Keywords: power station valve; sealing performance; leakage; analysis Introduction The arrival of science and technology has accelerated the pace of development of science and technology, and power plant systems want long-term progress and stable development, it is imperative to keep pace with the times and constantly transform , Continuous improvement, to ensure the stable operation of power plant system. When it comes to the steady development, the safety performance of the power plant must first be guaranteed and the quality of the power plant protected to some extent. The safety performance is closely related to the valve of the power plant, and the sealing performance has a vital influence on the valve. Therefore, Sealing puts forward higher requirements, higher challenges. The sealing performance can not be guaranteed, naturally leakage will occur, then it will affect the stable operation of the equipment, and even more adverse consequences, the economic losses caused by it will be great, so staff should attach great importance to the power station valves Sealing. Internal leakage and leakage is the main form of valve leakage, leakage usually occurs in the valve seat and the closing member above the contact surface. Leakage in the stuffing box, the link flange gasket appears higher frequency. The following article will be on the power station valve seal form a specific analysis.
1 power station valve seal form Power station valve seal forms: contact seal and non-contact seal two categories. Contact seal refers to the contact surface seal to remove contact with the gap, such as: seat sealing surface, packing or flange seal and so on. These reserved assembly gaps eliminate the need for a hermetically sealed non-contact seal that seals against the sealing surface. Dynamic seal, static seal type according to the relative motion of the dense secret contact. Contact and non-contact type collectively referred to as dynamic seal.
Elastic seal, the main form of non-elastic seal contact seal. Polymer elastic material is the main production of flexible sealing material, you want to reduce or completely remove the gap, you need to clever use of sealing material elastic deformation compensation. Structure is not complicated, the size is relatively compact, and the price inexpensive, good sealing performance. But the drawback is the use of temperature range there is a certain local, and the life also needs to be improved, the current life is shorter, only for low parameters of the seal.
Non-elastic materials, such as metal or graphite, form the non-elastomeric sealing surface and apply minimal amounts of elastic deformation and wear-compensating mechanism seals. This requires higher processing precision. Although the price is relatively high, its temperature is much wider and has a longer life. Contrary to the above, its application to high-parameter sealing is more.
2 power station valve sealing principle The following specific to the sealing principle of the power station valve for further discussion. The main task of the valve seal is to prevent leaks. The reasons for the leakage of the valve from many aspects, there are: the presence of intermittent seal and seal on both sides of the pressure on both sides. The main reason that affects the valve sealing performance of the power station is the gap problem of the sealing pair. Therefore, the main principle of power plant valve sealing is to use a variety of ways to reduce its leakage.
The waviness of the distance between the peaks and the smaller roughness dispersed on the surface of the wave form the surface of the valve of the power station. If the problem of media leakage can be reduced or avoided, the sealing performance of the power station valve can be further increased. Ideally, the gap between the sealing surfaces should be less than the diameter of the fluid molecule, but in practice there are often problems that are hard to achieve. In other words, the power plant valve surface structure of the metal even if the grinding is very fine, but its roughness still can not achieve the desired expectation, and higher than the water molecule diameter 30 times. Through the theoretical support and the accumulation of practical experience, we can see that the use of measures to improve the fineness of the sealing surface does not effectively act on the sealing of the valve. By increasing the specific pressure, the microscopic profile peak on the sealing surface is flattened so as to be plastically deformed so as to ensure the clearance becomes smaller and finally achieve the sealing effect on the fluid.
3 factors that affect the sealing performance of the valve 3.1 The physical properties of the media The physical properties of the media have a greater impact on its sealing in the process of the utility valve, its impact can not be ignored, its physical properties are divided into three areas including: Temperature, viscosity, hydrophilicity. Gas viscosity is less than the liquid viscosity, and the gas permeability is higher than the liquid. The theory shows that, not saturated steam, compressed gas and liquid compared to the occurrence of leakage is more frequent, but also more likely to occur. From the theory, we know that the sealing of the power station valve will get more accurate results if the gas is used. The gas station for the gas valve is to test the gas is a necessary condition.
Under the action of temperature, there will be some changes in the viscosity of liquids and gases. If the temperature is increased, the gas viscosity will be larger, the liquid is the opposite of the gas, the viscosity is relatively reduced. In addition to the temperature changes have a certain impact on the viscosity, but also on the size of the parts, sealing pair have a certain impact on the relaxation. The use of scientific and reasonable measures to make the valve sealing pair with thermal compensation can play a multiplier effect, which is of great significance to reduce the temperature on the valve seal of the power plant. Another important physical property of sealing performance of power station valves is the contact surface hydrophilicity, which is also very important. Capillary properties can easily lead to valve leakage. Destruction of hydrophilic properties tend to be when there is a thin oil film on the contact surface, when the damage is easy to happen. Therefore, you want to obtain a high degree of sealing the valve, try to eliminate the sealing surface of the valve cavity oil is necessary.
3.2 Sealing surface pressure on the valve sealing performance of the power station Another factor is the sealing surface pressure. The specific pressure on the power plant valve is very large, not only can affect the sealing performance of power station valves, but also have a great impact on their life expectancy. The specific pressure is the size of the pressure difference between the front of the valve and the valve and the additional sealing force of the decision. Bigger than the pressure will be subject to some damage to the power plant valves, pressure is smaller than the valve will result in leakage. Can be seen that the power plant valve sealing surface pressure is directly related to the pressure, you want to ensure the quality of power station valves, the best design should be involved in all aspects of the issues to be considered, the factors that will affect its tightness should be done The overall assessment, so as to make a scientific and reasonable than the size of the pressure.
3.3 Sealing Vice structure Sealing Vice structure is not absolutely rigid, the structure of the seal deputy will be affected by many factors, such as temperature changes, plus the sealing force changes will have a significant impact on the seal Vice will have a corresponding Variations and the sealing force between the vice adversely affect the valve so that the overall sealing performance changes. So to ensure the elastic deformation of the seal, can effectively avoid the seal pair of structural changes caused by the impact.
3.4 Seals Vice Quality The quality of the sealing valve has a certain impact on the overall valve sealing performance of the power station. The quality of the sealing sub-quality is affected by many aspects, including material selection, matching and manufacturing accuracy. From the material selection, in order to obtain a higher overall valve power plant sealing, you need to be in the valve stem packing letter sealing structure is formulated in the case, to choose a small coefficient of friction, good elasticity, high corrosion resistance Sealed packing. When the valve disc and valve seat sealing surface mild case, you need to increase the fluid resistance under certain circumstances, it can also improve the sealing of power station valves.
4 to enhance the valve sealing performance of the relevant measures Power station valve sealing performance is very important, the following on this issue put forward to enhance the power station valve sealing measures. The factors that can affect the tightness of the concrete analysis. First of all, we must do a good job of leakage prevention. In the selection of material should be within the scope of stress, a reasonable increase in pressure, the sealing surface micro-peak flattening, the production of elastic plastic deformation, to ensure that the intermittent smaller sealing surface to enhance the sealing performance of the valve. Second, the use of grease seal when the seal, but also to ensure the integrity of the film, so to improve the sealing of the power plant valves are also very helpful. Again, there must be elastic deformation between the seals. Finally, attention should be paid to the selection of the power plant's valves, which has a direct impact on the steady operation of its system. Should choose a flexible, ductile, corrosion-resistant materials.
References [1] Pan Minghao. Sealing performance of the valve [K] Association for Science and Technology Forum (second half), 2011 (02).
[2] Zhang Jie Feng. Valve leakage causes and improvements [J]. Science and Technology, 2009 (19).
[3] Zheng Jiannong, Sun Yezhu. Selection of imported power plant valves [J]. Thermal Power Generation, 2007 (02).
[4] Guo Lifeng, Wang Bangkun. Power station valve repair and green remanufacturing [J]. China equipment engineering, 2007 (06).
[5] Yang Yuanquan. Valve Design Manual [M] Beijing: Mechanical Industry Press, 1992.
Concrete Vibrator,Petrol Concrete Vibrator,Robin Engine Concrete Vibrator
Bison Machinery Co., Ltd. , http://www.tzengine.com
没有评论:
发表评论