Butterfly (English: the butterfly valve) Close (disc or disc) disc around the valve axis to achieve the opening and closing a valve in the pipe from the main cut and throttle use. Butterfly valve, opening and closing parts of a disc-shaped disc in the valve body around its own axis of rotation, so as to achieve the purpose of opening and closing or regulation. Butterfly valve fully open to fully closed is usually less than 90 °, butterfly valves and butterfly rod itself is not self-locking capability for positioning of the disc, install worm gear on the stem. Worm gear reducer, not only can make the disc capable of self-locking, stop in any position, but also to improve the operational performance of the valve disc. 
 Characteristics of industrial butterfly valves to high temperature, the applicable pressure range is also high, the valve nominal diameter, the body uses carbon steel, the valve plate seal with a metal ring instead of the rubber ring. Large-scale high-temperature butterfly valve with welded steel plate manufacturing, mainly for medium heat, smoke duct and gas pipelines. 
 In the 1930s, the United States invented the butterfly valve, the 1950s brought to Japan to 60 years in Japan, commonly used in China to promote 1970s. The world in general butterfly valve DN300 mm or more gradually replace the gate valve. Butterfly valves and gate valves compared to the opening and closing time is short and small installation space is small and light weight, the operating torque. To DN1000, for example, about 2T butterfly valve, gate valve about 3.5T, and the butterfly valve with a variety of drive combinations, with good durability and reliability. 
 The rubber seal butterfly valves drawback is that for throttle use, improper use will produce cavitation, so that rubber seat spalling, damage from happening. To this end, the international development of metal sealing butterfly valve, the cavitation area decreases in recent years, China has also developed metal sealing butterfly valve, in Japan in recent years has also developed resistance to cavitation, low vibration, low noise of the comb-shaped butterfly valves. 
 Generally the life of the seal seat in normal circumstances, 15 years -20 years of rubber, metal 80 years -90 years. But how the correct selection will have under the conditions required. 
 Butterfly valve opening degree of the relationship between the flow essentially linearly proportional to the change. Used to control the traffic flow characteristics and piping flow resistance is also closely related, such as two pipe install the valve size, form, etc. All the same, while the pipe loss coefficient, the valve flow difference will be great. 
 If the valve is throttling a significant reduction in state, the back of the valve plate prone to cavitation damage to the valve, generally at 15 °. 
 Butterfly valve in the opening shape of the valve shaft as the center, on both sides of the formation of complete different states along the flowing direction of the side of the disc front moving in the opening, body and disc front-end formation, the other side of the counter-current water direction moving the side of the body and the valve plate formed similar to the nozzle-shaped opening, the other side of a similar orifice shaped openings of the nozzle side flow faster than the throttle side more throttle side of the valve below the negative pressure , will always be a rubber seal off. 
 Butterfly valve operating torque, its value due to the opening and valve closing direction different horizontal butterfly valve, especially the large-diameter valve, the torque generated by the water depth, the valve shaft, the water head difference can not be ignored. In addition, the valve inlet side of the device elbow to form a bias current, the torque will be increased. When the valve is in the middle of the opening, due to the water flow of torque to work, the operating mechanism requires a self-locking. 
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