In the 1930s, the United States invented the butterfly valve
, and it was introduced to Japan in the 1950s. At present, butterfly valves above DN300 mm have gradually replaced gate valve
s in the world. Compared with gate valve, butterfly valve has short opening and closing time, small operating torque, small installation space and light weight. Taking DN1000 as an example, the butterfly valve is about 2T, while 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-sealed butterfly valve is that when it is used for throttling, cavitation will occur due to improper use, which will cause the rubber seat to peel off and damage. For this reason, metal-sealed butterfly valves have been developed internationally, and the cavitation area has been reduced. In recent years, my country has also developed metal-sealed butterfly valves. In Japan, comb-shaped butterfly valves with cavitation resistance, low vibration and low noise have also been developed in recent years. Generally, the life of the seal seat is 15-20 years for rubber and 80-90 years for metal under normal circumstances. But how to choose correctly depends on the working conditions. The relationship between the opening of the butterfly valve and the flow is basically a linear proportional change. 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 pipes are all the same, but the loss coefficient of the pipes is different, and the flow rate of the valve will be very different. If the valve is in a state of large throttling, cavitation is prone to occur on the back of the valve plate, which may damage the valve. Generally, it is used at a distance of 15°. When the butterfly valve is in the middle opening, 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 form different states. Therefore, one side of the valve body and the valve plate form a nozzle-like opening, and the other side is like a throttle hole-shaped opening. The nozzle side has a much faster flow rate than the throttle side, and negative pressure will be generated under the throttle side valve, often The rubber seal may come off. The operating torque of the butterfly valve varies depending on the opening degree and the opening and closing direction of the valve. Horizontal butterfly valves, especially large-diameter valves, due to the depth of water, the torque generated by the difference between the upper and lower heads of the valve shaft cannot be ignored. In addition, when an elbow is installed on the inlet side of the valve, a biased 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 the water flow torque.
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