The disadvantage of the rubber sealing butterfly valve is that when it is used for throttling, cavitation may occur due to improper use, and the rubber seat may be peeled off and damaged. To this end, the metal sealing butterfly valve has been developed internationally, and the cavitation zone has been reduced. In recent years, China has also developed a metal sealing butterfly valve. In recent years, a cam-shaped butterfly valve resistant to cavitation, low vibration and low noise has been developed in Japan. Generally, the life of the sealing seat is under normal conditions, rubber is 15-20 years, and metal is 80-90 years. However, how to choose correctly depends on the requirements of the working conditions. The relationship between the opening of the butterfly valve and the flow rate changes substantially linearly. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the piping. For example, the diameters and forms of the two pipe installation valves are all the same, and the pipe loss coefficient is different, and the valve flow difference is also large. If the valve is in a state of large throttle, the back of the valve plate is prone to cavitation and may damage the valve. Generally, it is used outside of 15°. When the butterfly valve is at the middle opening degree, the shape of the opening formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides are formed to complete different states. The front end of the butterfly plate moves along the water direction and the other side flows in the opposite direction. Therefore, one side valve body forms a nozzle-like opening with the valve plate, and the other side is similar to the orifice-shaped opening. The nozzle side has a much faster flow rate than the throttle side, and the negative pressure is generated under the throttle side valve. A rubber seal will come off.  The operating torque of the butterfly valve varies depending on the opening degree and the direction of opening and closing of the valve. Horizontal butterfly valves, especially large-diameter valves, cannot be ignored due to the water depth and the head difference between the valve shaft and the head. In addition, when the valve inlet side device is bent, a bias current is formed and the torque is increased. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the action of water flow torque. Zhengbang pump valve butterfly valve ordering instructions 1: Product model and name. 2 Nominal diameter (DN) 3. Rated flow coefficient KV 4. Nominal pressure and differential pressure 5. Valve body and valve component material 6. Flow characteristics 7. Applicable temperature is difficult 8 power supply voltage and control Signal 9 with accessory 10 using media composition