Double-seal pilot valve for nuclear power and opening and closing pressure setting method

Abstract

The application discloses a double-sealing pilot valve for nuclear power and an opening and closing pressure setting method, and belongs to the pilot valve field. The device comprises a valve cover, a valve body, a valve core, a valve seat, a valve rod, a bend pipe, a spiral coil pipe and a tee pipe. The valve rod is coaxially provided with an upper disc and a lower disc. The valve core has a gap with the inner wall of the valve body, and the bottom of the valve core can be in contact with the valve seat to form a seal. The upper chamber is communicated with the first channel of the tee pipe through an upper opening, the lower chamber is sequentially connected with the bend pipe, the spiral coil pipe and the second channel of the tee pipe through a lower opening, and the third channel of the tee pipe is used for being connected with the pressure relief port of the safety valve. The application is used in the pilot safety valve for nuclear power, is used for controlling the rapid response of the safety valve under the overpressure working condition, does not need to add an additional actuator, and saves the energy consumption. The number of turns and the placement mode of the spiral coil pipe and the area of the two discs on the valve rod can be adjusted to adapt to different setting pressures of the safety valve, and the application has high working condition applicability.

Description

Technical Field

[0001] This invention belongs to the field of pilot valves, and specifically relates to a double-sealed pilot valve for nuclear power and a method for setting the opening and closing pressure. Background Technology

[0002] A pilot-operated safety valve is a type of safety valve that relies on the medium discharged from a pilot valve to drive or control the main valve. The pilot valve itself is a standard spring-loaded direct-load safety valve. Safety valves belong to the category of automatic valves and are mainly used in boilers, pressure vessels, and pipelines to control pressure to within specified values, playing a crucial role in protecting personal safety and equipment operation. In large-scale pipeline projects such as nuclear power plants, the role and requirements of pilot-operated safety valves are even more stringent. In large nuclear reactors, pilot-operated safety valves primarily transmit their response through steam. When the pressure inside the pipeline exceeds the set pressure, the pilot valve opens first to release pressure, creating a pressure difference between the upper and lower chambers of the main valve. Driven by the medium force, the safety valve opens and releases the overpressure steam in the pipeline to the atmosphere. Simultaneously, when the pressure inside the pipeline falls below the set pressure, the pilot valve closes, and pressure begins to accumulate in the upper chamber of the safety valve connected to the pilot valve. The safety valve then closes again under the action of the medium pressure difference.

[0003] The performance of the pilot valve plays a crucial role in the opening of the safety valve and the safe and stable operation of the pipeline system. The rapid response of the pilot valve is decisive for the rapid opening of the safety valve under overpressure conditions. Conversely, under normal operating conditions, if the pilot valve's sealing performance is compromised, causing the safety valve to prematurely release pressure, it will lead to malfunctions in the pipeline system and energy loss.

[0004] Therefore, it is of great significance to study a double-sealed pilot valve for nuclear power and propose a method for setting its opening and closing pressure. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies in the prior art and provide a double-sealed pilot valve for nuclear power plants and a method for setting the opening and closing pressure. The device of this invention is used in pilot-operated safety valves for nuclear power plants and can be used to control the rapid response of the safety valve under overpressure conditions. This is mainly achieved by, under normal operating conditions, the medium force pushes the valve core and valve seat to form a hard seal, while condensate provides a liquid seal to the valve seat, forming a "double seal." Under overpressure conditions, rapid opening is achieved under the driving force of steam and condensate. Simultaneously, by adjusting the number of turns and the arrangement of the spiral coil, the area of ​​the upper and lower discs on the valve stem can be used to set the opening and closing pressure of the pilot valve, exhibiting high adaptability to various operating conditions.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a double-sealed pilot valve for nuclear power, comprising a valve cover, a valve body, a valve core, a valve seat, a valve stem, a bend, a spiral coil, and a tee.

[0008] The valve body has a valve cover and a valve seat at its top and bottom, respectively, and a valve stem is located in the hollow inner cavity of the valve body. An upper and lower disc are coaxially mounted on the valve stem, with the lower disc having a larger diameter than the upper disc. The surfaces of both discs are perpendicular to the valve stem axis. The outer circumferences of the upper and lower discs are slidably connected to the inner wall of the valve body, dividing the hollow inner cavity into three non-communicating chambers: an upper chamber, a middle chamber, and a lower chamber. The top of the valve stem passes through the valve cover and is located on the outside, while a valve core is fixed at its bottom. There is a gap between the valve core and the inner wall of the valve body, and both ends at the bottom can contact the valve seat to form a seal. The upper chamber is connected to the first channel of a three-way pipe through an upper opening, and the lower chamber is connected sequentially to a bend, a spiral coil, and the second channel of the three-way pipe through a lower opening. The third channel of the three-way pipe is used to connect to the pressure relief port of the safety valve.

[0009] Preferably, both the valve cover and the valve seat are sealed to the valve body.

[0010] Preferably, when the valve stem is in the upper limit position, the upper opening is located above the upper disk; when the valve stem is in the lower limit position, the lower opening is located below the lower disk.

[0011] Preferably, the bottom of the valve core has an arc-shaped protrusion structure, and when the valve stem is in the lower limit position, the protrusion end is lower than the top of the valve seat so that a seal is formed between the two.

[0012] Preferably, the second channel of the three-way pipe is located at the bottom of the three-way pipe, and the first channel and the second channel are located on the horizontal sides respectively.

[0013] Preferably, both the upper and lower openings are horizontally positioned.

[0014] Preferably, by adjusting the number of turns and the placement of the spiral coil, the high-temperature steam entering the second channel of the three-way pipe can be condensed into water and flow into the lower chamber through the bend.

[0015] Secondly, the present invention provides a method for setting the opening and closing pressure of a double-sealed pilot valve for nuclear power based on any one of the first aspects, as detailed below:

[0016] S1: In the initial state, the pressure inside the pilot valve has not reached the set pressure, and the pilot valve is in a static state. At this time, high-temperature and high-pressure steam continuously flows from the pressure relief port of the safety valve into the inner cavity of the pilot valve through the three-way pipe; part of the steam flows into the upper chamber of the pilot valve through the first channel and remains in a high-pressure state; part of the steam flows into the spiral coil through the second channel for pressure reduction and condensation, and the condensate formed enters the lower chamber of the pilot valve through the bend pipe under the push of the high-temperature and high-pressure steam.

[0017] S2: As the pressure inside the safety valve gradually increases, the upper chamber of the pilot valve remains under high pressure. Meanwhile, the steam in the lower chamber, after being depressurized and condensed by the spiral coil, has a significantly lower pressure than the upper chamber. Therefore, the resultant force on the valve stem is vertically downward, and this pressure is transmitted to the valve core, causing the valve core and valve seat to make tight contact and form a hard seal. At the same time, due to the pressure difference between the upper and lower chambers, the gradually increasing pressure causes the steam to mainly flow into the spiral coil connected to the three-way pipe. At this time, the volume of condensate in the spiral coil gradually increases and continuously flows into the lower chamber of the pilot valve. The volume of condensate in the lower chamber continuously increases and flows into the gap between the valve core and the inner wall of the valve body, forming a liquid seal between the valve core and the valve seat.

[0018] S3: When the main valve needs to be opened, ensure that the lower chamber of the pilot valve is filled with condensate and the pipeline system connected to the safety valve is under overpressure. When the high-temperature and high-pressure steam flows through the spiral coil again, the condensate in the spiral coil increases due to condensation. The high-temperature and high-pressure steam will push the condensate in the lower chamber, causing it to tend to push the lower disc of the valve stem upward. Since water is incompressible, it has a large thrust on the lower disc of the valve stem. At the same time, since the area of ​​the lower disc is larger than that of the upper disc, there will be a greater upward thrust, realizing the rapid opening of the pilot valve. Once the pilot valve is opened, due to the pressure difference and gravity, the water in the lower chamber of the pilot valve will flow out of the pilot valve along with the high-pressure steam, realizing the pressure relief of the safety valve.

[0019] S4: When the pressure relief process of the safety valve ends, the pilot valve needs to be closed. At this time, since the condensate is drained, the high-temperature and high-pressure steam will be de-cooled and depressurized again when it passes through the spiral coil. Therefore, the pressure in the lower chamber gradually decreases, while the steam flowing into the upper chamber is still high-pressure steam. So, under the driving force of the medium pressure difference, the combined force of the pressure and gravity on the upper disc is greater than the force on the lower disc. The valve stem drives the valve core to move downward, thereby closing the pilot valve.

[0020] S5: For different opening pressures of the safety valve, the range of the pilot valve's opening and closing pressure can be set by adjusting the number of turns and placement of the spiral coil, as well as the area of ​​the upper and lower discs, so as to achieve applicability of the safety valve to different set pressures.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1) This invention is used in nuclear power pilot-operated safety valves to control the rapid response of the safety valve under overpressure conditions. The device of this invention does not require the addition of an extra actuator, thus saving energy consumption.

[0023] 2) The device of the present invention can adapt to different set pressures of the safety valve by adjusting the number of turns and placement method of the spiral coil (including the placement angle of the central axis) and the area of ​​the two discs on the valve stem (i.e., the upper disc and the lower disc), and has high applicability to working conditions. Attached Figure Description

[0024] Figure 1 This is a three-dimensional schematic diagram of a pilot valve;

[0025] Figure 2 This is a sectional view of the pilot valve;

[0026] Figure 3 This is a schematic diagram of the valve stem;

[0027] Figure 4 This is a schematic diagram of a spiral coil;

[0028] In the diagram: 1. Valve cover; 2. Valve body; 3. Valve core; 4. Valve seat; 5. Valve stem; 5-1. Upper disc; 5-2. Lower disc; 6. Bend; 7. Spiral coil; 8. T-joint. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0030] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0031] In the description of this invention, it should be understood that expressions such as "high temperature" and "high pressure" are used only for distinguishing purposes and are "high" relative to the steam state at other locations in the overall pipeline. They should not be construed as indicating or implying relative importance or implicitly specifying the temperature and pressure limits of the indicated technical features.

[0032] like Figure 1 and 2As shown, this invention provides a double-sealed pilot valve for nuclear power plants. The double-sealed pilot valve mainly includes a valve cover 1, a valve body 2, a valve core 3, a valve seat 4, a valve stem 5, a bend 6, a spiral coil 7, and a three-way pipe 8. The left side of the three-way pipe 8 is the inlet of the pilot valve, which is connected to the safety valve. High-temperature, high-pressure steam flows into the valve body 2 through the three-way pipe 8. Part of the steam flows directly into the upper chamber of the pilot valve, while the other part flows into the lower chamber of the pilot valve through the spiral coil 7, where it is cooled and condensed. When the valve core 3 opens, the steam flows out of the pilot valve, thus relieving pressure on the safety valve.

[0033] The structure and connection methods of each component will be explained in detail below.

[0034] In the device of the present invention, a valve cover 1 is installed at the top opening of the valve body 2, and a valve seat 4 is installed at the bottom opening. The valve cover 1, the valve body 2 and the valve seat 4 together form the hollow inner cavity of the valve body 2, and a vertical valve stem 5 is installed in the hollow inner cavity of the valve body 2.

[0035] In a preferred embodiment of the present invention, both the valve cover 1 and the valve seat 4 are sealed to the valve body 2, and the connection method is a detachable connection.

[0036] In the device of the present invention, such as Figure 3 As shown, an upper disk 5-1 and a lower disk 5-2 are coaxially mounted on the middle section of the valve stem 5. There is a certain distance between the upper disk 5-1 and the lower disk 5-2, and the diameter of the lower disk 5-2 is larger than the diameter of the upper disk 5-1. The surfaces of both disks are perpendicular to the axial direction of the valve stem 5. The outer circumferences of both the upper disk 5-1 and the lower disk 5-2 are slidably and sealingly connected to the inner wall of the valve body 2, dividing the hollow inner cavity into three non-communicating chambers: an upper chamber, a middle chamber, and a lower chamber.

[0037] In other words, the inner cavity of the valve body 1 is mainly divided into an upper chamber and a lower chamber by the valve stem 5. The medium in the upper chamber is mainly high-temperature and high-pressure steam flowing in from the upper chamber of the safety valve. The lower chamber is a mixture of condensate and high-temperature steam formed after the high-temperature steam is depressurized and cooled down through the spiral coil 7.

[0038] In the device of the present invention, the top of the valve stem 5 passes through the valve cover 1 and is located on the outside, while the bottom is fixed with the valve core 3. During movement, the valve stem 5 can pull the movement of the valve core 3. There is a small gap between the valve core 3 and the inner wall of the valve body 2, which allows condensate to flow into the gap when it enters the lower chamber. The bottom ends of the valve core 3 can contact the valve seat 4 and form a hard seal. Here, a hard seal refers to a structurally feasible seal.

[0039] In a preferred embodiment of the present invention, the bottom of the valve core 3 has an arc-shaped protrusion structure, and when the valve stem 5 is in the lower limit position, the protrusion end is lower than the top of the valve seat 4 to form a seal between them. That is, as Figure 2 As shown in the enlarged view, the two ends of the valve core 3 contact the valve seat 4 to form a hard seal. The bottom is an arc-shaped convex shape, lower than the top of the valve seat 4, which serves as an end seal.

[0040] In the device of the present invention, an upper opening and a lower opening are respectively provided on the side wall of the valve body 2 on the same side. The upper chamber is connected to the first channel of the three-way pipe 8 through the upper opening, and the lower chamber is connected to the second channel of the bend pipe 6, the spiral coil 7 and the three-way pipe 8 in sequence through the lower opening. The third channel of the three-way pipe 8 is used to connect to the pressure relief port of the safety valve.

[0041] In a preferred embodiment of the present invention, when the valve stem 5 is at its upper limit position, the upper opening should be located above the upper disk 5-1. When the valve stem 5 is at its lower limit position, the lower opening should be located below the lower disk 5-2. That is to say, the up and down movement of the valve stem 5 will not affect the entry of high-temperature and high-pressure steam into the upper and lower chambers.

[0042] In a preferred embodiment of the present invention, the second channel of the three-way pipe 8 is located at the bottom of the three-way pipe 8, and the first and second channels are located on the horizontal sides respectively. Both the upper and lower openings are horizontally arranged. That is, the left end of the three-way pipe 8 is connected to the pressure relief port of the safety valve, the right end is connected to the upper chamber of the pilot valve, and the lower end is connected to the spiral coil 7.

[0043] In a preferred embodiment of the present invention, by adjusting the number of turns and placement of the spiral coil 7, the high-temperature steam entering the second channel of the three-way pipe 8 can condense into water and flow into the lower chamber through the bend pipe 6. Specifically, as shown... Figure 4 As shown, the inlet of the spiral coil 7 is connected to the lower outlet of the tee pipe 8, and the central axis of the spiral coil 7 is not absolutely perpendicular to the tee pipe 8. Figure 2 The spiral coil 7 is set horizontally as shown, but it can be adjusted to be vertical according to the actual working conditions. The high-pressure and high-temperature steam in the coil loses more heat along the way due to the increased frictional resistance and the increased heat exchange area with the outside. The pressure and temperature will decrease step by step, and eventually some of it will condense into water in the spiral coil 7. The condensate is pushed by the steam into the lower end of the pilot valve and flows into the gap between the valve core 3 and the inner wall of the valve body 2, which plays a liquid seal role on the valve seat 4. This liquid seal and the hard seal between the valve core 3 and the valve seat 4 together form a "double seal".

[0044] Based on any of the aforementioned double-sealed pilot valves for nuclear power, the present invention also provides a method for setting the opening and closing pressure, the method being as follows:

[0045] S1: In the initial state, the pressure inside the pilot valve has not reached the set pressure, and the pilot valve is in a static state. At this time, high-temperature and high-pressure steam continuously flows from the pressure relief port of the safety valve into the inner cavity of the pilot valve through the three-way pipe 8. Some steam flows into the upper chamber of the pilot valve through the first channel and remains under high pressure. Some steam flows into the spiral coil 7 through the second channel for pressure reduction and condensation. The condensate formed is pushed by the high-temperature and high-pressure steam and enters the lower chamber of the pilot valve through the bend pipe 6.

[0046] S2: As the pressure inside the safety valve gradually increases, the upper chamber of the pilot valve remains under high pressure. Meanwhile, the steam in the lower chamber, after being reduced in pressure and condensed by the spiral coil 7, has a significantly lower pressure than the upper chamber. Therefore, the resultant force on the valve stem 5 is perpendicularly downwards, and this pressure is transmitted to the valve core 3, causing it to contact the valve seat 4 tightly and form a hard seal. Simultaneously, due to the pressure difference between the upper and lower chambers, the gradually increasing pressure causes the steam to primarily flow into the spiral coil 7 connected to the three-way pipe 8. At this time, the volume of condensate in the spiral coil 7 gradually increases, continuously flowing into the lower chamber of the pilot valve. The increasing volume of condensate in the lower chamber flows into the gap between the valve core 3 and the inner wall of the valve body 2, forming a liquid seal between the valve core 3 and the valve seat 4.

[0047] Through the aforementioned "hard seal" and "liquid seal" effects, the pilot valve achieves "double sealing".

[0048] S3: When the main valve needs to be opened, ensure that the lower chamber of the pilot valve is filled with condensate, and that the pipeline system connected to the safety valve is under overpressure. At this time, the overpressure in the pipeline system needs to be controlled by the pilot valve to release pressure through the safety valve. The pipeline system, safety valve, and pilot valve are all under overpressure at this point. When the high-temperature, high-pressure steam flows through the spiral coil 7 again, the amount of condensate in the spiral coil 7 increases due to condensation. The high-temperature, high-pressure steam will push the condensate in the lower chamber, causing it to tend to push the lower disc 5-2 of the valve stem 5 upwards. Since water is incompressible, it exerts a large thrust on the lower disc 5-2 of the valve stem 5. Simultaneously, because the area of ​​the lower disc 5-2 is larger than that of the upper disc 5-1, there will be an even greater upward thrust, enabling the pilot valve to open quickly. Once the pilot valve opens, due to the pressure difference and gravity, the water in the lower chamber of the pilot valve will flow out of the pilot valve along with the high-pressure steam, thus releasing pressure from the safety valve.

[0049] S4: When the pressure relief process of the safety valve ends, the pilot valve needs to be closed. At this time, since the condensate is drained, the high-temperature and high-pressure steam will be de-heated and depressurized again when it passes through the spiral coil 7. Therefore, the pressure in the lower chamber gradually decreases, while the steam flowing into the upper chamber is still high-pressure steam. So, under the driving force of the medium pressure difference, the combined force of the pressure and gravity on the upper disc 5-1 is greater than the force on the lower disc 5-2. The valve stem 5 drives the valve core 3 to move downward, thereby closing the pilot valve.

[0050] S5: For different opening pressures of the safety valve, the range of the pilot valve's opening and closing pressure can be set by adjusting the number of turns and placement method of the spiral coil 7 (including horizontal placement and vertical placement of the central axis), as well as the area of ​​the upper disc 5-1 and the lower disc 5-2, so as to achieve applicability of safety valves with different set pressures.

[0051] This invention is used in nuclear power pilot-operated safety valves to control the rapid response of the safety valve under overpressure conditions. This invention does not require the addition of an extra actuator, thus saving energy consumption. By adjusting the number of turns and placement of the spiral coil, as well as the area of ​​the two discs on the valve stem, it can adapt to different set pressures of the safety valve, and has high applicability to various operating conditions.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A double-sealed pilot valve for nuclear power plants, characterized in that, It includes a valve cover (1), a valve body (2), a valve core (3), a valve seat (4), a valve stem (5), a bend (6), a spiral coil (7), and a tee pipe (8); The valve body (2) is provided with a valve cover (1) and a valve seat (4) at its top and bottom, respectively. A valve stem (5) is provided in the hollow inner cavity of the valve body (2). An upper disc (5-1) and a lower disc (5-2) are coaxially provided on the valve stem (5), and the diameter of the lower disc (5-2) is larger than that of the upper disc (5-1). The surfaces of the two discs are perpendicular to the axial direction of the valve stem (5). The outer circumferences of the upper disc (5-1) and the lower disc (5-2) are sealed and slidably connected to the inner wall of the valve body (2), dividing the hollow inner cavity into an unconnected upper cavity. The valve has a middle chamber and a lower chamber; the top of the valve stem (5) passes through the valve cover (1) and is located on the outside, and the bottom is fixed with a valve core (3); there is a gap between the valve core (3) and the inner wall of the valve body (2), and the bottom two ends of the valve core (3) can contact the valve seat (4) and form a seal; the upper chamber is connected to the first channel of the three-way pipe (8) through the upper opening, and the lower chamber is connected to the second channel of the bend pipe (6), the spiral coil (7) and the three-way pipe (8) in sequence through the lower opening. The third channel of the three-way pipe (8) is used to connect to the pressure relief port of the safety valve.

2. The double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, Both the valve cover (1) and the valve seat (4) are sealed to the valve body (2).

3. A double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, When the valve stem (5) is in the upper limit position, the upper opening is located above the upper disk (5-1); when the valve stem (5) is in the lower limit position, the lower opening is located below the lower disk (5-2).

4. A double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, The bottom of the valve core (3) has an arc-shaped protrusion structure, and when the valve stem (5) is in the lower limit position, the protrusion end is lower than the top of the valve seat (4) so ​​that a seal is formed between the two.

5. A double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, The second channel of the three-way pipe (8) is located at the bottom of the three-way pipe (8), and the first channel and the second channel are located on the horizontal sides respectively.

6. A double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, Both the upper and lower openings are horizontally positioned.

7. A double-sealed pilot valve for nuclear power plants according to claim 1, characterized in that, By adjusting the number of turns and placement of the spiral coil (7), the high-temperature steam entering the second channel of the three-way pipe (8) can be condensed into water and flow into the lower chamber through the bend pipe (6).

8. A method for setting the opening and closing pressure of a double-sealed pilot valve for nuclear power plants according to any one of claims 1 to 7, characterized in that, Specifically as follows: S1: In the initial state, the pressure inside the pilot valve has not reached the set pressure, and the pilot valve is in a static state. At this time, high-temperature and high-pressure steam continuously flows from the pressure relief port of the safety valve into the inner cavity of the pilot valve through the three-way pipe (8); some steam flows into the upper chamber of the pilot valve through the first channel and remains in a high-pressure state; some steam flows into the spiral coil (7) through the second channel for pressure reduction and condensation, and the condensate formed enters the lower chamber of the pilot valve through the bend pipe (6) under the push of the high-temperature and high-pressure steam. S2: As the pressure inside the safety valve gradually increases, the upper chamber of the pilot valve remains under high pressure. The steam in the lower chamber is significantly less than the pressure in the upper chamber due to the pressure reduction and condensation effect of the spiral coil (7). Therefore, the resultant force on the valve stem (5) is vertically downward, and this pressure is transmitted to the valve core (3), making the valve core (3) and the valve seat (4) in close contact and forming a hard seal. At the same time, due to the pressure difference between the upper and lower chambers, the gradually increasing pressure causes the steam to mainly flow into the spiral coil (7) connected to the three-way pipe (8). At this time, the volume of condensate in the spiral coil (7) gradually increases and continuously flows into the lower chamber of the pilot valve. The volume of condensate in the lower chamber continuously increases and flows into the gap between the valve core (3) and the inner wall of the valve body (2), forming a liquid seal between the valve core (3) and the valve seat (4). S3: When the main valve needs to be opened, ensure that the lower chamber of the pilot valve is filled with condensate and the pipeline system connected to the safety valve is in an overpressure state. When the high temperature and high pressure steam flows through the spiral coil (7) again, due to the condensation effect, the condensate in the spiral coil (7) increases. The high temperature and high pressure steam will push the condensate in the lower chamber to push the lower disc (5-2) of the valve stem (5) upward. Since water is incompressible, it has a large thrust on the lower disc (5-2) of the valve stem (5). At the same time, since the area of ​​the lower disc (5-2) is larger than that of the upper disc (5-1), there will be a greater upward thrust, realizing the rapid opening of the pilot valve. Once the pilot valve is opened, due to the pressure difference and gravity, the water in the lower chamber of the pilot valve will flow out of the pilot valve along with the high pressure steam, realizing the pressure relief of the safety valve. S4: When the pressure relief process of the safety valve ends, the pilot valve needs to be closed. At this time, since the condensate is drained, the high temperature and high pressure steam will be de-heated and de-pressurized again when it passes through the spiral coil (7). Therefore, the pressure in the lower chamber gradually decreases, while the steam flowing into the upper chamber is still high pressure steam. So, under the driving force of the medium pressure difference, the combined force of the pressure and gravity on the upper disc (5-1) is greater than the force on the lower disc (5-2). The valve stem (5) drives the valve core (3) to move downward, thereby closing the pilot valve. S5: For different opening pressures of the safety valve, the range of the pilot valve opening and closing pressure can be set by adjusting the number of turns and placement of the spiral coil (7), as well as the area of ​​the upper disc (5-1) and the lower disc (5-2), so as to achieve applicability of the safety valve to different set pressures.

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