The disadvantage of the rubber-sealed butterfly valve is that when it is used in throttling, cavitation will occur due to improper use, and the rubber seat will fall off and be damaged. Therefore, metal sealing butterfly valves have been developed at present, and the cavitation zone has been reduced. In recent years, my country has also developed metal sealing butterfly valves. In recent years, Japan has developed tooth-shaped butterfly valves that are resistant to cavitation, low vibration and low noise.
Generally, the service life of the sealing seat is 15-20 years for rubber and 80-90 years for metal under normal conditions. However, how to make the right choice depends on the requirements of the situation.
The relationship between the opening of the butterfly valve and the flow rate basically changes linearly. If it is used to control flow, its flow characteristics are also closely related to the flow resistance of the pipeline. For example, the diameter and form of the valves installed in the two pipelines are the same, the pipeline loss coefficient is different, and the flow rate of the valve is also very different.
If the valve is in a state with a large throttle range, the back of the valve plate is prone to cavitation, which may damage the valve. Generally, it is used beyond 15°. The hyperbolic cosine value of. The hyperbolic cosine value of. The hyperbolic cosine value of.
When the butterfly valve is in the middle opening, 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 form different states. The front end of the butterfly plate on one side moves in the direction of the flow, and the other side moves against the direction of the flow. The side valve body and the valve plate form a nozzle-shaped opening, and the other side is like a throttle hole-shaped opening. The nozzle side has a faster flow rate than the throttle side, and the hyperbolic cosine of negative pressure is generated under the throttle side valve. The hyperbolic cosine value of. The hyperbolic cosine value of.
The operating torque of butterfly valves varies with the degree of opening and the direction of valve opening and closing. Horizontal butterfly valves, especially large-diameter valves, cannot be ignored due to the depth of water and the difference between the upper and lower water heads of the valve shaft. In addition, when an elbow is installed on the inlet side of the valve, a bias flow is formed and the torque increases. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the effect of the water flow moment.