Like ball valves, butterfly valves need to solve several problems. In addition to the small floor area, the butterfly valve can also perform rapid opening and closing operations through pneumatic control. As a closing element, the ball of the valve is lighter than that of the closing element of the ball valve of the same size, and the butterfly valve requires less structural support. Butterfly valve has a highly sensitive structure, which is essential for modern applications. Because of their rugged structure, they require little maintenance. There are two types of butterfly valves: eccentric and concentric. The eccentricity type can be single offset, double offset or three offset types (single offset, double offset and three offset types). The types most needed in the business world are double offset and three offset types. These two subcategories of valves are also known as elite butterfly valves. Unfortunately, both kinds of production are carried out in the Turkish market. What are the differences? According to which criteria should we choose? In fact, let’s first look at the technical features that distinguish them. In the general application of concentric butterfly valve type, it is common in industry, especially in concentric market. This butterfly valve is also called standard type.
The shaft is located in the middle of the butterfly plate. During opening and closing, only a part of the disc / disc contacts or rubs with the seal. This behavior will cause the clapper to make a harsh noise during each opening and closing operation. Therefore, concentric butterfly valves are limited to pressure class ANSI150 (PN20). Advantages of double eccentric butterfly valve: in double eccentric butterfly valve, the shaft will not pass through the center of the valve in principle. It’s in the back. In fact, given the meaning of the word offset, the reference point distance can be given. Here, the shaft passes through the valve again, but this time it is behind. This balance provides a firm seal. The second balance prevents the valve from contacting the seal when the valve is fully open. Different from the ordinary concentric valve, this design reduces the wear of the gasket and prolongs the service life of the valve. In general applications, these two-stage balanced butterfly valves are limited to ANSI600 (PN100) pressure rating. Advantages of triple eccentric butterfly valve: triple eccentric butterfly valve is used in applications where complete sealing is crucial. For the double offset type, this air tightness cannot be achieved in some applications. Conventional butterfly valves can not solve the liquid containing tough chemicals or particles, which will damage the valve. In such applications, triple eccentric butterfly valves are tailored for large-scale applications. The triple eccentric butterfly valve is an improved design with three balance difference comparison valves and concentric butterfly valves. Similar to the double offset, it has 2 balances and the third balance weight has an additional balance offset of the funnel seat. This conical seal is fully compatible with the plug and is designed to match the seal. Due to this design, the seal will not be subject to any wear or friction during operation. This design is also better than double eccentric butterfly valve. This will provide advantages and long life for heavy-duty applications; It forms a low pressure zone (cavitation) and provides the best sealing.
Difference between central butterfly valve and single, double and triple eccentric butterfly valve
What is the difference between central butterfly valve and single, double and triple eccentric butterfly valve? Here is a detailed explanation of the difference between the central butterfly valve and the single, double and triple offset butterfly valves:
Center butterfly valve
The structural feature of the center butterfly valve is that the valve stem axis, the center of the butterfly plate and the center of the body are in the same position. The utility model has the advantages of simple structure and convenient manufacture. Common rubber lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and valve seat are always in the state of extrusion and scraping, large resistance distance and fast wear. In order to overcome extrusion, scraping and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or polytetrafluoroethylene, but its use is limited by temperature. This is why people traditionally think that the butterfly valve is not resistant to high temperature.
Single eccentric butterfly valve
In order to solve the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve is produced. Its structural feature is that the valve stem axis deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotation axis, disperse and reduce the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, due to the single eccentric structure in the whole opening and closing process of the valve, the scraping phenomenon between the butterfly plate and the valve seat has not disappeared, and the application range is similar to that of the concentric butterfly valve, so it is rarely used.
Double eccentric butterfly valve
Based on the single eccentric butterfly valve, the double eccentric butterfly valve which is widely used at present is further improved. The utility model is characterized in that the axis of the valve rod deviates from both the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to quickly separate from the valve seat after the valve is opened, greatly eliminates the unnecessary excessive extrusion and scraping between the butterfly plate and the valve seat, reduces the opening resistance, reduces the wear and improves the service life of the valve seat. At the same time, the double eccentric butterfly valve can also adopt metal seat, which improves the application of butterfly valve in high temperature field. However, because its sealing principle belongs to the position sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, and the sealing effect is produced by the elastic deformation caused by the extrusion of the valve seat through the butterfly plate. Therefore, it has high requirements for the closing position (especially the metal valve seat) and low pressure bearing capacity. This is why people traditionally think that the butterfly valve is not resistant to high pressure and has large leakage.
Triple eccentric butterfly valve
High temperature resistance, hard sealing and large leakage; Zero leakage, soft seal, but not resistant to high temperature. In order to overcome the contradiction of double eccentric butterfly valve, the butterfly valve is eccentric for the third time. The utility model is characterized in that the conical axis of the sealing surface of the butterfly plate deviates from the cylindrical axis of the body while the double eccentric valve rod axis position is eccentric, that is, after the third eccentricity, the sealing section of the butterfly plate is no longer true circle, but ellipse, and the shape of the sealing surface is asymmetric, one side is inclined to the centerline of the body and the other side is parallel to the centerline of the body.
The characteristic of this third eccentricity is that it fundamentally changes the sealing structure, no longer position sealing, but torque sealing, that is, it does not rely on the elastic deformation of the valve seat, but on the contact surface pressure of the valve seat to achieve the sealing effect. Therefore, the problem of zero leakage of the metal valve seat is solved in one fell swoop. Because the contact surface pressure is directly proportional to the medium pressure, it can withstand high pressure and high temperature
Purpose of concentric butterfly valve/center butterfly valve
Concentric butterfly valves are used for water and wastewater treatment plants, fire protection systems and natural gas supply.
Fire protection (indoor / outdoor)
Natural gas and flare gas
China concentric butterfly valve manufacturer www.sfutube.com supplies concentric butterfly valves for industrial use, in kinds of materials such as carbon steel, stainless steel, alloy steel, etc.