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Butterfly valve features and use of small knowledge
In the 1930s, the United States introduced the butterfly valve, which was later brought to Japan in the 1950s. However, it wasn't widely adopted in Japan until the 1960s. In our country, the promotion of butterfly valves began in the 1970s. Today, butterfly valves with a nominal diameter of DN300 mm and above have gradually replaced gate valves globally. Compared to gate valves, butterfly valves offer faster opening and closing times, require less installation space, and are lighter in weight. For example, a DN1000 butterfly valve weighs approximately 2 tons, while a corresponding gate valve weighs around 3.5 tons. Additionally, butterfly valves can easily be combined with various actuation devices, offering good durability and reliability.
One drawback of rubber-sealed butterfly valves is that when used for throttling, cavitation may occur due to improper operation, leading to damage or peeling of the rubber seat. To address this issue, international development has focused on metal-sealed butterfly valves, which have significantly reduced cavitation in recent years. In China, metal-sealed butterfly valves have also been developed, along with cavitation-resistant, low-vibration, and low-noise comb-shaped butterfly valves. Under normal conditions, the service life of a rubber seal is typically 15 to 20 years, whereas a metal seal can last 80 to 90 years. Choosing the right type depends on the specific working conditions.
The relationship between the opening of a butterfly valve and the flow is generally linear. If used for flow control, the flow characteristics are closely related to the resistance in the pipeline. For instance, even if two pipes have the same valve size and configuration, differences in the pipe loss coefficient can lead to significant variations in flow through the valve.
When the valve is in a partially open position, cavitation is more likely to occur on the back side of the disc, increasing the risk of damage. Therefore, butterfly valves are typically not used beyond a 15° opening. When fully open, the shape of the opening formed by the valve body and the front edge of the disc is centered on the shaft. One side of the disc moves with the flow, while the other side is against it, creating a nozzle-like opening on one side and an orifice-like opening on the other. The flow rate through the nozzle is higher than that through the orifice, and the throttling side may experience negative pressure, which can cause the rubber seal to detach.
The operating torque of a butterfly valve varies depending on the direction of opening and closing. For horizontal butterfly valves, especially large-diameter ones, the depth of the shaft can create a significant difference in torque due to head pressure. Additionally, if there is an elbow near the valve inlet, it can cause uneven flow, increasing the torque required. When the valve is in the middle of its opening, the water flow exerts a torque on the disc, so the operating mechanism must have self-locking capability to prevent unintended movement.