The butterfly valve is also called the butterfly valve. As the name implies, its key components are like a butterfly facing the wind and turning freely. The disc of a butterfly valve is a disc, which rotates around an axis in the valve seat. The size of the rotation angle is the opening and closing degree of the valve.
The structure of the butterfly valve
A butterfly valve is mainly composed of a valve body, living body, valve shaft, bearing, sealing device, operating mechanism, and accessory parts.\
The working principle of the butterfly valve
DIN butterfly valve is a valve that opens and closes according to the rotation of the valve stem while driving the disc plate to rotate. In the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, mainly the rotating disc plate. 90° is used for flow control. When the disc reaches 90°, the valve is fully open. At the same time, the angle of the disc can be changed to adjust the flow of the medium. It is generally installed in the diameter direction of the pipe. The butterfly valve and the valve stem have no locking ability. In order to effectively adjust the flow, a worm gear reducer is required. The butterfly valve with a worm gear reducer not only makes the butterfly valve self-locking but also changes the operating performance of the butterfly valve and adjusts the medium flow more accurately.
1. The butterfly valve has small flow resistance when it is fully opened. When the opening is between about 15° and 70°, it can perform sensitive flow control. Therefore, the application of butterfly valves is very common in the field of large-diameter adjustment. 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. Depending on the strength of the seal, it can also be used for powder and granular media.
2. The butterfly valve is suitable for flow adjustment. Since the pressure loss of the butterfly valve in the pipe is relatively large, about three times that of the gate valve when selecting the butterfly valve, the influence of the pressure loss of the pipeline system should be fully considered, and the strength of the butterfly plate withstand the pressure of the pipeline medium when it is closed should also be considered. In addition, it is necessary to consider the limitation of the working temperature of the elastic valve seat material at high temperatures.
3. The structural length and overall height of the butterfly valve are small, the opening and closing speed is fast, and it has good fluid control characteristics. The structural principle of the butterfly valve is most suitable for making large diameter valves. When a butterfly valve is required to control flow, the most important thing is to correctly select the specification and type of the butterfly valve so that it can work properly and effectively.
Din Butterfly Valve
Concentric butterfly valve The structural feature of this butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate, and the center of the body are in the same position.
The structure is simple and the manufacturing is convenient. Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of squeezing and scratching, large resistance distance, and fast wear. In order to overcome squeezing, scratching, and to ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but it is also subject to temperature restrictions in use. This is why traditionally people think that butterfly valves are not resistant to high temperatures. the reason.
The single eccentric butterfly valve solves the problem of the extrusion of the butterfly plate and the valve seat of the concentric butterfly valve, resulting in a single eccentric butterfly valve. Its structural feature is that the stem axis deviates from the center of the butterfly plate so that the lower end of the butterfly plate no longer becomes a rotation The axial center is dispersed, which reduces the excessive extrusion between the upper end of the butterfly plate and the valve seat.
However, because the single eccentric structure does not disappear from the scratching phenomenon of the butterfly plate and the valve seat during the entire switching process of the valve, and the application range is similar to that of the concentric butterfly valve, it is not used much.
2.1 Structural features of a single eccentric butterfly valve:
2.1.1 The center of rotation of the disc plate (that is, the center of the valve shaft) is located on the centerline of the valve body, and an A size 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.
2.1.2 When the valve is closed, the valve seat and the sealing surface of the valve plate are in a relatively interference contact state. To achieve the seal, it is mainly by pressing the sealing ring to expand in the peripheral direction to produce the sealing specific pressure and pipeline pressure against the valve plate. Force to make it sealed, so it can only be sealed in one direction
2.1.3 When the valve is opened, the contact side of the valve plate and the valve seat is separated from the valve seat, and the other side is always two-point contact along the axial direction of the half circumference. Repeated opening and closing of the sealing ring is easy to be damaged, affecting the sealing performance, and more It is impossible to achieve metal sealing.
2.1.4 From a geometric point of view, it is obvious that X does not exist in the above figure, and in turn, there is a certain amount of interference.
The double eccentric butterfly valve is further improved on the basis of the single eccentric butterfly valve, which is currently the most widely used double eccentric butterfly valve.
3.1. Structural features of the double eccentric butterfly valve:
The center of rotation of the valve plate (that is, the center of the valve shaft) forms an offset of dimension A on the sealing section of the valve plate and forms an offset of dimension B with the center of the valve body.
Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The life of the valve seat is improved. The scraping is greatly reduced, and at the same time, the double eccentric butterfly valve can also use a metal seat, which improves the application of the butterfly valve in the high-temperature field.
3.2 Sealing principle of a double eccentric butterfly valve
Because its sealing principle is a positional 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 the butterfly plate squeezing the valve seat produces a sealing effect, so the closing position is very demanding, especially for the metal valve seat. , Low-pressure bearing capacity, this is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.
The triple eccentric butterfly valve must be resistant to high temperatures and must use a hard seal, but the leakage is large and zero leakage must be used, but it is not resistant to high temperatures.
4.1. Structural features of triple eccentric butterfly valve:
The center of rotation of the valve plate (ie the center of the valve shaft) forms an offset A on the sealing section of the valve plate and an offset b with the center of the valve body; the centerline of the valve body sealing surface and the centerline of the valve seat (ie the centerline of the valve body) An angular offset of β is formed.
In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time. Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body, that is, after the third eccentricity, the sealing section of the butterfly plate is not Furthermore, it is a true circle, but an ellipse and its sealing surface shape is therefore asymmetrical, with one side inclined to the centerline of the body and the other side parallel to the centerline of the body.
The biggest feature of the triple eccentric butterfly valve is that the sealing structure is fundamentally changed. It is no longer a positional seal, but a torsion 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.
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