Butterfly valve, also known as flap valve, is a regulating valve with simple structure, which can be used for on-off control of medium in low-pressure pipeline. Butterfly valve refers to a valve whose closing part (valve disc or butterfly plate) is a disc and rotates around the valve shaft to open and close.
The valve can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil products, liquid metal and radioactive media. It is mainly used for cutting off and throttling on the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so as to achieve the purpose of opening, closing or adjustment.
In the 1930s, the United States invented the butterfly valve, which was introduced into Japan in the 1950s and was not widely used in Japan until the 1960s. It was promoted in China after the 1970s.
The main features of butterfly valve are: small operating torque, small installation space and light weight. Taking DN1000 as an example, the butterfly valve is about 2 tons, while the gate valve is about 3.5 tons, and the butterfly valve is easy to be combined with various driving devices, with good durability and reliability. The disadvantage of rubber sealed butterfly valve is that when it is used for throttling, cavitation will occur due to improper use, resulting in peeling and damage of rubber seat. Therefore, how to correctly select it should be based on the requirements of working conditions.
The relationship between the opening of butterfly valve and flow basically changes in linear proportion. If it is used to control the flow, its flow characteristics are also closely related to the flow resistance of the piping. For example, the diameter and form of the valves installed in the two pipelines are the same, and the flow of the valves will be very different if the pipeline loss coefficient is different. If the valve is in the state of large throttling range, cavitation is easy to occur on the back of the valve plate, which may damage the valve. Generally, it is used outside 15°. When the butterfly valve is in the middle opening, the opening shape formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and different states are formed on both sides. The front end of the butterfly plate on one side moves along the flow direction and the other side moves against the flow direction. Therefore, the valve body and the valve plate on one side form a nozzle like opening, and the other side is similar to a throttle hole like opening. The flow rate on the nozzle side is much faster than that on the throttle side, Negative pressure will be generated under the throttle side valve, and the rubber seal will often fall off.
The operating torque of butterfly valve has different values due to different opening and valve opening and closing directions. The torque generated by horizontal butterfly valve, especially large-diameter valve, due to water depth and difference between upper and lower heads of valve shaft can not be ignored. In addition, when the elbow is installed on the inlet side of the valve, a bias flow is formed, and the torque will increase. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the action of water flow dynamic moment.
Valve industry plays a very important role in the world economic development as an important link of equipment manufacturing industry. There are many valve industry chains in China. In general, China has entered the ranks of the world's largest valve countries.