In addition to the design of the sealing structure, there are many other factors that affect the sealing performance of cryogenic ball valves, such as the material of the sealing pair, the quality of the sealing pair, the specific pressure of the seal, and the physical properties of the medium. These factors will have a great impact on the performance of the valve. Influence. When designing the valve, the influence of these factors on the valve should be considered as much as possible to ensure its normal working condition.
1
Sealing material
Under low temperature conditions, the deformation of the sealing material should be considered. As the temperature decreases, the metal material will shrink and deform, resulting in a gap at the seal and a decrease in the specific pressure of the seal, thereby affecting the sealing performance. Therefore, when designing the sealing structure, it is necessary to choose a reasonable sealing material to ensure the sealing. Under the LNG working condition, the soft sealing method combining metal and non-metal materials is mostly used, so that on the one hand, it can reduce the friction when the valve is opened and closed, and prolong the service life of the valve; on the other hand, the cost is lower and the sealing performance is better. Most of the sealing materials are polytrifluorochloroethylene, because it has good sealing performance no matter what kind of working fluid it is used in, and polytetrafluoroethylene will produce cold flow at low temperature, so it is not suitable to use
2
Secondary quality of sealing
The quality of the sealing pair is mainly reflected in the surface processing quality of the sphere and the surface roughness of the sealing surface. Improving the roundness of the sphere and reducing its surface roughness can reduce the torque during the opening and closing process of the valve, increase the service life of the valve, and also improve the sealing performance of the valve. Therefore, it is very important to improve the surface processing quality of the sealing pair during design.
3
Seal specific pressure
The sealing specific pressure is the pressure per unit area of the sealing surface. The size of the sealing specific pressure directly affects the sealing performance, reliability and service life of the ball valve. However, the sealing specific pressure borne by the valve ball is not as high as possible. A larger sealing specific pressure is beneficial to sealing to a certain extent, but with the increase of the sealing specific pressure, the torque of the valve operation will also increase, which is not conducive to sealing. normal operation of the valve. Therefore, the selection of sealing specific pressure is another important content in the sealing design of ultra-low temperature ball valves.
4
physical properties of the medium
The physical properties such as the viscosity and temperature of the medium will have a certain impact on the seal. First of all, the greater the viscosity of the medium, the smaller its penetrability, and it is not easy to leak. The influence of the temperature of the medium on the seal is mainly reflected in the low temperature condition. The change of the sealing structure caused by the change of the size of some sealing parts will lead to leakage. At the same time, the sealing pressure of the sealing area will also change and destroy the seal. Therefore, when designing the sealing structure, the influence of temperature must be considered.