Butterfly (English: butterfly valve) is closed parts (valve or butterfly valve plate) for the disc, around the valve axis to achieve the opening and closing a valve, cut off from the main pipe and throttle use. Valve opening and closing parts of the butterfly is a disc-shaped plate, in the valve body around its own axis of rotation, so as to achieve the purpose of hoisting or regulation. Valve fully open to fully closed is usually less than 90 °, butterfly and butterfly rod itself is not self-locking capability, in order to position disc to install the valve stem worm reducer. The use of worm reducer, not only can make the disc with self-locking capability, the disc stopped at any position, but also to improve the operational performance of the valve. 
 Industry-specific characteristics of butterfly valves to high temperature, for higher pressure range, valves DN large carbon steel valve body, valve plates seal metal ring instead of the rubber ring. The use of large-scale high-temperature steel welding butterfly valve manufacturer, mainly for high-temperature medium duct smoke and gas pipelines. 
 30 years, the United States invented the butterfly, 50 years into Japan, the 1960s was widely used in Japan, and in the promotion of our country is what happened after the 1970s. The world in general DN300 mm butterfly valve has been gradually replaced. Compared with the butterfly valve opening and closing time is short, the operating torque, installation space is small and light weight. To DN1000, for example, butterfly about 2T, while the gate of about 3.5T, and the valve drive easily with a variety of combinations, with good durability and reliability. 
 Drawback is that rubber seal butterfly valve used for throttling, because improper use will produce cavitation, peeling off the rubber seat, damage from happening. To this end, we developed is now the international metal sealing butterfly valve, cavitation area decreases, in recent years, China has also developed a metal sealing butterfly valve, also developed in Japan in recent years, resistance to cavitation, low vibration, low noise, comb-shaped butterfly valve. 
 General life of the seal seat in normal circumstances, the rubber for 15 years -20 years -90 years, 80 years of metal. But how to properly use they should according to the conditions required. 
 Butterfly valve opening and the relationship between flow rate, essentially linearly proportional to the change. If used to control the flow, its flow characteristics and flow resistance of piping is also closely related, such as the installation of the valve bore two pipelines, all forms of the same, but different loss coefficient pipe, valves, flow difference will be great. 
 If the throttle valve in a significant reduction in the state, the valve plate on the back prone to cavitation, may damage the valve, generally used in a 15 ° outside. 
 Butterfly valve in the opening, the valve body and disc shape of the front-end to form an opening to the valve shaft as the center, on both sides to complete the formation of different states, the front side of the disc moving along the flow direction, the direction of the other side of the counter-current water The move, therefore, the side of the valve body and valve plate-shaped nozzle openings formed like the other side of the similar-shaped orifice opening, the nozzle side than the expenditure side of the flow much faster, and throttle valve below will produce negative side often there will be the rubber seals off. 
 Valve operating torque, due to open and close the valve opening and its value varies in different directions, horizontal butterfly valve, especially large-diameter valve, water depth, the valve shaft, the water head difference generated by the torque can not be ignored. In addition, the valve inlet side of the device when the elbow to form a bias current, torque will increase. Valve opening in the middle, because the water flow torque to work, organizations need to self-locking operation. 
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