Ball valve 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 range and sealing Comprehensive features with excellent performance.
However, the physical properties of PTFE, including a high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that the valve seat seal must be designed around these properties. Therefore, when the sealing material hardens, the reliability of the seal is compromised.
Moreover, PTFE has a low temperature resistance level and can only be used below 180°C. Above this temperature, the sealing material will age. When considering long-term use, it is generally only used at 120°C.
(2) Its adjustment performance is worse than that of the stop valve, especially the pneumatic valve (or electric valve).
Ball valve advantages:
(1) Has the lowest flow resistance (actually 0);
(2) Because it will not get stuck during operation (when there is no lubricant), it can be reliably used in corrosive media and low-boiling point liquids;
(3) Complete sealing can be achieved within a larger pressure and temperature range;
(4) Rapid opening and closing can be achieved. 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 impact in the operation.
(5) The spherical closing member can automatically locate at the boundary position;
(6) The working medium is reliably sealed on both sides;
(7) When fully open and fully closed, the sealing surfaces of the ball and valve seat are 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 systems;
(9) The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
(10) The closing parts can withstand the high pressure difference during closing.
(11) The ball valve with a fully welded body can be buried directly underground to protect the valve internal parts from corrosion. The maximum service life can be up to 30 years. It is the most ideal valve for oil and natural gas pipelines.
Since ball valves usually use rubber, nylon and PTFE as seat sealing ring materials, their service temperature is limited by the seat sealing ring material. The cut-off function of the ball valve is accomplished by the metal balls pressing against each other between the plastic valve seats under the action of the medium (floating ball valve).
Under the action of a certain contact pressure, the valve seat sealing ring will undergo elastic-plastic deformation in local areas. This deformation can compensate for the manufacturing accuracy and surface roughness of the ball and ensure the sealing performance of the ball valve.