A main steam valve station fast-opening and slow-closing front isolation valve and control method

Abstract

The present invention discloses a fast-opening and slow-closing pre-isolating valve and a control method for a main steam valve station, which belongs to the field of main steam valve stations. The pre-isolating valve includes a valve cover, a valve body, an air outlet pipe, a booster element, a valve stem and a valve disc. The valve body is divided into an upper cavity and a middle cavity by the valve stem, and is divided into a middle cavity and a lower cavity by a sleeve. The middle is connected by a throttle hole. The booster element is composed of a piston, a spring and a profile plate. The present invention is an important component of a nuclear power main steam valve station. It will remain closed under normal working conditions. When an accident occurs, it is required to open quickly in a short time. The device, through its own structural characteristics, converts a part of the high-speed fluid when the valve is opened into a driving force for opening the valve, shortens its opening time, and plays a reverse pushing role on the valve stem when closing, so that it closes slowly. At the same time, the opening and closing time can be changed by adjusting the spring stiffness and the position of the piston.

Description

Technical Field

[0001] The present invention belongs to the field of main steam valve stations, and in particular relates to a fast-opening and slow-closing pre-isolating valve and a method thereof. Background Art

[0002] As one of the three-level overpressure protection devices in the secondary circuit of a nuclear power plant, the main steam valve station is located outside the containment and plays a key role in the safe and reliable operation of the main steam system. The main steam valve station is composed of a valve group consisting of a main steam fast isolation valve, an atmospheric relief valve pre-isolation valve, a monitoring main steam safety valve and a working main steam safety valve. Figure 5 As shown, in the figure, a is the monitoring main steam safety valve, b is the main steam quick isolation valve, c is the front isolation valve of the atmospheric release valve, and d is the working main steam safety valve.

[0003] The atmospheric discharge valve pre-isolating valve is the only isolating valve before the atmospheric discharge valve, and is composed of a main valve and two solenoid valves.

[0004] When an accident occurs, the pre-isolating valve is required to open within a specified time and discharge the steam in the main steam pipeline into the atmosphere. Otherwise, it will cause huge damage to personnel and property. However, in current actual working conditions, the opening timeout often occurs.

[0005] Therefore, it is of great significance to study a pre-isolation valve that can be opened quickly under accident conditions and closed slowly when the accident is resolved to reduce damage to the valve itself and reduce noise and vibration. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects in the prior art and provide a main steam valve station fast opening and slow closing pre-isolating valve and control method. The pre-isolating valve of the present invention is an important component of the nuclear power main steam valve station. It will remain closed under normal working conditions. When an accident occurs, it is required to open quickly in a short time. The pre-isolating valve of the present invention, through its own structural characteristics, converts a part of the high-speed fluid when the valve is opened into a driving force for opening the valve, shortening its opening time. At the same time, it plays a reverse pushing role on the valve stem when closing, realizing its slow closing. At the same time, the opening and closing time can be changed by adjusting the stiffness of the spring and the position of the piston to adapt to different working conditions.

[0007] The specific technical solutions adopted in the present invention are as follows:

[0008] In a first aspect, the present invention provides a main steam valve station fast-opening and slow-closing front isolation valve, comprising a valve body, a valve cover, a booster element, a sleeve, a valve stem, and a valve disc;

[0009] The top of the valve body is sealed with a valve cover, a sleeve is fixed horizontally in the inner cavity, and a second outlet for communicating with the atmospheric relief valve is opened at the bottom; a limit piece is provided under the valve cover to enable the valve stem to slide only in the vertical direction; the valve stem is vertically arranged in the inner cavity of the valve body, the top is located in the limit piece, the lower part passes through the sleeve and forms a sliding pair, and a valve disc for controlling the opening and closing of the second outlet is fixed at the bottom; a disc-shaped positioning piece is fixed horizontally on the outer periphery of the valve stem above the sleeve, and the positioning piece and the sleeve divide the inner cavity of the valve body from top to bottom into an upper cavity, a middle cavity and a lower cavity; the upper cavity is used to communicate with the electromagnetic pilot valve through an air outlet pipe; a first outlet and an inlet are respectively provided on the side walls of the valve body, the inlet is used to connect the lower cavity with the main steam isolation valve, and the first outlet is used to connect the lower cavity with the safety valve;

[0010] The booster element includes a piston, a spring and an I-shaped plate; the spring is located in a sealed shell, and the bottom of the shell is fixed above the sleeve; an I-shaped plate is pressed on the top of the spring, which always has a vertical upward elastic force on the I-shaped plate; the I-shaped plate includes a horizontal upper plate, a vertical plate and a horizontal lower plate, the horizontal lower plate is located in the shell and contacts the top of the spring, the vertical plate passes through the shell and constitutes a sealed sliding pair, the horizontal upper plate is located outside the shell and is pressed on the bottom of the positioning member; the horizontal lower plate can slide up and down in a sealed manner in the shell and divide the inner cavity of the shell into an upper chamber and a lower chamber that are not connected to each other, and the lower chamber is connected to one end of the straight pipe section; a piston is provided in the straight pipe section, the other end of which is connected to the regulating pipeline, and the regulating pipeline is connected to the air outlet pipe.

[0011] Preferably, the positioning member and the sleeve are both provided with a plurality of throttling holes for fluid to pass through.

[0012] Preferably, the first outlet and the inlet are respectively opened on two opposite sides of the side wall of the valve body, and are coaxially arranged.

[0013] Preferably, the limiting member is a cylindrical structure and is located in the middle of the valve cover.

[0014] Preferably, the top cover and the main body of the booster element housing are detachably connected, and the vertical plate and the horizontal lower plate are detachably connected.

[0015] Preferably, the sealing area between the horizontal lower plate and the piston is filled with hydraulic oil.

[0016] Preferably, two boosting elements are provided and are symmetrically located between the inlet and the first outlet.

[0017] Preferably, the regulating pipeline is a curved pipe structure, including a horizontal section and a vertical section; the horizontal section is connected to the lower chamber of the booster element shell through a straight pipe section, and the vertical section is connected to the air outlet pipe.

[0018] In a second aspect, the present invention provides a control method for a fast-opening and slow-closing pre-isolation valve of a main steam valve station according to any one of the first aspects, specifically as follows:

[0019] S1: Connect the valve body's inlet to the main steam isolation valve, the first outlet to the safety valve, the second outlet to the atmospheric relief valve, and the upper chamber to the electromagnetic pilot valve through the outlet pipe. Under normal operating conditions, both the first and second outlets are closed. Adjust the spring stiffness and piston position to adjust the time the booster element pushes the valve stem, thereby changing the opening and closing time of the second outlet.

[0020] S2: In the initial state, the steam in the main steam isolation valve enters the valve body through the inlet, and slowly flows from the lower cavity through the middle cavity and the upper cavity into the outlet pipe. At this time, the pressure in the pre-isolation valve has not reached the set pressure, the steam flow rate is slow and does not generate a large driving force on the piston in the booster element, and the pre-isolation valve remains stationary;

[0021] S3: When the pressure in the front isolation valve reaches the set pressure, the main steam isolation valve will close quickly. At this time, the front isolation valve needs to be opened quickly, as follows:

[0022] The electromagnetic pilot valve connected to the air outlet pipe opens quickly to relieve the pressure of the front isolation valve. At this time, the pressure difference between the front isolation valve and the outlet of the air outlet pipe is large, and the flow rate of the fluid in the valve increases; the high-speed fluid generates an impact force on the piston in the booster element through the air outlet pipe, and the piston moves in the direction of the spring. The hydraulic oil filled in the sealing area between the horizontal lower plate and the piston generates an upward thrust on the I-plate and causes it to move axially upward. The I-plate has an upward driving force on the valve stem; as the pressure in the valve gradually decreases, the pressure difference between the outlet of the air outlet pipe and the valve causes the valve stem to move axially upward. At the same time, under the combined action of the thrust of the gas at the second outlet and the driving force of the I-plate, the valve stem drives the valve disc with a large acceleration to quickly open the second outlet;

[0023] S4: When the second outlet of the front isolation valve reaches the fully open state, the solenoid pilot valve will close quickly, and the pressure in the upper chamber of the front isolation valve will increase and gradually remain stable; when the pressure in the upper chamber is higher than the second outlet pressure, the fluid will exert a downward force on the valve stem, causing it to move downward gradually; during the movement, as the spring in the booster element is compressed, there will always be an upward thrust on the valve stem, reducing the downward movement speed of the valve stem and valve disc, and realizing the slow closing of the second outlet;

[0024] S5: When the pressure of the main steam isolation valve reaches the set pressure again, repeat steps S3 and S4 to achieve rapid opening and slow closing of the second outlet.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The pre-isolation valve of the present invention is a key valve in the main steam valve station of a nuclear power plant. When an accident occurs, the valve structure of the present invention can further shorten the opening time of the pre-isolation valve, ensuring that the pressure in the system remains stable. At the same time, when the pressure returns to normal, the valve can be slowly closed, reducing valve damage, noise and vibration.

[0027] 2) The opening and closing time of the pre-isolating valve (specifically the second outlet) of the present invention can be changed by adjusting the spring stiffness and the position of the piston. The specific principle is to change the position of the piston, thereby changing the time for the piston to compress the hydraulic oil in the booster element, thereby changing the time when the I-plate starts to push the valve stem; by changing the spring stiffness, the reverse pushing force of the I-plate on the valve stem when the valve is closed is changed, thereby achieving the purpose of changing the valve closing time and enhancing the adaptability of the device to different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the inlet and outlet distribution of the front isolation valve;

[0029] Figure 2 It is a sectional three-dimensional view of the front isolation valve;

[0030] Figure 3 This is a cross-sectional structural diagram of the front isolation valve;

[0031] Figure 4 It is a schematic diagram of the structure of the booster element;

[0032] Figure 5 It is the overall structural model of the main steam valve station;

[0033] In the figure: 1. Valve cover; 2. Valve body; 3. Air outlet pipe; 4. Thrust element; 41. Piston; 42. Spring; 43. I-plate; 5. Adjustment pipeline; 6. Sleeve; 7. Valve stem; 8. Valve disc; 9. Positioning piece; 10. Limiting piece. DETAILED DESCRIPTION

[0034] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0035] The pre-isolating valve of the present invention is an important component of the main steam valve station of a nuclear power plant. It will remain closed under normal operating conditions. When an accident occurs, it is required to open quickly in a short time. The pre-isolating valve of the present invention, through its own structural characteristics, converts a part of the high-speed fluid when the valve is opened into a driving force for opening the valve, shortening its opening time. At the same time, it plays a reverse pushing role on the valve stem when closing, realizing its slow closing. A main steam valve station fast opening and slow closing pre-isolating valve provided by the present invention has one inlet and two outlets, and mainly includes a valve body 2, a valve cover 1, a booster element 4, a sleeve 6, a valve stem 7 and a valve flap 8. The structural connection method of each component will be described in detail below.

[0036] like Figures 1 to 3 As shown, the valve body 2 is sealed with a valve cover 1 at the top. A sleeve 6 is fixed horizontally within the inner cavity. A second outlet is defined at the bottom, communicating with the atmospheric relief valve. This means the outlet pressure of the second outlet is atmospheric pressure. A stopper 10 is located below the valve cover 1, restricting the movement of the valve stem 7 to a vertical direction. The valve stem 7 is vertically positioned within the inner cavity of the valve body 2, its top positioned within the stopper 10, its lower portion extending through the sleeve 6, and a valve disc 8 fixed to its bottom. The valve stem 7 can slide up and down within the sleeve 6, forming a sliding pair. The valve disc 8 matches the size of the second outlet and controls its opening and closing. A disc-shaped locating member 9 is fixed horizontally to the outer periphery of the valve stem 7 above the sleeve 6. The locating member 9 and the sleeve 6 divide the inner cavity of the valve body 2 into an upper chamber, a middle chamber, and a lower chamber, from top to bottom. The upper chamber is connected to an outlet pipe 3, which communicates with the solenoid pilot valve. Under normal operating conditions, the outlet pipe 3 is closed. The side wall of the valve body 2 is provided with a first outlet and an inlet, the inlet is used to connect the lower chamber with the main steam isolation valve, and the first outlet is used to connect the lower chamber with the safety valve. The first outlet is closed by default.

[0037] In this embodiment, the positioning member 9 and the sleeve 6 are each provided with multiple orifices for fluid passage, interconnecting the upper, middle, and lower chambers. The first outlet and inlet can be located on opposite sides of the sidewall of the valve body 2, coaxially arranged. The stopper 10 is a cylindrical structure located in the center of the valve cover 1.

[0038] like Figure 4 As shown, the booster element 4 mainly consists of a sealed housing and a straight pipe section. The straight pipe section is provided with a piston 41, and the sealed housing is provided with a spring 42 and an I-shaped plate 43. The connection method of the above components is as follows:

[0039] The spring 42 is located inside the sealed shell, and the bottom of the shell is fixed above the sleeve 6. A type plate 43 is pressed on the top of the spring 42, which always has a vertical upward elastic force on the type plate 43. In other words, the spring 42 in the booster element 4 is initially in a compressed state, and has an upward pushing force on the type plate 43, so that it fits tightly with the valve stem 7. The type plate 43 includes a horizontal upper plate, a vertical plate and a horizontal lower plate. The horizontal lower plate is located in the shell and contacts the top of the spring 42. The vertical plate passes through the shell and forms a sealed sliding pair. The horizontal upper plate is located outside the shell and is pressed on the bottom of the positioning member 9. In other words, the vertical plate can slide up and down in the shell, and the connection between the two is sealed. The horizontal lower plate can slide up and down in a sealed manner in the shell and divide the inner cavity of the shell into an upper chamber and a lower chamber that are not connected to each other. One side of the lower chamber is connected to one end of the straight pipe section. A piston 41 is provided in the straight pipe section, and the piston 41 can completely block the cross section of the straight pipe section at that location, forming a space that is not connected to each other on both sides of the piston 41. The other end of the straight pipe section is connected to the regulating pipe 5, which is in turn connected to the air outlet pipe 3. In other words, the size of the horizontal lower plate should be able to cover the cross-section of the inner cavity of the shell, be sealed around the periphery of the shell, and be able to slide up and down along the inner wall of the shell.

[0040] In this embodiment, the top cover of the booster element 4 housing is detachably connected to the main body, for example, by bolts, allowing the cover to be detached from the main body. The vertical plate and horizontal lower plate are also detachably connected, for example, by bolts, allowing the entire I-shaped plate to be disassembled. This structure facilitates easier installation and maintenance of the various components of the booster element 4.

[0041] In this embodiment, the sealing area between the horizontal lower plate and the piston 41 is filled with hydraulic oil. When the piston 41 is impacted, it will move in the direction close to the spring, compressing the hydraulic oil in the cavity, thereby pushing the I-plate 43 to move upward; on the contrary, when the I-plate 43 is subjected to downward pressure, it will also squeeze the hydraulic oil in the cavity, thereby pushing the piston 41 to move in the direction away from the spring. Two boosting elements 4 can be provided, that is, symmetrically located between the inlet and the first outlet. The regulating pipeline 5 is a curved pipe structure, including a horizontal section and a vertical section, wherein the horizontal section is connected to the lower chamber of the boosting element 4 shell through a straight pipe section, and the vertical section is connected to the outlet pipe 3.

[0042] The control method of the fast-opening and slow-closing pre-isolating valve of the main steam valve station is as follows:

[0043] S1: Connect the inlet of valve body 2 to the main steam isolation valve, the first outlet to the safety valve, and the second outlet to the atmospheric relief valve. The upper chamber is connected to the solenoid pilot valve via outlet pipe 3. Under normal operating conditions, both the first and second outlets are closed. By adjusting the stiffness of spring 42 and the position of piston 41, the time that booster element 4 pushes valve stem 7 can be adjusted, thereby varying the opening and closing timing of the second outlet.

[0044] Under normal operating conditions, the pre-isolation valve is closed, meaning both outlets are shut. In the event of an emergency, the main steam isolation valve will close to protect the downstream piping of the nuclear power plant's secondary circuit. At this point, the pre-isolation valve must be opened quickly, typically within 5 seconds, to quickly release the high-temperature, high-pressure steam within the device and ensure safe and stable operation of the entire system.

[0045] S2: In the initial state, the pressure in the front isolation valve has not reached the set pressure, and the front isolation valve remains stationary. At this time, the pressure in the valve is slowly increasing, as follows:

[0046] Steam within the main steam isolation valve enters valve body 2 through the inlet. It then flows slowly from the lower chamber through the middle and upper chambers through the throttle holes in sleeve 6 and valve stem 7, into outlet pipe 3. Since steam primarily flows out through the main steam isolation valve, the fluid velocity within the pre-isolation valve is relatively low, and the fluid does not exert significant force on piston 41 within booster element 4, causing the pre-isolation valve to remain stationary.

[0047] S3: When the pressure in the front isolation valve reaches the set pressure, the main steam isolation valve will close quickly. At this time, the front isolation valve needs to be opened quickly, as follows:

[0048] The electromagnetic pilot valve connected to the outlet pipe 3 opens quickly, relieving the pressure of the pre-isolating valve. Because the electromagnetic pilot valve directly releases the high-temperature, high-pressure gas within the valve into the atmosphere, the pressure difference between the pre-isolating valve and the outlet of the outlet pipe 3 is large, and the flow rate of the fluid within the valve increases. The high-speed fluid exerts an impact force on the piston 41 within the booster element 4 through the outlet pipe 3, causing the piston 41 to move in the direction of the spring 42. The hydraulic oil filled in the sealing area between the horizontal lower plate and the piston 41 exerts an upward thrust on the I-type plate 43, causing it to move axially upward. The I-type plate 43 exerts an upward force on the valve stem 7. As the pressure within the valve gradually decreases, the pressure difference between the outlet of the outlet pipe 3 and the valve causes the valve stem 7 to move axially upward. At the same time, under the combined action of the thrust of the gas at the second outlet and the driving force of the I-type plate 43, the valve stem 7 drives the valve disc 8 with a large acceleration, causing the second outlet to open rapidly.

[0049] S4: When the second outlet of the pre-isolation valve reaches full open, the solenoid pilot valve rapidly closes. Steam begins to accumulate in the upper chamber of the pre-isolation valve, causing the pressure to rise and gradually stabilize. When the pressure in the upper chamber exceeds the pressure at the second outlet, the fluid exerts a downward force on the valve stem 7, causing it to gradually move downward. During this movement, as the spring 42 in the booster element is compressed, it exerts a constant upward force on the valve stem 7, slowing the downward movement of the valve stem 7 and valve disc 8, thereby slowly closing the second outlet.

[0050] S5: When the pressure of the main steam isolation valve reaches the set pressure again, repeat steps S3 and S4 to achieve rapid opening and slow closing of the second outlet.

[0051] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A main steam valve station fast opening and slow closing pre-isolating valve, characterized in that: It comprises a valve body (2), a valve cover (1), a thrust element (4), a sleeve (6), a valve stem (7) and a valve disc (8); The valve body (2) is sealed with a valve cover (1) at the top, a sleeve (6) is fixed horizontally in the inner cavity, and a second outlet for communicating with the atmospheric relief valve is opened at the bottom; a limiter (10) is provided below the valve cover (1) for allowing the valve stem (7) to slide only in the vertical direction; the valve stem (7) is vertically arranged in the inner cavity of the valve body (2), the top is located in the limiter (10), the lower part passes through the sleeve (6) and forms a sliding pair, and a valve flap (8) for controlling the opening and closing of the second outlet is fixed at the bottom; a disc-shaped positioning member (9) is fixed horizontally on the outer periphery of the valve stem (7) located above the sleeve (6), and the positioning member and the sleeve (6) divide the inner cavity of the valve body (2) from top to bottom into an upper cavity, a middle cavity and a lower cavity; the upper cavity is used to communicate with the electromagnetic pilot valve through the air outlet pipe (3); a first outlet and an inlet are respectively opened on the side wall of the valve body (2), the inlet is used to communicate the lower cavity with the main steam isolation valve, and the first outlet is used to communicate the lower cavity with the safety valve; The boosting element (4) includes a piston (41), a spring (42) and an I-shaped plate (43); the spring (42) is located in a sealed shell, and the bottom of the shell is fixed above the sleeve (6); the top of the spring (42) is pressed with an I-shaped plate (43), which always has a vertical upward elastic force on the I-shaped plate (43); the I-shaped plate (43) includes a horizontal upper plate, a vertical plate and a horizontal lower plate, the horizontal lower plate is located in the shell and contacts the top of the spring (42), the vertical plate passes through the shell and forms a sealed sliding pair, and the horizontal upper plate is located outside the shell and is pressed on the bottom of the positioning member (9); the horizontal lower plate can slide up and down in a sealed manner in the shell and divide the inner cavity of the shell into an upper chamber and a lower chamber that are not connected to each other, and the lower chamber is connected to one end of the straight pipe section; a piston (41) is provided in the straight pipe section, the other end of which is connected to the regulating pipeline (5), and the regulating pipeline (5) is connected to the outlet pipe (3).

2. A main steam valve station fast opening and slow closing pre-isolating valve according to claim 1, characterized in that: The positioning member (9) and the sleeve (6) are both provided with a plurality of throttling holes for fluid to pass through.

3. A main steam valve station fast opening and slow closing pre-isolating valve according to claim 1, characterized in that: The first outlet and the inlet are respectively opened on two opposite sides of the side wall of the valve body (2), and the two are coaxially arranged.

4. A main steam valve station fast opening and slow closing pre-isolating valve according to claim 1, characterized in that: The limiting member (10) is a cylindrical structure and is located in the middle of the valve cover (1).

5. The main steam valve station fast opening and slow closing pre-isolating valve according to claim 1 is characterized in that: The top cover and the main body of the boosting element (4) shell are detachably connected, and the vertical plate and the horizontal lower plate are detachably connected.

6. A main steam valve station fast opening and slow closing pre-isolating valve according to claim 1, characterized in that: The sealing area between the horizontal lower plate and the piston (41) is filled with hydraulic oil.

7. The main steam valve station fast opening and slow closing pre-isolating valve according to claim 1 is characterized in that: There are two boosting elements (4) symmetrically located between the inlet and the first outlet.

8. The main steam valve station fast opening and slow closing pre-isolating valve according to claim 1 is characterized in that: The regulating pipeline (5) is a curved pipe structure, comprising a horizontal section and a vertical section; the horizontal section is connected to the lower chamber of the booster element (4) shell through the straight pipe section, and the vertical section is connected to the air outlet pipe (3).

9. A control method using the fast-opening and slow-closing pre-isolating valve of the main steam valve station according to any one of claims 1 to 8, characterized in that: The details are as follows: S1: The inlet of the valve body (2) is connected to the main steam isolation valve, the first outlet is connected to the safety valve, the second outlet is connected to the atmospheric relief valve, and the upper chamber is connected to the electromagnetic pilot valve through the outlet pipe (3); under normal working conditions, the first outlet and the second outlet are both in a closed state; by adjusting the stiffness of the spring (42) and the position of the piston (41), the time for the booster element (4) to push the valve stem (6) is adjusted to change the opening and closing time of the second outlet; S2: In the initial state, the steam in the main steam isolation valve enters the valve body (2) through the inlet, and slowly flows from the lower cavity through the middle cavity and the upper cavity into the outlet pipe (3). At this time, the pressure in the front isolation valve has not reached the set pressure, the steam flow rate is slow and does not generate a large driving force on the piston (41) in the booster element (4), and the front isolation valve remains in a static state; S3: When the pressure in the front isolation valve reaches the set pressure, the main steam isolation valve will close quickly. At this time, the front isolation valve needs to be opened quickly, as follows: The electromagnetic pilot valve connected to the air outlet pipe (3) opens quickly to relieve the pressure of the front isolation valve. At this time, the pressure difference between the front isolation valve and the outlet of the air outlet pipe (3) is large, and the flow rate of the fluid in the valve increases; the high-speed fluid generates an impact force on the piston (41) in the booster element (4) through the air outlet pipe (3), and the piston (41) moves in the direction of the spring (42). The hydraulic oil filled in the sealing area between the horizontal lower plate and the piston (41) generates an upward thrust on the I-type plate (43) and causes it to move axially upward. The I-type plate (43) has an upward driving force on the valve stem (6); as the pressure in the valve gradually decreases, the pressure difference between the outlet of the air outlet pipe (3) and the valve causes the valve stem (7) to move axially upward. At the same time, under the combined action of the thrust of the gas at the second outlet and the driving force of the I-type plate (43), the valve stem (7) drives the valve disc (8) with a large acceleration to quickly open the second outlet; S4: When the second outlet of the front isolation valve reaches a fully open state, the electromagnetic pilot valve will close quickly, and the pressure in the upper chamber of the front isolation valve will increase and gradually remain stable; when the pressure in the upper chamber is higher than the second outlet pressure, the fluid will exert a downward thrust on the valve stem (7), causing it to gradually move downward; during the movement, as the spring (42) in the booster element is compressed, there will always be an upward thrust on the valve stem (7), reducing the speed of the downward movement of the valve stem (7) and the valve disc (8), thereby achieving slow closing of the second outlet; S5: When the pressure of the main steam isolation valve reaches the set pressure again, repeat steps S3 and S4 to achieve rapid opening and slow closing of the second outlet.

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