4 balls tightness
The most important seat sealing material for ball valves is polytetraoxyethylene (PTFE), which is sensitive to almost all chemical substances, and has low friction coefficient, stable performance, not easy to age, wide temperature application range and sealing performance Excellent comprehensive characteristics. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require the design of valve seat seals to focus on these characteristics. The plastic material of the valve seat seal also includes filled PTFE, nylon and many other materials. However, when the sealing material becomes hard, the reliability of the seal will be damaged, especially in the case of low pressure difference. In addition, synthetic rubber such as butyl rubber can also be used as a valve seat sealing material, but its applicable medium and temperature range drugs are limited. In addition, if the medium is not lubricated, the use of synthetic rubber is likely to jam the ball.
In order to meet the use requirements of industrial applications such as high temperature, high pressure, strong erosion, long life, etc., metal-sealed ball valves have been greatly developed in the past ten years. Especially in developed industrial countries, such as the United States, Italy, Germany, Spain, the Netherlands, etc., the structure of the ball valve has been continuously improved, and there have been all-welded body direct-buried ball valves, lifting ball valves, and ball valves in long-distance pipelines, oil refining equipment, etc. The industrial field is more and more widely used, with large diameter (3050mm), high pressure (70MPa) and wide temperature range (-196~8159C) ball valves appearing, so that the technology of the ball valve has reached a new level.
5 Ball valve design and manufacturing
Due to the application of Computer Aided Design (CAD), Computer Aided Manufacturing (CAM) and Mulberry Manufacturing System (FMS) in the valve industry, the design and manufacture of ball valves have reached a whole new level. Not only has it completely innovated the valve design calculation method, but also reduced the heavy and repetitive routine design work of professional and technical personnel, so that technicians have more energy to improve, improve product performance and new product development, and shorten the research and development cycle of new products. , Improve labor productivity in an all-round way, and in the process of research and development of lifting rod type metal sealing ball valve, due to the application of CAD/CAM, a wide rod spiral flat made by computer-aided design and computer-aided CNC machine tools has appeared, which is a metal seal. The ball valve has no scratches and wear during the opening and closing process, so that the sealing performance and service life of the ball valve are greatly improved. When the ball valve is fully opened, the flow resistance is very small, almost equal to zero, so the equal diameter ball valve is widely used in oil and gas pipelines because it is easy to clean the pipeline. Because the ball of the ball valve is wiped during the opening and closing process, most ball valves can be used in media with suspended solid particles. Depending on the material of the sealing ring, it can also be used in powder and granular media.
6 Ball valve applicable occasions
Since the ball valve usually uses rubber, nylon and polytetraoxyethylene as the seat sealing ring material, its use temperature is limited by the valve seat sealing ring material. The cut-off effect of the ball width is achieved by the metal ball being pressed against each other between the plastic valve seats under the action of the medium (floating ball valve). Under the action of certain contact pressure, the valve seat sealing ring deforms elastically and plastically 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 seat sealing ring of the ball valve is usually made of plastic, when selecting the structure and performance of the ball valve, it is necessary to consider the fire resistance and fire resistance of the ball valve, especially in the petroleum, chemical, metallurgical and other sectors, in the flammable and explosive media The use of ball valves in the equipment and piping system of the United States should pay more attention to fire resistance and fire prevention.
Generally, in two-position adjustment, strict sealing performance, mud, abrasion, necking channel, rapid opening and closing action (1/4 turn opening and closing), high pressure cut-off (large pressure difference), low noise, cavitation and vaporization, In piping systems with a small amount of leakage to the atmosphere, small operating torque and small fluid resistance, ball valves are recommended.
Ball valves are also suitable for piping systems with light structure, low pressure cut-off (small pressure difference), and corrosive media.
Ball valves can also be used in low temperature (cryogenic) devices and pipeline systems.
In the oxygen pipeline system of the metallurgical industry, ball valves that have undergone strict degreasing treatment are required.
When the main lines in the oil and gas pipelines need to be buried underground, full-diameter welded ball valves are required.
When adjusting performance is required, a ball valve with a special structure with a V-shaped opening should be selected.
In petroleum, petrochemical, chemical, electric power, and urban construction, metal-to-metal sealed ball valves can be used for piping systems with operating temperatures above 200°C.
7 Principles of application of ball valves
For oil and natural gas pipelines, pipelines that need to be cleaned, and buried in the ground, use all-pass and all-welded ball valves; for buried in the ground, choose all-pass welded or flanged ball valves; branch pipes , Choose flange connection, welding connection, full-pass or reduced diameter ball valve.
For the transportation pipeline and storage equipment of refined oil, use flanged ball valves.
For city gas and natural gas pipelines, use floating ball valves with flange connection and internal thread connection.
In the oxygen pipeline system in the metallurgical system, a fixed ball valve that has undergone strict degreasing treatment and flanged connection should be used.
For low-temperature piping systems and devices, low-temperature ball valves with bonnets should be used. In the pipeline system of the catalytic cracking unit of the oil refining unit, a lifter-type ball valve can be selected.
In the equipment and piping systems of corrosive media such as acid and alkali in chemical systems, it is advisable to use all stainless steel ball valves made of austenitic stainless steel and polytetraoxyethylene as the seat and sealing ring.
Metal-to-metal sealing ball valves can be used in piping systems or devices for high-temperature media in metallurgical systems, power systems, petrochemical installations, and urban heating systems.
When flow adjustment is required, a worm-gear drive, pneumatic or electric ball valve with V-shaped opening can be selected.