Introduction to the knowledge of the butterfly valve in the application process

The knowledge of the butterfly valve in the application process;

In the 1930s, the United States invented the butterfly valve. It was introduced to Japan in the 1950s and was widely used in Japan in the 1960s. In China, it was promoted in the 1970s. At present, butterfly valves in the world generally have been replaced by DN300 mm butterfly valves. Compared with the gate valve, the butterfly valve has a short opening and closing time, a small operating torque, a small installation space and a light weight. Taking DN1000 as an example, the butterfly valve is about 2T, and the gate valve is about 3.5T, and the butterfly valve is easy to combine with various driving devices, and has good durability and reliability. 
The disadvantage of the rubber sealing butterfly valve is that when it is used for throttling, cavitation may occur due to improper use, and the rubber seat may be peeled off and damaged. To this end, the metal sealing butterfly valve has been developed internationally, and the cavitation zone has been reduced. In recent years, China has also developed a metal sealing butterfly valve. In recent years, a cam-shaped butterfly valve resistant to cavitation, low vibration and low noise has been developed in Japan. 
Generally, the life of the sealing seat is under normal conditions, rubber is 15-20 years, and metal is 80-90 years. However, how to choose correctly depends on the requirements of the working conditions.
The relationship between the opening of the butterfly valve and the flow rate changes substantially linearly. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the piping. For example, the diameters and forms of the two pipe installation valves are all the same, and the pipe loss coefficient is different, and the valve flow difference is also large. 
If the valve is in a state of large throttle, the back of the valve plate is prone to cavitation and may damage the valve, and is generally used outside of 15°. 
When the butterfly valve is at the middle opening degree, the shape of the opening formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides are formed to complete different states. The front end of the butterfly plate moves along the water direction and the other side flows in the opposite direction. Therefore, one side of the valve body and the valve plate form a nozzle-like opening, and the other side is similar to the orifice-shaped opening, the nozzle side is much faster than the throttle side, and the negative pressure is generated under the throttle side valve, often A rubber seal will come off.
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The operating torque of the butterfly valve varies depending on the opening degree and the direction of opening and closing of the valve. Horizontal butterfly valves, especially large-diameter valves, cannot be ignored due to the water depth and the head difference between the valve shaft and the head. In addition, when the valve inlet side device is bent, a bias current is formed and the torque is increased. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the action of water flow torque.