Power circulation device of cooling system for offshore high-voltage direct-current transmission interface transformer

Abstract

Disclosed in the present utility model is a power circulation device of a cooling system for an offshore high-voltage direct-current transmission interface transformer. The power circulation device comprises a main circulation pump, a support system, a pipeline system and an instrument system. The support system serves to carry and fix the pipeline system, and various instruments are mounted on the pipeline system to meet the convenience of operation and visibility. The present utility model enables fresh water of an interface transformer to absorb heat in an oil-water heat exchanger and exchange heat with seawater in a non-contact manner in a seawater heat exchanger. In the present utility model, a nitrogen pressure-stabilizing pipeline, a deionization pipeline, a water-replenishing device, a terminal box, etc., are structurally integrated into a conventional direct-current main circulation device, thus realizing the minimum occupation rate of space and meeting the compactness of apparatus layout of an offshore platform. Space inside the device is maximally utilized while maintenance and overhaul are met, and the mechanical structure is simplified to the maximum extent while the system functions are achieved, thereby achieving an optimized innovative design of the entire system.

Description

A power circulation device for offshore high-voltage direct current transmission connecting transformer cooling system

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 2023236448034 filed with the Chinese Patent Office on December 29, 2023, entitled “A Power Circulation Device for an Offshore High-Voltage Direct Current Transmission Connection Transformer Cooling System,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The utility model belongs to the technical field of cooling systems, and in particular relates to a power circulation device for a cooling system of an offshore high-voltage direct current transmission connection transformer. Background Art

[0004] The design and structure of offshore HVDC transmission must be safe, accurate, rational, reliable, and easy to maintain. The design and manufacturing of the cooling system is based on ensuring that it can adapt to the various operating conditions of offshore platforms under various environmental conditions. The public cooling system must be able to withstand not only normal operating voltages and currents, but also certain surge voltages and currents caused by malfunctioning valve trigger systems, failures in various parts of the station, or AC system failures.

[0005] The public cooling system must be able to operate stably for a long time, and its mechanical structure must be strong and easy to maintain. Equipment components must meet the requirements of free expansion, contraction and tensile strength, and deformation, leakage, abnormal vibration and other defects or functional disorders that affect the normal operation of the valve body are not allowed. The design of the piping system ensures that the water resistance along the entire process is minimized. The selection of materials takes into account the possibility of corrosion, aging and loss caused by long-term high-voltage operation of the system. Various plastic components are designed to avoid aging due to corona discharge, and corona discharge-resistant materials are used. Parts and components are easy to move and replace during maintenance, and large parts are easy to hoist and position for maintenance.

[0006] However, the water cooling system in the existing technology is divided into two parts, namely the main circulation power circulation device and the secondary circulation water treatment device, which occupies a large area and still requires additional pipe supports on the outside, which is costly, has poor versatility, and increases maintenance costs; the existing power circulation device does not meet the offshore corrosion protection requirements.

[0007] Utility Model Content

[0008] In order to solve the deficiencies in the prior art, the utility model provides a power circulation device for an offshore high-voltage direct current transmission link transformer cooling system which has a compact and stable structure and is easy to operate and maintain.

[0009] The utility model adopts the following technical solutions.

[0010] A power circulation device for an offshore high-voltage direct current transmission connection transformer cooling system comprises a main circulation pump, a support system, a piping system, and an instrumentation system. The support system comprises an electric control box support, a terminal box support, a main filter water inlet pipe support, a main filter support, a seawater plate exchange water inlet pipe support, a water supply pump outlet pipe support, a precision filter pipe support, a nitrogen bottle support, and a main pump outlet multi-bracket. All of the supports are fixed to a base by bolts. The electric control box is fixed to the electric control box support by bolts. The nitrogen bottle is fixed to the nitrogen bottle support by a ring. The nitrogen pipeline is fixed to the nitrogen bottle support by a pipe code and a pipe seat. The main pump outlet multi-bracket is connected to the electric control box support and the nitrogen bottle support by bolts. The piping system comprises a main circulation pipeline, a deionization pipeline, a nitrogen pressure-stabilizing pipeline, a main filter, a degassing tank, an expansion tank, a water supply device, a main pump leak detection device, and an electric heater. These are connected in sequence to form the piping system, and the electric heater is placed in the degassing tank. The instrumentation system is an instrument provided on the piping system.

[0011] Optionally, the main circulation pipeline includes an oil-water heat exchanger outlet pipeline, a main circulation pump inlet pipeline, a pump inlet corrugated compensator, a pump outlet corrugated compensator, a main circulation pump outlet pipeline, a first check valve, a second check valve, a main filter inlet pipeline, a main filter, and a seawater plate exchanger inlet pipeline, which are connected in sequence to form the main circulation pipeline. The oil-water heat exchanger outlet pipeline, the main filter inlet pipeline, and the main circulation pump inlet pipeline are fixed to the main pump outlet multi-bracket through pipe code and pipe socket, and the main circulation pump outlet pipeline is fixed to the H-steel on the upper part of the electric control box bracket through pipe code and pipe socket.

[0012] Optionally, the first check valve is a vertical check valve, and the second check valve is a horizontal check valve.

[0013] Optionally, the deionization pipeline includes an ion tank water inlet pipeline, an ion tank, an ion tank water outlet pipeline, and a precision filter pipeline, which are sequentially connected to form the deionization pipeline.

[0014] Optionally, the precision filter pipeline inlet is connected to the ion tank water outlet pipeline via bolts, and the precision filter pipeline outlet is connected to the expansion tank water inlet via bolts.

[0015] Optionally, the nitrogen pressure-stabilizing pipeline includes an expansion tank, a nitrogen pipeline, and an expansion tank water outlet pipe, which are sequentially connected to form the nitrogen pressure-stabilizing pipeline.

[0016] Optionally, the water replenishment device includes a first water replenishment pipeline, a water storage tank, a water storage tank outlet pipeline, a water replenishment pump, a water replenishment pump outlet pipeline, and a second water replenishment pipe, which are connected in sequence to form a water replenishment device; the first water replenishment pipeline includes an automatic water replenishment interface, a manual water replenishment interface and two Y-type filters in parallel.

[0017] Optionally, the water supply pump outlet pipeline is fixed to the water supply pump outlet pipeline bracket through a pipe code and a pipe seat, and the conductivity transmitter and two safety switch boxes are fixed to the water supply pump outlet pipeline bracket through bolts.

[0018] Optionally, the two main circulation pumps are connected in parallel, one for use and one for backup, and are fixed to the base by bolts, the main circulation pump inlet is connected to the main circulation pump water inlet pipeline, and the main circulation pump outlet is connected to the main circulation pump water outlet pipeline;

[0019] Optionally, the two water supply pumps are connected in parallel, one for use and one for backup, fixed to the base by bolts, and connected to the water supply system at both ends.

[0020] Optionally, the nitrogen pressure-stabilizing pipeline is connected to 6 nitrogen cylinders, 2 for use and 4 for backup, and is placed outside the device.

[0021] Optionally, the diameter of the main circulation pipeline is DN250, and the diameter of the deionization pipeline is DN50.

[0022] Optionally, the accuracy of the main filter is 50 μm, and the filter element of the main filter is a stainless steel filter element with a standard mesh and small water resistance.

[0023] Optionally, an aeration device is provided at the bottom of the expansion tank.

[0024] Optionally, the expansion tank is provided with two sets of independent capacitive liquid level sensors and one set of magnetic flap type liquid level sensor, which are installed on the outside of the expansion tank.

[0025] The beneficial effect of this utility model is that, compared with the existing technology, it provides a compact, stable, and easy-to-operate and maintain offshore HVDC transmission link transformer cooling system power circulation device. The device integrates nitrogen pressure-stabilizing pipelines, deionization pipelines, water supply devices, terminal boxes, and other components into a traditional DC main circulation device, minimizing space usage and ensuring a compact layout for offshore platform equipment. The device maximizes space utilization while ensuring maintenance and overhaul, and simplifies the mechanical structure to the greatest extent possible while achieving system functionality, thereby achieving an optimized and innovative design for the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic structural diagram 1 of a power circulation device for an offshore HVDC transmission link transformer cooling system according to the present invention;

[0027] FIG2 is a structural schematic diagram 2 of a power circulation device of an offshore HVDC transmission link transformer cooling system according to the present invention;

[0028] FIG3 is a front view of a power circulation device for an offshore HVDC transmission link transformer cooling system according to the present invention;

[0029] FIG4 is a top view of a power circulation device of a cooling system for an offshore HVDC transmission link transformer according to the present invention;

[0030] FIG5 is a side view of a power circulation device of a cooling system for an offshore HVDC transmission link according to the present invention;

[0031] The accompanying drawings are marked as follows: 1. main circulation pump; 2. main circulation pipeline; 3. deionization pipeline; 4. nitrogen pressure-stabilizing pipeline; 5. main filter; 6. degassing tank; 7. expansion tank; 8. water supply device; 9. main pump leak detection device; 10. electric heater; 11. oil-water heat exchanger outlet pipeline; 12. main circulation pump inlet pipeline; 13. pump inlet corrugated compensator; 14. pump outlet corrugated compensator; 15. main circulation pump outlet pipeline; 16. first check valve; 17. second check valve; 18. main filter inlet pipeline; 19. seawater plate exchanger inlet pipeline; 20. ion tank inlet pipeline; 21. ion tank ; 22. Ion tank outlet pipe; 23. Precision filter pipe; 24. Nitrogen pipe; 25. Expansion tank outlet pipe; 26. First water supply pipe; 27. Water storage tank; 28. Water storage tank; 29. ​​Water supply pump; 30. Water supply pump outlet pipe; 31. Second water supply pipe; 32. Electric control box bracket; 33. Terminal box bracket; 34. Main filter inlet pipe bracket; 35. Main filter bracket; 36. Seawater plate inlet pipe bracket; 37. Water supply pump outlet pipe bracket; 38. Precision filter pipe bracket; 39. Nitrogen bottle bracket; 40. Main pump outlet multi-bracket; 41. Base. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts are all within the scope of protection of the present invention.

[0033] As shown in Figures 1-5, a power circulation device for a cooling system of an offshore HVDC transmission transformer includes a main circulation pump 1, a support system, a piping system, and an instrument system.

[0034] The support system includes an electric control box support 32, a terminal box support 33, a main filter water inlet pipe support 34, a main filter support 35, a seawater plate exchange water inlet pipe support 36, a water supply pump outlet pipe support 37, a precision filter pipe support 38, a nitrogen bottle support 39, and a main pump outlet multi-connection support 40;

[0035] The pipeline system includes a main circulation pipeline 2, a deionization pipeline 3, a nitrogen pressure stabilizing pipeline 4, a main filter 5, a degassing tank 6, an expansion tank 7, a water replenishing device 8, a main pump leak detection device 9, and an electric heater 10, which are connected in sequence to form a pipeline system;

[0036] The instrument system is an instrument arranged on the pipeline system.

[0037] In a preferred but non-limiting embodiment of the present invention, the main circulation pipeline includes an oil-water heat exchanger outlet pipeline 11, a main circulation pump inlet pipeline 12, a pump inlet corrugated compensator 13, a pump outlet corrugated compensator 14, a main circulation pump outlet pipeline 15, a first check valve 16, a second check valve 17, a main filter inlet pipeline 18, a main filter 5, and a seawater plate exchange inlet pipeline 19, which are connected in sequence to form the main circulation pipeline.

[0038] It is worth noting that bellows compensators are installed before and after the main circulation pump to reduce the impact of the main pump vibration on the system; the main circulation pump is designed with a leak detection tank with a liquid level switch in the tank to detect minor leaks in time; valves are installed before and after the main circulation pump to facilitate main pump fault inspection and repair when the main pump is connected to the fresh water system without stopping operation; two vertical and horizontal check valves are installed on the main circulation pump outlet pipe. If one of the check valves fails, the system can continue to operate, thereby improving system stability; the diameter of the main circulation pipe is DN250.

[0039] In a further preferred but non-limiting embodiment, to prevent rigid particles that may be washed away by the rapidly flowing circulating cooling water and enter the valve body, a main filter 5 with a precision of 50 μm is installed in the pipeline, using a stainless steel filter element with a standard mesh size and low water resistance. The filter is equipped with a differential pressure switch to indicate the degree of filter element contamination, prompting the operator to clean it, and this is an online manual cleaning method.

[0040] Furthermore, the electric heater 10 is placed in the degassing tank 6 and is configured to adjust the cooling water temperature when the temperature is extremely low in winter or the oil-water heat exchanger is out of operation, so as to avoid the cooling water temperature being too low. When the electric heater is running, the connected desalination water system cannot be shut down, and the flow of cooling water in the pipeline must be maintained, even if the oil-water heat exchanger has been shut down.

[0041] In a preferred but non-limiting embodiment of the present invention, the deionization pipeline includes an ion tank water inlet pipeline 20, an ion tank 21, an ion tank water outlet pipeline 22, and a precision filter pipeline 23, which are sequentially connected to form a deionization pipeline.

[0042] The deionization circuit is a branch connected in parallel to the main desalination water circuit. It primarily consists of a mixed-bed ion exchanger, a precision filter, and related accessories. It is configured to absorb some of the anions and cations in the coolant in the desalination water circuit. By continuously removing ions from the cooling water, it prevents adverse consequences such as electrolytic corrosion or other electrical breakdown of metal contact materials during long-term operation. The deionization line has a diameter of DN50.

[0043] The nitrogen pressure stabilizing pipeline includes an expansion tank 7, a nitrogen pipeline 24, and an expansion tank outlet pipe 25, which are connected in sequence to form a nitrogen pressure stabilizing pipeline. The nitrogen pressure stabilizing pipeline is connected to 6 nitrogen cylinders, 2 for use and 4 for backup, and is placed outside the device.

[0044] Further optionally, the precision filter pipeline 23 has its inlet connected to the ion tank outlet pipeline by bolts, and its outlet connected to the expansion tank inlet by bolts. The precision filter adopts high precision 5μm to intercept resin particles that may break and flow out.

[0045] The expansion tank 7 is connected to the desalination system's water treatment circuit and works in conjunction with a nitrogen pressure regulator to maintain constant pressure in the pipeline. It also works with the makeup water circuit and deionization circuit to replenish the medium. An aeration device is installed at the bottom of the expansion tank to increase nitrogen solubility and more effectively remove oxygen from the medium during degassing. The expansion tank also buffers volume changes caused by temperature fluctuations in the desalination system.

[0046] It is worth noting that the expansion tank is equipped with two independent capacitive liquid level sensors and one magnetic flap liquid level sensor, installed on the outside of the expansion tank to display the liquid level in the expansion tank, using the "one out of two" principle for output. The sensors should have a self-test function and automatically exit operation in advance if a sensor fails or the measured value exceeds the range, preventing false protection trips.

[0047] In a preferred but non-limiting embodiment of the present invention, the water replenishment device includes a first water replenishment pipeline 26, a water storage tank 27, a water storage tank outlet pipeline 28, a water replenishment pump 29, a water replenishment pump outlet pipeline 30, and a second water replenishment pipe 31, which are connected in sequence to form a water replenishment device.

[0048] In a preferred but non-limiting embodiment of the present invention, all the brackets are fixed to the base by bolts, the main circulation pump outlet pipe 15 is fixed to the H-steel on the upper part of the electric control box bracket 32 ​​through a pipe code and a pipe seat, the electric control box is fixed to the electric control box bracket by bolts, six nitrogen cylinders are fixed to the nitrogen cylinder bracket 39 by a ring, and the nitrogen pipeline 24 is fixed to the nitrogen cylinder bracket through a pipe code and a pipe seat.

[0049] In a preferred but non-limiting embodiment of the present invention, the oil-water heat exchanger outlet pipe 11, the main filter inlet pipe 18, and the main circulation pump inlet pipe 12 are fixed to the main pump outlet multi-bracket 40 through pipe code pipe sockets, and the main pump outlet multi-bracket is connected to the electric control box bracket 32 ​​and the nitrogen bottle bracket 39 by bolts.

[0050] In a further preferred but non-limiting embodiment, the water supply pump outlet pipeline 30 is fixed to the water supply pump outlet pipeline bracket 37 through a pipe code and a pipe socket, and the conductivity transmitter and two safety switch boxes are fixed to the water supply pump outlet pipeline bracket by bolts.

[0051] The two main circulation pumps 1 are connected in parallel, one for use and one for backup, and are fixed to the base 41 by bolts. The main circulation pump inlet is connected to the main circulation pump water inlet pipeline, and the main circulation pump outlet is connected to the main circulation pump water outlet pipeline.

[0052] The two water supply pumps 29 are connected in parallel, one for use and one for backup, and are fixed to the base 41 by bolts, with both ends connected to the water supply system; the first water supply pipeline 26 includes an automatic water supply interface, a manual water supply interface and two Y-type filters in parallel.

[0053] The beneficial effect of this utility model lies in that, compared with the prior art, it provides a compact, stable, and easily operable and maintainable offshore HVDC transmission link transformer cooling system power circulation device. Structurally, the nitrogen pressure-stabilizing pipeline 4, deionization pipeline 3, water supply device 8, and terminal box are integrated into a conventional DC main circulation system, minimizing space usage and ensuring a compact layout for offshore platform equipment. The internal space of the device is maximized while ensuring maintenance and overhaul, while minimizing the mechanical structure while achieving system functionality, thereby achieving an optimized and innovative design for the entire system.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention. Industrial Applicability

[0055] This utility model provides a compact, stable, and easy-to-operate and maintain offshore HVDC transmission link transformer cooling system power circulation device. The device integrates nitrogen pressure-stabilizing piping, deionization piping, water supply devices, and terminal boxes into a conventional DC main circulation device, minimizing space usage and ensuring a compact layout for offshore platform equipment. The device maximizes internal space utilization while ensuring maintenance and overhaul, and simplifies the mechanical structure to the greatest extent possible while still achieving system functionality, resulting in an optimized, innovative design for the entire system and enhanced practicality.

Claims

1. A power cycle device for a variable cooling system of a high-voltage DC power transmission connection at sea, comprising a main circulation pump (1), a support system, a pipeline system, and an instrument system, characterized in that: The support system includes an electric control box support (32), a terminal box support (33), a main filter inlet pipeline support (34), a main filter support (35), a seawater heat exchanger inlet pipeline support (36), a make-up water pump outlet pipeline support (37), a precision filter pipeline support (38), a nitrogen cylinder support (39), and a main pump outlet multi-connection support (40). All the supports are fixed to the base by bolts. The electric control box is fixedly connected to the electric control box support (32) by bolts. The nitrogen cylinder is fixed to the nitrogen cylinder support (39) by a clamping ring. The nitrogen pipeline (24) is fixed to the nitrogen cylinder support (39) by pipe clamps and pipe seats. The main pump outlet multi-connection support (40) is connected to the electric control box support (32) and the nitrogen cylinder support (39) by bolts; The pipeline system includes a main circulation pipeline (2), a deionized water pipeline (3), a nitrogen pressure stabilizing pipeline (4), a main filter (5), a degassing tank (6), an expansion tank (7), a make-up water device (8), a main pump leak detection device (9), and an electric heater (10). They are connected in sequence to form a pipeline system. The electric heater (10) is placed in the degassing tank (6); The instrument system is an instrument provided on the pipeline system.

2. The power cycle device for a variable cooling system of a high-voltage DC power transmission connection at sea according to claim 1, characterized in that: The main circulation pipeline (2) includes an oil-water heat exchanger outlet pipeline (11), a main circulation pump inlet pipeline (12), a pump inlet bellows compensator (13), a pump outlet bellows compensator (14), a main circulation pump outlet pipeline (15), a first check valve (16), a second check valve (17), a main filter inlet pipeline (18), a main filter (5), and a seawater heat exchanger inlet pipeline (19). They are connected in sequence to form the main circulation pipeline. The oil-water heat exchanger outlet pipeline (11), the main filter inlet pipeline (18), and the main circulation pump inlet pipeline (12) are fixed to the main pump outlet multi-connection support (40) by pipe clamps and pipe seats. The main circulation pump outlet pipeline (15) is fixed to the upper H-beam of the electric control box support (32) by pipe clamps and pipe seats.

3. The power cycle device for a variable cooling system of a high-voltage DC power transmission connection at sea according to claim 2, characterized in that: The first check valve (16) is a vertical check valve, and the second check valve (17) is a horizontal check valve.

4. The power cycle device for a variable cooling system of a high-voltage DC power transmission connection at sea according to claim 1, characterized in that: The deionized water pipeline (3) includes an ion tank inlet pipeline (20), an ion tank (21), an ion tank outlet pipeline (22), and a precision filter pipeline (23). They are connected in sequence to form the deionized water pipeline.

5. The power cycle device for a variable cooling system of a high-voltage DC power transmission connection at sea according to claim 4, characterized in that: The inlet of the precision filter pipeline (23) is connected to the outlet water pipeline (22) of the ion tank by bolts, and the outlet of the precision filter pipeline (23) is connected to the inlet of the expansion tank (7) by bolts.

6. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 1, wherein: The nitrogen pressure stabilizing pipeline (4) includes an expansion tank (7), a nitrogen pipeline (24), and an expansion tank outlet pipeline (25), which are connected in sequence to form a nitrogen pressure stabilizing pipeline.

7. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 1, wherein: The water replenishing device (8) includes a first water replenishing pipeline (26), a water storage tank (27), a water storage tank outlet pipeline (28), a water replenishing pump (29), a water replenishing pump outlet pipeline (30), and a second water replenishing pipe (31), which are connected in sequence to form a water replenishing device; The first water replenishing pipeline (26) includes an automatic water replenishing interface, a manual water replenishing interface, and two Y-type filters connected in parallel.

8. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 7, wherein: The water replenishing pump outlet pipeline (30) is fixed to the water replenishing pump outlet pipeline bracket (37) through pipe codes and pipe seats, and the conductivity transmitter and two safety switch boxes are fixed to the water replenishing pump outlet pipeline bracket by bolts.

9. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 1, wherein: The two main circulation pumps (1) are connected in parallel, one in use and one in reserve, and are fixed to the base (41) by bolts. The inlet of the main circulation pump is connected to the main circulation pump inlet pipeline, and the outlet of the main circulation pump is connected to the main circulation pump outlet pipeline.

10. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 7, wherein: The two water replenishing pumps (29) are connected in parallel, one in use and one in reserve, and are fixed to the base (41) by bolts, and both ends are connected to the water replenishing system.

11. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 6, wherein: The nitrogen pressure stabilizing pipeline (4) is connected to 6 nitrogen cylinders, 2 in use and 4 in reserve, and is placed outside the device.

12. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to claim 1, wherein: The diameter of the main circulation pipeline (2) is DN250, and the diameter of the deionized water pipeline (3) is DN50.

13. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to any one of claims 1-12, wherein: The precision of the main filter (5) is 50μm, and the filter element of the main filter (5) is a stainless steel filter element with a standard mesh and low water resistance.

14. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to any one of claims 1-13, wherein: An aeration device is provided at the bottom of the expansion tank (7).

15. The power circulation device of the variable cooling system for offshore high-voltage DC transmission connection according to any one of claims 1-14, wherein: The expansion tank (7) is provided with two sets of independent capacitive liquid level sensors and one set of magnetic flap liquid level sensors, which are installed on the outer side of the expansion tank (7).

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