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The advantages and disadvantages of the new type butterfly valve with the body and seat as a conjoined member

by:Sure     2021-08-18
An existing relatively advanced butterfly valve is a triple eccentric metal hard-sealed butterfly valve. The valve body and the valve seat are connected components, and the sealing surface layer of the valve seat is welded with temperature-resistant and corrosion-resistant alloy materials. The multi-layer soft laminated sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this butterfly valve has high temperature resistance, is easy to operate, and has no friction when opening and closing. When closing, the torque of the transmission mechanism is increased to compensate for the sealing, which improves the performance. One of the more advanced butterfly valves is the triple eccentric metal hard-sealed butterfly valve. The valve body and the valve seat are connected components, and the sealing surface layer of the valve seat is welded with temperature-resistant and corrosion-resistant alloy materials. The multi-layer soft laminated sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this butterfly valve has high temperature resistance, light operation, no friction when opening and closing, and when closing, the torque of the transmission mechanism increases to compensate for the sealing, which improves the butterfly valve. The advantages of sealing performance and extended service life. However, this butterfly valve still has the following problems in the process of use:    1. Since the multilayer soft and hard stacked sealing ring is fixed on the valve plate, when the valve plate is normally open, the medium will form a positive erosion on its sealing surface, and the metal sheet is sandwiched. After being scoured, the soft sealing tape in the medium directly affects the sealing performance.   2. Due to structural conditions, this structure is not suitable for valves with a diameter below DN200, because the overall structure of the valve plate is too thick and the flow resistance is large.   3. Due to the principle of the triple eccentric structure, the seal between the sealing surface of the valve plate and the valve seat depends on the torque of the transmission device to press the valve plate against the valve seat. In the positive flow state, the higher the medium pressure, the tighter the sealing extrusion. When the flow channel medium flows back, as the medium pressure increases, when the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, the seal begins to leak.   high-performance three-eccentric two-way hard-sealed butterfly valve, characterized in that: the valve seat sealing ring is composed of multiple layers of stainless steel sheets on both sides of a soft T-shaped sealing ring. The sealing surface of the valve plate and the valve seat is an oblique cone structure, and the surface of the oblique cone of the valve plate is welded with temperature-resistant and corrosion-resistant alloy materials; the spring fixed between the pressure plate of the adjusting ring and the adjusting bolt of the pressure plate are assembled together.  This structure effectively compensates for the tolerance zone between the shaft sleeve and the valve body and the elastic deformation of the valve stem under the medium pressure, and solves the sealing problem of the valve in the two-way interchangeable medium conveying process. The sealing ring is composed of a soft T-shaped multi-layer stainless steel sheet on both sides, which has the dual advantages of a metal hard seal and a soft seal, and has a sealing performance of zero leakage regardless of low temperature and high temperature.  The test proves that when the pool is in a positive flow state (the flow direction of the medium is the same as the rotation direction of the butterfly plate), the pressure on the sealing surface is generated by the torque of the transmission device and the effect of the medium pressure on the valve plate. When the positive medium pressure increases, the tighter the oblique cone surface of the valve plate and the sealing surface of the valve seat are squeezed, the better the sealing effect. In the reverse flow state, the seal between the valve plate and the valve seat depends on the torque of the driving device to press the valve plate against the valve seat. With the increase of the reverse medium pressure, when the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, the deformation energy stored by the spring of the adjusting ring after being loaded compensates for the tight pressure of the sealing surface of the valve plate and the valve seat Play the role of automatic compensation. Therefore, the utility model does not install soft and hard multi-layer sealing rings on the valve plate as in the prior art, but directly installs on the valve body. Adding an adjustment ring between the pressure plate and the valve seat is a very ideal two-way hard sealing method. . It can replace gate valves, globe valves and ball valves. The development of the butterfly valve and its easy-to-use knowledge in the application process The butterfly valve was invented in the United States in the 1930s, and it was 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. ? 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 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 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 in the direction of the flowing water, and the other side is against the direction of the flowing 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 negative pressure will be generated under the throttle side valve. 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, cannot be ignored due to the depth of water and the torque produced by 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 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.
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