic force of the first spring 108 also pushes the valve core 109 downward. The combined force of the two forces makes the valve core 109 tightly pressed against the valve seat inside the valve body 101, thereby cutting off the medium flow channel and realizing the reliable closure of the valve. When it is necessary to open the valve, the electromagnetic coil 208 is energized. The electromagnetic coil 208 generates an electromagnetic force, which is sufficient to overcome the elastic force of the second spring 214 and the upward force of the medium on the valve core 109, and pulls the moving iron core 212 upward. When the moving iron core 212 moves upward, the push rod 215 is compressed back into the mounting groove 216, and the connecting rod 210 moves upward simultaneously, driving the valve stem 105 and valve core 109 to move upward, causing the valve core 109 to leave the valve seat, opening the medium passage and realizing the opening of the valve. The four sets of internally recessed return spring assemblies combine precise action with flexible adjustment.

[0027] Please see Figure 9 The sensing module 3 includes a component housing 301, which is fixedly installed on the upper end of the explosion-proof housing 201. A cover 306 is installed on one side of the component housing 301, and screws are connected to the four corners of the cover 306, securing it to the component housing 301 for easy opening and internal debugging. Two inductive switches 302 are fixedly installed on one side of the component housing 301, arranged vertically aligned. The inductive switches 302 can be non-contact position detection elements such as proximity switches, Hall effect switches, or photoelectric switches. A linkage rod 304 is fixedly installed on the upper end of the moving iron core 212, passing through a through hole in the middle of the fixed iron core 211 and extending into the component housing 301. Two sensing blocks 307 are connected to the linkage rod 304. The sensing blocks 307 are ring-shaped or block-shaped and are fitted onto the linkage rod 304. Adjusting nuts 303 are provided on the upper and lower sides of the sensing blocks 307, allowing the sensing blocks 307 to be positioned at any point on the linkage rod 304 and their axial position to be adjusted during debugging. A limit pin 305 is provided at the lower end of the linkage rod 304 to limit its axial rotation. The lower end of the linkage rod 304 is restrained on the moving iron core 212 by a countersunk nut, ensuring synchronous movement between the linkage rod 304 and the moving iron core 212. A plastic guide sleeve is fitted onto the linkage rod 304, which is embedded in the inner wall of the through hole of the fixed iron core 211 to reduce friction during sliding and achieve electrical isolation. The dual-set inductive switches 302 can accurately sense the valve position status, simultaneously transmit signals to multiple control units, and serve as backups for each other, increasing safety redundancy.

[0028] This product is an explosion-proof, high-temperature, and high-pressure venting solenoid valve, mainly used in the fuel gas pipelines of petrochemical gas turbines. It allows for remote venting of residual gas in pipelines and pressure relief during unit shutdown and maintenance, preventing explosions. It is compatible with the gas supply systems of self-owned power plants in refining and coal chemical industries, and can be connected to ESD / SIS interlocks to meet the requirements of explosion-proof, high-temperature, and high-pressure hazardous operating conditions.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. An explosion-proof high-temperature and high-pressure solenoid valve, characterized in that: The device includes a valve assembly (1), an execution module (2) is fixedly installed on the valve assembly (1), a sensing module (3) is installed on the execution module (2), the valve assembly (1) includes a valve body (101), the valve body (101) has docking flanges (102) at both ends, a heat insulation bracket (103) is fixedly installed on the upper end of the valve body (101), and ventilation openings are provided around the heat insulation bracket (103). A valve sleeve (104) is threaded on the valve body (101), a valve core (109) is slidably installed in the valve sleeve (104), a valve stem (105) is fixedly installed on the valve core (109), and a first spring (108) is provided in the valve sleeve (104).

2. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 1, characterized in that: The execution module (2) includes an explosion-proof housing (201) fixedly installed on the upper end of the heat insulation bracket (103). Both ends of the explosion-proof housing (201) are fixedly installed with end caps (202). A terminal block (203) is fixedly installed on the surface of the explosion-proof housing (201). A protective sleeve (204) is fixedly installed on the terminal block (203). A sealing cap (205) is threaded onto the end of the protective sleeve (204). A wire hole (206) is provided on the side wall of the protective sleeve (204).

3. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 2, characterized in that: An electromagnetic coil (208) is fixedly installed inside the explosion-proof housing (201). An upper magnetic plate (207) is provided at the upper end of the electromagnetic coil (208), and a lower magnetic plate (209) is provided at the lower end of the electromagnetic coil (208). A fixed iron core (211) is fixedly installed inside the electromagnetic coil (208), and a movable iron core (212) is slidably installed inside the electromagnetic coil (208). A PEEK guide sleeve (213) is sleeved on the outer wall of the movable iron core (212). A connecting rod (210) is fixedly installed at the lower end of the movable iron core (212), and a pin (217) is provided at the lower end of the connecting rod (210). An installation groove (216) is opened on the movable iron core (212), and a second spring (214) is provided in the installation groove (216). A top rod (215) is slidably installed in the installation groove (216).

4. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 3, characterized in that: The sensing module (3) includes a component housing (301) fixedly installed on the upper end of the explosion-proof housing (201). A cover (306) is installed on one side of the component housing (301). Two sensing switches (302) are fixedly installed on one side of the component housing (301) and the two sensing switches (302) are aligned vertically. A linkage rod (304) is fixedly installed on the upper end of the moving iron core (212) and the linkage rod (304) extends into the component housing (301). Two sensing blocks (307) are connected to the linkage rod (304). Adjusting nuts (303) are provided on the upper and lower sides of the sensing blocks (307). A limit pin (305) is provided at the lower end of the linkage rod (304).

5. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 3, characterized in that: The valve sleeve (104) is provided with a Y-shaped sealing ring (106) at the upper end. A sealing gasket is provided between the contact end face of the valve sleeve (104) and the valve body (101). An O-ring sealing ring (107) is provided on the valve stem (105) and the outer wall of the valve sleeve (104). Bolts are connected at the four corners of the bottom of the heat insulation bracket (103). The heat insulation bracket (103) is fixedly installed on the valve body (101) by bolts.

6. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 3, characterized in that: One end of the first spring (108) is connected to the top of the valve sleeve (104), and the other end of the first spring (108) is connected to the valve core (109).

7. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 3, characterized in that: An explosion-proof gasket is provided at the connection between the end cap (202) and the explosion-proof housing (201). The connecting rod (210) is connected to the valve stem (105) by a pin (217). The sleeve (204) is provided with threads. The sealing cap (205) is connected to the sleeve (204) by threads.

8. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 3, characterized in that: The top rod (215) is slidably mounted on the moving iron core (212) through the mounting groove (216). One end of the second spring (214) is connected to the bottom of the mounting groove (216), and the other end of the second spring (214) is connected to the top rod (215).

9. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 4, characterized in that: The cover (306) is connected to screws at the four corners. The cover (306) is fixedly installed on the component housing (301) by screws. The fixed iron core (211) has a through hole in the middle. The linkage rod (304) passes through the fixed iron core (211) through the through hole.

10. The explosion-proof high-temperature and high-pressure solenoid valve according to claim 4, characterized in that: The sensing block (307) is restricted to the linkage rod (304) by the adjusting nut (303), the lower end of the linkage rod (304) is restricted to the moving iron core (212) by the countersunk nut, and a plastic guide sleeve is fitted on the linkage rod (304).

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