The ball valve usually uses rubber, nylon and polytetrafluoroethylene as the seat sealing ring material, so its service temperature is limited by the seat sealing ring material. The cut-off function of the ball valve is completed by the mutual compression between the metal ball and 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 will undergo elastic-plastic deformation in some areas. This deformation can compensate the manufacturing accuracy and surface roughness of the ball and ensure the sealing performance of the ball valve.
In addition, since the valve seat seal ring of the ball valve is usually made of plastic, the fire resistance and fire prevention of the ball valve should be considered in the selection of the structure and performance of the ball valve, especially in the petroleum, chemical, metallurgical and other departments, when using the ball valve in the equipment and pipe type system of flammable and explosive media, the fire resistance and fire prevention should be paid more attention to.
In general, ball valves are recommended for pipeline systems with two-position adjustment, strict sealing performance, mud, wear, necking channels, rapid opening and closing action (1/4 turn opening and closing), high pressure cut-off (large differential pressure), low noise, cavitation and gasification, a small amount of leakage to the atmosphere, small operating torque and small fluid resistance. The ball valve is also applicable to the pipeline system with light structure, low pressure cutoff (small differential pressure) and corrosive medium.Ball valves can also be used in low temperature (cryogenic) devices and piping systems. In the oxygen pipeline system of metallurgical industry, ball valves with strict degreasing treatment need to be used.
When the main pipelines in oil and gas pipelines need to be buried underground, full bore welded ball valves need to be used. When the regulating performance is required, the ball valve with V-shaped opening and special structure shall be selected. In petroleum, petrochemical, chemical, electric power and urban construction, metal to metal sealed ball valves can be selected for pipeline systems with operating temperatures above 200 ℃.