Advantages and disadvantages of ball valve and scope of application
Advantages of ball valve
(1) has the lowest flow resistance (actually 0);
(2) Because it will not get stuck in the work (in the absence of lubricants), it can be reliably applied to corrosive media and low boiling point liquid;
(3) in a large range of pressure and temperature, can achieve complete sealing;
(4) It can realize fast opening and closing, and the opening and closing time of some structures is only 0.05~0.1s, so as to ensure that it can be used in the automation system of the test bed. Quick open and close the valve, operation without impact.
(5) The spherical closing parts can be automatically positioned on 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 seat is isolated from the medium, so the high speed through the medium of the valve will not cause the erosion of the sealing surface; (8) Compact structure, light weight, it can be considered as a reasonable valve structure for low temperature medium system; (9) The valve body is symmetrical, especially the welded valve body structure, can withstand the stress from the pipeline well; (10) The closing parts can withstand the high pressure difference during closing. (11) All-welded valve ball valve, can be directly buried in the ground, so that the valve inner parts are not corroded, ≤ service life of up to 30 years, is the ideal valve for oil and gas pipelines.
Disadvantages of ball valves (1) Because the main valve seat sealing ring material is polytetrafluoroethylene, it is inert to almost all chemical substances, and has a small coefficient of friction, stable performance, not easy to aging, a wide range of temperature application and excellent sealing performance. However, the physical properties of polytetrafluoroethylene, including high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the seat be designed around these characteristics. So, when the sealing material hardens, the reliability of the seal is compromised. Moreover, the temperature resistance of polytetrafluoroethylene is low, and can only be used under the condition of less than 180 ℃. Above this temperature, the sealing material will age. In the case of long-term use, it is generally only used at 120 ℃. (2) its regulating performance is poor relative to the globe valve, especially the pneumatic valve (or electric valve).
Application range of ball valve Because ball valves usually use rubber, nylon and polytetrafluoroethylene as seat sealing ring materials, its use temperature is limited by the seat sealing ring material. The cut-off of ball valves is done by pressing metal spheres between plastic seats under the action of medium (floating ball valves). The seat sealing ring undergoes local elastic-plastic deformation under a certain contact pressure. This deformation can compensate for the manufacturing accuracy and surface roughness of the sphere and ensure the sealing performance of the ball valve. Because the seat sealing ring of the ball valve is usually made of plastic, in choosing the structure and performance of the ball valve, the fire resistance and fireproof of the ball valve should be considered, especially in petroleum, chemical, metallurgy and other sectors. Ball valves should be used in equipment and pipeline systems of flammable and explosive media, and more attention should be paid to fire resistance and fire prevention. Generally, ball valves are recommended in pipeline systems with dual adjustment, strict sealing performance, mud, wear, shrinkage channel, rapid opening and closing action (1/4 rpm opening and closing), high-pressure cut-off (large pressure difference), low noise, air hole and gasification phenomena, a small amount of leakage into the atmosphere, low operating torque and low fluid resistance. Ball valves are also suitable for pipeline systems with light structure, low-pressure cut-off (small pressure difference) and corrosive media. Ball valves can also be used in cryogenic (deep cooling) devices and pipeline systems. In the oxygen pipeline system of the metallurgical industry, strictly degreasing ball valves need to be used. When the main line in the pipeline and the gas pipeline needs to be buried underground, a full-path welded ball valve needs to be used. When adjusting performance is required, a ball valve with a special structure with a V-shaped opening is required. In petroleum, petrochemical, chemical, electric power and urban construction, metal-to-metal sealed ball valves can be used for pipeline systems with operating temperatures above 200 degrees.