Butterfly Valve Development and Application Introduction

One of the main drawbacks of rubber-seated butterfly valves is that they can experience cavitation when used for throttling, especially if not operated correctly. This can lead to damage or detachment of the rubber seat. To address this issue, metal-seated butterfly valves have been developed internationally, significantly reducing cavitation effects. In recent years, China has also introduced its own version of metal-seated butterfly valves. Additionally, Japan has developed a cam-shaped butterfly valve that is resistant to cavitation, vibration, and noise, making it more suitable for critical applications.

Under normal operating conditions, the service life of a rubber sealing seat typically ranges from 15 to 20 years, while a metal sealing seat can last between 80 to 90 years. However, the correct choice depends on the specific working conditions and requirements of the system in which the valve is installed.

The relationship between the opening angle of a butterfly valve and the flow rate is generally linear. When used for flow control, the valve's performance is closely related to the resistance in the piping system. For example, even if two valves are installed with the same diameter and design, differences in pipe loss coefficients can result in significant variations in flow characteristics.

If the valve is operated at a high degree of throttling, cavitation is more likely to occur on the backside of the disc, potentially causing damage. Therefore, it is generally recommended to operate the valve outside of the 15° range to avoid such issues.

At intermediate opening positions, the shape of the flow passage formed by the valve body and the disc is symmetrical around the shaft. One side of the disc moves with the water flow, while the other side flows in the opposite direction. This results in one side of the valve forming a nozzle-like opening, while the other resembles an orifice. The nozzle side experiences a much higher flow velocity, creating a low-pressure area on the throttling side, which can cause the rubber seal to come loose.

The operating torque of a butterfly valve varies depending on the opening position and the direction of operation. For horizontal butterfly valves, especially those with large diameters, the impact of water depth and pressure difference across the valve shaft should not be overlooked. Moreover, when there is a bend upstream of the valve, a cross-current may develop, increasing the required torque. At intermediate openings, the actuation mechanism must be self-locking to counteract the torque caused by the flowing medium.