Firstly, sanitary butterfly valve flow is approximately linear. The difference between a neutral butterfly valve and an eccentric butterfly valve is not large. Centerline butterfly valve is suitable as a control valve and small-caliber process valve.
Secondly, both the double eccentric butterfly valve and the triple eccentric butterfly valve can realize quick separation, and the more closed they are, the tighter they will be. So how can we make a choice between them? A soft seal butterfly valve usually suits double eccentric butterfly valve. It is convenient in processing and manufacturing. However, triple eccentric butterfly valve involves a more complex procedure. But the character of close-tight is more prominent, as well as the uneasiness to be interfered with. As a result, it is appropriate to apply metal seal. There is currently no comprehensive analysis on the market. Some people think that no matter what the circumstances, it is recommended to use three eccentric metal seal, which is not correct. In particular, it is not advisable to recommend use of large-diameter, normal-temperature water systems because it is much more difficult to replace a metal seal than a soft seal. Therefore, large-diameter water system used in normal temperature butterfly valve should be soft seal. But it is the last retort to use the hard seal when the conditions are harsh such as inconvenience for maintenance and replacement, or high temperature. In order to facilitate the replacement of metal seals in harsh conditions, the valve body can generally be extended for some length, and opened a central opening so that it becomes easier to uninstall.
Thirdly, the choice of vacuum butterfly valve will be discussed. Vacuum butterfly valve is divided into soft rubber seal and metal seal. Structurally, they can be neutral, eccentric, and leveraged. For the case of high vacuum requirements, the general choice is soft seal. Requiring a certain temperature, we have to use metal seal. In order to obtain good results, the surfaces should be processed to gain suitable roughness and cleanliness. Its surface should not be painted, nor can it be coated with general anti-rust oil. Only vacuum grease is allowed.
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