The high performance butterfly valves are simple, it is small and lightweight, and its installed size is small too. Butterfly valves can fast switching, and it can 90 ° back and forth rotation, its drive torque is small. What's more, it has the good flowing-control function and seal-off characteristics at the same time. In the occasions with large and medium caliber as well as low and middle pressure, butterfly valves are the dominant forms in valves. When butterfly valve is fully opening, the thickness of butterfly-board is only resistance when the medium is flowing through the valve, so the resistance generated by this valve is small, so it has the good flowing-control characteristics. In the aspect of sealed type, it can be divided into two types, namely, the elastic sealed type and metal sealed type. The seal on elastic sealed butterfly valve can be inserted on the valve or attached around the butterfly-board. The service life of metal sealed valve is generally longer than that of the elastic sealed valve, but metal sealed valve is difficult to be completely sealed. Metal sealed valve can adapt to the situation with relatively higher temperature, while the elastic sealed valve is affected by the temperature limit. If PTFE butterfly valves are required to be the flowing-controller, the key is to correctly choose the size and type of butterfly valves. The structural principle of butterfly valves is particularly applied to make the large-diameter valves. Butterfly valves can not only be widely used in oil, gas, chemical, water processed and other general industries, they can be also applied in the cooling water system of the thermal power plant. The commonly-used butterfly valves have two kinds, namely, wafer butterfly valve and flanged butterfly valve. The wafer butterfly valve is to use the stubs to connect the valve between the flanges of two pipelines. The flanged butterfly valve is the valve with flange, it is using stubs to connect the flanges on the two sides of the valve to the flange on the pipeline. With the applications of the anti-corrosive synthetic rubber and wafer type butterfly valve, the performance of butterfly valve can thus be enhanced, and it can fulfill the different working conditions. In the recent decade, metal sealed butterfly valve has gotten rapidly development. With the applications of high-temperature-proof, low-temperature-proof, corrosion-proof, erosion-proof and high-strength alloys in the butterfly valve, metal sealed butterfly valves are thereby widely used in the high-temperature, low-temperature, strong erosion and other working conditions, and butterfly valves are partially replaced globe valves, gate valves and ball valves. Butterfly valves can transport mud, and it will accumulate the least liquid in the pipe outlet. When it is under the low pressure, it can achieve the good sealed performance.
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