The ball valve is evolved from the cock valve. Its opening and closing part is a sphere, which rotates 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing. Ball valve is mainly used to cut off, distribute and change the direction of medium flow in pipeline. The ball valve with V-shaped opening also has good flow regulation function.
It has the lowest flow resistance (actually 0);
(2) It can be used reliably in corrosive media and low boiling point liquids because it can not be stuck at work (in the absence of lubricants);
(3) Complete sealing can be achieved in a larger range of pressure and temperature.
(4) Fast start-up and shut-down can be realized, and the start-up and shut-down time of some structures is only 0.05-0.1s, so as to ensure that they can be used in the automation system of the test bed. When the valve is opened and closed quickly, there is no impact in operation.
_Spherical closure can locate automatically at the boundary position.
_The working medium is reliable in sealing on both sides.
_When fully open and fully closed, the sealing surface of the sphere and 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.
_Compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic medium system.
_The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
_The closing part can withstand the high pressure difference when closing. _The ball valve with fully welded body can be buried directly underground, so that the inner parts of the valve can not be eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.
(1) Because PTFE is the main seating ring material of ball valves, it is inert to almost all chemical substances, and has the comprehensive characteristics of small friction coefficient, stable performance, not easy to aging, wide temperature application range and excellent sealing performance. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor heat conductivity, require that the design of seat seals must be based on these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is destroyed. Moreover, PTFE has a lower temperature resistance and can only be used at less than 180 C. Over this temperature, the sealing material will age. Considering the long-term use, it is usually not used at 120 C.
(2) Its regulating performance is worse than that of globe valves, especially pneumatic valves (or electric valves).