Butterfly valve, also known as butterfly valve, is designed based on the free rotation of butterflies dancing in the wind. The core component, the valve disc, is disc-shaped and rotates around an axis inside the valve seat. By rotating the angle, the opening degree of the valve can be controlled, thereby achieving the function of fluid control.

Detailed structure of butterfly valve

The structure of a butterfly valve mainly includes the valve body, valve disc (or living body), valve shaft, bearings, sealing device, operating mechanism, and some ancillary components. Among them, the valve disc is the core component of the butterfly valve, and its disc-shaped design rotates around an axis inside the valve seat, controlling the opening degree of the valve through the rotation angle. In addition, it also includes some auxiliary components such as bearings and sealing devices to ensure the smooth operation of the butterfly valve and the accuracy of fluid control.

Structural form of butterfly valve

There are various structural forms of butterfly valves, depending on their application scenarios and design requirements. But overall, its core structure includes key components such as valve body, valve disc, valve shaft, etc. Through the clever combination and synergistic effect of these components, the purpose of fluid control is achieved. In addition, depending on different usage conditions, butterfly valves may also be equipped with various auxiliary components such as bearings, sealing devices, and operating mechanisms to ensure their stable and reliable operation.

Working principle of butterfly valve

Butterfly valves drive the disc to open and close by rotating the valve stem. In the valve body of the butterfly valve, there is a cylindrical channel where the disc-shaped butterfly plate rotates around the axis. This rotation action is mainly used to adjust the flow rate. When the butterfly plate rotates to 90 °, the valve will be fully opened. Meanwhile, by changing the angle of the butterfly plate, the flow rate of the medium can be precisely adjusted. Butterfly valves are usually installed in the diameter direction of pipelines. It is worth noting that butterfly valves and valve stems themselves do not have locking functions. In order to regulate flow more effectively, worm gear reducers are usually equipped. This not only enhances the self-locking ability of the butterfly valve, but also improves its operational performance and more accurately controls the medium flow rate.

When the butterfly valve is fully open, the flow resistance is relatively small. Within the opening range of approximately 15 ° to 70 °, it can achieve sensitive flow control, making it widely used in the field of large-diameter regulation. Due to the wiping nature of its butterfly plate movement, butterfly valves are particularly suitable for media with suspended solid particles. At the same time, depending on the strength of the seal, it can also be used for powder and granular media.

2. Butterfly valves are mainly used for flow regulation. However, it should be noted that since the pressure loss of butterfly valves in pipelines is about three times that of gate valves, the pipeline system's ability to withstand pressure loss must be fully considered when selecting. At the same time, it is necessary to consider the strength of the butterfly plate to withstand the pressure of the pipeline medium when closed, as well as the working temperature limit of the elastic valve seat material at high temperatures.

Butterfly valves have the characteristics of compact structure, small overall height, fast opening and closing speed, and good fluid control characteristics, making them particularly suitable for making large-diameter valves. When used for flow control, it is crucial to choose the appropriate specifications and types to ensure that it can work efficiently and appropriately.

Next, we will delve into the classification of butterfly valves.

1. Concentric butterfly valve

The characteristic of a concentric butterfly valve is that its stem axis, butterfly plate center, and body center are all in the same position. This structure enables butterfly valves to operate more flexibly, while also ensuring the smoothness of fluid flow through the valve.

Concentric butterfly valves are not only structurally simple and easy to manufacture, but also widely used in practical production, especially rubber lined butterfly valves, which are deeply loved by users. However, this butterfly valve also has certain shortcomings. Due to the constant squeezing and scraping between the butterfly plate and the valve seat, the resistance distance increases and the wear rate accelerates. To overcome this drawback and ensure good sealing performance, valve seats are usually made of elastic materials such as rubber or polytetrafluoroethylene. But these materials are limited by temperature during use, which to some extent affects the high temperature resistance of butterfly valves.

2. Single eccentric butterfly valve

In order to solve the problem of mutual compression between the butterfly plate and the valve seat in concentric butterfly valves, engineers designed a single eccentric butterfly valve. The uniqueness of this butterfly valve lies in the offset between its stem axis and the center of the butterfly plate, which means that the upper and lower ends of the butterfly plate no longer serve as the axis of rotation, effectively dispersing and reducing excessive compression between the upper and lower ends of the butterfly plate and the valve seat.

However, although the design of the single eccentric butterfly valve can reduce the compression between the butterfly plate and the valve seat, the scraping phenomenon between the butterfly plate and the valve seat still exists throughout the entire process of valve opening and closing. In addition, its application scope is similar to that of concentric butterfly valves, so it is not widely used in practical applications.

Next, we will take a detailed look at the structural characteristics of a single eccentric butterfly valve.

The structural feature of a single eccentric butterfly valve is that the center of rotation of its disc plate, i.e. the center of the valve shaft, is located on the centerline of the valve body and forms an A-size offset with the sealing section of the valve plate. This design allows the valve plate to perform soft sealing appropriately even when the relative sealing surface deviates by a distance.

When the valve is closed, the valve seat and the sealing surface of the valve plate are in a relatively interference fit contact state. The achievement of sealing mainly relies on compressing the sealing ring, causing it to expand in the peripheral direction to generate sealing pressure, and combined with the force of pipeline pressure on the valve plate, to jointly achieve the sealing effect. However, please note that this design can only achieve one-way sealing.

During the valve opening process, the contact surface between the valve plate and the valve seat will gradually detach, with one side completely detached and the other side always maintaining two-point contact along the axial direction of the half circumference. This opening and closing method can easily lead to repeated wear of the sealing ring, thereby affecting the sealing performance, and metal sealing is even more difficult to achieve.

From a geometric perspective, it can be seen that in a single eccentric butterfly valve, the X dimension actually does not exist, but rather there is a certain degree of interference. This is in stark contrast to the design of the double eccentric butterfly valve.

Next, we will delve into the structural characteristics of the double eccentric butterfly valve. The double eccentric butterfly valve is further optimized based on the single eccentric butterfly valve and has become the most widely used type of butterfly valve. Its uniqueness lies in the offset of dimension A formed by the rotation center of the valve plate and the sealing section of the valve plate, as well as the offset of dimension B formed by the center of the valve body. This dual bias design has significantly improved the performance and applicability of the double eccentric butterfly valve.

Its structural feature is that the axis of the valve stem deviates from both the center of the butterfly plate and the center of the valve body, forming a double eccentric design. This feature enables the butterfly plate to quickly detach from the valve seat when the valve is opened, significantly reducing unnecessary excessive compression and scratching, thereby reducing opening resistance, wear, and extending the service life of the valve seat. In addition, the double eccentric butterfly valve also adopts a metal valve seat, further expanding its application range in high temperature environments.

Next, let's learn about the sealing principle of the double eccentric butterfly valve. Its sealing structure is based on positional sealing, that is, a line contact is formed between the butterfly plate and the valve seat. When the butterfly plate presses against the valve seat, it will undergo elastic deformation, thereby forming a sealing effect. However, it should be noted that this sealing method has very strict requirements for the closed position, especially for metal valve seats, which have relatively low pressure bearing capacity. This is also one of the traditional reasons why butterfly valves are not resistant to high pressure and have a large leakage rate.

triple eccentric butterfly valve

The three eccentric butterfly valve has a certain degree of high temperature resistance in design, thanks to its specific structure. However, in order to achieve zero leakage, soft sealing technology is usually required, and soft sealing technology often performs poorly in high temperature environments, so the application of triple eccentric butterfly valves in high temperature environments is limited to some extent.

The structural feature of the three eccentric butterfly valve lies in its unique eccentric design. Firstly, the center of rotation of the valve plate forms an A-offset with the sealing section of the valve plate, while forming a B-offset with the center of the valve body. In addition, an angle deviation of β is formed between the centerline of the valve body sealing surface and the centerline of the valve seat. This structural design aims to solve the leakage problem of double eccentric butterfly valves in high temperature environments. By introducing the third eccentricity, which further offsets the valve stem axis on the basis of double eccentricity, and deflects the conical axis of the butterfly plate sealing surface from the cylindrical axis of the body, the sealing section of the butterfly plate becomes elliptical, and its sealing surface shape also becomes asymmetric. This design enables the three eccentric butterfly valve to fundamentally change its sealing structure, shifting from position sealing to torque sealing, relying on the contact surface pressure of the valve seat rather than elastic deformation to achieve sealing effect.