The main valve seat seal ring material is polytetrafluoroethylene (PTFE). It is inert to almost all chemical substances, has the comprehensive characteristics of small friction coefficient, stable performance, easy to aging, wide application temperature excellent sealing performance. But the physical characteristics of PTFE have high expansion coefficient, sensitivity to cold flow poor thermal conductivity, so sealing design of valve seat must be carried out around these characteristics. Seat sealing plastic materials, including PTFE filled PTFE, nylon other materials. However, when the sealing material becomes hard, the reliability of the seal will be destroyed, especially in the case of low pressure difference. In addition, synthetic rubber such as nitrile rubber can also be used as seat sealing material, but its suitable medium temperature range are limited. In addition, it is lubricated easy to jam the ball with synthetic rubber.
In order to meet the requirements of industrial applications such as high temperature, high pressure, strong scouring long service life, metal sealed ball valves have been greatly developed in recent ten years. The v-ball valve used to regulate the flow rate also has a rapid development. Especially in industrial developed countries, the structure of ball valve is constantly improved, such as all welded valve body ball valve used in oil natural gas pipeline, lifting rod type ball valve, high temperature ball valve with V-shaped opening adjustment ball valve used in cracking unit, etc., so that the technology of ball valve reaches a new level.
The advantages of ball valves are as follows:
1. All welded ball valve can be directly buried in the ground, so that the valve internals are corroded. It has a service life of 40 years is an ideal valve for oil gas pipelines.
2. In the higher working pressure higher working temperature range, it can achieve complete sealing.
3. The ball valve with - shaped opening ball has good flow regulation function.
4. Because of its compact structure light weight, it can be considered as a reasonable valve structure for low temperature medium system.
5. The symmetrical valve body, especially the welded valve body structure, can well withstand the stress the pipeline.
6. The closing part can withstand the high pressure difference when closing.
7. It has low flow resistance.
8. It can be reliably used in corrosive medium low boiling point liquid because it will get stuck when working.
9. The opening closing time of some structures is only 0.5 ~ 1s, which can be used in the automatic system of the test-bed. When the valve is opened closed quickly, the operation has no impact.
10. The spherical closures can be positioned automatically on the boundary.
11. The double-sided seal is reliable.
12. When the valve is fully open fully closed, the sealing surface of the ball valve seat is isolated the medium, so the medium passing through the valve at high speed will erode the sealing surface.
13. Once the medium pressure in the chamber is higher than 1.33 times of the design pressure, it can be automatically discharged into the outlet pipeline the inlet pipeline.
14. It can be designed to have fireproof sealing function. V10, with anti-static function.