The
ball valve is evolved from the plug valve. Its opening and closing part is a sphere, which uses the sphere to rotate 90° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the direction of the medium flow in the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function.
advantage:
①Has the lowest flow resistance (actually 0);
②Because it will not get stuck during work (when there is no lubricant), it can be reliably used in corrosive media and low-boiling liquids; ③Complete sealing can be achieved in a larger pressure and temperature range;
④ Fast opening and closing can be realized, and the opening and closing time of some structures is only 0.05~0.1s to ensure that it can be used in the automation system of the test bench. When opening and closing the valve quickly, there is no shock in operation.
⑤The spherical closure can be automatically positioned on the boundary position;
⑥The working medium is reliably sealed on both sides;
⑦When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause the erosion of the sealing surface;
⑧Compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic medium system;
⑨The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
⑩The closing piece can withstand the high pressure difference when it is closed.
⑩The ball valve with fully welded body can be directly buried in the ground, so that the internal parts of the valve are not corroded, and the service life can be up to 30 years. It is the most ideal valve for oil and natural gas pipelines.
shortcoming:
①Because the main seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has a small friction coefficient, stable performance, not easy to age, wide temperature application range and excellent sealing performance The comprehensive characteristics. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require the design of valve seat seals to focus on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is impaired. Moreover, the temperature resistance of PTFE is low, and it can only be used at less than 180°C. Above this temperature, the sealing material will deteriorate. In the case of long-term use, it will generally only be used at 120°C.
②The adjustment performance of the ball valve is worse than that of the stop valve, especially the pneumatic valve (or electric valve).
