There are many types of butterfly valves. If it is divided from the point of view of sealing form, it can be mainly divided into the following three types
1. Center seal butterfly valve (concentric butterfly valve, center line butterfly valve)
Structure features: the stem axis, the center of the butterfly plate and the center of the body are in the same position, simple structure and convenient manufacturing.
Sealing principle: Soft seal is generally used, the sealing surface of the disc and the seat is in contact with the surface or the line, and the sealing effect is generated by the elastic deformation caused by the disc squeezing the seat.
Advantages and disadvantages: Because the disc and the seat are always in the state of squeezing and scraping, the resistance is large and the wear is fast. In order to overcome extrusion, scratching, and ensure sealing performance, the valve seat is basically made of rubber or polytetrafluoroethylene and other elastic materials, but it is also limited by temperature in use.
Second, single eccentric butterfly valve
Structural features: the stem axis deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate are no longer the rotating axis, disperses and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the seat.
Sealing principle: Similar to the center seal butterfly valve, but the single eccentric design helps to reduce the scratch of the disc and the seat.
Advantages and disadvantages: Although the single eccentric structure improves the shortcomings of the concentric butterfly valve to a certain extent, the scratching phenomenon of the butterfly plate and the valve seat has not completely disappeared during the whole switching process of the valve, so its application scope is similar to the concentric butterfly valve and has not been widely used.
Three, double eccentric butterfly valve
Structural features: the stem axis deviates from the center of the butterfly plate and from the center of the body. This double eccentric design allows the disc to release from the seat immediately after the valve is opened.
Sealing principle: the sealing surface of the disc and the seat is in line contact, and the elastic deformation caused by the disc squeezing the seat produces a sealing effect. Due to the effect of double eccentricity, the unnecessary excessive extrusion and scratching between the disc and the seat are greatly eliminated, the opening resistance is reduced, the wear is reduced, and the life of the seat is improved.
Advantages and disadvantages: Double eccentric butterfly valve is the most widely used butterfly valve type. Its advantages are good sealing performance, small operating torque, wear resistance, long service life and so on. At the same time, due to the significant reduction of scratching, double eccentric butterfly valves can also use metal seats, which improves the application range of butterfly valves in high temperature fields. However, it should be noted that the double eccentric butterfly valve has high requirements for the closing position, especially the metal seat, which has a relatively low pressure capacity.
In addition, butterfly valves can also be classified according to the connection method (such as clamping, flange, welding, etc.), driving method (such as electric, pneumatic, hydraulic, manual, etc.), sealing surface material (such as soft seal, hard seal, etc.) and working pressure and working temperature. Different types of butterfly valves have different characteristics and scope of application, and users can choose according to specific needs.