Analysis and Discussion on Structural Performance of Full-Scale Spring Safety Valve Wan Shengjun Harbin Haguo Valve Co., Ltd., Harbin 150046, Heilongjiang, and proposed a practical method to improve the performance of safety valves.
The safety valve is an indispensable overpressure protection device for steam boilers and various pressure vessels. It requires safe operation, reliable performance, tight shut-off, rapid take-off and returning to the seat, and the opening and closing pressure difference is 47, and the maximum is not more than 10. The working principle of the safety valve analyzes the main factors affecting the performance of the safety valve.
1 The working principle of the full-quantity spring safety valve The spring-type safety valve is opened and closed by the medium pressure and its own spring force. When the medium pressure reaches and exceeds the safety valve pressing force, the valve opens and reaches the full stroke, discharging excess medium to prevent the container from overpressure. As the pressure of the container decreases, the lift of the valve flap gradually decreases. When the pressure drops to the return pressure of the safety valve, the spring force is greater than the lift of the valve flap, the valve immediately stops the leak, and there is no leakage before and after the valve is closed. It is the ideal safety valve action process. However, it is difficult to fully realize this ideal process on the machine. Usually there is a problem of front leakage and back leakage, which affects the performance of the safety valve.
2Performance analysis 2.1Safety valve take-off pressure Safety valve take-off pressure refers to the pressure on the inlet side when the safety valve moves steam strongly, which is the main performance index of the safety valve. In order to ensure the safe and normal operation of the boiler and pressure vessel, there is a strict requirement for the take-off accuracy of the safety valve. The straightness coaxiality of the take-off pressure error value has a great influence on the take-off accuracy.
2.1.1 Effect of spring on the take-off pressure To achieve the correct take-off pressure, it is first required to correctly calculate the spring force and ensure accuracy in manufacturing. Free height error is ± inner diameter error is ± verticality is not greater than 5 and safety valve take-off pressure error value take-off pressure climb allowable error shoulder 3 0.7 below ± 0.03 parent take-off pressure 7.0 or more should consider the effect of temperature change on spring stiffness, with temperature The rise of the spring, the spring stiffness decreases, and the valve take-off accuracy is reduced. Therefore, an insulated heat sink should be added between the valve body and the spring to prevent the spring from being heated, and at the same time, a spring material that is less affected by temperature is used.
2, 2 manufacturing precision valve stem valve assembly consisting of valve sleeve and other sliding parts such as guide sleeves should be ensured above the surface, reduce friction, otherwise, will increase the starting pressure, increase the opening and closing pressure on the cover It fundamentally eliminates the force of the spring on the horizontal direction of the valve flap, and ensures that the valve flap can return to the initial sealing position after the valve takes off.
2.2.2 Valve structure The structure of the valve flap has a great influence on the leakage. Generally, the method of reducing the contact width between the valve seat and the valve sealing surface and increasing the sealing specific pressure is adopted to improve the sealing performance of the valve. However, after the medium is vented, the valve flap generates a strong impact force when it returns to the seat. If the width of the sealing surface is too small, it will be plastically deformed and damaged. At the same time, the moment before the high temperature and high pressure valve is closed, a short time leak occurs between the valve disc and the valve seat, and then the sealing is stopped. This leakage is similar to the gas throttling through the small hole. When the gas is ejected through the small holes, it is expanded by the throttling effect, the temperature is lowered, and the temperature of the metal at the leaking portion is also lowered, and the degree of reduction is proportional to the amount of steam leakage. Relationship between gas cooling degree and initial pressure and superheat of medium 2. According to the previous analysis, when a small leak occurs somewhere on the sealing surface, the metal shrinks due to cooling, and the gap of the valve seat valve is increased. The amount is increased and a large leak occurs. In order to solve the above part of the composition. The sealing surface adopts an elastic sealing lip, which serves as a main sealing function, and the outer impact-resistant surface and the sealing surface have a very small inclination. The valve stem and the valve seat and disc sealing surface should be perpendicular, that is, the spring force acts perpendicularly on the sealing surface. Otherwise, the spring force will be unevenly distributed on the sealing surface of the valve seat, and local leakage will occur before the rebound pressure is reached, which will affect the take-off. Precision.
2.1.3 Valve structure With the increase of pressure and temperature, the safety valve will leak to different extents before the jump, which will affect the valve's take-off accuracy. Therefore, the structure of the valve is improved, and the upper and lower adjusting rings are added. 1. The lower adjusting ring forms an annular discharge pressure zone between the valve seat flaps, so that a small amount of steam leaking initially accumulates in the pressure zone, and the valve flap is enlarged. The area of ​​the force increases the lift of the flap. Adjusting the height of the lower adjustment ring can change the pressure in the discharge pressure zone, change the lift of the valve flap, and obtain a satisfactory take-off pressure. The upper adjustment ring changes the direction of the discharge of the medium and adjusts the lift of the flap. The upper and lower adjusting ring structure can accurately adjust the take-off pressure of the safety valve and the lift of the valve flap to make the valve take off accurately and quickly reach the full stroke, effectively solving the front leakage and frequency jump, and ensuring the take-off precision of the valve.
2.2 Safety valve leakage Leakage is the most common problem in safety valves. Even if the leakage of 1 will cause a large loss of heat energy, the valve should be guaranteed to be free of leakage. The process of leakage according to action can be divided into front leakage and back leakage. The leakage before the safety valve takes off is called front leakage, and the leakage after closing is called back leakage.
2.2.1 Manufacturing precision After the machining, the valve seat and the disc sealing surface should be ground with a grinding tool to ensure the smoothness is above, so that the valve flap and the valve seat can be sealed with only a small force. . The main mating components such as the valve body guide sleeve valve stem and spring cover should be machined by CNC machine tools to ensure the coaxiality after assembly, so that the central axis of the valve stem seat and disc assembly is perpendicular to the center line of the valve. Ensure that the spring force acts vertically on the valve seat and closes with the small spherical surface. It is guided by the guide sleeve to eliminate the lateral component of the valve stem. Only the vertical force acts on the sealing surface to ensure the seal. The smaller the spherical radius of the valve stem, the universal direction The better the sex, the more accurate the seal.
The force point of the earth valve stem should be as low as possible, preferably lower than the sealing surface, to reduce the tendency of the valve flap to tilt in the horizontal direction during the valve switching process, to increase the stability of the valve flap and prevent the valve from leaking.
2.3 Safety valve opening and closing pressure difference Opening and closing pressure difference is an indicator to measure the sensitivity and economy of the safety valve. If the pressure difference is too small, the safety valve will be too sensitive, which directly affects the installation position of the safety valve, and is prone to oscillating vibration and frequency jump; if the pressure difference is too large, the discharge medium is too much and uneconomical. Therefore, the steam boiler safety supervision regulations require that the opening and closing pressure difference is 4,7 of the setting pressure, and the maximum is not more than 1 or less, and the factors affecting the opening and closing pressure difference are simply analyzed.
When the spring is biased, it will exert a lateral force on the valve flap, which will cause friction between the valve flap and the guide sleeve, and increase the opening and closing pressure difference.
Therefore, the lower spring seat and the valve stem are in spherical contact, and a guide sleeve is added in the middle of the valve stem to offset the lateral component force due to the spring deflection, thereby improving the performance of the safety valve.
2.3.2 Medium reaction force The adjustment ring can change the discharge direction of the medium to make it spray downward, which has a reaction force to the valve flap. Under the push of the static pressure and reaction force of the medium, the valve flap quickly reaches the full stroke. The upper adjusting ring can change the reaction force of the medium to the valve flap, adjust the return pressure of the valve, and obtain a reasonable opening and closing pressure difference. 5 is the valve lift curve of the upper adjusting ring at different positions when the adjusting ring is not installed. Lower the upper ring, increase the lift of the valve disc, increase the differential pressure between the opening and closing; adjust the opening height to turn the corner of the 460th page, and when the lip reaches a sufficient sealing pressure, it will contact the sealing surface of the valve seat and bear the rest. Spring load. This can ensure that the sealing surface has sufficient sealing specific pressure, and can withstand the impact load, preventing the sealing surface from being plastically deformed and damaged. The sealing lip and the emergency sump can effectively prevent leakage. When the steam pressure is close to the take-off pressure, when part of the steam leaks, this part of the steam is concentrated in the annular groove, increasing the upward thrust of the valve flap, so that the valve reaches the take-off pressure, and then quickly Take off. In addition, when a small amount of steam leaks, the sealing surface is throttled to cool down, the sealing surface temperature is lower than the lip surface, the lip is bent downward, the contact area between the valve flap and the valve seat sealing surface is reduced, the sealing specific pressure is increased, and the sealing is improved. Ability to effectively prevent pre- and post-discharge.
2.2.3 The influence of the valve stem pressure point on the center of the valve seat If the inner diameter of the valve disc of the safety valve is smaller than the inner diameter of the valve seat, when the action point of the valve stem force on the valve disc deviates from the center of the valve seat, the valve is subjected to the force state 4. Steam pair The torque of the valve flap = corpse 21 + 2 B 1 +, because the price range is equal to the fly interval area, 1 = corpse 2, torque wealth = 2 faint + plant 3102, so the steam force produces an unbalanced moment on the valve flap. Due to the existence of the unbalanced torque, the sealing force of the right half of the valve flap, especially at the third portion, is reduced, and the sealing force is zero at the take-off pressure, and leakage occurs. In order to solve this problem, the following measures can be taken.
0 valve seat center; 0 valve center, 〃, point relative, point interval medium to the valve force; Qiao 00 〃 interval medium to the valve force force valve flap sealing surface diameter is smaller than the valve seat sealing surface diameter, so even if there is relative Eccentricity, the medium does not create an unbalanced moment on the flap.
The stem of the valve stem adopts a spherical structure, and the valve stem and the valve disc assembly are greatly changed. The specific distribution company designs the concrete within the power supply range of the company. However, these management systems should be closely integrated with the distribution automation system to strengthen the demand management while improving the efficiency and economic benefits while managing the distribution network.
3.4 Analysis of Distribution System in Market Environment In the traditional mode, the operation of distribution network is aimed at economic operation. There are many contents related to economic operation of distribution network, mainly including power flow calculation load forecasting network reconstruction reactive power optimization and Voltage adjustment topology analysis fault diagnosis and recovery static security analysis and so on. In the market environment, some content changes accordingly, which is determined by the market mechanism.
Power flow calculation is the basic tool for power system analysis. The power flow calculation under market conditions depends on the purpose of power flow calculation. If the power flow calculation is related to economic interests, the results of power flow calculation must be persuasive, and the data used must be Accurate, this requires a higher data source for the actual system.
In the load forecasting under the market environment, the power demand curve is strictly declared by large users. Therefore, the consideration of load forecasting is relatively small, and to a certain extent, the difficulty of load forecasting is reduced.
In the market environment, the reconstruction of the distribution network asks that the target of the operation has changed. It is no longer aimed at the minimum network loss, but the goal of optimizing the electricity cost, which is completely different from the traditional economic operation. However, within a larger user, there may be network reconfiguration, and the operational goal should be that the network loss is minimal.
The reactive power optimization and voltage adjustment of the user-side power market have different settlement tariffs. Therefore, the goal of reactive power optimization should also be based on electricity prices, rather than the smallest network loss.
4 Prospects for Distribution Automation and Management Systems In the power market environment, the distribution of the distribution network is connected to the upper ring of the 455th page, and the lift of the valve disc is reduced, reducing the differential pressure between the opening and closing.
2.3.3 When the valve flap back pressure valve reaches the full stroke, the balance equation of the force is the impact force of the FS=P1+P2+P3C3 medium on the valve flap; the household 3 is the reaction force acting on the valve flap when the medium is vented; The corpse is a spring compression force.
By the formula 3, when the left force is greater than the right side, the valve is closed. Change the size of the left force of Equation 3 to change the valve return pressure. Therefore, a back pressure adjustment mechanism is added to the upper portion of the flap. At this time, the balance of force is 2577, 26 + support = household 1 + household 2+ household 34; the function of the management system will change, this change is mainly caused by competition in the market environment. When large users participate in market competition, a corresponding increase in facilities is required to ensure the effective implementation of the electricity market, and the investment in these facilities requires a recycling process. When the user's capacity reaches a certain scale, although the investment is large, it can be recovered through the market. In other words, the power market is beneficial to the power distribution company.
Distribution automation and management system is an important means of implementation to improve the economic efficiency of power suppliers and users. Therefore, it should follow the principle of practical feasibility and developability, effectively complete the integration of various functions, and realize resource sharing information sharing.
For the larger users in the distribution network, because of the large amount of electricity used, there are some automation problems within these users. Compared with the distribution network, these automation integrations are developing at the same time. It should also develop some small-scale Zeng Ming. Electricity market theory and application elbow. Beijing China Power went out of history, Han Fang. The status quo and prospects of China's electricity market. Electric Yu Er, Han Fang, Xie Kai, etc., electricity market elbow. Beijing China Electric Power Press, 1999.
Yang Yuyu. Distribution network elbow. Beijing China Electric Power Press, Liu Jian. Distribution automation system elbow. Beijing China Power Publishing Zeng Ming. Commercialization of the power industry and the electricity market. Beijing China Electric Power Press, 1998.
Edit Li Shijie back pressure chamber pressure adjustment back pressure, can change the valve flap downward pressure difference.
3 Conclusion In summary, the valve structure and manufacturing accuracy have a great impact on the performance of the safety valve. Therefore, when designing a spring safety valve with excellent performance, it should adopt a scientific and reasonable structural form, and use materials that meet the requirements of working conditions. In the manufacturing process, the machining accuracy of the parts should be absolutely guaranteed.
Editor Zhou Naiwen
Stone Pedestal,Pave Stone Pedestal,Plastic Pedestal For Wpc Floor,Adjustable Height Waterproof Pedestal
Jiangxi Taurus Technology Co., Ltd , https://www.chinapedestal.com