The difference in the structure of the 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 the concept of this 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 triple eccentric butterfly valve? Many users are not particularly clear. Let’s learn together.
Concentric butterfly valves, single eccentric butterfly valves, double eccentric butterfly valves and triple eccentric butterfly valves actually reflect a process of opening and closing with less and less effort and less and less wear on the sealing surface. By setting the position of the rotating shaft of the butterfly valve plate, the sealing and opening states of the butterfly valve can be changed. Under the same conditions, the torque of the valve when opening is increasing in sequence. When the valve is opened, the rotation angle required for the valve plate to separate from the seal is smaller in sequence.
The structural feature of the concentric butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate and the center of the valve body are at the same position. Generally speaking, if concentric butterfly valves can be used, it should be used as much as possible. Because concentric type does not require high sealing performance in terms of structure or operation, it is a conventional product. In order to overcome extrusion, scraping, and ensure sealing performance, the valve seat of the concentric butterfly valve is basically made of rubber or PTFE and other elastic materials, which is a soft sealing butterfly valve. This makes the use of concentric butterfly valves subject to temperature limitations. In order to solve the extrusion problem of the butterfly plate and the valve seat, a single eccentric butterfly valve was invented. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate.
Double eccentric butterfly valve is the most widely used. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate and the center of the valve body. It deviates from the two center positions, so it is called double eccentric butterfly valve. Many of them are line sealed. When the sealing surface is closed, there is friction between the disc plate and the valve seat, and the sealing effect is very good. It has the characteristics of small area and strong pressure. After the valve is opened, the butterfly plate can immediately break away from the valve seat, which greatly eliminates unnecessary excessive extrusion and scraping between the plate and seat, reduces the opening resistance distance, wear, and improves the service life of the valve seat.
The triple eccentric butterfly valve has a third eccentricity on the basis of the double eccentric butterfly valve. The shape of the sealing pair is not a positive cone, but an oblique cone. Most of them are short distance force and surface seal. The stem shaft of the triple eccentric butterfly valve is a three-section shaft structure. The two shaft sections of the three-section shaft valve stem are concentric, and the centerline of the center section shaft deviates from the axis of the two ends by a center distance, and the butterfly plate is installed in the middle. on the shaft. Such an eccentric structure makes the butterfly plate a double eccentric shape when it is fully open, and a single eccentric shape when the butterfly plate turns to the closed position. Due to the effect of the eccentric shaft, when it is close to closing, the butterfly plate moves a distance into the sealing cone surface of the valve seat, and the butterfly plate matches the sealing surface of the valve seat to achieve reliable sealing performance. It makes up for the contradiction that the hard seal has a poor seal, and the soft seal has a good sealing effect but is not resistant to high temperature.
When to use a concentric butterfly valve, when to choose a double eccentric butterfly valve or a triple eccentric butterfly valve, mainly depends on the working conditions and budget.
Post time: Nov-28-2022