Mechanical seal device for a pump with a forced circulation structure

Abstract

This invention discloses a mechanical seal device for pumps with a forced circulation structure, belonging to the technical field of mechanical seals for pumps. It solves the problems of high-temperature medium impact, poor cooling effect, and weak start-stop adaptability in existing medium-pressure feedwater pump mechanical seals. The device includes a pump shaft, a sealing cavity, and an end cover. The sealing cavity contains a fixed sliding ring and a sliding compression ring, with the sliding compression ring connected to a rotating cooling pipe. A heat transfer sensing piston monitors the friction temperature in real time, automatically triggering the opening of the cooling water circuit. Water pressure drives the rotating cooling pipe to rotate synchronously with the pump shaft and spray water, forming a forced circulation flow field within the sealing cavity. Simultaneously, an anti-impact guide ring prevents high-temperature media from directly impacting the moving and stationary sealing rings. Combined with hydraulic transmission and a spring preload structure, adaptive sealing compensation is achieved. This invention improves cooling efficiency by over 60%, extends the mechanical seal life to over 5 years, and its overall structural dimensions are fully compatible with existing standard mechanical seals, allowing for direct replacement and installation.

Description

Technical Field

[0001] This invention belongs to the field of mechanical seal technology for pumps, specifically relating to a mechanical seal device for pumps with a forced circulation structure, which is particularly suitable for the shaft end seal of centrifugal pumps such as medium-pressure feedwater pumps in power plants under high temperature, high pressure, and frequent start-stop conditions. Background Technology

[0002] Centrifugal pumps are core fluid transport equipment in industries such as power, chemical, and mining. Among them, medium-pressure feedwater pumps in power plants, as key auxiliary equipment for boiler feedwater, are responsible for providing continuous and stable water supply during unit operation. Currently, mechanical seals are commonly used at the shaft ends of medium-pressure feedwater pumps. However, existing technologies, such as the MD80-260C / 6S horizontal multistage radially split centrifugal pump, have revealed the following core defects in their mechanical seals during long-term operation: Direct impact from high-temperature media: In the initial stage of operation, high-temperature feed water (usually 180-200℃) directly impacts the dynamic and static sealing rings of the mechanical seal. The materials of the dynamic and static seals have limited high-temperature resistance and are prone to thermal deformation and thermal cracking, leading to seal failure.

[0003] Poor cooling effect: Traditional mechanical seal structures lack forced circulation design, resulting in poor water flow in the mechanical seal, uneven heat exchange, and the easy formation of overheated areas, which accelerates the aging of the seal components.

[0004] Poor start-stop adaptability: Power plant units start and stop frequently for peak shaving, with a single feedwater pump starting and stopping more than 200 times a year. Mechanical seals are subjected to alternating temperature and pressure shocks for a long time, and the sealing surface has insufficient compensation capacity, resulting in a high risk of leakage. The average life of mechanical seals is only 1-2 years, which seriously affects the reliability of pump unit operation.

[0005] Therefore, developing a mechanical seal device for pumps with functions such as high temperature shock resistance, automatic forced circulation cooling, and adaptive seal compensation has become the key to solving the above-mentioned industry pain points. Summary of the Invention

[0006] To address the problems of high-temperature medium impact, poor cooling effect, and weak start-stop adaptability of existing pump mechanical seals, this invention provides a pump mechanical seal device with a forced circulation structure. The forced circulation cooling is automatically triggered by temperature sensing. Combined with an anti-impact flow guiding structure and adaptive seal compensation, it significantly improves the service life and operational reliability of the mechanical seal under high-temperature and frequent start-stop conditions.

[0007] The technical solution of the present invention is as follows: A mechanical seal device for a pump with a forced circulation structure includes a pump shaft, a sealing cavity rotatably connected to the outside of the pump shaft, an end cover fixedly connected to the side of the sealing cavity away from the medium end of the pump shaft, a fixed sliding ring slidably connected to the side of the sealing cavity near the medium end, a sliding compression ring slidably connected to the side of the sealing cavity away from the fixed sliding ring, and a rotating cooling pipe fixedly connected to the side of the sliding compression ring away from the medium end. The rotary cooling pipe has a slidable limit ring on its outer contour, a second return spring between the limit ring and the sliding compression ring, a sealing piston tube slidably connected inside the rotary cooling pipe, a second limit tension spring between the sealing piston tube and the rotary cooling pipe, a transmission gear fixedly connected to the outer contour of the rotary cooling pipe, the transmission gear slidably connected to the limit ring, and an external gear ring on the outer contour of the pump shaft meshing with the transmission gear.

[0008] Preferably, an anti-impact guide ring is fixedly connected to the fixed sliding ring. The anti-impact guide ring and the limiting slip ring have the same cross-sectional projection size. The end of the limiting slip ring closer to the fixed sliding ring is longer than the rotating cooling pipe. The length of the limiting slip ring that is longer than the rotating cooling pipe is the same as the length of the anti-impact guide ring.

[0009] Preferably, the length of the rotating cooling pipe is the same as the inner cross-sectional length of the sealed cavity, and multiple radial water spray holes are uniformly opened on the wall of the rotating cooling pipe.

[0010] Preferably, a circulating piston tube is fixedly connected to the side of the sliding compression ring away from the pump shaft. The circulating piston tube is slidably connected to the sealing cavity. A main cooling water pipe is slidably connected to the circulating piston tube. A wedge-shaped piston rod is slidably connected to the main cooling water pipe. A first limiting tension spring is provided between the wedge-shaped piston rod and the main cooling water pipe. A sliding wedge-shaped shaft is slidably connected to the main cooling water pipe. A first return spring is provided between the sliding wedge-shaped shaft and the main cooling water pipe. The sliding wedge-shaped shaft and the wedge-shaped piston rod are wedge-shaped engaged. The end of the main cooling water pipe away from the sealing cavity is connected to an external cooling water system.

[0011] Preferably, a transmission air chamber is fixedly connected to the outside of the main cooling water pipe in the sealed cavity, and a heat transfer sensing piston is slidably connected in the transmission air chamber. The heat transfer sensing piston is slidably connected to the pump shaft, and a driven wedge piston is slidably connected to the end of the transmission air chamber away from the heat transfer sensing piston. The driven wedge piston is wedge-shapedly engaged with the sliding wedge shaft.

[0012] Preferably, the heat transfer sensing piston has a gas flow channel inside, and the heat transfer sensing piston is made of copper alloy or aluminum alloy with a thermal conductivity ≥200W / (m). It is made of a fast heat transfer material (K).

[0013] Preferably, a pre-tightening spring is provided between the heat transfer sensing piston and the transmission air chamber, and the heat transfer sensing piston and the sealed cavity are slidably connected through each other.

[0014] Preferably, a transmission hydraulic chamber is fixedly connected to one side of the pump shaft medium end of the sealed cavity, a fixed piston is slidably connected in the transmission hydraulic chamber, the fixed piston is slidably connected to the pump shaft, a driven hydraulic chamber is fixedly connected to the lower side of the transmission hydraulic chamber, a driven piston is slidably connected in the driven hydraulic chamber, and the driven piston is fixedly connected to a fixed sliding ring.

[0015] Preferably, a hydraulic connecting pipe is provided between the transmission hydraulic chamber and the driven hydraulic chamber to connect the two, and the transmission hydraulic chamber and the driven hydraulic chamber are filled with temperature-resistant hydraulic oil.

[0016] Preferably, a convex ring is provided on the outer side of the pump shaft relative to the fixed piston, and the convex ring and the pump shaft are integrally formed.

[0017] Compared with the prior art, the present invention has the following beneficial effects: Temperature-sensing automatic forced circulation cooling: The friction temperature between the pump shaft and the sealed cavity is monitored in real time by a heat transfer sensing piston. When the temperature exceeds the set threshold, the cooling water circuit is automatically triggered to open. The water pressure drives the circulation piston tube and the rotating cooling tube. With the meshing of the transmission gear and the pump shaft, the rotating cooling tube rotates synchronously with the pump shaft and sprays water in all directions, forming a forced circulation flow field in the sealed cavity. This completely solves the problems of poor water flow and uneven heat exchange in traditional mechanical seals, and improves the cooling efficiency by more than 60%.

[0018] High-temperature medium impact protection design: Through the cooperation between the pump shaft convex ring and the fixed piston, the fixed sliding ring and the anti-impact guide ring are automatically pushed out before the pump starts, forming a flow guide barrier in front of the dynamic and static sealing rings, guiding the high-temperature medium to the side wall of the sealing cavity, avoiding direct impact on the dynamic and static sealing rings, and effectively reducing thermal shock damage to the sealing surface.

[0019] Adaptive seal compensation: Combining hydraulic transmission and spring preload structure, the fixed piston and heat transfer sensing piston form dual positioning of the pump shaft from the inside and outside respectively. The sliding extrusion ring can automatically compensate for the wear of the sealing surface under water pressure. At the same time, during the pump start-up and shutdown process, the automatic start-up and shutdown of the cooling system can effectively alleviate the impact of alternating temperature on the sealing surface, extending the mechanical seal life to more than 5 years.

[0020] Direct replacement installation: The overall structural dimensions of this device are fully compatible with existing standard mechanical seals, requiring no modification to the pump body and shaft structure. It can be directly replaced and installed during unit maintenance, resulting in a short construction period and low modification costs. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a half-sectional view of the structure of the present invention; Figure 3 This is a half-sectional view of the medium-end sealing and fixing structure of the present invention; Figure 4 This is a half-sectional view of the transmission structure of the cooling system of the present invention; Figure 5 This is a schematic diagram showing the connection between the heat transfer sensing piston and the transmission air chamber of the present invention; Figure 6 This is a half-sectional schematic diagram of the main cooling water pipe of the present invention; Figure 7 For the present invention Figure 6 Enlarged view of point A in the middle; Figure 8 This is a half-sectional schematic diagram of the rotating cooling tube of the present invention; Figure 9 For the present invention Figure 8 Enlarged diagram of point B in the middle.

[0023] In the diagram: 100, pump shaft; 200, end cap; 300, sealing cavity; 400, fixed piston; 401, transmission hydraulic cavity; 402, driven hydraulic cavity; 403, hydraulic connecting pipe; 404, driven piston; 405, fixed sliding ring; 406, anti-impact guide ring; 500, transmission air cavity; 501, heat transfer sensing piston; 502, preload spring; 503, driven wedge piston; 600, main cooling water pipe; 601, wedge piston column; 602, sliding wedge shaft; 603, first return spring; 604, first limiting tension spring; 605, sliding compression ring; 606, circulating piston tube; 607, second return spring; 700, rotating cooling pipe; 701, limiting slip ring; 702, sealing piston tube; 703, transmission gear; 704, second limiting tension spring. Detailed Implementation

[0024] 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.

[0025] like Figures 1 to 9 As shown, the present invention provides a mechanical seal device for a pump with a forced circulation structure, including a pump shaft 100, a sealing cavity 300 rotatably connected to the outside of the pump shaft 100, an end cap 200 fixedly connected to the side of the sealing cavity 300 away from the medium end of the pump shaft 100, a fixed sliding ring 405 slidably connected to the side of the sealing cavity 300 near the medium end, a sliding compression ring 605 slidably connected to the side of the sealing cavity 300 away from the fixed sliding ring 405, and a rotating cooling pipe 700 fixedly connected to the side of the sliding compression ring 605 away from the medium end. Among them, a limiting slip ring 701 is slidably connected on the outer contour of the rotary cooling pipe 700, and a second return spring 607 is provided between the limiting slip ring 701 and the sliding compression ring 605. A sealing piston pipe 702 is slidably connected through the rotary cooling pipe 700, and a second limiting tension spring 704 is provided between the sealing piston pipe 702 and the rotary cooling pipe 700. A transmission gear 703 is fixedly connected on the outer contour of the rotary cooling pipe 700, and the transmission gear 703 is slidably connected through the limiting slip ring 701. An external gear ring is provided on the outer contour of the pump shaft 100, and the external gear ring of the pump shaft 100 meshes with the transmission gear 703.

[0026] An anti-impact guide ring 406 is fixedly connected to the fixed sliding ring 405. The anti-impact guide ring 406 has the same cross-sectional projection size as the limiting slip ring 701. The end of the limiting slip ring 701 closest to the fixed sliding ring 405 is longer than the rotating cooling pipe 700. The length of the limiting slip ring 701 that is longer than the rotating cooling pipe 700 is the same as the length of the anti-impact guide ring 406.

[0027] The length of the rotating cooling pipe 700 is the same as the inner cross-sectional length of the sealed cavity 300, and multiple radial water spray holes with a diameter of 2-3mm are evenly opened on the pipe wall of the rotating cooling pipe 700. The axis of the water spray hole forms a 45° angle with the axis of the rotating cooling pipe 700 to enhance the disturbance effect of the water spray.

[0028] A circulating piston tube 606 is fixedly connected to the side of the sliding compression ring 605 away from the pump shaft 100. The circulating piston tube 606 is slidably connected to the sealing cavity 300. The circulating piston tube 606 is slidably connected to the main cooling water pipe 600. The main cooling water pipe 600 is slidably connected to the wedge-shaped piston column 601. A first limiting tension spring 604 is provided between the wedge-shaped piston column 601 and the main cooling water pipe 600. The main cooling water pipe 600 is slidably connected to the sliding wedge-shaped shaft 602. A first return spring 603 is provided between the sliding wedge-shaped shaft 602 and the main cooling water pipe 600. The sliding wedge-shaped shaft 602 and the wedge-shaped piston column 601 are wedge-shaped engaged. The end of the main cooling water pipe 600 away from the sealing cavity 300 is connected to the external cooling water system. The cooling water system pressure is set to 0.3-0.5 MPa.

[0029] A transmission air chamber 500 is fixedly connected to the outside of the main cooling water pipe 600 in the sealed cavity 300. A heat transfer sensing piston 501 is slidably connected inside the transmission air chamber 500. The heat transfer sensing piston 501 is slidably connected to the pump shaft 100. A driven wedge piston 503 is slidably connected to the end of the transmission air chamber 500 away from the heat transfer sensing piston 501. The driven wedge piston 503 is wedge-shapedly engaged with the sliding wedge shaft 602.

[0030] The heat transfer induction piston 501 has a gas flow channel inside. The heat transfer induction piston 501 is made of copper alloy with a thermal conductivity of 380 W / (m). K) can quickly transfer the frictional heat of the pump shaft 100 to the air in the transmission air chamber 500.

[0031] A preload spring 502 is provided between the heat transfer sensing piston 501 and the transmission air chamber 500. The heat transfer sensing piston 501 is slidably connected to the sealing chamber 300. The preload force of the preload spring 502 is 50-80N, ensuring that the heat transfer sensing piston 501 is always in close contact with the pump shaft 100.

[0032] A transmission hydraulic chamber 401 is fixedly connected to one side of the pump shaft 100 at the medium end of the sealed cavity 300. A fixed piston 400 is slidably connected inside the transmission hydraulic chamber 401. The fixed piston 400 is slidably connected to the pump shaft 100. A driven hydraulic chamber 402 is fixedly connected to the lower side of the transmission hydraulic chamber 401. A driven piston 404 is slidably connected inside the driven hydraulic chamber 402. The driven piston 404 is fixedly connected to a fixed sliding ring 405.

[0033] A hydraulic connecting pipe 403 is provided between the transmission hydraulic chamber 401 and the driven hydraulic chamber 402 to connect the two. The transmission hydraulic chamber 401 and the driven hydraulic chamber 402 are filled with synthetic hydraulic oil that is resistant to temperatures from -20℃ to 200℃.

[0034] A convex ring is provided on the outer side of the pump shaft 100 relative to the fixed piston 400. The convex ring and the pump shaft 100 are integrally formed, and the height of the convex ring is 5-8mm.

[0035] Working principle and usage process of this invention: Before the medium-pressure feedwater pump starts, the convex ring on the pump shaft 100 will squeeze the fixed piston 400 into the transmission hydraulic chamber 401, forcing the hydraulic oil in the transmission hydraulic chamber 401 into the driven hydraulic chamber 402 through the hydraulic connecting pipe 403. This, in turn, pushes the driven piston 404 and the fixed sliding ring 405 towards the medium end, causing the anti-impact guide ring 406 to extend in front of the dynamic and static sealing rings. At the same time, the preload spring 502 in the transmission air chamber 500 pushes the heat transfer sensing piston 501 to always be in close contact with the pump shaft 100, positioning the pump shaft 100 from the outside and ensuring that the coaxiality error between the sealing chamber 300 and the pump shaft 100 is ≤0.05mm.

[0036] When the feedwater pump starts running, the pump shaft 100 rotates at high speed, while the sealing cavity 300 remains stationary. High-temperature feedwater (184℃, 1.22MPa) enters the pump body from the medium end. At this time, the anti-impact guide ring 406 guides the high-temperature feedwater to the side wall of the sealing cavity 300, preventing it from directly impacting the dynamic and static sealing rings and effectively reducing thermal shock to the sealing surface. As the pump shaft 100 continues to rotate, frictional heat is generated between the pump shaft 100 and the heat transfer sensing piston 501. Simultaneously, the heat from the high-temperature medium is transferred to the sealing cavity 300, causing the temperature of the heat transfer sensing piston 501 to gradually increase.

[0037] When the temperature of the heat transfer sensing piston 501 rises to 80°C, the air in the transmission air chamber 500 expands due to heat, and the air pressure increases to above 0.2 MPa, pushing the driven wedge piston 503 to slide away from the transmission air chamber 500. Through the wedge-shaped engagement between the driven wedge piston 503 and the sliding wedge shaft 602, the sliding wedge shaft 602 slides towards the driven wedge piston 503 under the elastic force of the first return spring 603. Then, under the action of the first limiting tension spring 604, the wedge piston column 601 slides towards the circulating piston tube 606, the water passage of the main cooling water pipe 600 is unlocked, and cooling water enters the circulating piston tube 606 and fills it.

[0038] When the water pressure inside the circulating piston tube 606 reaches 0.3 MPa, it pushes the sliding compression ring 605 and the rotating cooling tube 700 to slide towards the medium end until the sliding compression ring 605 is in contact with the stationary ring seat of the dynamic and static sealing rings, forming axial compensation for the sealing surface. At the same time, the limiting slip ring 701 slides synchronously with the rotating cooling tube 700. When the front end of the limiting slip ring 701 contacts the anti-impact guide ring 406, the anti-impact guide ring 406 pushes the limiting slip ring 701 to slide in the opposite direction relative to the rotating cooling tube 700, no longer blocking the water spray holes on the rotating cooling tube 700. At the same time, the front end of the sealing piston tube 702 contacts the fixed sliding ring 405, and the fixed sliding ring 405 pushes the sealing piston tube 702 to slide in the opposite direction, unlocking the water passage of the rotating cooling tube 700, and the cooling water in the circulating piston tube 606 enters the rotating cooling tube 700.

[0039] Since the transmission gear 703 meshes with the external gear ring of the pump shaft 100, the rotating cooling pipe 700 rotates synchronously with the pump shaft 100. Cooling water is sprayed into the surrounding area of ​​the sealing cavity at a 45° angle through the spray holes on the rotating cooling pipe 700, forming a forced circulation flow field, which quickly removes the heat from the dynamic and static sealing rings and the sealing cavity 300, so that the temperature of the sealing surface is stabilized below 60°C.

[0040] When the water pump stops running, the pump shaft 100 gradually slows down, reducing frictional heat. The temperature of the heat transfer induction piston 501 drops below 60°C, lowering the air pressure in the transmission air chamber 500. The driven wedge piston 503 slides in the opposite direction, pushing the sliding wedge shaft 602 and the wedge piston column 601 back to their original positions, thus closing the water passage of the main cooling water pipe 600. After the cooling water in the rotary cooling pipe 700 is drained, under the action of the second return spring 607 and the second limiting tension spring 704, the limiting slip ring 701, the sealing piston pipe 702, the sliding compression ring 605, and the rotary cooling pipe 700 sequentially reset, awaiting the next start-up.

[0041] Implementation effect verification This invention was applied to the retrofitting of the mechanical seals of the MD80-260C / 6S medium-pressure feedwater pumps in Units #1 and #2 of a power plant. After 18 months of continuous operation following the retrofit, the mechanical seals showed no leakage or overheating, with the sealing surface temperature stabilizing at 55-60℃ and the water flow rate remaining stable at 2-3 m³ / h. The cooling efficiency was improved by 72% compared to before the retrofit. It is estimated that the service life of a single mechanical seal can be extended from 1.5 years to 6 years, reducing annual mechanical seal replacement costs by approximately 120,000 yuan. Simultaneously, it avoids unplanned unit downtime due to mechanical seal failure, resulting in significant economic benefits.

[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A mechanical seal device for a pump with a forced circulation structure, comprising a pump shaft (100), characterized in that: A sealing cavity (300) is rotatably connected to the outside of the pump shaft (100). An end cap (200) is fixedly connected to the side of the sealing cavity (300) away from the medium end of the pump shaft (100). A fixed sliding ring (405) is slidably connected to the side of the sealing cavity (300) near the medium end. A sliding compression ring (605) is slidably connected to the side of the sealing cavity (300) away from the fixed sliding ring (405). A rotating cooling pipe (700) is fixedly connected to the side of the sliding compression ring (605) away from the medium end. A limit ring (701) is slidably connected to the outer contour of the rotating cooling pipe (700). A second return spring (607) is provided between the limiting slip ring (701) and the sliding compression ring (605). A sealing piston tube (702) is slidably connected through the rotary cooling pipe (700). A second limiting tension spring (704) is provided between the sealing piston tube (702) and the rotary cooling pipe (700). A transmission gear (703) is fixedly connected to the outer contour of the rotary cooling pipe (700). The transmission gear (703) is slidably connected through the limiting slip ring (701). An external gear ring is provided on the outer contour of the pump shaft (100). The external gear ring of the pump shaft (100) meshes with the transmission gear (703).

2. The mechanical seal device for a pump with a forced circulation structure according to claim 1, characterized in that: An anti-impact guide ring (406) is fixedly connected to the fixed sliding ring (405). The anti-impact guide ring (406) and the limiting slip ring (701) have the same cross-sectional projection size. The end of the limiting slip ring (701) closer to the fixed sliding ring (405) is longer than the rotating cooling pipe (700). The length of the limiting slip ring (701) that is longer than the rotating cooling pipe (700) is the same as the length of the anti-impact guide ring (406).

3. The mechanical seal device for a pump with a forced circulation structure according to claim 2, characterized in that: The length of the rotating cooling pipe (700) is the same as the inner cross-sectional length of the sealed cavity (300), and multiple radial water spray holes are uniformly opened on the pipe wall of the rotating cooling pipe (700).

4. The mechanical seal device for a pump with a forced circulation structure according to claim 1, characterized in that: The side of the sliding compression ring (605) away from the pump shaft (100) is fixedly connected to a circulating piston tube (606). The circulating piston tube (606) is slidably connected to the sealing cavity (300). The circulating piston tube (606) is slidably connected to a main cooling water pipe (600). The main cooling water pipe (600) is slidably connected to a wedge-shaped piston column (601). A first limiting tension spring (604) is provided between the wedge-shaped piston column (601) and the main cooling water pipe (600). The main cooling water pipe (600) is slidably connected to a sliding wedge-shaped shaft (602). A first return spring (603) is provided between the sliding wedge-shaped shaft (602) and the main cooling water pipe (600). The sliding wedge-shaped shaft (602) and the wedge-shaped piston column (601) are wedge-shaped engaged. The end of the main cooling water pipe (600) away from the sealing cavity (300) is connected to an external cooling water system.

5. The mechanical seal device for a pump with a forced circulation structure according to claim 4, characterized in that: The sealed cavity (300) is fixedly connected to a transmission air chamber (500) on the outside of the main cooling water pipe (600). A heat transfer sensing piston (501) is slidably connected inside the transmission air chamber (500). The heat transfer sensing piston (501) is slidably connected to the pump shaft (100). A driven wedge piston (503) is slidably connected to one end of the transmission air chamber (500) away from the heat transfer sensing piston (501). The driven wedge piston (503) is wedge-shapedly engaged with the sliding wedge shaft (602).

6. The mechanical seal device for a pump with a forced circulation structure according to claim 5, characterized in that: The heat transfer sensing piston (501) has a gas flow channel inside, and the heat transfer sensing piston (501) has a thermal conductivity ≥200W / (m). It is made of a fast heat transfer material (K).

7. The mechanical seal device for a pump with a forced circulation structure according to claim 5, characterized in that: A preload spring (502) is provided between the heat transfer sensing piston (501) and the transmission air chamber (500), and the heat transfer sensing piston (501) is slidably connected to the sealing chamber (300).

8. The mechanical seal device for a pump with a forced circulation structure according to claim 7, characterized in that: The sealed cavity (300) is fixedly connected to a transmission hydraulic cavity (401) on one side of the medium end of the pump shaft (100). A fixed piston (400) is slidably connected inside the transmission hydraulic cavity (401). The fixed piston (400) is slidably connected to the pump shaft (100). A driven hydraulic cavity (402) is fixedly connected to the lower side of the transmission hydraulic cavity (401). A driven piston (404) is slidably connected inside the driven hydraulic cavity (402). The driven piston (404) is fixedly connected to a fixed sliding ring (405).

9. The mechanical seal device for a pump with a forced circulation structure according to claim 8, characterized in that: A hydraulic connecting pipe (403) is provided between the transmission hydraulic chamber (401) and the driven hydraulic chamber (402) to connect the two.

10. The mechanical seal device for a pump with a forced circulation structure according to claim 8, characterized in that: A raised ring is provided on the outer side of the pump shaft (100) relative to the fixed piston (400).

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