Butterfly valve is also called butterfly valve. As its name suggests, its key components are like butterflies whirling freely in the wind. The disc of butterfly valve is a disc, which rotates around an axis in the valve seat. The rotation angle is the opening and closing degree of the valve.
01 structure of butterfly valve
Butterfly valve is mainly composed of valve body, body, valve shaft, bearing, sealing device, operating mechanism and auxiliary parts.
Structural form of butterfly valve:
02 working principle of butterfly valve
Butterfly valve is a kind of valve that can be opened and closed by rotating the valve stem and driving the disc plate to rotate at the same time. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, mainly rotating the disc plate 90 ° for flow control. When the disc plate reaches 90 °, the valve is fully open, and the angle of the disc plate can be changed to adjust the medium flow. It is generally installed in the diameter direction of the pipeline. The butterfly valve and valve stem have no locking ability. In order to effectively regulate the flow, a worm gear reducer needs to be installed. The butterfly valve with worm gear reducer not only has self-locking ability, but also can change the operating performance of the butterfly valve and more accurately regulate the medium flow.
1. When the butterfly valve is fully opened, it has small flow resistance. When the opening is about 15 ° ~ 70 °, it can carry out sensitive flow control. Therefore, the application of butterfly valve is very common in the field of large-diameter regulation. Since the movement of the butterfly plate of the butterfly valve is wiping, most butterfly valves can be used for media with suspended solid particles. According to the strength of the seal, it can also be used for powdery and granular media.
2. Butterfly valve is suitable for flow regulation. As the pressure loss of butterfly valve in the pipe is relatively large, which is about three times that of gate valve, when selecting butterfly valve, the influence of pressure loss on pipeline system should be fully considered, and the strength of butterfly plate bearing pipeline medium pressure when closing should also be considered. In addition, the working temperature limit of elastic seat material at high temperature must be considered.
3. The butterfly valve has small structural length and overall height, fast opening and closing speed, and good fluid control characteristics. The structural principle of butterfly valve is most suitable for making large-diameter valves. When the butterfly valve is required to be used for flow control, the most important thing is to correctly select the specification and type of butterfly valve so that it can work properly and effectively.
03 classification of butterfly valves
1. Concentric butterfly valve
Concentric butterfly valve the structural feature of this kind of butterfly valve is that the valve stem axis, butterfly plate center and body center 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.
2. Single eccentric butterfly valve
In order to solve the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve is produced. Its structural feature is that the axis of the valve stem 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 scope of application is similar to that of the concentric butterfly valve, so it is rarely used.
Structural features of single eccentric butterfly valve:
1. The rotation center of the disc plate (i.e. the center of the valve shaft) is located on the centerline of the valve body, and a dimension a offset is formed on the sealing section of the valve plate. The single eccentric butterfly valve is that the rotation center of the disc plate is on the centerline of the valve body, and the valve plate deviates a distance from the sealing surface, which is suitable for soft sealing.
2. When the valve is closed, the sealing surface of the valve seat and the valve plate is in the contact state of relative interference. In order to achieve the sealing, the sealing ring is mainly pressed to expand in the peripheral direction, resulting in the force of the sealing specific pressure and pipeline pressure on the valve plate, so it can only be sealed in one direction.
3. When the valve is opened, one side of the contact between the valve plate and the valve seat is separated from the valve seat, and the other side is always in two-point contact along the axial direction of the semicircle. Repeated opening and closing of the sealing ring is easy to be damaged, affecting the sealing performance, and it is impossible to realize metal sealing.
4. From the perspective of geometry, it is obvious that x in the above figure does not exist, and there is some interference on the contrary.
3. Double eccentric butterfly valve
The double eccentric butterfly valve is further improved and formed on the basis of the single eccentric butterfly valve, which is the most widely used double eccentric butterfly valve at present.
Structural features of double eccentric butterfly valve:
The rotation center of the valve plate (i.e. the center of the valve shaft) forms a dimension a offset from the sealing section of the valve plate and a dimension B offset from the center of the valve body.
The utility model is characterized in that the axis of the valve rod deviates from the center of the butterfly plate and the center of the body. The effect of double eccentricity enables the butterfly plate to leave the valve seat immediately 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.
Sealing principle of double eccentric butterfly valve
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 elastic deformation caused by squeezing the valve seat through the butterfly plate produces the sealing effect, it has high requirements for the closing position, especially the metal valve seat, with low pressure bearing capacity. This is why people traditionally think that the butterfly valve is not resistant to high pressure and has large leakage.
4. Triple eccentric butterfly valve
The triple eccentric butterfly valve must be resistant to high temperature and must use hard seal, but the leakage is large and must have zero leakage. It must use soft seal, but it is not resistant to high temperature.
Structural features of triple eccentric butterfly valve:
The rotation center of the valve plate (i.e. the center of the valve shaft) forms an a offset on the sealing section of the valve plate and a B offset with the center of the valve body; The center line of the sealing surface of the valve body forms an angle with the center line of the valve seat (i.e. the center line of the valve body) β Angular offset of.
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 is deflected 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 its 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 biggest feature of the three eccentric butterfly valve is that it fundamentally changes the sealing structure. It is no longer a position seal, but a torque seal, that is, it does not rely on the elastic deformation of the valve seat, but completely depends on the contact surface pressure of the valve seat to achieve the sealing effect.
