The different structure of butterfly valve distinguishes four types of butterfly valves, namely: concentric butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve. What is this concept of eccentricity? How to decide when to use concentric butterfly valve, when to use single eccentric butterfly valve, when to use double eccentric butterfly valve and three eccentric butterfly valve? Many customers are not particularly clear. We might as well share it together.
Concentric butterfly valves, single eccentric butterfly valves, double eccentric butterfly valves and triple eccentric butterfly valves reflect a process of opening and closing with less and less effort, and the sealing surface wear is getting smaller and smaller. The sealing and opening state of the butterfly valve is changed by setting the position of the rotating axis of the butterfly valve plate. Under the same conditions, the valve is subjected to a larger torque than one at each opening degree. The turning angle required to disengage the valve plate from the seal when the valve is opened is smaller one than the other.
The structural feature of concentric butterfly valve is that the stem axis center, butterfly plate center, and valve body center are in the same position. In general, in principle, concentric butterfly valves are used as much as possible when they can be used. Because concentric butterfly valves are not required to be highly sealed either structurally or operationally, they are conventional products. In order to overcome extrusion, scraping, and ensure sealing performance, the seat of concentric butterfly valve basically adopts elastic materials such as rubber or PTFE, and is a soft seal butterfly valve. This makes the concentric butterfly valve restricted in use by the temperature. In order to solve the problem of extrusion of butterfly plate and seat of concentric butterfly valve, single eccentric butterfly valve is also produced. Its structural feature is that the stem axis is off the center of the butterfly plate.
The double eccentric butterfly valve is the most widely used. Its structural feature is that the stem axis is off from both the center of the butterfly plate and the center of the valve body. It is called double eccentric butterfly valve because of the two eccentric positions. Many of the double eccentric butterfly valves have a linear seal, which produces friction between the disc and the valve seat when closing the sealing surface, and the sealing effect is very good. It has the characteristics of small area and large pressure. After the valve is opened, the butterfly plate can be quickly disengaged from the valve seat, which greatly eliminates the unnecessary excessive extrusion and scraping between the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves the life of the valve seat.
Triple eccentric butterfly valve has a third eccentric on the basis of double eccentric butterfly valve, and the shape of the sealing sub is not positive cone, but oblique cone. It is mostly short distance force and face seal. The stem shaft of the triple eccentric butterfly valve is a three-section shaft structure, and the two shaft sections of this three-section shaft are concentric, while the center section shaft centerline deviates from the two end axes by a center distance, and the butterfly plate is mounted on the middle shaft section. Such an eccentric structure makes the butterfly plate become double eccentric in the fully open position and single eccentric when the plate is rotated to the closed position. Due to the eccentric shaft, the butterfly plate moves into the sealing cone of the valve seat at a distance when it is close to closing, and the sealing surface of the butterfly plate and the valve seat seal coincide to achieve reliable sealing performance. It makes up for the contradiction that the hard seal is poorly sealed and the soft seal is good but not resistant to high temperature.
When to use concentric butterfly valve, when to choose double eccentric butterfly valve or triple eccentric butterfly valve, it mainly depends on the working condition and budget.