Hardware knowledge: the development and use of butterfly valves

The development and use of butterfly valves

1. The development of butterfly valves: The butterfly valve was invented in the United States in the 1930s and introduced to Japan in the 1950s. It was only widely used in Japan in the 1960s, and it was promoted in my country after the 1970s. At present, butterfly valves above DN300 mm have gradually replaced gate valves in the world. Compared with gate valves, butterfly valves have shorter opening and closing times, small operating moments, small installation space and light weight. Take 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, which has 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, causing the rubber seat to peel off and damage. For this reason, metal-sealed butterfly valves have been developed internationally, and the cavitation zone has been reduced. In recent years, my country has also developed metal-sealed butterfly valves. In Japan, comb-shaped butterfly valves with cavitation resistance, low vibration and low noise have also been developed in recent years. Generally, the life of the seal seat is 15-20 years for rubber and 80-90 years for metal under normal conditions. However, the correct selection depends on the requirements of the working conditions. 2. The use of butterfly valve: 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 piping. For example, two pipelines are installed with the same valve diameter and form, but the pipeline loss coefficient is different, and the flow rate of the valve will also be 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 outside 15°.

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 are formed to complete different states. The front end of the butterfly plate on one side moves in the direction of the flow of water, and the other side flows backward. The water moves in the direction of the water. Therefore, one side of the valve body and the valve plate form a nozzle-like opening, and the other side is similar to a throttle opening. The nozzle side has a much faster flow rate than the throttle side, and the throttle side valve will produce negative Pressure, rubber seals often fall off. ?

The operating torque of butterfly valve has different values u200bu200bdue to different opening and valve opening and closing directions. Horizontal butterfly valves, especially large-diameter valves, due to the depth of water, the torque generated by the difference between the upper and lower water heads of the valve shaft cannot be ignored. In addition, when the elbow is installed on the inlet side of the valve, a bias flow is formed, and the torque will increase. 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.