Technical Considerations for High-Temperature Valve Design

Valves are indispensable in fluid control activities and play a key role in all fluid control. Modern science and technology has developed rapidly, and great breakthroughs and development have been achieved in different industries, so the demand for high temperature valves has become more and more, and the requirements for high temperature valve design have become higher and higher.

1. Factors that restrict the design of high temperature valves

1.1. Thermal expansion quantity

The difference between the thermal expansion and the heat withstand of the substance is an important condition for determining the difference in the amount of thermal expansion, so we should take the constraints of this condition into account in the design activities of the valve at high temperature. In order to make the temperature in the spool quickly reach the same as the temperature in the fluid, and then direct the heated high temperature fluid into the valve with a very low temperature, so that the valve stem with a small side area can effectively do a good job of heat dissipation. Because the heat dissipation conditions of the valve are not the same as those of other substances, especially in terms of expansion, although it is heated at the same time, it is different in the amount of expansion after. Therefore, it is necessary to ensure the gap of the valve work, and at the same time, it is necessary to increase the scope of control, which can avoid the situation of the parts being stuck, and can significantly reduce the damage of the parts due to the rise in temperature.

1.2. Thermal alternations

The medium will have a great impact on the role of the parts in terms of thermal alternations, such as the contact of the seat and the guide, which may be due to the change of the thermal alternations of the medium, resulting in loosening and losing the previous sealing function. Therefore, in the previous design, it is necessary to carry out tight seam welding of the valve seat and the supported joint to ensure that its sealing function is not damaged. When we design, we also need to take into account the sealing selection effect in the case of thermal alternations, so that we can reduce the influence of thermal alternations on high temperature valves at the source, avoid the consumption of parts, and thus increase the service life of high temperature valves.

2, the valve body required materials,

2.1 Material in the valve body

If you want to ensure the requirements of high temperature valves for structural materials, you should meet the following standards: hardness, impact force, abrasion resistance. When we choose the material inside the valve body, the thermal expansion of the material should be taken as a focus. The risk of component damage at high temperatures should also be taken into account. The material inside the valve body is made of rusty steel, which can be processed by surfacing welding on the table, so as to ensure the characteristics of wear-resistant and cavitation of the valve body, so that they can work normally in high temperature environment. In a high temperature environment, the medium corrosion will have a great impact on the choice of materials, because it is used in a high temperature environment, so you should choose materials with good material properties, such as carbon steel, high temperature resistant alloy steel, stainless steel, etc., as the material material of the valve body, which can ensure that the valve body can work normally in a high temperature environment.

2.2. Design of shell in terms of wall thickness

When designing the shell, the pressure that may occur during specific use should be considered, and it should be designed as a fixed value of the shell pressure resistance, so as to ensure sufficient pressure resistance and effectively reduce the corrosion to a low degree.

2.3. Sealing design of the middle part

The middle seal can be designed to force a wood seal. Its principle is to close the flange bolt well, so that the sealing gasket uses pressure to produce a compressibility effect, and then there is a relatively small gap on the surface. In the design of medium temperature small diameter valves, such a forced seal is very commonly used. Specifically, the forced wood seal is composed of the following parts: valve body, floating valve cover, sealing ring, etc. Before we perform the booster operation, we should fix the restraining bolts and move the floating cover up. The purpose of this is to maintain a good sealing capacity of the valve cover and the elastic pad. When the medium exerts pressure on it, it can move upward, it can effectively contain the bolt. The sealing pressure of the valve cover and the elastic pad has a positive connection, and they can be strengthened with the rise of the pressure, which can produce a good sealing effect.

2.4, high temperature bolts do a good job of connection

Because the bolt needs to work in a high temperature environment, several major problems should be considered: the bolt also has a change in the performance of the connection, the relaxation of the force, and so on. In view of the above problems, we can make the following design: first, to avoid the spiral thread in the high temperature environment bite death. Second, in addition to scientific and reasonable material selection, the thread should also be designed as a coarse thread to strengthen the radius of the gap within an appropriate range. Third, once the steel bolt is at 300 ° C for a long time, the force will be relatively relaxed. Therefore, it is necessary to ensure that the remaining preload is higher than the required value, and the stability of the connection should be checked.

2.5, the coordination of the gap should be scientific

The valve stem and the upper seal seat should ensure a reasonable gap, and the thermal expansion index of the material should ensure that the latter is greater than the former, otherwise it is prone to wear problems.

3. Some variables to pay attention to

3.1. Chafing problem

If the mutual force of the material is very small, it is easy to bruise due to external constraints and influences. For example, in the pipeline system, the valve seat and spool often appear bruised, and their bruises are mainly caused by the entry of large particles. In addition, the vibration related impact may also have a great impact and abrasion, so in order to reduce the abrasion phenomenon in the use of activities, it is necessary to make a reasonable choice of sealing materials, but also to ensure that the matching of hardness in the sealing room is controlled in an appropriate range.

3.2. Thickness of surfacing layer

In order to achieve the hardening of the inside of the high temperature valve, the thickness of the surfacing layer should be confirmed. The use of some useful experiments to determine the thickness of the surfacing layer, the more appropriate thickness should be >4mm, 4mm thickness will better isolate the outside high temperature, reduce the impact of external high temperature on the inside material, to ensure the internal life of the valve.

4. Summary

Now the use of high temperature valve technology is gradually increasing, everyone's requirements for high temperature valve technology is becoming higher and higher, although now China's high temperature valve technology has achieved some results, but there are still many problems have not been solved. Therefore, we should carry out a more detailed analysis and research on the design technology of high temperature valves, through the research of high temperature valve technology, the identification of materials, the treatment of internal parts, explore the problems that should be paid attention to high temperature valve technology, vigorously promote the development of technology, increase the scope of use of high temperature valves, and strive to improve the service life of high temperature valves.