1. Advantages:
(1) Has the lowest flow resistance (actually 0);
(2) It can be reliably used in corrosive media and low-boiling liquids because it will not get stuck during operation (when there is no lubricant);
(3) Complete sealing can be achieved in a wide range of pressure and temperature;
(4) It can realize rapid opening and closing, 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 the valve is opened and closed quickly, there is no shock in operation.
(5) The spherical closure can be automatically positioned at the boundary position;
(6) The working medium is reliably sealed on both sides;
(7) When 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 erosion of the sealing surface;
(8) With compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature medium system;
(9) The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
(10) The closing member can withstand the high pressure difference when closing.
(11) The ball valve with fully welded valve body can be directly buried in the ground, so that the valve internals are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.
2. Disadvantages:
(1) Because the most important valve 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 sealing. Comprehensive characteristics of excellent performance. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of valve seat seals must be carried out around these characteristics. Therefore, when the sealing material becomes hard, the reliability of the sealing is damaged. Moreover, PTFE has a low temperature resistance grade and can only be used below 180 °C. Above this temperature, the sealing material will degrade. In the case of long-term use, it is generally only used at 120 °C.
(2) Its adjustment performance is worse than that of globe valves, especially pneumatic valves (or electric valves).
3. Scope
Since the ball valve usually uses rubber, nylon and PTFE as the material of the seat seal, its operating temperature is limited by the material of the seat seal. The cut-off function of the ball valve is accomplished by pressing the metal ball against the plastic valve seat under the action of the medium (floating ball valve).
Under the action of a certain contact pressure, the valve seat sealing ring undergoes elastic-plastic deformation in local areas. This deformation can compensate for the manufacturing accuracy and surface roughness of the sphere and ensure the sealing performance of the ball valve.
And because the valve seat sealing ring of the ball valve is usually made of plastic, when choosing the structure and performance of the ball valve, the fire resistance and fire resistance of the ball valve should be considered, especially in the petroleum, chemical, metallurgical and other departments, in flammable and explosive media. If ball valves are used in the equipment and pipeline systems, more attention should be paid to fire resistance and fire protection.
