Water pump turbine seal ring

Abstract

The present application relates to the technical field of fluid seal, and especially to a water pump water turbine sealing ring, which comprises a movable ring, a driving adjustment unit, a sealing unit, a pressure detection unit and a pressure balance unit, wherein the driving adjustment unit is used to drive the movable ring to move along the axial direction of the runner; the sealing unit comprises a first sealing structure arranged on the radial lower side of the movable ring and a second sealing structure arranged on the shaft hole of the driving adjustment unit; the pressure detection unit comprises a pressure leading mechanism and a detection mechanism; and the pressure balance unit is used to balance the pressure of the low-pressure area of the back cover and the high-pressure area of the working cavity. The axial position of the movable ring is accurately controlled by the driving adjustment unit, and the sealing gap can be adjusted in real time according to the working condition; the double sealing structure of the labyrinth seal and the metal bellows is adopted to effectively prevent the high-pressure water from leaking; and the pressure balance unit is arranged to connect the high-pressure area and the low-pressure area through the balance water pipe, so as to reduce the pressure difference between the inside and outside of the movable ring, reduce the sealing load, and prolong the service life.

Description

Technical Field

[0001] This invention relates to the field of fluid sealing technology, specifically to a water pump turbine sealing ring. Background Technology

[0002] Pumped storage is currently the most widely used green, low-carbon, clean, and flexible power source. Accelerating the development of pumped storage is an urgent requirement for building a new power system with new energy sources as the mainstay, and it plays an important role in ensuring the safe and stable operation of the power system and supporting the large-scale development of renewable energy.

[0003] Pump-turbines are the core components of pumped-storage power generation systems. To meet the demands of power grid peak shaving, emergency backup, frequency regulation, and phase modulation, pump-turbines frequently need to switch operating conditions, undergoing various hydraulic transition processes in the process. Currently, this type of unit still has the following significant drawbacks in operation:

[0004] First, in the bladeless zone between the runner outlet and the movable guide vanes, strong dynamic-static interference between the rotating runner and the stationary movable guide vanes causes significant pressure pulsations. These pressure pulsations, transmitted to the upper crown clearance, easily superimpose with self-excited pressure pulsations generated by unstable flow within the clearance, thus inducing vibration of the pump turbine top cover. If the vibration frequency couples with the plant's natural frequency, it may cause resonance, leading to a serious safety accident.

[0005] Secondly, during the frequent switching of operating conditions of the unit, the rapid changes in flow rate and pressure may cause hydraulic abrupt changes and hydraulic vibrations in the water conveyance system, which in turn cause violent fluctuations in the axial water thrust of the internal flow field of the unit, seriously threatening the safe and stable operation of the pumped storage unit.

[0006] In addition, under pump operation, the pressure in the impeller flow channel gradually increases from the inlet to the outlet. The huge radial pressure difference will cause some fluid to leak from the impeller outlet to the crown gap and the lower ring gap, resulting in a reduction in unit efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a water pump turbine sealing ring to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A water pump turbine sealing ring, comprising:

[0010] The movable ring is movably connected to the working chamber of the water pump turbine runner rear cover.

[0011] A drive adjustment unit is connected to the movable ring, and the drive adjustment unit is used to drive the movable ring to move along the axial direction of the rotating wheel;

[0012] A sealing unit, the sealing unit comprising a first sealing structure disposed on the radially lower side of the movable ring, and a second sealing structure disposed in the shaft hole through which the drive adjustment unit passes;

[0013] A pressure detection unit, comprising a pressure-inducing mechanism and a detection mechanism, wherein the pressure-inducing mechanism is used to induce the pressure around the rear cover and front cover of the water pump turbine runner to the detection mechanism, and the detection mechanism is disposed on the ground and is used to detect the pressure around the rear cover and front cover;

[0014] A pressure balancing unit is used to balance the pressure in the low-pressure area of ​​the rear cover and the high-pressure area of ​​the working chamber.

[0015] Preferably, the drive adjustment unit includes an electric actuator and a transmission assembly; the electric actuator is fixedly mounted on the top cover of the water pump turbine, and its output end is connected to the movable ring through the transmission assembly.

[0016] Preferably, the transmission assembly includes a connecting rod, the upper end of which is connected to the output end of the electric actuator, and the lower end of which is fixedly connected to the movable ring. The connecting rod and the movable ring are fixed by welding, and reinforcing ribs are arranged around the connecting rod.

[0017] Preferably, the number of electric actuators is several, and the several electric actuators are evenly arranged around the top cover of the water pump turbine.

[0018] Preferably, the first sealing structure includes a labyrinthine sealing groove, which is formed in the rear cover, and the movable ring and the rear cover are connected to each other.

[0019] Preferably, the second sealing structure includes an adjusting bracket, a metal bellows seal, a skeleton oil seal, and an oil level indicator. The metal bellows seal is disposed inside the adjusting bracket and outside the connecting rod. The skeleton oil seal is disposed above the metal bellows seal and connected to the adjusting bracket. The oil level indicator is disposed on the adjusting bracket.

[0020] Preferably, the metal bellows seal includes a lower cover, an upper cover, and a metal bellows sheet. The two ends of the metal bellows sheet are respectively connected to the upper cover and the lower cover, and the upper cover and the lower cover are both sleeved on the outside of the connecting rod.

[0021] Preferably, the pressure-taking mechanism includes a pressure-taking tube, a pressure-stabilizing ring, and a small tube. The rear cover and the front cover are respectively connected to different pressure-stabilizing rings through the pressure-taking tubes. A plurality of pressure-taking tubes are respectively arranged around the rear cover and the front cover. The pressure-stabilizing rings are connected to the ground through the small tubes.

[0022] Preferably, the detection mechanism includes a pressure sensor, and the pressure sensor is disposed on the side of the tube closest to the ground.

[0023] Preferably, the pressure balancing unit includes a balancing water pipe, the two ends of which are respectively connected to the low-pressure area of ​​the rear cover and the high-pressure area of ​​the working chamber.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention achieves precise control of the axial position of the moving ring through the drive adjustment unit, and can adjust the sealing gap in real time according to the working conditions, effectively suppressing pressure pulsation in the gap area; it adopts a double sealing structure of labyrinth seal and metal bellows, which effectively prevents high-pressure water leakage and adapts to high pressure differential environment; at the same time, a pressure balancing unit is set up to connect the high and low pressure areas through the balancing water pipe, reduce the pressure difference inside and outside the moving ring, reduce the sealing load, and extend the service life. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the connection structure between the present invention and the water turbine. Figure 1 ;

[0026] Figure 2 This is a schematic diagram of the connection structure between the present invention and the water turbine. Figure 2 ;

[0027] Figure 3 This is a schematic cross-sectional view of the internal structure of the turbine of the present invention. Figure 1 ;

[0028] Figure 4 This is a schematic diagram showing the position and structure of the movable ring and the drive adjustment unit of the present invention;

[0029] Figure 5 This is a schematic diagram of the connection structure between the movable ring and the connecting rod of the present invention. Figure 1 ;

[0030] Figure 6 This is a schematic diagram of the connection structure between the movable ring and the connecting rod of the present invention. Figure 2 ;

[0031] Figure 7 This is a schematic diagram of the connection structure between the movable ring and the rear cover of the present invention;

[0032] Figure 8 This is a schematic diagram of the working cavity location structure of the present invention;

[0033] Figure 9This is a schematic diagram of the connection structure of the connecting rod, the drive adjustment unit, and the second sealing structure of the present invention;

[0034] Figure 10 This is a schematic diagram showing the position and structure of the electric actuator, connecting rod, and adjusting bracket of the present invention;

[0035] Figure 11 This is a schematic diagram of the connection structure between the front cover and the small tube of the present invention;

[0036] Figure 12 This is a schematic diagram of the connection structure of the rear cover, small tube, and balance water pipe of the present invention;

[0037] Figure 13 This is a schematic diagram of the connection structure of the pressure tapping tube, the voltage stabilizing tube, and the small tube of the present invention;

[0038] Figure 14 This is a schematic diagram of the connection structure between the small tube and the pressure sensor of the present invention;

[0039] Figure 15 This is a schematic diagram of the adjustable radial clearance of the present invention.

[0040] In the diagram: 1. Movable ring, 2. Seat ring, 3. Fixed guide vane, 4. Rear cover, 5. Control console, 6. Water pump turbine main shaft, 7. Runner, 8. Front cover, 9. Electric actuator, 10. Connecting rod, 11. Reinforcing rib, 12. Labyrinth seal groove, 13. Adjusting bracket, 14. Metal bellows seal, 15. Skeleton oil seal, 16. Oil level indicator, 17. Balance water pipe, 18. Low pressure zone, 19. High pressure zone, 100. Pressure tapping pipe, 101. Pressure stabilizing pipe, 102. Small pipe, 103. Pressure sensor, 401. Working chamber, 1401. Lower cover, 1402. Upper cover, 1403. Metal bellows. Detailed Implementation

[0041] 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.

[0042] Please see Figure 1-15 The present invention provides a technical solution:

[0043] A water pump turbine sealing ring, as shown in the instruction manual. Figure 1As shown, it includes: a movable ring 1; a working chamber 401 is provided on the rear cover 4 of the water pump turbine runner; the movable ring 1 is movably connected to the working chamber 401; the movable ring 1 is a semi-trapezoidal ring structure with a sloping lower part and an open upper part, and is integrally cast from stainless steel. During manufacturing, it can be machined on a large gantry lathe to ensure its geometric accuracy and structural strength. (See attached instruction manual.) Figure 3 The diagram shows a movable ring 1, a seat ring 2, a fixed guide vane 3, a rear cover 4, a control console 5, a water pump turbine main shaft 6, a runner 7, and a front cover 8. The lower inclined surface of the movable ring 1 corresponds to and fits against the cut mating surface on the rear cover 4, forming an adjustable radial clearance. This design keeps the inlet of the gap between the upper crown and the lower ring away from the bladeless area, i.e., away from the area with the most intense pressure pulsation in the main flow channel, thus significantly suppressing the pressure pulsation transmitted from the main flow to the gap between the upper crown and the lower ring. The rear cover 4 has a cut mating surface opposite to the movable ring 1, the shape of which matches the corresponding contour of the movable ring 1. Furthermore, because the radius of the radial clearance formed by the cut portion of the movable ring 1 and the runner rear cover 4 is significantly smaller than the radius of the conventional upper crown and lower ring gap inlet, the pressure difference between the gap inlet and outlet is significantly reduced, thus reducing the overall pressure level in the gap area. This not only helps to balance axial forces but also effectively controls the leakage in the gap area. Furthermore, the upper crown movable ring of the present invention can automatically adjust its axial position according to the pressure change inside the gap, thereby changing the size of the radial gap and realizing real-time dynamic adjustment of the axial force under different operating conditions.

[0044] The drive adjustment unit is connected to the movable ring 1 and is used to drive the movable ring 1 to move along the axial direction of the rotating wheel 7.

[0045] The sealing unit includes a first sealing structure disposed on the radially lower side of the movable ring 1, and a second sealing structure disposed in the shaft hole through which the drive adjustment unit passes.

[0046] The pressure detection unit includes a pressure-inducing mechanism and a detection mechanism. The pressure-inducing mechanism is used to introduce the pressure around the rear cover 4 and front cover 8 of the water pump turbine runner to the detection mechanism. The detection mechanism is set on the ground and is used to detect the pressure around the rear cover 4 and front cover 8.

[0047] The pressure balancing unit is used to balance the pressure in the low-pressure zone 18 of the rear cover 4 and the high-pressure zone 19 of the working chamber 401, thereby reducing the sealing pressure and extending its service life.

[0048] The drive adjustment unit includes an electric actuator 9 and a transmission assembly. The electric actuator 9 is fixedly installed on the top cover of the water pump turbine, and its output end is connected to the movable ring 1 through the transmission assembly.

[0049] The transmission assembly includes a connecting rod 10, the upper end of which is connected to the output end of the electric actuator 9, and the lower end of which is fixedly connected to the movable ring 1. The connecting rod 10 and the movable ring 1 are fixed by welding, and reinforcing ribs 11 are arranged around the connecting rod 10.

[0050] There are several electric actuators 9, and these electric actuators 9 are evenly arranged around the top cover of the water pump turbine.

[0051] The first sealing structure includes a labyrinthine sealing groove 12, which is located on the rear cover 4.

[0052] The second sealing structure includes an adjusting bracket 13, a metal bellows seal 14, a skeleton oil seal 15, and an oil level indicator 16. The metal bellows seal 14 is disposed inside the adjusting bracket 13 and sleeved on the outside of the connecting rod 10, serving as the first seal; the skeleton oil seal 15 is disposed above the metal bellows seal 14 and installed in the reserved groove of the adjusting bracket 13, serving as the second seal; the oil level indicator 16 is disposed on the adjusting bracket 13 for observing whether the seal has failed.

[0053] The metal bellows seal 14 includes a lower cover 1401, an upper cover 1402, and a metal bellows sheet 1403. The two ends of the metal bellows sheet 1403 are respectively connected to the upper cover 1402 and the lower cover 1401. Both the upper cover 1402 and the lower cover 1401 are fitted onto the outside of the connecting rod 10. The metal bellows seal 14 is welded together from the metal bellows sheet 1403 and its two ends, the upper cover 1402 and the lower cover 1401 (both upper and lower covers 1401 are flange structures). The entire assembly is then welded and fixed to the connecting rod 10 and the top cover of the water pump turbine, and a pressure test is performed to ensure absolute sealing. In this embodiment, the skeleton oil seal 15 can be a multi-lip skeleton oil seal 15 or a combination of multiple skeleton oil seals 15 to enhance sealing reliability.

[0054] The pressure balancing unit includes a balancing water pipe 17. The two ends of the balancing water pipe 17 are respectively connected to the low-pressure area 18 of the rear cover 4 and the high-pressure area 19 of the working chamber 401 of the water pump turbine. The balancing water pipe 17 is used to balance the pressure in the upper crown gap. The two ends of the balancing water pipe 17 are respectively connected to the low-pressure area 18 of the rear cover 4 and the high-pressure area 19 of the working chamber 401. The high-pressure water entering the working chamber of the movable ring 1 is led to the low-pressure area 18 of the rear cover 4, thereby maintaining the pressure balance between the two chambers. The balancing water pipe 17 is made of stainless steel and is welded and fixed to the rear cover 4.

[0055] In this embodiment, the water pump turbine sealing ring also includes a control unit, which mainly includes: a signal acquisition module, a central processing controller, a drive command module, and a human-machine interface (the human-machine interface is integrated into the control console 5), as detailed in the appendix to the specification. Figure 1 Included with instruction manual Figure 2 The dashed line represents the electrical signal connection between the pressure sensor 103 and the control console 5 in the small tube 102.

[0056] The signal acquisition module includes a pressure detection unit and a position feedback component;

[0057] The pressure detection unit includes a pressure-introducing mechanism and a detection mechanism. The pressure-introducing mechanism is used to introduce the pressure around the rear cover and front cover of the water pump turbine runner to the detection mechanism. The detection mechanism is set on the ground and is used to detect the pressure around the rear cover and front cover. The detection mechanism includes a pressure sensor 103 (in actual use, a local pressure gauge can also be used to detect the pressure).

[0058] The pressure tapping tubes 100 of the front cover 8 and the rear cover 4 collect the pressure of the front and rear cavities of the rotating wheel 7 through multiple pressure tapping points (such as points on the front cover 8 and the rear cover 4), and summarize the pressure to the pressure stabilizing tube 101. The pressure stabilizing tube 101 is connected to a small tube 102, which is attached to the instruction manual. Figure 4 The terms "small tube 102 corresponding to the front cover 8" and "small tube 102 corresponding to the rear cover 4" are used respectively for clarification. Finally, the pressure signal is converted into a standard electrical signal (-mA in this embodiment) by the pressure sensor 103 (a piezoelectric or capacitive pressure transmitter in this embodiment) installed in the small tube 102, as shown in the attached manual. Figure 14 As shown, the small tube 102 and the pressure sensor 103 are connected by a thread. The design employing multi-point pressure tapping and a pressure stabilizing tube 101 effectively obtains a stable average pressure value within the cavity, avoiding local fluctuations caused by single-point measurements. (See attached instruction manual.) Figure 13 The diagram shows the connection structure of the pressure tapping tube 100, the voltage stabilizing tube 101, and the small tube 102.

[0059] The position feedback component includes a displacement sensor (in this embodiment, a magnetostrictive displacement sensor or an LVDT linear displacement sensor) integrated on each electric actuator 9 or connecting rod 10, for real-time and accurate feedback of the actual axial position of the moving ring 1.

[0060] The central controller is a PLC (Programmable Logic Controller) used to receive the current operating status signals of the unit (such as "turbine mode", "pump mode", "start-up", "steady-state operation", "transition process" etc.) from the power plant monitoring system (such as DCS); the drive command module (in this embodiment, a servo driver or frequency converter array) converts the displacement command into precise control signals for each electric actuator 9 (in actual use, these can be pulse, analog, or bus signals), driving the motor to rotate forward or reverse, thereby pulling or pushing the movable ring 1 axially through the transmission components.

[0061] The human-machine interface integrated on the touch screen of the control console 5 is used to display information such as the pressure of the front cover 8 / rear cover 4, the pressure difference ΔP, the current position of the moving ring 1, the status of each electric actuator 9, and the alarm of the sealing system (such as the abnormality of the oil level indicator 16) in real time; at the same time, it allows operators to set or modify the target pressure difference, target clearance, and control parameters (such as PID parameters) under different operating conditions according to the characteristics of the unit.

[0062] Working principle:

[0063] (1) The principle of gap adjustment:

[0064] The movable ring 1 fits against the cut mating surfaces on the front and rear cover plates 4 of the rotating wheel 7 via its lower inclined surface, forming an adjustable radial clearance around the rotating wheel 7 (the radial clearance is specified in the instruction manual). Figure 15 (Gap A and gap B in the middle).

[0065] Under turbine operating conditions, the area behind the runner 7 (on the side of the rear cover 4) is a high-pressure zone 19. When the pressure in this area increases, the force acting on the movable ring 1 drives it to move upward axially, either directly or via the electric actuator 9, increasing the radial clearance A between the inclined surface of the movable ring 1 and the mating surface of the rear cover 4 plate of the runner 7. This keeps the "entrance" of the upper crown clearance away from the main high-pressure pulsation source in the bladeless area between the runner 7 and the movable guide vane, effectively blocking and attenuating the transmission of high-intensity pressure pulsations to the upper crown clearance area.

[0066] Under pump operating conditions, the pressure in front of impeller 7 (on the side of front cover 8) increases significantly. At this time, the movable ring 1 is driven, or driven by the electric actuator 9, to move axially downward, reducing the radial clearance B between it and the front cover 8 plate of impeller 7. This causes the "outlet" of the lower ring clearance to contract, increasing leakage flow resistance, thereby significantly reducing the leakage flow from the high-pressure area 19 at the outlet of impeller 7 to the clearance and improving pump efficiency.

[0067] (2) Leakage control and hydraulic balance principle:

[0068] Fluid that may leak from the high-pressure zone 19 at the outlet of the impeller 7 first reaches the labyrinth seal structure at the bottom of the moving ring 1. The fluid undergoes multiple collisions, throttling, and vortex dissipation within the labyrinthine slits, significantly reducing its pressure and kinetic energy, achieving effective pressure reduction and flow control in the first stage. After initial pressure reduction via the labyrinth seal, the pressure of the fluid entering the working chamber of the moving ring 1 may still fluctuate. At this point, the balancing water pipe 17 directly connects the high-pressure zone 19 of the working chamber 401 of the moving ring 1 with the low-pressure zone 18 of the rear cover 4; according to the principle of communicating vessels, the pressure between the two zones will automatically seek balance through this pipe. When the pressure inside the movable ring 1 is too high, the fluid flows to the low-pressure zone 18 through the balancing water pipe 17; conversely, it is replenished, thereby automatically maintaining the internal pressure of the movable ring 1 at a relatively stable and low level. This avoids the additional load or vibration caused by the accumulation of pressure inside the cavity. The combined effect of the above-mentioned gap adjustment (changing the pressure action area) and pressure balancing (reducing the internal pressure) can significantly regulate and balance the axial water thrust acting on the impeller 7, thereby improving operational stability.

[0069] (3) Sealing principle of connecting rod 10

[0070] To allow the connecting rod 10 to drive the movable ring 1 to move up and down while preventing fluid leakage from the pump turbine, a composite seal is installed at the point where the connecting rod 10 exits: First, a metal bellows acts as a flexible, axially expandable seal, with its two ends welded to the connecting rod 10 and the pump turbine's fixed structure, forming an absolutely static seal barrier that completely isolates the fluid inside the equipment. Its flexibility compensates for the axial movement of the connecting rod 10 without affecting the seal integrity. Above the metal bellows seal, a skeleton oil seal 15 is installed as a redundant safety barrier. Its sealing lip tightly grips the connecting rod 10, preventing further upward leakage of fluid in extreme cases (assuming the main seal fails) and providing early warning time for maintenance.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A water pump turbine sealing ring, characterized in that, include: The movable ring is movably connected to the working chamber of the water pump turbine runner rear cover. A drive adjustment unit is connected to the movable ring, and the drive adjustment unit is used to drive the movable ring to move along the axial direction of the rotating wheel; A sealing unit, the sealing unit comprising a first sealing structure disposed on the radially lower side of the movable ring, and a second sealing structure disposed in the shaft hole through which the drive adjustment unit passes; A pressure detection unit, comprising a pressure-inducing mechanism and a detection mechanism, wherein the pressure-inducing mechanism is used to induce the pressure around the rear cover and front cover of the water pump turbine runner to the detection mechanism, and the detection mechanism is disposed on the ground and is used to detect the pressure around the rear cover and front cover; A pressure balancing unit is used to balance the pressure in the low-pressure area of ​​the rear cover and the high-pressure area of ​​the working chamber. The first sealing structure includes a labyrinthine sealing groove; The second sealing structure includes an adjusting bracket, a metal bellows seal, a skeleton oil seal, and an oil level indicator; The pressure balancing unit includes a balancing water pipe, the two ends of which are respectively connected to the low-pressure area of ​​the rear cover and the high-pressure area of ​​the working chamber. The drive adjustment unit includes an electric actuator and a transmission assembly; the electric actuator is fixedly mounted on the top cover of the water pump turbine, and its output end is connected to the movable ring through the transmission assembly. The transmission assembly includes a connecting rod, the upper end of which is connected to the output end of the electric actuator, and the lower end of which is fixedly connected to the movable ring. The connecting rod and the movable ring are fixed by welding, and reinforcing ribs are arranged around the connecting rod. The metal bellows seal is disposed inside the adjusting bracket, the metal bellows seal is disposed outside the connecting rod, the skeleton oil seal is disposed above the metal bellows seal, the skeleton oil seal is connected to the adjusting bracket, and the oil level indicator is disposed on the adjusting bracket. The metal bellows seal includes a lower cover, an upper cover, and a metal bellows sheet. The two ends of the metal bellows sheet are respectively connected to the upper cover and the lower cover. The upper cover and the lower cover are both sleeved on the outside of the connecting rod. The pressure-taking mechanism includes a pressure-taking tube, a pressure-stabilizing ring, and a small tube. The rear cover and the front cover are respectively connected to different pressure-stabilizing rings through the pressure-taking tubes. Several pressure-taking tubes are respectively arranged around the rear cover and the front cover. The pressure-stabilizing rings are connected to the ground through the small tubes. The movable ring is a semi-trapezoidal ring structure with a sloping lower part and an open upper part. The sloping lower part of the movable ring corresponds to and fits against the mating surface formed by cutting on the back cover, forming an adjustable radial gap.

2. The water pump turbine sealing ring according to claim 1, characterized in that: The number of electric actuators is several, and the several electric actuators are evenly arranged around the top cover of the water pump turbine.

3. A water pump turbine sealing ring according to claim 1, characterized in that: The labyrinth-style sealing groove is formed in the rear cover, and the movable ring and the rear cover are connected to each other.

4. A water pump turbine sealing ring according to claim 1, characterized in that: The detection mechanism includes a pressure sensor, and the pressure sensor is installed on the side of the tube closest to the ground.

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