In the 1930s, the United States invented the butterfly valve and introduced it into Japan in the 1950s, it was widely used in Japan till 1960s. But butterfly valve was popularized in china after the 1970s. At present, butterfly valves whose size are over 300mm have gradually replaced the gate valve in the world. Compared with gate valves, butterfly valves have shorter opening and closing time, smaller installation space and lighter weight. Take DN1000 for example, the butterfly valve is about 2 tons, while the gate valve is about 3.5 tons. And the butterfly valve can combine with a variety of driving devices, which has good durability and reliability.
The disadvantage of rubber seal butterfly valve is that when it was used for throttling, the improper use can cause cavitation, which can make rubber peel off, damage, etc. Therefore, people have developed hard seal butterfly valves which can reduce the cavitation. Recent years, China has also developed metal seal butterfly valves, and Japan invented comb-shaped butterfly valves with cavitation resistance, low vibration and low noise.
Under normal circumstances, the service life of seal seat is 15-20 years for rubber, and 80-90 years for metal. But how to choose the right one should base on the requirement.
The opening degree and the flow rate of the butterfly valve has basically kept the linear relationship. The flow characteristic is also closely related to piping flow resistance, when it comes to flow control. If two pipes are installed with valves which have same diameter and form, and the pipeline loss coefficient is different, the flow of valves will be different.
If the valve is in a condition of a large throttle, the back of the valve plate is prone to cavitation, which can probably damage the valve, so it is often used over 15 degree.
When the butterfly valve had a moderate opening degree, the valve body and front end of the valve plate formed an opening which centered on valve shaft. The two sides would have different situations, the front end of the butterfly plate would move with the current, while the other side would move against the current. So one side of the valve body and the plate formed an opening with nozzle, another side formed an opening with throttle. The one with nozzle is faster than that of with throttle. But the one with throttle would have negative pressure, which would lead to falling off of the rubber seal.
Butterfly valve operating torque differs in the opening degree and directions of the opening and closing. For horizontal butterfly valve, especially large diameter valve, we can't ignore the torque from the head difference of upper and down of valve shaft due to the water depth. In addition, if we connect elbows with the inlet side of the valve, the torque would increase due to the bias flow. When the opening degree of the valve is moderate, the operating mechanism needs to be self-locking due to the torque of the water flow.
