Water hammer protection system and method for long distance water delivery pump station and design method

Abstract

The present application relates to a long distance water delivery pump station water hammer protection system and method and design method, comprising: a low-level water inlet tank, the water inlet tank is connected with a pipeline front section with a water pump, a low-level control valve and an ascending pipeline; a high-level water outlet tank, the water outlet tank is connected with a pipeline rear section of a horizontal or descending pipeline, an overflow tank is arranged between the pipeline front section and the pipeline rear section, and a high-level control valve is arranged between the overflow tank and the water outlet tank at a position close to the water outlet tank. The present application utilizes the overflow tank to divide the water delivery system into two weakly associated front section pump station water delivery subsystem and rear section gravity flow water delivery subsystem. Only the water on the front side of the overflow tank and the limited water in the pipeline can flow back into the water pump, without causing the problem of water pump reverse rotation overspeed, thereby reducing the difficulty of water hammer protection. For the rear side gravity flow pipeline, the pipeline is controlled not to generate negative pressure or small negative pressure. The system engineering has low cost and reliable operation, and is an excellent solution for the water hammer of the inclined pipeline.

Description

Technical Field

[0001] This invention relates to a water hammer protection system and method for long-distance water conveyance pumping stations, as well as a design method for such a system. It is a safety facility and method for water conveyance systems, a system and method for preventing water hammer damage during long-distance water conveyance, and a design method for the water hammer protection system. Background Technology

[0002] Pumping stations are a common water supply method in long-distance water transfer projects and municipal engineering. When a pump experiences a power outage, the water in the pipeline continues to flow due to inertia, which can easily cause water column separation, pipeline rupture, collapse, or damage from subsequent high-pressure water column re-entry. Rapid backflow of water in the pipeline can also damage the pump and pipeline. Furthermore, during project scheduling, such as normal startup, flow regulation, or shutdown, water hammer can occur, potentially damaging pumps, pipes, and valves in the water delivery system. Therefore, water hammer protection for pumping station water delivery systems to ensure system safety under various operating conditions is a crucial issue that needs to be addressed in engineering design and operation scheduling.

[0003] There are various types of pipeline layouts in pumping station water conveyance systems. From the perspective of pipeline direction, they can be roughly summarized as follows: ① The pipeline slopes upwards along the pipeline, meaning that the elevation of the pipeline centerline increases with the station number (local bulges and descents are ignored); ② The pipeline rises at the beginning and then becomes horizontal or descends at the end, meaning that the elevation of the pipeline centerline slopes upwards first, then becomes nearly horizontal, with little or no rise, and the distance between the beginning and end sections is relatively long; ③ The pipeline is nearly horizontal, meaning that the elevation of the pipeline centerline hardly increases or rises very little with the station number, and the main function of the pumping station is to convey water across long distances; ④ The pipeline slopes downwards first and then rises along the pipeline.

[0004] For water pipeline layouts ① and ④, the focus of water hammer protection is to prevent rapid backflow of water within the pipeline and excessively rapid changes in flow velocity, which could cause positive pressure damage to the water supply system. This is generally achieved through methods such as two-stage slow-closing control valves. For water pipeline layout ③, the task of water hammer protection is to prevent localized water column separation and subsequent water hammer damage to the pipeline. However, for water pipeline layout ②, the water in the initial rising section is at a higher position at the end, resulting in higher relative pressure and faster velocity decay, making backflow highly likely. Conversely, the water in the subsequent horizontal section is at a lower position at the end, resulting in lower relative pressure and slower velocity decay. The significant difference in velocity change rate between the water before and after the inflection points in the rising and horizontal sections makes water column separation highly likely, and subsequent water column closure can cause destructive engineering accidents. Therefore, water hammer protection is more challenging, and overcoming this difficulty through design and treatment processes is a problem that needs to be solved. Summary of the Invention

[0005] To address the layout problem of type ② water conveyance pipelines, this invention proposes a water hammer protection system and method for long-distance water pumping stations, along with a design approach. The system and method meticulously arrange hydraulic elements such as water tanks and control valves, improving water hammer protection, enhancing operational reliability, and reducing costs.

[0006] The objective of this invention is achieved as follows: a water hammer protection system for long-distance water pumping stations, comprising: a low-level inlet pool connected to a front section of a pipeline equipped with a water pump, a low-level control valve, and an ascending pipe; a high-level outlet pool connected to a rear section of a horizontal or descending pipeline, wherein the ascending pipe, horizontal or descending pipe is equipped with multiple air valves; an overflow pool is provided between the front and rear sections of the pipeline; a high-level control valve is provided near the outlet pool between the overflow pool and the outlet pool; the overflow pool is an open pool to the atmosphere, and an overflow weir is provided in the middle of the pool, dividing the pool into a pre-weir pool and a post-weir pool.

[0007] Furthermore, the parameters of the overflow tank are calculated as follows:

[0008] Determine the height of the overflow tank:

[0009] The height h1 of the pool is determined according to the following formula:

[0010]

[0011] Where: h0 is the water level in the outlet pool; i is the number of sections in the gravity flow section pipe; λ i Let L be the friction coefficient of pipe segment i; i Let D be the length of pipe segment i; i Let be the diameter of pipe segment i; ζ i V is the local resistance coefficient of pipe segment i; i Let be the flow velocity in pipe segment i; and g be the acceleration due to gravity.

[0012] The height of the overflow weir is determined by the following formula:

[0013] h2>h0

[0014] In the formula: h2 is the height of the overflow weir;

[0015] The area of ​​an overflow tank is determined according to the following formula:

[0016]

[0017] In the formula: A is the area of ​​the overflow pool; Q is the design flow rate of the water conveyance system; h3 is the bottom elevation of the overflow pool.

[0018] The water hammer protection method for long-distance water conveyance pumping stations using the above system is as follows:

[0019] The water conveyance system is divided into two weakly interconnected subsystems: an upstream pumping station and a downstream gravity-fed water conveyance system. When a sudden power outage or malfunction causes the pumps to stop unexpectedly, only a limited amount of water in the forebay and riser pipes can flow back into the pumps, preventing overspeed and reverse pumping. Furthermore, as water flows back into the upstream pumping station subsystem, the water volume and pressure gradually decrease. For the downstream gravity-fed water conveyance system, the overflow tank is open to the atmosphere and stores a certain amount of water in the forebay. Even if the pumps stop unexpectedly, the water stored in the forebay can sustain water delivery for a period, preventing immediate impact on the downstream pipes. In this case, simply closing the high-level control valve slowly will prevent negative pressure or only a small negative pressure from forming in the downstream gravity-fed water conveyance system.

[0020] The design method for the water hammer protection system of the long-distance water conveyance pumping station described above includes the following steps:

[0021] Step 1, determine the height of the overflow tank:

[0022] The height h1 of the pool is determined according to the following formula:

[0023]

[0024] The height of the overflow weir is determined by the following formula:

[0025] h2 > h0;

[0026] Step 2, determine the area of ​​the overflow tank:

[0027]

[0028] Step 3, Water hammer calculation of the front-end pumping water conveyance system: Perform water hammer calculation for the front-end pumping water conveyance system and determine two key parameters: ① the closing time t1 of the control valve to ensure that no overpressure problem occurs in the front end; ② the amount of water Q1 entering the outlet pool before the water pump backflows; the overflow pool is taken as the normal water level boundary, and the water level is the height h2 of the overflow weir.

[0029] Step 4, Water hammer calculation for the downstream gravity-fed water conveyance system:

[0030] Water hammer calculations were performed on the downstream gravity-fed water conveyance system to determine two key parameters: ① the closing time t2 of the control valve to ensure no overpressure issues occur in the downstream section; ② the volume of water Q2 entering the outlet pool during the valve closing process. The overflow pool was designed with a constant water level boundary, where the water level was the height h2 of the overflow weir.

[0031] Step 5: Determine the front and rear areas of the overflow tank:

[0032] The formula for calculating the area of ​​the rear side of the overflow tank is:

[0033]

[0034] In the formula: A2 is the area of ​​the back pool of the overflow pool;

[0035] If A ≥ A² + A₀, the formula for calculating the area of ​​the forebay of an overflow water tank is:

[0036] A1 = A - A2

[0037] In the formula: A0 is the area of ​​the pipe in front of the overflow pool; A1 is the area of ​​the forebay of the overflow pool.

[0038] Otherwise, the formula for calculating the area of ​​the forebay of an overflow pool is:

[0039] A1 = A0

[0040] The total area of ​​the overflow pool increases as follows:

[0041] A = A1 + A2.

[0042] The advantages and beneficial effects of this invention are as follows: This invention utilizes an overflow pool to divide the water conveyance system into two weakly correlated subsystems: a front-end pumping station subsystem and a rear-end gravity-flow subsystem. The front-end pumping station subsystem only needs to consider water hammer protection for excessively rapid flow velocity decay, while the rear-end gravity-flow subsystem only needs to consider water hammer protection for excessively slow flow velocity decay. Only a limited amount of water in front of the overflow pool and within the pipeline can flow back into the pump, preventing pump reversal and overspeed issues. Furthermore, as water flows back, the water volume and pressure within the system gradually decrease, reducing the difficulty of water hammer protection. For the rear-end gravity-flow pipeline, slowly closing the control valve at the end can control the pipeline to prevent or minimize negative pressure. The system has low engineering costs, reliable operation, and is an excellent solution for preventing water hammer in inclined pipelines. Attached Figure Description

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] Figure 1 This is a schematic diagram of the system described in Embodiment 1 of the present invention;

[0045] Figure 2 This is a schematic diagram of a traditional inclined pipe pumping station water conveyance system;

[0046] Figure 3 This is a schematic diagram of the technical route of the design method described in Embodiment 4 of the present invention;

[0047] Figure 4It is the feature line mesh described in Embodiment 4 of the present invention. Detailed Implementation

[0048] Example 1:

[0049] This embodiment is a water hammer protection system for long-distance water conveyance pumping stations, such as... Figure 1 As shown. This embodiment includes: a low-level inlet pool 1, which is connected to the front section of a pipeline equipped with a water pump 2, a low-level control valve 3, and an ascending pipe 4; a high-level outlet pool 5, which is connected to the rear section of a horizontal or descending pipe 6; multiple air valves 7 are provided on the ascending pipe, horizontal or descending pipe; an overflow pool 8 is provided between the front and rear sections of the pipeline; a high-level control valve 9 is provided near the outlet pool between the overflow pool and the outlet pool; the overflow pool is an open pool to the atmosphere, and an overflow weir 801 is provided in the middle of the pool, dividing the pool into a pre-weir pool 802 and a post-weir pool 803.

[0050] The pipeline rises at the beginning and then becomes horizontal or descends at the end; that is, the centerline elevation of the pipeline initially slopes upwards, then becomes nearly horizontal with less upward movement or slopes downwards. Both the initial and subsequent sections are relatively long. The engineering layout is as follows: Figure 2 As shown, the difficulty in water hammer protection lies in the fact that the water in the upstream rising pipe is at a higher position at the end, resulting in higher relative pressure and faster velocity decay, making backflow highly likely. Conversely, the water in the downstream horizontal pipe is at a lower position at the end, resulting in lower relative pressure and slower velocity decay. Therefore, the water before and after the inflection point in both the rising and horizontal sections is highly susceptible to water column separation, and the subsequent water column merging can cause destructive engineering accidents.

[0051] When implementing water hammer protection, the ideal approach is to slow down the rate of velocity change in the upstream rising pipe and accelerate the rate of velocity change in the downstream horizontal pipe. This would ensure a more uniform rate of velocity change within the pipe, preventing water column separation. However, this requirement presents some challenges for continuous water delivery systems.

[0052] Traditional water hammer protection solutions typically employ the following: ① Selecting a check valve as the type of control valve after the pump; ② Installing an air tank downstream of the control valve; ③ Installing several air valves along the pipeline (see...). Figure 2 After a power outage due to a pump malfunction, the high-pressure gas on the upper side of the air tank expands, forcing water from the lower side into the pipeline, causing the check valve to close quickly. Subsequently, the air tank replenishes water into the rear pipeline, slowing down the rate of change in flow velocity.

[0053] The disadvantages of this protection scheme are: ① The action time of the check valve is difficult to control, which can easily cause water hammer during valve closure. The check valve closes under the action of three-dimensional water flow. Its dynamic characteristics and closing time are strongly correlated with the initial flow velocity, pump head, air tank configuration, and other application scenarios. When it closes, it generates a negative flow velocity, causing water hammer during valve closure. ② The air tank replenishes water to the system, slowing down the rate of change of flow velocity, making the rate of change of flow velocity of the water in the upstream pipeline closer to that of the downstream pipeline, thus avoiding water column separation. The required air tank volume is generally large. ③ The equipment, civil engineering, and operation and maintenance costs are high. This protection scheme requires air tank volumes of tens to hundreds of cubic meters. At a cost of approximately 100,000 yuan per cubic meter of air tank, the equipment cost ranges from several hundred to tens of millions of yuan. In addition, it requires the construction of supporting plant buildings, which presents challenges in operation and maintenance, land occupation, etc., resulting in high project costs.

[0054] The proposed solution in this embodiment is applicable to water conveyance systems where the pipeline rises at the front and flows horizontally or downwards at the rear. The key to this protection scheme is the installation of an overflow tank at the junction of the front and rear pipelines, dividing the two sections into two weakly interconnected water conveyance subsystems. The front pumping station subsystem includes an inlet tank, a pump, a low-level control valve, and the rising pipeline ("front section"). The rear gravity-flow subsystem includes an outlet tank, a high-level control valve, and the horizontal or descending pipeline ("rear section"). No check valve is required at the pump outlet; a control valve is installed before the outlet tank. During operation, water from the inlet tank is pumped up and flows through the front pipeline into one side of the overflow tank. After overflowing, the water flows through the rear pipeline into the outlet tank. Thus, the original pumping station water conveyance system is transformed into two parts: the front pumping station subsystem and the rear gravity-flow subsystem.

[0055] In the upstream pumping station water conveyance subsystem, the pipeline slopes upwards, and effective protection can generally be achieved by slowly closing a two-stage control valve. The limited water volume in the overflow weir forebay of the overflow-type water tank results in less backflow, thus reducing the difficulty of pump reversal protection and pipeline overpressure protection. In the downstream gravity-flow water conveyance subsystem, the control valve is located at the end of the pipeline. When a pump fails and loses power, the control valve closes simultaneously, generating a pressure surge wave that propagates upstream.

[0056] The advantages of replacing the air tank with an overflow pool are:

[0057] (1) Good water hammer protection. For type ② water transmission systems, after a pump failure and power outage, the flow velocity decay rate in the upstream pipeline is too fast, while the flow velocity decay rate in the downstream pipeline is too slow, which easily leads to water column separation. Traditional protection schemes use air tanks to slow down the flow velocity decay rate in the upstream pipeline, bringing it closer to the flow velocity decay rate in the downstream pipeline, thereby reducing the possibility of water column separation. Even with a large-volume air tank, horizontal pipelines usually generate a vacuum of several meters, which is a large negative pressure. Considering the uncertainties of equipment parameters and operating conditions, such as the flow resistance and height of the air tank, pipeline local resistance, and water flow rate, liquid column separation may still occur.

[0058] This solution uses an overflow tank to divide the water conveyance system into two weakly interconnected subsystems: a pumping station subsystem and a gravity-flow subsystem. The upstream pumping station subsystem only needs to address water hammer protection due to excessively rapid flow velocity decay, while the downstream gravity-flow subsystem only needs to address water hammer protection due to excessively slow flow velocity decay. Only a limited amount of water in front of the overflow tank and within the pipeline can flow back into the pumps, preventing pump reversal and overspeed issues. Furthermore, as water flows back, the water volume and pressure within the system gradually decrease, reducing the difficulty of water hammer protection. For the downstream gravity-flow pipeline, slowly closing the control valve at the end can control the pipeline to prevent or minimize negative pressure.

[0059] (2) Low project cost. Traditional air tank protection solutions typically cost tens of millions of yuan for equipment, supporting facilities, land acquisition and resettlement, operation and maintenance, etc., while this solution only requires the construction of an overflow water tank, with a cost of around one million yuan.

[0060] (3) High operational reliability. The problems of traditional water hammer systems mainly stem from the two mechanical devices used in traditional solutions: check valves and air tanks. ① The check valves in traditional solutions close under three-dimensional flow conditions, generating a negative flow velocity upon closure, causing water hammer during valve closure. The closure time and flow velocity are affected by various factors such as initial flow velocity, pump head, and air tank configuration, making them difficult to determine accurately. ② The air tank contains many key hydraulic parameters, including diameter, total height, initial water level, inflow resistance, outflow resistance, and polytropic index. These parameters have a significant impact on the water hammer process. The more parameters there are, the greater the uncertainty. Moreover, due to technological limitations, current theoretical models or calculation software generally only use a few parameters, or even just assume the volume of the air tank. Therefore, from the perspective of theoretical models and equipment parameters, the protective effect of traditional solutions has a certain degree of uncertainty; and the uncertainty caused by mechanical equipment failure or malfunction has not been considered. In contrast, this solution uses fixed structures for protection, and the parameters of the overflow pool are relatively simple to determine. The control valve can be a conventional manual or electric valve, with a mature theoretical model and well-defined equipment parameters. The valve's opening and closing requirements are low, and it can be controlled manually or automatically. Once the design is completed, its structural parameters are fixed, eliminating issues related to theoretical models, equipment parameters, and mechanical failures, thus ensuring high reliability.

[0061] Example 2:

[0062] This embodiment is an improvement upon the above embodiment, and a refinement of the parameter calculation for the overflow water tank in the above embodiment. The parameter calculation for the overflow water tank in this embodiment is as follows:

[0063] Determine the height of the overflow tank:

[0064] The height h1 of the pool is determined according to the following formula:

[0065]

[0066] Where: h1 is the height of the pool, m; h0 is the water level of the outlet pool, m; i is the number of sections in the gravity flow section pipe; λ i Let L be the friction coefficient of pipe segment i; i Let D be the length of pipe segment i, in meters; i Let ζ be the diameter of pipe segment i, in meters (m); i V is the local resistance coefficient of pipe segment i; i Let be the flow velocity in pipe segment i, m / s; and g be the acceleration due to gravity, m / s². 2 .

[0067] The height of the overflow weir is determined according to the following formula:

[0068] h2>h0

[0069] In the formula: h2 is the height of the overflow weir, in meters.

[0070] The area of ​​an overflow tank is determined according to the following formula:

[0071]

[0072] In the formula: A is the area of ​​the overflow pool, in meters. 2 Q represents the design flow rate of the water conveyance system, in meters. 3 / s; h3 is the bottom elevation of the overflow pool.

[0073] It should be noted that h0, h1, h2, and h3 are water levels determined with reference to a certain horizontal plane, such as... Figure 1 The figure shown is not the actual water level in the pool.

[0074] Example 3:

[0075] This embodiment describes a water hammer protection method for long-distance water conveyance pumping stations, as described above. The method is as follows:

[0076] The water conveyance system is divided into two weakly correlated subsystems: an upstream pumping station subsystem and a downstream gravity-flow subsystem. The upstream pumping station subsystem only needs to address water hammer protection for excessively rapid flow velocity decay, while the downstream gravity-flow subsystem only needs to address water hammer protection for excessively slow flow velocity decay. In the event of a sudden power outage or malfunction causing the pumps to stop unexpectedly, only a limited amount of water in the forebay and riser pipes can flow back into the pumps, preventing pump reversal and overspeed issues. Furthermore, as backflow occurs in the upstream pumping station subsystem, the water volume and pressure gradually decrease, reducing the difficulty of water hammer protection. For the downstream gravity-fed water conveyance subsystem, since the overflow pool is open to the atmosphere and stores a certain amount of water in the pool behind the weir, the water stored in the pool behind the weir can maintain water conveyance for a period of time in the event that the water pump stops operating unexpectedly, thus avoiding immediate impact on the downstream water pipe. In this case, it is only necessary to slowly close the high-level control valve, and the downstream gravity-fed water conveyance subsystem will not generate negative pressure or only a small negative pressure.

[0077] The method described in this embodiment overcomes the problem of determining the closing time of the check valve in traditional gas-filled water hammer systems. Since the overflow tank is open, the water in the forebay and the water in the downstream section of the pipeline are only weakly correlated after the pump is powered off. Only the water in the forebay enters the downstream tank due to inertia, while the water in the downstream tank cannot enter the forebay. Furthermore, the water volume in the forebay is limited, thus preventing a large amount of water from returning and impacting the pump blades, causing the pump to overspeed and reverse. Sufficient time is also provided to close the lower control valve. The water in the downstream tank can continue to supply water for a period after the pump is powered off, preventing liquid column separation in the downstream pipeline due to sudden water interruption. This provides ample time to close the upper control valve, completely solving the difficulty of designing the check valve closing time. Only a simple control valve is needed, greatly reducing project costs.

[0078] Example 4:

[0079] This embodiment describes a design method for a water hammer protection system for a long-distance water conveyance pumping station, as follows (the technical route of the design is as follows). Figure 3 As shown):

[0080] 1. Determine the height of the overflow tank:

[0081] The height of an overflow pool includes two aspects: ① the height of the pool body; ② the height of the overflow weir.

[0082] The height h1 of the pool is determined according to the following formula:

[0083]

[0084] Where: h1 is the height of the pool, m; h0 is the water level of the outlet pool, m; i is the number of sections in the gravity flow section pipe; λ i Let L be the friction coefficient of pipe segment i; i Let D be the length of pipe segment i, in meters; i Let ζ be the diameter of pipe segment i, in meters (m); i V is the local resistance coefficient of pipe segment i; i Let be the flow velocity in pipe segment i, m / s; and g be the acceleration due to gravity, m / s². 2 .

[0085] The height of the overflow weir is determined according to the following formula:

[0086] h2>h0 (2)

[0087] In the formula: h2 is the height of the overflow weir, in meters (m).

[0088] 2. Determine the area of ​​the overflow tank:

[0089] The area of ​​an overflow tank is determined according to the following formula:

[0090]

[0091] In the formula: A is the area of ​​the overflow pool, in meters. 2 Q represents the design flow rate of the water conveyance system, in meters. 3 / s; h3 is the bottom elevation of the overflow pool.

[0092] 3. Water hammer calculation for the upstream pumping subsystem:

[0093] Water hammer calculations were performed on the upstream pumping system to determine two key parameters: ① the closing time t1 of the control valve to ensure no overpressure occurs upstream; ② the volume of water Q1 entering the outlet pool before the pump backflows. The overflow pool is defined by a constant water level boundary, with the water level being the height h2 of the overflow weir.

[0094] 4. Water hammer calculation for the downstream gravity-fed water conveyance system:

[0095] Water hammer calculations were performed on the downstream gravity-fed water conveyance system to determine two key parameters: ① the closing time t2 of the control valve to ensure no overpressure occurs in the downstream section; ② the volume of water Q2 entering the outlet pool during the valve closing process. The overflow pool was designed with a constant water level boundary, defined as the height h2 of the overflow weir.

[0096] The area of ​​an overflow tank is determined according to the following formula:

[0097] The governing equations for water hammer in pipelines include the momentum equation and the continuity equation:

[0098]

[0099]

[0100] In the formula: H is the piezometric head, m; x is the distance along the centerline of the pipe, m; V is the water velocity, m / s; g is the acceleration due to gravity, m / s². 2 t is time, s; f is the Darcy-Weisbach friction coefficient; D is the pipe diameter, m; a is the water hammer wave velocity, m / s; α is the pipe inclination angle. Equations (4) and (5) are usually solved using the method of characteristics. Figure 4 The feature line mesh shown has the following feature line equations:

[0101] C + :H i =C P -B P Q i (6)

[0102] C - :H i =C M +B MQ i (7)

[0103] Where: H i The head at the current time step is m; H i-1 A' represents the head of the water at the previous time step and the previous space step, in meters; A' represents the pipe area, in meters. 2 Q i-1 m represents the flow of the previous time step and the previous spatial step. 3 / s; Δx is the spatial step size, in meters. H i+1 Let m and Q be the head of the water at the previous time step and the next space step, respectively. i+1 m represents the flow rate between the previous time step and the next spatial step. 3 / s;

[0104] The formula for calculating the flow rate of a valve in a pipeline is:

[0105]

[0106] In the formula: Q Pi For valve flow rate, m 3 / s;C d A is the valve flow coefficient; G The valve opening area is in meters. 2 g is the acceleration due to gravity, m / s² 2 ;ΔH Pi The pressure head difference between the valve inlet and outlet is expressed in meters (m).

[0107] With the orifice fully open, the valve flow rate under constant flow conditions is:

[0108]

[0109] In the formula: the subscript r indicates that the valve is fully open; ΔH r The pressure head difference between the inlet and outlet when the valve is fully open is expressed in meters (m).

[0110] Define the dimensionless valve flow coefficient:

[0111]

[0112] When the valve is fully open, τ = 1; when the valve is closed, τ = 0. Therefore:

[0113]

[0114] Since the direction of water flow changes during hydraulic transients, equation (11) becomes:

[0115]

[0116] From equations (6) and (7), we know that:

[0117] ΔH Pi =C P -C M -(B P +B M )Q Pi (13)

[0118] Combining equations (12) and (13), we get:

[0119]

[0120] Summarized as follows:

[0121]

[0122] Since the right side of equation (15) contains the unknown quantity Q Pi Therefore, it cannot be solved directly. An iterative calculation program can be used to solve it; the specific method is as follows:

[0123] (1) Assume the initial value of the flow rate at this calculation time step is Q. Pi Equal to the traffic Q of the previous time step P That is, Q Pi =Q P .

[0124] (2) Calculate the flow rate Q′ using equation (15). Pi .

[0125] (3) Calculate Q′ Pi With Q Pi The difference between the two, if the absolute value of the error between them is less than the error limit ε, that is, |Q′ Pi -Q P |≤ε, then Q′ Pi That is Q Pi The calculated value is then used; if the requirements are not met, proceed to step (4). Generally, the calculation accuracy is set to ε = 10. -5 ~10 -4 .

[0126] (4) Assumption Repeat steps (2) to (3) until the calculation results meet the accuracy requirements.

[0127] 5. Determine the front and rear areas of the overflow tank:

[0128] The formula for calculating the area of ​​the rear side of the overflow tank is:

[0129]

[0130] In the formula: A2 is the rear area of ​​the overflow pool, in meters. 2 .

[0131] If A ≥ A² + A₀, the formula for calculating the area of ​​the front side of the overflow tank is:

[0132] A1 = A - A2 (17)

[0133] In the formula: A0 is the area of ​​the pipe on the front side of the overflow pool, in m². 2 A1 is the front area of ​​the overflow pool, in meters. 2 Otherwise, the formula for calculating the area of ​​the overflow tank front side is:

[0134] A1 = A0 (18)

[0135] The total area of ​​the overflow pool increases as follows:

[0136] A = A1 + A2 (19)

[0137] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred arrangements, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention (such as the form of the water conveyance system, the form of the overflow pool, the application of various formulas, the order of steps, etc.) without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. Water hammer protection system for long-distance water conveyance pumping stations, including: The system includes a low-level inlet pool connected to the front section of a pipeline equipped with a water pump, a low-level control valve, and an ascending pipe; a high-level outlet pool connected to the rear section of a horizontal or descending pipeline; multiple air valves installed on the ascending, horizontal, or descending pipeline; an overflow pool located between the front and rear sections of the pipeline; and a high-level control valve located near the outlet pool between the overflow pool and the outlet pool. The overflow pool is open to the atmosphere and has an overflow weir in the middle, dividing it into a pre-weir pool and a post-weir pool. The overflow water tank is characterized by the following parameter calculation: Determine the height of the overflow tank: The height h1 of the pool is determined according to the following formula: In the formula: is the water level in the outlet pool; i is the number of sections in the gravity flow section pipe; Let be the friction coefficient of pipe segment i; Let i be the length of segment i of the pipe; Let be the diameter of pipe segment i; Let be the local resistance coefficient of pipe segment i; Let be the flow velocity in pipe segment i; and g be the acceleration due to gravity. The height of the overflow weir is determined according to the following formula: In the formula: The height of the overflow weir; The area of ​​an overflow tank is determined according to the following formula: In the formula: A is the area of ​​the overflow pool; This refers to the design flow rate of the water conveyance system. This refers to the bottom elevation of the overflow pool. It is a water level determined with reference to a certain horizontal plane, not the actual water level in the overflow pool.

2. A method for water hammer protection of long-distance water conveyance pumping stations using the system described in claim 1, characterized in that, The method is as follows: The water conveyance system is divided into two weakly correlated subsystems: a front-end pumped water conveyance system and a rear-end gravity-flow water conveyance system. The front-end pumped water conveyance system includes an inlet pool, a water pump, a low-level control valve, and an ascending pipe ("front section"). The rear-end gravity-flow water conveyance system includes an outlet pool, a high-level control valve, and a horizontal or descending pipe ("rear section"). When the water pump unexpectedly stops due to a sudden power outage or malfunction, only a limited amount of water in the forebay and ascending pipe can flow back into the water pump, thus preventing the water pump from reversing and overspeeding. On the other hand, as backflow of water occurs in the upstream pumping station water conveyance subsystem, the water volume and pressure in the upstream pumping station water conveyance subsystem gradually decrease. For the downstream gravity flow water conveyance subsystem, since the overflow pool is open to the atmosphere and stores a certain amount of water in the weir-back pool, the water stored in the weir-back pool can maintain water conveyance for a period of time in the event of an unexpected pump stoppage, thus avoiding immediate impact on the downstream water pipe. In this case, it is only necessary to slowly close the high-level control valve, and the downstream gravity flow water conveyance subsystem will not generate negative pressure or only a small negative pressure.

3. A design method for a water hammer protection system for a long-distance water conveyance pumping station as described in claim 1, characterized in that, The steps of the method are as follows: Step 1, determine the height of the overflow tank: Pool height Determined according to the following formula: ； The height of the overflow weir is determined according to the following formula: ； Step 2, determine the area of ​​the overflow tank: ； Step 3, Water hammer calculation for the upstream pumping subsystem: Perform water hammer calculation for the upstream pumping subsystem to determine two key parameters: ① Closing time of the low-position control valve. ① Ensure no overpressure occurs at the front end; ② Before the water pump reverses flow, the amount of water entering the outlet pool... The overflow pool is defined by the normal water level boundary, which is the height of the overflow weir. ; Step 4, Water hammer calculation of the downstream gravity-fed water conveyance subsystem: Water hammer calculations were performed on the downstream gravity-fed water conveyance subsystem to determine two key parameters: ① Closing time of the high-level control valve. ① Ensure no overpressure occurs in the downstream section; ② During the closing process of the high-level control valve, the amount of water entering the outlet pool... The overflow pool is defined by the normal water level boundary, which is the height of the overflow weir. ; Step 5: Determine the areas of the back and front pools of the overflow tank: The formula for calculating the area of ​​the backwater of an overflow-type water tank is: In the formula: The area of ​​the back pool of the overflow water tank; like The formula for calculating the area of ​​the forebay of an overflow water tank is: In the formula: The area of ​​the pipes at the front of the overflow tank; The area of ​​the forebay of the overflow pool; Otherwise, the formula for calculating the area of ​​the forebay of an overflow pool is: The total area of ​​the overflow pool increases as follows: 。

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