[Abstract] The top-mounted magnetic flap level gauge is used in water conservancy projects. Its advantage lies in adapting to high water head and large flow, so it has attracted much attention and attention. Therefore, the paper focuses on the selection design, model test and application of the magnetic flap level gauge, and focuses on the discussion on the discharge coefficient, cavitation, air supplement, and vibration of the discharge valve of the magnetic flap level gauge. .
1 Introduction
The top-mounted magnetic flap level gauge (referred to as the magnetic flap level gauge) has the advantages of adapting to large flow and high head in the application process of water conservancy projects, and also has the advantages of no vibration and airless within the pressure-bearing flow range The exhaust valve with corrosion characteristics is therefore the own discharge valve of the hydro-generator block bypass valve [1]. Magnetic flap level gauges are mainly used in the discharge and energy dissipation of water conservancy projects. In recent years, they have been widely used in various water conservancy projects in my country. However, from an overall point of view, the application of magnetic flap level gauges in my country is still relatively small. At present, the types of gates in my country’s water conservancy projects are relatively diverse, mainly including arc gates, flat gates, magnetic flap level gauges, and butterfly valves [2]. In the process of selecting the type of bottom hole working gate, due to the existence of some unreasonable factors, it will affect the realization of the function in the design to a large extent [3]. As a large-caliber discharge device that exceeds the water head, the safety and stability of the operation of the magnetic flap level gauge have attracted much attention and attention. Therefore, this research starts from the comparison of the selection of magnetic flap level gauges, model tests and application tests, and conducts research and analysis on the cavitation, vibration, flow coefficient and air supplement of the discharge valve.
2 Test analysis of top-mounted magnetic flap level gauge
2.1 The content of the test
In the process of exploring the discharge coefficient of the magnetic flap level gauge, as well as the coefficient and vibration, cavitation and other issues, the selected nozzle diameter is 288mm, and research and analysis are carried out on this model. When the test is launched, the content mainly includes two aspects. On the one hand, it analyzes the two more common magnetic flap level gauge outlet configurations, the diversion cover and the straight pipe section, as the object, and compares and analyzes its impact on the valve discharge. ; On the other hand, it is to analyze the role of supplemental air in valve stability and vibration. This is mainly due to the high-speed water flow that may cause cavitation problems. Therefore, it is necessary to carry out experiments in this aspect.
2.2 Test principle
In this study, when measuring the flow capacity of a valve, the selected index is the emission coefficient, which is a commonly used and important index. The larger the discharge coefficient, the lower the pressure the fluid will withstand when it flows through the valve. In other words, the larger the emission factor, the better the emission performance. When the discharge coefficient of the valve is smaller, it means that the greater the pressure loss of the fluid in the process of flowing through the valve, the worse the discharge performance of the valve. The calculation formula of the emission coefficient formula is shown in formula (1). In formula (1), Cd represents the discharge coefficient of the valve, and v represents the average velocity of the fluid flowing through the valve, in m/s. g represents the acceleration due to gravity, and the unit is m/s2. H= v22g +ΔH means the sum of the static water head and the dynamic water head in front of the valve, and the unit is m. Among them, the calculation formula of H is shown in formula (2). In formula (2), the valve flow rate is represented by Q, and the unit is m3/s. The inlet flow velocity of the valve is represented by vi, and the outlet flow velocity is represented by v0, both in m/s. The area of the inlet section of the valve is expressed in Ai, and the area of the outlet section is expressed in A0, both in m2. The inlet pressure of the valve is represented by pi, and the outlet pressure is represented by p0, both in Pa. The elevation of the inlet center of the valve is represented by zi, and the elevation of the outlet center is represented by z0, both in m.
2.3 System tested
When measuring valve flow, electromagnetic flow is used. When measuring the valve pressure, a pressure sensor is used. The measurement of valve body vibration is mainly measured and obtained through acceleration sensors. The acceleration sensor is mainly located in the axial, vertical and radial horizontal of the valve body, and measures the vibration of the valve body at the same time. In the process of measuring the pressure, the position of the inlet and outlet should be appropriate, not too close or too far away, otherwise it will affect the accuracy of the measurement data. Under normal circumstances, the water flow will not be disturbed by factors such as flow path, environment and valve operation, so the test value can represent the real flow state. Since the pressure pipe of the magnetic flap level gauge is mainly buried in the main body of the hydraulic engineering, the water flow will be directly discharged into the atmosphere after flowing through the outlet side shroud or the direct flow section. Considering this factor, in the process of measuring the inlet and outlet pressure, the selected measuring section is 1 times the diameter of the front and back of the valve body. The measurement content, sensor model and accuracy selected by the test system of this study.
3 Test results of top-mounted magnetic flap level gauge
In the process of the test, it is mainly deployed under a head of 70m, and the test is mainly carried out under three working conditions. The first working condition is equipped with straight pipe section, but no air supplement is performed; the second working condition is equipped with straight pipe section and air supplement is performed; the third working condition is equipped with a deflector, but no air supplement is performed. In the process of controlling the valve opening, the opening mainly rises from 10% to 100%. At the same time, signals such as valve flow, pressure and vibration are collected. Finally, draw the relationship curve, including the relationship between valve opening and discharge coefficient, valve body vibration, etc.
3.1 Comparison results of the two configurations
Through the test and calculation results of related data, the relationship between the valve opening and the emission coefficient of the first working condition and the third working condition is drawn. The following three conclusions can be drawn from Figure 1. First, the larger the valve coefficient, the larger the valve opening, and the relationship between the two is a positive correlation. But when the valve opening reaches more than 80%, the coefficient tends to be stable. Second, when the valve opening does not reach 30%, the discharge coefficient of the deflector is lower than that of the straight pipe section. Third, when the valve opening is between 40% and 80%, in terms of emission coefficient, the diversion cover is higher than the straight pipe section.
3.2 The effect of supplemental air on vibration
Combining the results of Table 1 and Figure 1, the following conclusions can be drawn: First, when the valve opening is below 30%, the vertical and axial vibration of the valve body is greater than that of the valve without air supplementation. Working conditions. Under the condition of supplemental air, the radial vibration is smaller than the condition without supplementary air. Second, when the valve opening is more than 40%, the valve body vibration under the supplementary air condition is lower than that under the condition without air supplementation. That is to say, when the valve opening is large, in order to reduce the vibration of the valve body and promote its stability, proper air supplement is a more effective way. At the same time, the above test results further illustrate that air supplement is also a better way to improve the pressure distribution of the fluid inside the valve.
4 Application of top-mounted magnetic flap level gauge
The above model test results show that the magnetic flap level meter equipped with a flow deflector has the advantage of a high discharge coefficient and a better function of dispersing the flowing water in the process of discharging flowing water. At the same time, the impact on downstream scouring is also relatively small, so it has more advantages in terms of the stability of valve operation. In addition, it will also increase the friction between air and water to a certain extent, and it also has a better advantage in terms of energy dissipation effect. In a reservoir water replenishment project, a <a href=”http://www.sj000.cn/” target=”_blank”>magnetic flap level gauge equipped with a diversion cover is used, which are imported pipes and drive cylinders. , Nozzle, sliding sleeve and diversion cover.
In order to explore the discharge characteristics of the magnetic flap level gauge, an important part is to conduct field tests. The principle of the field test is the same as above. However, there are also certain differences between field test and theoretical research, that is, there are certain differences in the structure of model test and test system. The main difference lies in the process of field test, because there is no way to arrange pressure sensors on the valve outlet side, so in the calculation In the process, the pressure on the outlet side is atmospheric pressure. During the test, the head height is 123m, and the working conditions are mainly to start the test under the two working conditions of supplementary air and no supplementary air. In the process of analysis, comparative analysis is mainly done by drawing a schematic diagram of the relationship curve.
4.1 Replenishing Qi effect
The data analysis of the magnetic flap level gauge of the diversion cover can mainly draw the following conclusions: First, the valve opening is closely related to the discharge coefficient. In order to improve the efficiency of water discharge, it should be controlled when the valve is operating at a large opening. Second, supplemental air has little effect on the emission coefficient. When the opening reaches more than 50%, and under the condition of supplementary air, the coefficient will gradually increase. Third, when the valve opening is between 40% and 50%, the model has a higher coefficient than the prototype emission coefficient.
4.2 Vibration and stability analysis
Combining the data results in Figure 2, the following conclusions are drawn: First, as the valve opening increases, the change trend of the valve body vibration is N-shaped, and the change trends of the prototype and the model are consistent. Second, supplemental air can improve the vibration level of the valve body, especially for prototypes. In short, in order to promote the efficient and stable operation of the cone valve, appropriate air supplement measures should be taken.
5 Conclusion
This research starts with the application of fixed cone valves in water conservancy projects, and takes a certain reservoir water replenishment project as the object of field test, and compares the effects of model tests and field prototype tests to explore the cavitation and erosion of fixed cone valves during operation. Vibration and stability issues. Through the investigation, the following conclusions are mainly drawn: First, in the application process of the fixed cone valve, its discharge coefficient is higher at a large opening and its performance is better. Second, when economic conditions allow, the diversion cover should be configured as much as possible to improve the effect of energy dissipation and promote its stable operation. Finally, in terms of reducing valve body vibration and suppressing cavitation problems, proper air supplementation is an effective means and should be paid attention to.
Post time: 26-09-21