Detailed analysis of the difference between ball valve and butterfly valve
Published: March 14, 2016 Author: 【191566.com】
The biggest difference between the two is that the butterfly valve's opening and closing piece is a plate, while the ball valve is a ball. The valve plate of the butterfly valve and the spool of the ball valve both rotate around their own axis; the butterfly valve can adjust the flow rate by the opening degree; the ball valve is not convenient to do this. The sealing surface of the ball valve is a spherical surface, and the sealing surface of a butterfly valve is a circular cylindrical surface. The butterfly valve is characterized by fast opening and closing speed, simple structure and low cost, but its tightness and pressure bearing capacity are not good. Ball valves are limited by volume and resistance to opening and closing, making it difficult to achieve large calibers.
Butterfly valve has simple structure, low cost, and large adjustable range. Ball valve is usually suitable for liquids and gases without particulate impurities, small fluid pressure loss, good sealing performance and high cost.
Small diameter ball selection valve, large diameter butterfly valve
In general, it is more economical to use threaded ball valves for small caliber (below DN50). Ball valves above DN50 are generally flanged. Large caliber ball valves are more expensive due to processing technology and materials, but because of the tightness of the ball valve and its own flow characteristics It is widely used in some industries, such as paper industry, natural gas industry and high pressure field. Butterfly valves are generally used in large-diameter occasions (above DN50), with a simple structure and relatively low price. The pressure is generally below PN16 (the eccentric butterfly valve is generally below PN40). Compared with ball valves, the butterfly valve has poor sealing performance.
If used for rough flow adjustment, the linearity of the butterfly valve is better than that of the O-ball valve.
Butterfly valve introduction
Butterfly valve: Butterfly valve is a valve that uses a disc-type opening and closing member to revolve around 90 ¡ã to open, close and adjust the fluid channel.
Advantages: ① Simple structure, small size, light weight, and low consumables; used in large-caliber valves; ② rapid opening and closing, small flow resistance; ③ can be used for media with suspended solid particles, and can also be used for powder according to the strength of the sealing surface And granular media.
It can be used for two-way opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways of metallurgy, light industry, power, petrochemical systems, etc.
Disadvantages: ① The flow adjustment range is not large. When it is turned on to 30%, the flow will be more than 95%. ② Due to the limitation of the structure of the butterfly valve and the sealing material, it should not be used in high temperature and high pressure piping systems. The general working temperature is below 300 ¡ã C and below PN40. ③ The sealing performance is poor compared to ball valves and globe valves, so it is used in places where the sealing requirements are not very high.
Ball valve introduction
Ball valve: It is evolved from a plug valve. Its opening and closing member is a ball. The ball is rotated 90 ¡ã around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the medium flow direction on the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function.
Advantages: ① has the lowest flow resistance (actually 0); ② can not be stuck during work (without lubricant), so it can be reliably used in corrosive media and low boiling point liquids; ③ in the larger It can be completely sealed within the 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, so as to ensure that it can be used in the test bench automation system. When opening and closing the valve quickly, the operation is shock-free. ⑤The spherical closure can be automatically positioned at the boundary position; ⑥The working medium is reliably sealed on both sides; ⑦When fully open and fully closed, the sealing surface of the ball and valve seat is isolated from the medium, so the medium passing through the valve at high speed will not Causes erosion of the sealing surface; 紧凑 compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature media systems; 对称 valve body symmetry, especially the welded valve body structure, can well withstand the stress from the pipeline ⑩The closing part can withstand the high pressure difference when closing. ⑾Ball-welded ball valve can be directly buried in the ground, so that the internal parts of the valve are not eroded, and the maximum service life is up to 30 years. It is the most ideal valve for oil and gas pipelines.
Disadvantages: ①Because the main valve seat sealing material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has a small coefficient of friction, stable performance, not easy to age, wide temperature range and sealing Comprehensive performance with excellent performance. However, the physical characteristics of PTFE, including higher expansion coefficient, sensitivity to cold flow, and poor thermal conductivity, require that the design of the valve seat seal must be based on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is impaired. Moreover, PTFE has a low temperature resistance grade and can only be used at temperatures below 180 ¡ã C. Beyond this temperature, the sealing material will age. In the case of long-term use, it is generally not used at 120 ¡ã C. ② Its regulating performance is worse than that of globe valves, especially pneumatic valves (or electric valves).