Air valve arrangement method to prevent secondary pipe rupture in long-distance gravity flow water supply projects

Abstract

This invention discloses a method for arranging air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects. In long-distance gravity pressurized flow water transmission projects, valve actions caused by flow rate adjustments and operating condition changes can lead to drastic changes in the hydraulic parameters of the water transmission system, resulting in hydraulic transients throughout the system. This can cause abnormal water supply in adjacent pipelines or, in severe cases, pipe bursts, jeopardizing the normal and stable operation of the entire water transmission system. This invention establishes a pipe burst model, discusses the pipe burst process, derives a general formula for the arrangement of air valves in long-distance gravity flow water supply, analyzes the physical process of underground buried pipe bursts in actual engineering projects using practical engineering cases, and establishes a reasonable mathematical analysis model based on the pipe burst process, proposing elevation requirements for air valve arrangement. The rational arrangement of air valves and the verification of whether the air valve arrangement scheme can effectively prevent secondary pipe bursts have significant engineering application value.

Description

Technical Field

[0001] This invention relates to an air valve arrangement method, particularly an air valve arrangement method for preventing secondary pipe bursts in long-distance gravity flow water supply systems. It proposes a widely applicable and effective criterion for preventing secondary pipe bursts, and can provide more effective theoretical guidance for air valve arrangement in long-distance gravity flow water conveyance projects. Background Technology

[0002] In long-distance gravity-fed pressurized water conveyance projects, valve actions caused by flow rate adjustments and changes in operating conditions can lead to drastic changes in the hydraulic parameters of the system, resulting in hydraulic transients across the entire system. This can range from minor issues like abnormal water supply to serious problems like pipe bursts, jeopardizing the normal and stable operation of the entire system. Air valves are frequently used for water hammer protection in long-distance gravity-fed water conveyance projects, making their placement particularly important.

[0003] After a pipe burst, the working pressure of the water flow in the pipeline is released, and the pressure at the burst point drops to atmospheric pressure. A large amount of water leaks from the burst point, and the resulting water hammer pressure drop wave propagates forward and backward along the pipeline from the burst point. The greater the original working pressure at the burst point, the greater the pressure drop water hammer wave. Due to the unevenness of the pipeline layout, the water flow at the point with the lower original working pressure in the pipeline may vaporize during the propagation of this pressure drop wave, which will then generate a violent water hammer, leading to a secondary pipe burst and negative pressure damage. Therefore, after a pipe burst, the first priority should be to prevent negative pressure. Thus, it is crucial to ensure that negative pressure protection measures (usually air valves) are in place and that their performance is reliable.

[0004] Generally, the effectiveness of water hammer protection depends on the number and location of air valves. Pipe bursts are highly random and uncontrollable. Once a water supply accident occurs, both the direct and secondary hazards will have serious consequences. While direct hazards cannot be avoided after a pipe burst, secondary hazards must be minimized to ensure the project does not experience a chain reaction of bursts that escalate the accident. The basic method for preventing pipe burst accidents and secondary disasters is to pre-determine potential burst points and verify the rationality of the pipeline layout and negative pressure protection measures.

[0005] Currently, there is no literature or standard that systematically analyzes and demonstrates the placement of air valves in water supply pipeline systems. Article 7.4.7 of my country's national standard, "Code for Design of Outdoor Water Supply (GB50013-2006)," stipulates that venting facilities should be installed at the elevated points of water supply pipelines (channels), and for vertically arranged pipelines with gentle slopes, venting valves should be installed approximately every 1000m. The American Water Resources Association (AWWA) recommends a spacing of 380m to 760m. Based on actual engineering projects (… Figure 3Taking the dangerous pipe burst point 1) as an example, the distance between Av6 and Av7 is 702.672m, which meets the specification requirements. However, assuming that a pipe burst occurs at the dangerous pipe burst point (chainage K3+164.474), a negative pressure of -9.4m will be generated at chainage K2+069.925, which exceeds the pipeline negative pressure control standard. This shows that the existing specifications only stipulate the horizontal distance of the air valve installation, which is no longer effective in preventing secondary pipe bursts in long-distance gravity flow water supply projects.

[0006] Long-distance gravity flow water supply systems require a certain elevation difference in the terrain, relying on gravity to flow. Many gravity flow water supply systems, while ensuring a certain cover layer thickness, have pipelines laid parallel to the undulating terrain. Therefore, gravity flow water supply is significantly constrained by the terrain. In gravity flow water supply projects, the pipeline installation elevation varies considerably. Traditional methods of arranging air valves at regular intervals do not account for the significant elevation changes in the water supply pipelines and are no longer effective in preventing secondary pipe bursts.

[0007] It is evident that designing an air valve arrangement scheme that maximizes the efficiency of air valves for long-distance gravity flow water supply projects has become an urgent technical problem to be solved. Summary of the Invention

[0008] Purpose of the invention: The purpose of this invention is to provide an air valve arrangement method to prevent secondary pipe bursts in long-distance gravity flow water supply projects. Based on the traditional air valve protection perspective and the specification of the air valve installation position in terms of horizontal distance, this invention explores an elevation requirement for air valve arrangement in long-distance gravity flow water supply projects that can effectively prevent secondary pipe bursts, in order to determine a reasonable air valve arrangement method and check whether the air valve arrangement scheme can effectively prevent secondary pipe bursts.

[0009] Technical solution: This invention provides a method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects, comprising the following steps:

[0010] An air valve is installed at the protruding point of the pipeline;

[0011] The pipe section between the convex points is used with an elevation difference ΔH from the convex point. D Dividing the line segment by +h, we obtain a stepped auxiliary line segment; where △H D is the maximum vacuum control value for the pipeline, and h is the actual pressure at the rupture point after the pipe bursts.

[0012] An air valve is installed at the intersection of the pipeline and the auxiliary line segment;

[0013] Check whether the horizontal distance between the installed air valves exceeds the specification requirements, and add an air valve between adjacent air valves that exceed the specification requirements.

[0014] As a preferred option, the maximum vacuum control value for the pipeline is 8m. For pipelines laid in the open, h = 0; for pipelines laid in the buried, h is the thickness of the soil cover above the pipeline.

[0015] Furthermore, the method also includes performing a simulated calculation of the dangerous pipe burst point based on a preset dangerous pipe burst point, to obtain the pressure and flow rate changes at the same pipe burst point before and after the addition of the air valve.

[0016] This invention provides a method for inspecting air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects, comprising the following steps:

[0017] Calculate the elevation difference between adjacent air valves A and B, as well as the intermediate convex and concave points;

[0018] The installation elevation of the air valve and the maximum elevation difference between the convex and concave points of the intermediate pipe section are compared with ΔH. D +h are compared;

[0019] If the maximum elevation difference exceeds ΔH D +h, then add an air valve to the pipe section between air valves A and B until the maximum elevation difference is within ΔH. D Within +h.

[0020] As a preferred option, determine whether additional air valves are needed for air valves A and B using the following formula:

[0021] [|Z A -Z B |、|Z A -Z C |、|Z A -Z D |、|Z B -Z C |、|Z B -Z D |、|Z C -Z D |] max ≤ΔH D +h

[0022] Among them, Z A It is the installation elevation of air valve A, Z B It is the installation elevation of air valve B, Z C It is the elevation of the pipe protrusion, Z. D It is the elevation of the concave point of the pipeline.

[0023] Based on the same inventive concept, this invention provides an air valve installation system for preventing secondary pipe bursts in long-distance gravity flow water supply projects, comprising:

[0024] The initial setup module is used to install an air valve at the protruding point of the pipeline;

[0025] The auxiliary line segment setting module is used to set the pipe segments between the convex points according to the elevation difference ΔH between the convex points and the convex point elevations. D +h line segments are used to divide the line segments into stepped auxiliary line segments;

[0026] The inspection and improvement module is used to add air valves at the intersection of pipelines and auxiliary lines; and to check whether the horizontal distance between the installed air valves exceeds the specification requirements, and to add air valves between adjacent air valves where the distance exceeds the specification requirements.

[0027] Based on the same inventive concept, this invention provides an air valve inspection system for preventing secondary pipe bursts in long-distance gravity flow water supply projects, comprising:

[0028] The elevation data calculation module is used to calculate the elevation difference between adjacent air valves A and B and the intermediate convex and concave points;

[0029] The air valve inspection module is used to compare the installation elevation of the air valve with the maximum elevation difference between the convex and concave points of the intermediate pipe section and ΔH. D Compare with h; if the maximum elevation difference exceeds ΔH... D +h, then add an air valve to the pipe section between air valves A and B until the maximum elevation difference is within ΔH. D Within +h.

[0030] Based on the same inventive concept, the present invention provides a computer system including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements either the method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects or the method for inspecting air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects.

[0031] Beneficial Effects: Based on the method of characteristics, this invention views the pipe burst process as a continuous leakage process, obtaining the unsteady flow during a pipe burst in an underground buried pipeline and the general criteria for the elevation arrangement of air valves to prevent secondary pipe bursts in long-distance gravity flow water supply. This has significant engineering application value for determining a reasonable air valve arrangement and checking whether the air valve arrangement scheme can effectively prevent secondary pipe bursts. Compared with the prior art, this invention solves the elevation requirements for air valve arrangement to prevent secondary pipe bursts in gravity flow water supply systems. As long as the installation elevation of the air valve meets the requirement that the relevant elevation difference does not exceed the sum of the buried pipe depth and the maximum vacuum control value, secondary pipe bursts can be effectively prevented, allowing the air valves to function more effectively, thereby saving engineering investment. Attached Figure Description

[0032] Figure 1 A schematic diagram illustrating the propagation of water hammer after a pipe burst during buried pipe installation.

[0033] Figure 2 This is a preliminary layout diagram of the air valve in Example 1.

[0034] Figure 3 This is a diagram showing the elevation of the pipe centerline and auxiliary line segments in Example 1.

[0035] Figure 4 This is a supplementary layout diagram for the air valve in Example 1.

[0036] Figure 5 This is a diagram showing the location of the dangerous pipe burst point in Example 1.

[0037] Figure 6 This is a diagram showing the change in hydraulic parameters of the pipe burst at point 1 under the condition of valve non-closing in Example 1.

[0038] Figure 7 This is a diagram showing the change in hydraulic parameters at danger point 2 when the valve is not closed in Example 1.

[0039] Figure 8 This is a diagram showing the arrangement of the air valve along the line in Example 2.

[0040] Figure 9 This is a diagram showing the layout of the air valve at the dangerous pipe burst point 1 in Example 2.

[0041] Figure 10 This is a diagram showing the layout of the air valve at the dangerous pipe burst point 2 in Example 2.

[0042] Figure 11 This is a diagram showing the change in hydraulic parameters of the pipe burst at point 1 under the condition of valve non-closing in Example 2.

[0043] Figure 12 This is a diagram illustrating the change in hydraulic parameters at point 2 where the pipe bursts under the condition of valve closure in Example 2. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0045] To gain a deeper understanding of the technical solution of this invention, the installation principle of the air valve for preventing secondary pipe bursts during long-distance gravity flow water transport is explained as follows.

[0046] Long-distance gravity flow water conveyance systems require a certain elevation difference in the terrain. The water flows by gravity using this elevation difference. Many gravity flow water conveyance systems are laid parallel to the undulations of the terrain while ensuring a certain thickness of the overburden layer. Therefore, gravity flow water supply is greatly constrained by the terrain.

[0047] Figure 1 The installation method shown is buried pipe installation. The uppermost blue line is the piezometer head line, and the black line is the pipe installation layout line. The dangerous pipe burst point is the local low point C between two adjacent air valves A and B. Assuming a pipe burst occurs at point C, the piezometer head at point C will rapidly drop to a point h above the pipe centerline elevation (h is the actual pressure at the burst point after the burst, which is usually related to factors such as the pipe installation method and the shape of the burst opening). Therefore, the burst point will experience the following... Figure 1 The pressure drop shown in the diagram is ΔH, which forms a water hammer pressure drop wave that propagates along the upstream and downstream directions of the pipeline.

[0048] Draw parallel lines L1, L2, and L3 upwards from the point of pipe burst C, parallel to the piezometric head line. The elevation difference between parallel lines L1 and L2 is ΔH. D This value is the maximum control value for the vaporization pressure of the water flow; the elevation difference between the two parallel lines L2 and L3 is h, which is the actual pressure at the burst point after the pipe bursts.

[0049] exist Figure 1 In the pipeline layout, parallel line L1 intersects with the pipeline at points A upstream and B downstream. If the water hammer pressure drop wave generated at the burst point C does not attenuate during propagation, the wave will continue to damage the pipeline upstream of point A and downstream of point B, causing the water flow vacuum in the pipeline at points upstream of point A and downstream of point B to exceed the control value ΔH. D Since the pipeline has been damaged, pressure-equalizing measures (air valves) must be installed near points A and B of the pipeline to prevent or block the continued propagation of the ΔH pressure drop wave.

[0050] Because the hydraulic gradient during water conveyance is very small, approximately 1‰, the angles between the parallel lines, the head line, and the horizontal line are very small. Furthermore, the installation interval between the two air valves will not be too long. Therefore, parallel lines L1, L2, and L3 can be approximated as horizontal lines.

[0051] Therefore, under the condition of buried pipe laying, the elevation difference between air valve A and local low point C should be less than or equal to ΔH. D The sum of h and h.

[0052] Although pipe bursts are highly random and their exact location is difficult to pinpoint, gravity-fed water supply systems typically incorporate distributed water hammer protection measures (air valves) along the pipeline. As long as the air valves are properly arranged, they can effectively interrupt the propagation path of the ΔH pressure drop wave during a pipe burst by allowing a large influx of air. If the elevations of two adjacent air valves and the distance between the pipe's convex point C and concave point D are known, the theoretical elevation difference between these four points should approximately satisfy:

[0053] [|Z A -ZB |、|Z A -Z C |、|Z A -Z D |、|Z B -Z C |、|Z B -Z D |、|Z C -Z D |] max ≤ΔH D +h

[0054] In the above formula, Z A It is the installation elevation of air valve A, Z B It is the installation elevation of air valve B, Z C It is the elevation of the pipe protrusion, Z. D It is the elevation of the concave point of the pipeline.

[0055] The hydraulic transition works generated by normal valve operation in the system are calculated and controlled based on the premise that the water supply pipeline does not experience negative pressure, with air valves serving as a safety reserve. Referring to the design guidelines for water diversion projects, SL430-2008, the minimum pressure head of the culvert should not be less than 2m. At the pipeline outlet, it can be appropriately reduced according to specific circumstances, but should not be less than 1m. Currently, there are no clear standards or regulations specifying the effectiveness and application of air valves in water supply engineering for preventing water hammer. Two main viewpoints exist: one is that air valves serve as a safety reserve against negative pressure in water supply pipelines; the other is that air valves are a safety measure to control negative pressure in water supply pipelines. The former, at least in design, does not allow negative pressure in water supply pipelines (e.g., the national standard [Outdoor Water Supply Design Code - GB50013-2018]). To prevent negative pressure, multiple water hammer protection measures are required in the water supply pipeline. The main purpose of installing air valves in the pipeline is not water hammer protection, but rather to facilitate water filling and emptying and to remove free air masses from the pipeline during normal operation. Air valves can serve as the last safety reserve against water hammer, only taking effect after other safety measures have failed. The latter allows negative pressure in the pipeline, the magnitude of which is determined by the pipeline's resistance to negative pressure, the air valve's air intake and exhaust capacity, and the safety margin for water vaporization. The negative pressure control standard of -2.0m mainly refers to the electromechanical design code for hydropower plants DL / T5186-2004 and the design code for pumping stations GB / T50265-2010. To control negative pressure, air valve operation and air intake in the pipeline are permitted. The air intake volume of the air valve and the effectiveness of negative pressure control depend on the installation location and diameter of the air valve. This report primarily treats the air valve as a safety reserve for preventing negative pressure in the water supply pipeline. It only considers the air valve as a safety measure to control negative pressure in the event of a pipe burst. Furthermore, it studies the appropriate installation location of the air valve in the event of a pipe burst. If a pipe burst occurs in the system, it will cause water hammer and pressure drop throughout the system. The maximum vacuum degree is determined according to ΔH. D Control measures to ensure no secondary disasters occur, and if necessary, review and add water hammer protection measures to the system.

[0056] Vacuum control value △H D The setting of this value has a significant impact on pipeline safety after a pipe rupture. If the value is set too low, it will lead to an excessive number of air valves in the pipeline, increasing project costs and affecting the overall strength of the pipeline. If the value is set too high, and the pressure drop wave from the rupture propagates rapidly, the pressure stabilization measures will be relatively far from the rupture point, resulting in a slow response and increasing the risk of secondary ruptures. Under normal circumstances, for a safety margin, the influence of the size of the rupture opening on the post-rupture pressure can be ignored. The maximum vacuum control value △H D The value can be taken as 8m; for pipes laid in the open, h = 0; for pipes laid in the buried, h can be taken as the soil cover thickness above the pipe.

[0057] The following description, in conjunction with the accompanying drawings and examples, further illustrates the method for the installation and inspection of air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects provided by embodiments of the present invention. In the examples below, the water supply system is a pure gravity flow system, and water hammer during pump shutdown is not considered.

[0058] Example 1

[0059] Taking a long-distance gravity-flow water supply project as an example, the water supply system is a dual-pipe system with a total transmission line length of approximately 38.2 km, a pipe diameter of 2.4 m, and is laid underground with a 3 m layer of soil covering. The pipe material is ductile iron, and the water hammer velocity is approximately 1000 m / s. The design flow rate is 15 m³ / s. 3 / s, inlet water level is 65m, design elevation of the pipe center at the starting point is 61.5m, outlet water level is 12.5m, design elevation of the pipe center at the end point is 7.4m, total drop is 54.1m, design flow rate is 15m³ / s. 3 / s; The highest point of the pipe centerline elevation is 61.504m, with a maximum drop of 0.004m. To ensure the stable and safe operation of the water transmission system, the maximum pressure of each pipe section should not exceed the pipeline pressure standard, and negative pressure should not occur along the pipeline. In the event of a pipe burst, the maximum vacuum pressure of the water vaporization pressure in the water transmission system and the maximum internal water pressure should not exceed the pipeline pressure standard. After a pipe burst, the negative pressure in the water transmission system should not exceed the minimum pressure control standard, and the maximum pressure should not exceed the pipeline pressure standard. Under the above control standards, numerical simulation calculations are performed on this project using the method of characteristics, taking a portion of the pipe section as an example.

[0060] This invention provides a method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects, the steps of which are as follows:

[0061] (1) Install an air valve at the protruding point of the pipeline.

[0062] Preliminary layout diagram of air valves is shown below. Figure 2 As shown.

[0063] (2) Draw the elevation difference ΔH between the point and the convex point. D +h (here, take 11m) auxiliary line segment.

[0064] See the diagram for the pipeline centerline elevation and auxiliary line segments. Figure 3 As shown.

[0065] (3) Install air valves at intersections and pipe sections where the horizontal distance exceeds the specification requirement (1000m).

[0066] See the supplementary layout diagram for air valves. Figure 4 As shown.

[0067] (4) Calculate the dangerous pipe bursting point.

[0068] A hydraulic transient process analysis was conducted on the above-mentioned project using a pipe burst model. The pipe burst occurred within 0.2 seconds, and the upstream and downstream valves at the burst point were not closed. Results such as pressure and flow rate changes at the same burst point before and after the addition of the air valve, and the maximum and minimum pressure envelopes upstream and downstream of the burst point, were obtained. Figures 6-7 As shown.

[0069] Depend on Figures 6-7 It can be seen that the pressure change at the burst point was extremely drastic. Within a very short time, the pressure at the burst point dropped from the initial pressure to 3m (3m of soil cover). Then, due to the local resistance at the burst opening, the pressure rose slightly and stabilized at a lower pressure level (corresponding to the two burst conditions of 7.8m and 12.5m respectively). The leakage flow rate at the burst point increased from the initial flow rate of 7.5m. 3 The flow rate increases rapidly, then stabilizes at a relatively high level (corresponding to 21.2m / s for the two pipe burst conditions). 3 / s and 18.6m 3 / s). The pressure statistics for the two dangerous pipe rupture points in this section are shown in Table 2.

[0070] Table 1. Calculation results of pipe bursts at different locations under valve-free conditions.

[0071]

[0072] As shown in Table 1, when the air valves are installed according to the present invention, although the system experiences severe water hammer pressure drop after a pipe rupture, the reasonable arrangement of the air valves can effectively block the propagation path of the water hammer wave, suppress further pressure drop in the pipeline, and ensure that secondary accidents do not occur in pipelines that have not ruptured.

[0073] It is evident that the method of this invention can effectively solve the problem of preventing secondary pipe bursts during long-distance gravity flow water transport.

[0074] Example 2

[0075] Taking a long-distance gravity-flow water supply project as an example, the water supply system is a dual-pipe system with a total transmission line length of approximately 38.2 km, a pipe diameter of 2.4 m, and is laid underground with a 3 m layer of soil covering. The pipe material is ductile iron, and the water hammer velocity is approximately 1000 m / s. The design flow rate is 15 m³ / s. 3 / s, inlet water level is 65m, design elevation of the pipe center at the starting point is 61.5m, outlet water level is 12.5m, design elevation of the pipe center at the end point is 7.4m, total drop is 54.1m, design flow rate is 15m³ / s. 3 / s; The highest point of the pipe centerline elevation is 61.504m, with a maximum drop of 0.004m. To ensure the stable and safe operation of the water supply system, the maximum pressure of each pipe section should not exceed the pipeline pressure standard, and negative pressure should not occur along the pipeline. In the event of a pipe burst, the maximum vacuum pressure of the water vaporization pressure in the water supply system and the maximum internal water pressure should not exceed the pipeline pressure standard. After a pipe burst, the negative pressure of the water supply system should not exceed the minimum pressure control standard, and the maximum pressure should not exceed the pipeline pressure standard. Under the above control standards, numerical simulation calculations of this project are performed using the method of characteristics. Taking a portion of the pipe section as an example, the air valve layout diagram is as follows. Figure 8 As shown.

[0076] This invention provides a method for inspecting air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects, the steps of which are as follows:

[0077] (1) Calculate the elevation difference between adjacent air valves and the intermediate convex and concave points.

[0078] (2) The installation elevation of the air valve and the maximum elevation difference between the convex and concave points of the intermediate pipe section are compared with ΔH. D +h is compared.

[0079] (3) If the maximum elevation difference exceeds ΔH D +h, then add an air valve to the pipe section between the two air valves until the maximum elevation difference is within ΔH. D Within +h.

[0080] (4) Perform simulation calculations for the dangerous point of the tube to burst.

[0081] Number the air valves in this pipe section and calculate the elevation difference between adjacent air valves and the intermediate protrusions and depressions. The air valve setting parameters are shown in Table 2.

[0082] Table 2 Air Valve Setting Parameters

[0083]

[0084] In practical engineering, pipe burst points have a certain degree of randomness. Generally, the most likely locations for pipe bursts are local high points, bends, and joints. However, this paper primarily studies whether secondary pipe bursts can be prevented under the most unfavorable pressure conditions. Therefore, the burst point in this paper is selected as a local low point. The water pressure is highest at this local low point, and a burst can easily lead to unfavorable negative pressure at the high point, causing a secondary burst. After a pipe burst, the pipeline pressure drops sharply. By installing an air valve, the propagation path of the water hammer pressure drop wave generated at the burst point can be effectively blocked, ensuring that the system will not experience serious secondary disasters in the short term.

[0085] For this water supply system, the main analysis focuses on whether the installation of air valves can prevent secondary pipe bursts. The pipe section between Av6 and Av7 has a point with a convex-concave elevation at station K3+164.474 and a pipe center elevation of 43.15m, which has an elevation difference of 13.417m from Av6, exceeding the standard of 11m in formula (1). Therefore, a pipe burst calculation is performed on the local low point of this section, station K3+164.474, with a pipe center elevation of 43.15m, which is considered a potential burst point. To verify the rationality of formula (1), an air valve (installation elevation 48.655m) is added at station K2+739.925 for comparative burst calculation. The pipe section between Av8 and Av9 has no protrusions or depressions, but the installation elevation of the air valves differs by 16.976m, exceeding the standard of 11m in formula (1). Therefore, a local low point closer to this section, at station K5+232.47 with a pipe center elevation of 28.55m, was selected as the dangerous pipe burst point 2 for pipe burst calculation. To verify the rationality of formula (1), an air valve (installation elevation of 42m) was added at station K4+068.715 for pipe burst comparison calculation.

[0086] The air valve layout diagrams for hazards 1 and 2 are as follows: Figure 9 , Figure 10 As shown.

[0087] A hydraulic transient process analysis of the above-mentioned project was conducted using a pipe burst model. The pipe burst occurred within 0.2 seconds, and the upstream and downstream valves at the burst point were not closed. Results were obtained including pressure and flow changes at the same burst point before and after the addition of the air valve, the maximum and minimum pressure envelopes upstream and downstream of the burst point, and the air intake of the newly added air valve. Figures 11-12 As shown.

[0088] Depend on Figures 11-12 It can be seen that the pressure change at the burst point was extremely drastic. Within a very short time, the pressure at the burst point dropped from the initial pressure to 3m (3m of soil cover). Then, due to the local resistance at the burst opening, the pressure rose slightly and stabilized at a low pressure level (corresponding to the two burst conditions of 7.7m and 21.2m respectively). The leakage flow rate at the burst point increased from the initial flow rate of 7.5m. 3 The flow rate increases rapidly, then stabilizes at a relatively high level (corresponding to 14.7m / s for the two pipe burst conditions). 3 / s and 18.4m 3 / s). Both the air valves added at dangerous pipe rupture point 1 and dangerous pipe rupture point 2 allowed a small amount of air to enter shortly after the rupture. Pressure statistics for these two dangerous pipe rupture points are shown in Table 2.

[0089] Table 3. Calculation results of pipe bursts at different locations under valve-free conditions.

[0090]

[0091] As shown in Table 2, before the installation of air valves, the pressure in some pipelines was lower than the minimum pressure control standard, making them highly susceptible to secondary pipe bursts. After the installation of air valves, although a severe water hammer pressure drop occurred after a pipe burst, the reasonable arrangement of the air valves effectively blocked the propagation path of the water hammer wave, suppressed further pressure drops in the pipelines, and ensured that secondary accidents did not occur in pipelines that had not burst.

[0092] It is evident that the method of this invention can effectively solve the problem of preventing secondary pipe bursts during long-distance gravity flow water transport.

[0093] Example 3

[0094] This invention discloses an air valve installation system for preventing secondary pipe bursts in long-distance gravity flow water supply projects, comprising: an initial setting module for installing air valves at the convex points of the pipeline; and an auxiliary segment setting module for dividing the pipe segments between the convex points using an elevation difference ΔH from the convex points. D +h line segment division results in stepped auxiliary line segments; the inspection and improvement module is used to add air valves at the intersection of the pipe and the auxiliary line segments; and to check whether the horizontal distance between the deployed air valves exceeds the specification requirements, and to add air valves between adjacent air valves where the distance exceeds the specification requirements. This system embodiment and the aforementioned deployment method embodiment belong to the same inventive concept, and specific implementation details are as described in the above method embodiment, and will not be repeated here.

[0095] Example 4

[0096] This invention discloses an air valve inspection system for preventing secondary pipe bursts in long-distance gravity flow water supply projects, comprising: an elevation data calculation module for calculating the elevation difference between adjacent air valves A and B and the intermediate convex and concave points; and an air valve inspection module for comparing the installation elevation of the air valves and the maximum elevation difference between the convex and concave points of the intermediate pipe section with ΔH. D Compare with h; if the maximum elevation difference exceeds ΔH... D +h, then add an air valve to the pipe section between air valves A and B until the maximum elevation difference is within ΔH. D Within +h. This system embodiment and the aforementioned test method embodiment share the same inventive concept; for specific implementation details, please refer to the above method embodiment, which will not be repeated here.

[0097] Example 5

[0098] This invention also discloses a computer system, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements either the method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects or the method for inspecting air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects.

Claims

1. A method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects, characterized in that, Includes the following steps: An air valve is installed at the protruding point of the pipeline; The pipe sections between the convex points are used in accordance with the elevation difference of the convex points. By dividing the line segments, we obtain a stepped auxiliary line segment; where △H D is the maximum vacuum control value for the pipeline, and h is the actual pressure at the rupture point after the pipe bursts. An air valve is installed at the intersection of the pipeline and the auxiliary line segment; Check whether the horizontal distance between the installed air valves exceeds the specification requirements, and add an air valve between adjacent air valves that exceed the specification requirements.

2. The method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects according to claim 1, characterized in that, The maximum vacuum control value for the pipeline is 8m. For pipelines laid in the open, h=0; for pipelines laid in the buried, h is the thickness of the soil cover above the pipeline.

3. The method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects according to claim 1, characterized in that, It also includes performing simulation calculations of dangerous pipe burst points based on preset dangerous pipe burst points, and obtaining the pressure and flow changes at the same pipe burst point before and after the addition of an air valve.

4. The method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects according to claim 1, characterized in that, It also includes the following steps: Calculate the elevation difference between adjacent air valves A and B, as well as the intermediate convex and concave points; The installation elevation of the air valve and the maximum elevation difference between the protrusions and indentations of the intermediate pipe section are compared with... Compare; If the maximum elevation difference exceeds Then, add an air valve to the pipe section between air valves A and B until the maximum elevation difference is within the specified range. Within.

5. The method for installing air valves to prevent secondary pipe bursts in long-distance gravity flow water supply projects according to claim 4, characterized in that, Determine whether additional air valves are needed for air valves A and B using the following formula: ； Among them, Z A It is the installation elevation of air valve A, Z B It is the installation elevation of air valve B, Z C It is the elevation of the pipe protrusion, Z. D It is the elevation of the concave point of the pipeline.

6. An air valve installation system for preventing secondary pipe bursts in long-distance gravity flow water supply projects, characterized in that, include: The initial setup module is used to install an air valve at the protruding point of the pipeline; The auxiliary line segment setting module is used to set the pipe segments between the convex points according to the elevation difference of the convex points. By dividing the line segments, we obtain a stepped auxiliary line segment; where △H D is the maximum vacuum control value for the pipeline, and h is the actual pressure at the rupture point after the pipe bursts. The inspection and improvement module is used to add air valves at the intersection of pipelines and auxiliary lines; and to check whether the horizontal distance between the installed air valves exceeds the specification requirements, and to add air valves between adjacent air valves where the distance exceeds the specification requirements.

7. An air valve installation system for preventing secondary pipe bursts in long-distance gravity flow water supply projects according to claim 6, characterized in that, Also includes: The elevation data calculation module is used to calculate the elevation difference between adjacent air valves A and B and the intermediate convex and concave points; The air valve inspection module is used to compare the installation elevation of the air valve with the maximum elevation difference between the protrusions and concave points of the intermediate pipe section. Compare; if the maximum elevation difference exceeds Then, add an air valve to the pipe section between air valves A and B until the maximum elevation difference is within the specified range. Within.

8. A computer system comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements the air valve installation method for preventing secondary pipe bursts in long-distance gravity flow water supply projects according to any one of claims 1-5.

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