In addition to the design of the sealing structure, there are many other factors affecting the sealing performance of low temperature ball valve, such as the material of the seal pair, the quality of the seal 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. In the design of the valve, as far as possible to take into account the impact of these factors on the valve, in order to ensure its normal working state.
1. Sealing auxiliary material
At low temperature, the deformation of sealing secondary materials should be considered. Metal materials will shrink and deformation with the decrease of temperature, resulting in clearance at the sealing place, sealing pressure reduction, thus affecting the sealing performance. Therefore, in the design of sealing structure, we must choose a reasonable sealing material to ensure the sealing. In the LNG working condition, most of the soft sealing method combining metal and non-metal materials is used, which on the one hand can reduce the friction when the valve is opened and closed, and increase the service life of the valve; On the other hand, the cost is lower and the sealing is better. Sealing materials are mostly made of polytrifluorochloroethylene, because it has good sealing performance no matter what kind of working medium it is applied to, and polytetrafluoroethylene will produce cold flow at low temperature, so it is not suitable.
2. Sealing pair quality
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 ball and reducing its surface roughness can reduce the torque during the valve opening and closing process, improve 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. Sealing pressure
The sealing specific pressure is the pressure per unit area of the sealing surface. The sealing pressure directly affects the sealing, reliability and service life of the ball valve. However, the sealing pressure of the valve ball is not the greater the better. The larger sealing pressure is beneficial to the sealing to a certain extent, but with the increase of the sealing pressure, the torque of the valve operation will increase, which is not conducive to the normal operation of the valve. Therefore, the selection of sealing specific pressure is another important content of ultra-low temperature ball valve sealing design.
4. Physical properties of the medium
The viscosity, temperature and other physical properties of the medium will have a certain impact on the seal. First of all, the greater the viscosity of the medium, the smaller its permeability, not easy to leak. The influence of the temperature of the medium on the sealing is mainly reflected in the change of the sealing structure caused by the change of the size of some sealing parts under low temperature conditions, which leads to leakage. At the same time, the sealing pressure in the sealing area will also change and destroy the sealing. Therefore, when designing the sealing structure, the influence of temperature must be considered.
Post time: May-16-2023