In the 30 's, the United States invented the butterfly valve, introduced to Japan in the 50, to the 60 to be widely used in Japan, and the promotion in China is the 70. The main features of the butterfly valve are: Small operating torque, small installation space and light weight. Take DN1000 for example, butterfly valve about 2T, and gate valve about 3.5T, and butterfly valve with a variety of drive device combination, have good durability and reliability. Rubber seal Butterfly Valve is the disadvantage of throttling use, due to improper use will produce cavitation, rubber block spalling, damage and so on, so how to choose the right according to the working conditions. The relationship between the opening of the butterfly valve and the flow rate is basically a linear proportional change. If used to control flow, its flow characteristics and piping flow resistance also have a close relationship, such as two pipe installation valve diameter, form and so the same, and the loss coefficient of the pipeline, valve flow difference will be very large.
If the valve is in a large throttle range, the back of the valve plate is prone to cavitation, there is damage to the valve may, generally used outside the 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 axis. The two sides form the completion of different states, one side of the butterfly plate front of the flow direction and move, the other side of the countercurrent water direction, therefore, one side of the valve body and the valve plate formed like nozzle-shaped openings, the other side similar throttle hole-shaped openings, Nozzle side than the throttle side of the flow of more quickly, and the throttle side of the valve will produce negative pressure, often appear rubber seals off. Butterfly valve operating torque, due to open and valve opening and closing direction of different values, horizontal butterfly valve, especially large diameter valve, due to water depth, valve shaft, water head difference of the torque generated can not be neglected. In addition, the valve inlet side device elbow, the formation of drift, torque will be increased. When the valve is in the middle opening, the operating mechanism needs self-locking because of the effect of the flow torque.
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