In the 30s, the butterfly valve was invented in United States, introduced to the Japan in the 50s, and was widely used in Japan in the 60s, and it was promoted in China after the 70s. At present, butterfly valves above DN300 mm in the world have gradually replaced gate valves. Compared with gate valves, butterfly valves have short opening and closing time, small operating torque, small installation space and light weight. Taking DN1000 as an example, the butterfly valve is about 2T, and the gate valve is about 3.5T, and the butterfly valve is easy to combine with various driving devices, with good durability and reliability.
The disadvantage of the rubber seal butterfly valve is that when it is used for throttling, cavitation will occur due to improper use, which will cause the rubber seat to peel off and be damaged. In recent years, China has also developed metal sealed butterfly valves, and in recent years, Japan has also developed comb-shaped butterfly valves with cavitation resistance, low vibration and low noise.
The service life of the general sealing seat is 15-20 years for rubber and 80-90 years for metal under normal conditions. However, how to choose correctly depends on the requirements of working conditions.
The relationship between the opening of a butterfly valve and the flow rate is basically linear and proportional. If it is used to control the flow rate, its flow characteristics are also closely related to the flow resistance of the piping, such as the diameter and form of the valves installed in the two pipelines are the same, and the pipeline loss coefficient is different, and the flow rate of the valve will be very different.
If the valve is in a state of large throttling, the back of the valve plate is prone to cavitation, and there is a possibility of damaging the valve, so it is generally used outside 15°.
When the butterfly valve is in the middle opening, the opening shape 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 along the direction of flowing water, and the other side moves against the direction of flowing water, therefore, the valve body on one side and the valve plate form a nozzle-shaped opening, and the other side is similar to the throttle hole-shaped opening, the nozzle side is much faster than the throttle side, and the negative pressure will be generated under the throttle side valve, and the rubber seal often falls off.
The operating torque of butterfly valve, due to the different opening and opening direction of the valve, its value is different, and the horizontal butterfly valve, especially the large-diameter valve, due to the water depth, the torque generated by the difference between the upper and lower head of the valve shaft can not be ignored. In addition, when an elbow is installed on the inlet side of the valve, a deflection 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 action of the water flow torque.
Post time: Aug-22-2024
