An air tank with adjustable top elevation of the air chamber

Abstract

This utility model relates to an air tank with adjustable top elevation of the air chamber, comprising a vertical tank body, a water chamber at the bottom of the tank body, and a water pressure pipeline connected to the bottom of the tank body via a connecting pipe. A piston is installed inside the tank body, slidingly engaging with the inner wall of the tank. At least one sealing structure is provided on the contact surface between the piston and the inner wall of the tank body. The space between the water chamber and the piston at the top of the tank body is an air chamber. A piston rod connected to the piston extends through a perforation at the top of the tank body and connects to a drive mechanism. The drive mechanism is electrically connected to a controller, which is electrically connected to a water pump in a pumping station pressurized water supply system. After receiving a power outage signal from the water pump, the controller sends a control signal to control the drive mechanism to drive the piston downwards. After returning to normal operation, the controller controls the drive mechanism to drive the piston back to its original position. At least one vent is provided at the top of the tank body. While meeting the requirements for air tank surge amplitude, this design can further improve the extreme pressure at the bottom of the air tank, thereby improving the extreme pressure along the hydraulic transition process.

Description

Technical Field

[0001] This utility model relates to the technical field of air tanks in pump station pressurized water supply systems, and particularly to air tanks with adjustable air chamber top elevation. Background Technology

[0002] In long-distance water conveyance projects with high head and low flow rate, air tanks are commonly used to address water hammer issues after power outages during pumping. Air tanks are widely used due to their ease of operation, maintenance, installation, and management, and there is considerable experience in their design and application. Common types of air tanks include vertical and horizontal models, with vertical air tanks being more prevalent.

[0003] The initial absolute pressure and height of the air tank chamber determine not only the surge amplitude within the air tank but also the pressure amplitude at the bottom of the air tank, thus affecting the pressure envelope along the pipeline. A higher initial absolute pressure in the air tank chamber (i.e., a lower initial operating water level) results in a smaller chamber height, a smaller surge amplitude, and a larger bottom pressure amplitude. Therefore, when designing air tank dimensions, it is necessary to comprehensively consider both the surge amplitude within the air tank and the bottom pressure amplitude, and to select an appropriate initial operating water level and chamber height from an economic perspective.

[0004] The elevation of the top of the air chamber in existing air tanks is fixed. In addition, in order to fully reflect water hammer pressure and ensure that the maximum and minimum pressures along the pipeline meet the specifications, existing conventional air tank types often require a large size. Utility Model Content

[0005] To address the aforementioned problems, the present invention aims to provide an air tank with an adjustable top elevation, which, while satisfying the surge amplitude of the air tank, can further improve the extreme pressure at the bottom of the air tank, thereby improving the extreme pressure along the hydraulic transition process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An air tank with adjustable top elevation includes a vertical tank body. The lower part of the tank body is a water chamber. The bottom of the tank body is connected to a water pressure pipeline via a connecting pipe. A piston that slides against the inner wall of the tank body is installed inside the tank body. At least one sealing structure is provided on the contact surface between the piston and the inner wall of the tank body. The space between the water chamber and the piston in the upper part of the tank body is an air chamber. A piston rod connected to the piston extends through a perforation at the top of the tank body to the top of the tank body and is connected to a drive mechanism. The drive mechanism is electrically connected to a controller. The controller is electrically connected to a water pump in the pressurized water supply system of the pumping station. After receiving a power failure signal from the water pump, the controller sends a control signal to control the drive mechanism to drive the piston to move down. After returning to normal, the controller controls the drive mechanism to drive the piston to reset. At least one vent is provided at the top of the tank body.

[0007] As a specific embodiment, the cross-sectional area of ​​the connecting pipe is greater than or equal to 15% of the cross-sectional area of ​​the water pressure pipeline.

[0008] As a specific embodiment, the sealing structure adopts a combination structure of a Step seal ring and two guide rings on both sides. A middle sealing groove is opened in the middle of the outer side of the piston for installing the Step seal ring. The Step seal ring is installed in the middle sealing groove and contacts the inner wall of the tank. Outer sealing grooves are opened on the upper and lower sides of the middle sealing groove on the outer side of the piston for installing the guide rings on both sides. The guide rings are installed in the outer sealing grooves and have a clearance fit with the inner wall of the tank.

[0009] As a specific embodiment, the driving mechanism is a linear driving mechanism, which drives the piston to move up and down.

[0010] As a specific embodiment, both the piston and the piston rod are made of rigid materials.

[0011] As a specific embodiment, a pressure measuring hole is provided on the top of the tank, and a pressure sensor is installed in the pressure measuring hole. The pressure sensor is electrically connected to the controller. The pressure sensor detects the pressure inside the pressure measuring hole in real time and sends it to the controller. The controller receives the pressure signal sent by the pressure sensor and determines whether the detected pressure is greater than the local atmospheric pressure. When the detected pressure is greater than the local atmospheric pressure, the controller controls the drive mechanism to drive the piston to move upward and reset to press against the top surface of the tank.

[0012] As a specific embodiment, the diameter of each vent hole is 1 / 10 of the diameter of the water pressure pipeline.

[0013] As a specific embodiment, a flexible material layer is provided on the top surface of the piston at the positions corresponding to the vent hole and the pressure measuring hole.

[0014] As a specific embodiment, the controller is equipped with an alarm module that issues an alarm when the piston moves upward and resets due to air leakage from the air tank.

[0015] This utility model has the following beneficial effects: This utility model discloses an air tank with adjustable top elevation of the air chamber. Under the premise of satisfying the surge amplitude of the air tank, it further improves the extreme value of the pressure at the bottom of the air tank, thereby improving the extreme value of the pressure along the line during the hydraulic transition process.

[0016] This invention relates to an air tank with an adjustable top elevation. Utilizing piston pressurization, it effectively mitigates the pressure drop at the bottom of the air tank, thereby reducing subsequent pressure rebound and pressure fluctuations within the pipeline. This ensures the stability and safety of the water supply pipeline after a power outage at the pumping station. The device maintains a constant initial water level in the air tank without increasing the height or cross-sectional area of ​​the air tank, saving on construction costs and improving pressure extremes along the pipeline during hydraulic transitions. It can be applied to water hammer protection design for air tanks in long-distance water supply projects and can also provide valuable reference for air cushion pressure regulating chambers in power plants. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the air tank with adjustable top elevation of the air chamber according to this utility model; Figure 2 This is a schematic diagram of the air tank structure of the present invention when the piston rotates and presses down to the target position; Figure 3 This is a schematic diagram of the piston sealing structure of the novel air tank of this utility model; Figure 4 This is a top view of the air tank with adjustable air chamber elevation according to the present invention. Figure 5 This is a plan view of a long-distance water conveyance system. Figure 6 This is a schematic diagram showing the relevant dimensions of the novel air tank of this utility model; Figure 7 This is a simulation of the piezometric head and centerline height of a water conveyance system under constant flow conditions in an application example of this utility model. Figure 8 This is a process line showing the elevation change of the top of the air tank chamber in this utility model embodiment; Figure 9 The pressure change process lines at the bottom of conventional air tanks and the novel air tank of this invention are shown. Figure 10 This is a partially enlarged view of the pressure change process lines at the bottom of a conventional air tank and the novel air tank of this invention; Figure 11 This is another enlarged view of the pressure change process lines at the bottom of a conventional air tank and the novel air tank of this invention; Figure 12 The water level change process lines are for conventional air tanks and the novel air tank of this invention; Figure 13 This is a partially enlarged view of the water level change process lines of a conventional air tank and the novel air tank of this invention; Figure 14 The pressure change process lines of the air chambers of conventional air tanks and the novel air tank of this invention are shown. Figure 15This is a partially enlarged view of the pressure change process lines in the air chambers of a conventional air tank and the novel air tank of this invention; Figure 16 This is another enlarged view of the pressure change process lines of the air chamber of a conventional air tank and the novel air tank of this utility model; Figure 17 The maximum pressure package route for conventional air tanks and the novel air tank of this utility model; Figure 18 This is a partially enlarged view of the maximum pressure package route of a conventional air tank and the novel air tank of this invention; Figure 19 The minimum pressure package route for conventional air canisters and the novel air canister of this invention; Figure 20 This is a partially enlarged view of the minimum pressure package route for a conventional air canister and the novel air canister of this invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: See Figures 1 to 4 An air tank with adjustable top elevation includes a vertical tank body 11, with a water chamber at the bottom of the tank body 11.

[0019] The bottom of the tank 11 is connected to the water pressure pipeline 2 via a connecting pipe 21, and the cross-sectional area of ​​the connecting pipe 21 is greater than or equal to 15% of the cross-sectional area of ​​the water pressure pipeline 2.

[0020] A perforation is provided at the center of the top surface of the tank body 11. A piston 12 is installed inside the tank body 11, slidingly engaging with the inner wall of the tank body 11. At least one sealing structure 121 is provided on the contact surface between the piston 12 and the inner wall of the tank body 11. See also... Figure 3 The sealing structure 121 can be a combination of a step seal ring and two guide rings. A middle sealing groove is opened in the middle of the outer side of the piston 12 for installing the step seal ring. The step seal ring is installed in the middle sealing groove and contacts the inner wall of the tank body 11. Outer sealing grooves are opened on the upper and lower sides of the middle sealing groove on the outer side of the piston 12 for installing the guide rings on both sides. The guide rings are installed in the outer sealing grooves and have a clearance fit with the inner wall of the tank body 11.

[0021] The space between the water chamber and the piston 12 at the top of the tank 11 is a gas chamber, which is used to hold compressed gas. The top elevation of the gas chamber can be changed by the vertical displacement of the piston 12.

[0022] The piston rod 122, connected to the piston 12, extends through a perforation at the top of the tank 11 and connects to the linear drive mechanism 13 above the tank 11. The linear drive mechanism 13 can be a mechanism that uses an electric motor as a power source and directly or indirectly outputs linear motion. The linear drive mechanism 13 is electrically connected to a controller, which is electrically connected to the water pump in the pumping station's pressurized water supply system. After receiving a power outage signal from the water pump, the controller sends a control signal to control the linear drive mechanism 13 to drive the piston 12 downward. After the system returns to normal operation, the controller controls the linear drive mechanism 13 to drive the piston 12 back to its original position.

[0023] Both piston 12 and piston rod 122 are made of rigid material.

[0024] See Figure 4 At least one vent hole 111 and one pressure measuring hole 112 are provided on the outer side of the perforation at the top of the tank body 11. In this embodiment, three vent holes 111 and one pressure measuring hole 112 are provided, and the three vent holes 111 and one pressure measuring hole 112 are evenly distributed around the outer periphery of the perforation with the perforation as the center. The diameter of each vent hole 111 and pressure measuring hole 112 is 1 / 10 of the diameter of the water supply pressure pipeline 2.

[0025] A flexible material layer 123, such as rubber, is provided on the top surface of the piston 12 at the positions corresponding to the vent 111 and the pressure measuring hole 112. Alternatively, a flexible material layer 123 covering all or most of the top surface of the piston 12 can be provided on the top surface of the piston 12.

[0026] A pressure sensor is installed inside the pressure measuring hole 112, and the pressure sensor is electrically connected to the controller. The pressure sensor detects the pressure inside the pressure measuring hole 112 in real time and sends it to the controller. The controller receives the pressure signal sent by the pressure sensor and determines whether the detected pressure is greater than the local atmospheric pressure. When the detected pressure is greater than the local atmospheric pressure (at which point the tank is leaking), the controller controls the linear drive mechanism 13 or the rotary drive mechanism to drive the piston 12 to move upward and reset, pressing against the inner top surface of the tank 11. The flexible material layer 123 on the top surface of the piston 12 seals all the vent holes 111 and the pressure measuring hole 112, ensuring the safety and reliability of the air tank and preventing air leakage due to failure of the piston 12 sealing structure 121, thereby eliminating the occurrence of air tank failure.

[0027] Preferably, the controller is equipped with an alarm module that issues an alarm when the piston 12 moves upward and resets due to air leakage from the air tank.

[0028] Considering that the air tank may be located in the middle of the pump station's pressurized water supply system, the piston 12 of the novel air tank of this invention should be depressed at the moment the pressure reduction wave arrives at the air tank. This ensures that the pressure reduction process of the pump shutdown water hammer and the pressurization effect achieved by the piston 12 depression are superimposed, preventing unnecessary negative pressure or overpressure damage to the pipeline. The preliminary estimate of the depressurization time of the air tank piston 12 can be determined based on the length of the water supply pipeline before the air tank, i.e.: Depressurization time of air tank piston 12 - Water pump power failure time = Length of water supply pipeline before air tank / Water hammer wave velocity.

[0029] The duration of piston 12's downward pressure in the air tank should be taken into account to avoid the superposition of positive pressure waves reflected from the outlet, which could cause overpressure in the pipeline. The preliminary estimate of the duration of piston 12's downward pressure in the air tank can be determined based on the length of the water pipeline after the air tank, i.e.: duration of piston 12's downward pressure in the air tank < 2 × length of water pipeline after the air tank / water hammer wave velocity.

[0030] The initial estimate of the downward pressure of piston 12 of the air tank should take into account ensuring that the downward pressure will not cause the air tank to leak. The initial estimate of the downward pressure of piston 12 of the air tank can be determined based on the initial water level of the air tank, the amplitude of the surge inside the air tank, and the installation elevation of the bottom of the air tank, that is: the downward pressure of piston 12 of the air tank ≤ the initial water level of the air tank - the amplitude of the surge inside the air tank - the installation elevation of the bottom of the air tank - the safe water depth.

[0031] The timing, duration, and amount of piston 12 pressing down on the air tank were determined by adjusting the values ​​based on preliminary estimates through transient flow numerical simulation.

[0032] A long-distance water transport project incorporating the novel air tank of this utility model adopts a "two-in-use, one-standby" pump unit layout. (See also...) Figure 5 This long-distance water transmission system includes an inlet pool 3, a pumping station, an air tank 1, a water pressure pipeline 2, and an outlet pool 4. The pumping station pumps water from the inlet pool 3 to the outlet pool 4 through the water pressure pipeline 21. The air tank 1 is installed behind the pumping station and connected to the water pressure pipeline 2. The pumping station is equipped with three centrifugal pumps 5, two of which are in normal operation and one is on standby. The design flow rate of a single pump is 3.25 m³ / s, the design head is 186.00 m, and the rated speed is 750 r / min. Each centrifugal pump 5 is equipped with a check valve 6. The specific calculation conditions are as follows: upstream design water level, downstream design water level, two pump units operating at the design head, and both pump units pumping water simultaneously with power off. The piezometric head and pipeline centerline elevation of the pipeline under steady-state conditions after pumping are as follows. Figure 7 As shown.

[0033] At present, researches on hydraulic transients are generally dominated by one-dimensional numerical simulation. In the following, numerical simulation of the above working conditions is carried out through application examples by using program calculation. By studying the bottom pressure of the air chamber, the water level in the air chamber, the air chamber pressure of the air chamber, and the maximum and minimum pressure envelope curves, further analysis is conducted on the practicability of the novel air chamber of the present utility model in aspects such as improving the extreme pressure along the line during hydraulic transients.

[0034] The mathematical model of the novel air chamber of the present utility model is similar to that of a conventional air chamber, and the transformation of the mathematical model is mainly achieved by controlling and changing the elevation of the top of the air chamber.

[0035] It is assumed that the air in the closed pressurized air chamber satisfies the ideal gas state equation. Since the transient process is very rapid, the expansion or compression process of air is close to an adiabatic condition, which is in line with the actual situation for an air chamber with a small volume.

[0036] The main equations are as follows: (1) Where: H A is the absolute pressure of the gas in the air chamber; V is the volume of the gas in the air chamber; n is the exponent of the gas state equation, 1 < n < 1.4, and an average value of 1.2 is adopted in design calculation; C is a constant related to the initial state of the gas in the air chamber.

[0037] (2) Where: H P is the pressure at the connecting node between the air chamber and the pipeline, which is a relative pressure; k is the hydraulic loss coefficient at the connecting node between the air chamber and the pipeline, which shall take different values when flowing in and out according to the sign of Q S Q S is the flow rate flowing into the air chamber; Z is the water level in the air chamber; H B is the local atmospheric pressure, which is related to the local elevation; the meanings of other symbols are the same as above.

[0038] (3) Where: dz is the change of water level within time dt; A C is the cross-sectional area of the air chamber; the meanings of other symbols are the same as above.

[0039] (4) Where: Q U is the flow rate at the upstream node of the air chamber; Q D is the flow rate at the downstream node of the air chamber; the meanings of other symbols are the same as above.

[0040] C+ : (5) C- : (6) In the formula, H P C is the pressure at the connection point between the air tank and the pipeline; p and B p C is an intermediate variable. p and B p C is calculated using equation (7); M and B M C is an intermediate variable. M and B M The result is obtained by calculation using equation (8); the meanings of other symbols are the same as before.

[0041]

[0042] (7)

[0043] (8) In the formula: H i-1 and H i+1 Q is the head of water at the previous time step before and after the node being calculated; i-1 and Q i+1 The flow rate at the previous moment before and after the node is calculated; B is the characteristic impedance of the pipeline, which is calculated by equation (9); R is the head loss coefficient, which is calculated by equation (10); other symbols have the same meaning as before.

[0044] (9) In the formula: a is the water hammer wave velocity; g represents the gravitational acceleration; A represents the cross-sectional area of ​​the pipe; other symbols have the same meaning as before.

[0045] (10) In the formula: f is the Darcy-Weisbach friction loss coefficient; ∆x is the average pipe length; D is the pipe diameter; other symbols have the same meaning as before.

[0046] Equations (1) to (10) are used to solve for the pressure and flow rate of the pressure air tank node, and can be used to determine the gas volume, pressure and water level changes in the air tank.

[0047] Surge amplitude inside the air tank It can be estimated using the following formula: (11) Pressure change amplitude at the bottom of the air tank It can be estimated using the following formula: (12) Where: ν0 is the initial flow velocity in the pipeline after the pump; L is the length of the water pipeline after the air tank; f is the cross-sectional area of ​​the pipeline; g is the acceleration due to gravity; A C σ is the cross-sectional area of ​​the air tank; σ is an intermediate variable, calculated by equation (13).

[0050] (13) In the formula: m is the ideal gas polynomial, which is taken as 1.0 for isothermal changes, 1.4 for adiabatic changes, and 1.2 for numerical calculations; p0 is the absolute pressure of the gas in the air tank; l0 is the initial height of the air tank chamber.

[0051] In this application example, the water hammer protection effects of a conventional air tank and the novel air tank of this invention are compared through hydraulic transition calculations. The calculation results are as follows: Figures 9 to 18 As shown, the initial parameters for both types of air tanks are: air chamber height l = 3m, initial operating water level h = 525m, air tank area S = 50m², and connecting pipe diameter d = 1m (see the dimensioning of air tank parameters for details). Figure 6 The novel air tank piston of this utility model adopts a downward pressure pattern of 0.1m every 10 seconds, such as... Figure 8 As shown.

[0052] When the pump unit experiences a power outage, the valve after the pump closes, and the pressure in the pipeline after the pump begins to drop. Because the water hammer wave propagates rapidly and the air tank is installed after the pump, when the water hammer just reaches the bottom of the air tank, the novel air tank of this invention, due to the smaller piston pressure, is not significantly different from a conventional air tank, and the reflection effect of the air tank on the water hammer wave is not much different. However, the pressure drop at the bottom is a gradual process. Using piston pressurization can effectively alleviate the pressure drop at the bottom of the air tank.

[0053] When the water level in the air tank rises due to the reflected positive pressure wave and the backflow of water, the pressure in the air chamber increases. However, because the pressure drop at the bottom of the air tank is alleviated, the pressure rise at the bottom of the air tank is also reduced, and the maximum pressure in the air chamber is correspondingly reduced.

[0054] Depend on Figures 9 to 14 It can be seen that the new air tank using this utility model can ensure that the minimum surge wave of the air tank is not significantly different. (See also...) Figure 12 and Figure 13 The lowest surge wave of a conventional air tank is 523.11m, while that of the novel air tank of this invention is 523.06m, a difference of only 0.05m.

[0055] At the same time, it alleviated the pressure drop at the bottom of the air tank, see Figure 9 and Figure 10The minimum pressure was increased from 97.72m for conventional air tanks to 99.02m for the new air tanks, thus effectively reducing the maximum pressure reflected back from the bottom of the air tank. (See [link]). Figure 11 The maximum pressure decreased from 300.51 m³ in the conventional air tank to 298.49 m³ in the new air tank. The minimum and maximum pressures in the air chamber were also improved; see [link to relevant documentation]. Figure 14 and Figure 15 The minimum pressure increased from 110.83 m for a conventional air tank to 112.18 m. (See [reference needed]). Figure 16 The maximum pressure decreased from 310.80m to 308.89m.

[0056] from Figures 17 to 20 It can be seen that the new air tank of this utility model can effectively improve the extreme pressure values ​​along the line during the hydraulic transition process. The minimum pressure increases from 3.22m for conventional air tanks to 3.97m for the new air tank, and the maximum pressure decreases from 300.51m for conventional air tanks to 298.50m for the new air tank.

[0057] Therefore, compared to conventional air tanks, this invention effectively improves the water hammer protection effect of air tanks while maintaining the same tank shape parameters and similar minimum surge wave characteristics. This advantage allows for optimization of the air tank shape. Numerical calculations have verified that, while achieving the same water hammer protection effect, the novel air tank of this invention can reduce the cross-sectional area by 1 m², meaning the air tank volume can be reduced by 5.2 m³ (air tank height 5.2 m), a reduction of nearly 2%. For air tanks, which have extremely high economic costs, this significantly reduces investment and is of great practical significance.

[0058] The above description is only a specific embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural transformations made based on the contents of this utility model specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.

Claims

1. An air tank with adjustable top elevation, comprising a vertical tank body (11), the lower part of which is a water chamber, and the bottom of the tank body (11) being connected to a water pressure pipeline (2) via a connecting pipe (21), characterized in that: Inside the tank (11), a piston (12) is installed that slides with the inner wall of the tank (11). At least one sealing structure (121) is provided on the contact surface between the piston (12) and the inner wall of the tank (11). The space between the water chamber and the piston (12) at the top of the tank (11) is an air chamber. The piston rod (122) connected to the piston (12) passes through the perforation at the top of the tank (11) and extends to the top of the tank (11) to be connected to the drive mechanism. The drive mechanism is electrically connected to a controller. The controller is electrically connected to the water pump in the pumping station pressurized water supply system. After receiving the power failure signal of the water pump, the controller sends a control signal to control the drive mechanism to drive the piston to move down. After the normal state is restored, the controller controls the drive mechanism to drive the piston to reset. At least one vent hole (111) is provided at the top of the tank (11).

2. The air tank with adjustable top elevation according to claim 1, characterized in that: The cross-sectional area of ​​the connecting pipe (21) is greater than or equal to 15% of the cross-sectional area of ​​the water pressure pipeline (2).

3. The air tank with adjustable top elevation according to claim 1, characterized in that: The sealing structure (121) adopts a combination structure of a step seal ring and two guide rings on both sides. A middle sealing groove is opened in the middle of the outer side of the piston (12) for installing the step seal ring. The step seal ring is installed in the middle sealing groove and contacts the inner wall of the tank (11). An outer sealing groove is opened on the upper and lower sides of the middle sealing groove on the outer side of the piston (12) for installing the guide rings on both sides. The guide rings are installed in the outer sealing groove and are in clearance fit with the inner wall of the tank (11).

4. The air tank with adjustable top elevation according to claim 1, characterized in that: The driving mechanism is a linear driving mechanism, which drives the piston (12) to move up and down.

5. The air tank with adjustable top elevation according to claim 1, characterized in that: Both the piston (12) and the piston rod (122) are made of rigid materials.

6. The air tank with adjustable top elevation according to claim 1, characterized in that: A pressure measuring hole (112) is provided on the top of the tank (11). A pressure sensor is installed inside the pressure measuring hole (112). The pressure sensor is electrically connected to the controller. The pressure sensor detects the pressure inside the pressure measuring hole (112) in real time and sends it to the controller. The controller receives the pressure signal sent by the pressure sensor and determines whether the detected pressure is greater than the local atmospheric pressure. When the detected pressure is greater than the local atmospheric pressure, the controller controls the drive mechanism to drive the piston (12) to move upward and reset to press against the top surface inside the tank (11).

7. The air tank with adjustable top elevation according to claim 1, characterized in that: The diameter of each vent (111) is 1 / 10 of the diameter of the water pressure pipeline (2).

8. The air tank with adjustable top elevation according to claim 6, characterized in that: A flexible material layer (123) is provided on the top surface of the piston (12) at the position corresponding to the vent hole (111) and the pressure measuring hole (112).

9. The air tank with adjustable top elevation according to claim 6, characterized in that: The controller is equipped with an alarm module. When the piston (12) moves upward and resets due to air leakage from the air tank, the alarm module will issue an alarm.

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