The Working Principle of Butterfly Valve

Aug. 08, 2020

The butterfly valve is a valve that uses a circular butterfly plate as a switch part and rotates with the valve stem to open, close and adjust the fluid passage. The butterfly plate of the butterfly valve is installed in the direction of the pipe diameter. The butterfly plate rotates around the high pressure, and the rotation angle is between 0° and 90°. When the rotation reaches 90°, the valve is in a fully open state.


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, 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 end of the butterfly plate, centered on the valve shaft, forms a different state from each other. The front end of the reverse butterfly plate moves in the direction of the flow of water, and the other side moves against the direction of the flow move. 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 is generated under the throttle side valve, which often occurs The rubber seal has come off.


The butterfly valve and butterfly stem have no self-locking ability. For the positioning of the butterfly plate, a worm gear reducer should be installed on the valve stem. The use of worm gear reducer can not only make the butterfly plate have self-locking ability, make the butterfly plate stop at any position, but also improve the operation performance of the valve.


The operating torque of the butterfly valve has different values due to the different opening and closing directions of the valve. The horizontal butterfly valve, especially the large diameter valve, 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 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.


The butterfly valve has a simple structure, consisting of only a few parts, and saves materials; it is small in size, light in weight, small in installation size, small in driving torque, easy and fast to operate, and can be opened and closed quickly by rotating 90°; and it also has a good The flow adjustment function and closing and sealing characteristics of the butterfly valve are the dominant valve form in the application field of large and medium caliber and medium and low pressure.When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body, so the pressure drop produced by the valve is small, so it has better flow control characteristics.The butterfly valve has two sealing types: elastic seal and metal seal. Elastic sealing valve, the sealing ring can be embedded in the valve body or attached to the periphery of the butterfly plate.Valves with metal seals generally have a longer life than valves with elastic seals, but it is difficult to achieve a complete seal. Metal seals can adapt to higher operating temperatures, while elastic seals have the defect of being limited by temperature.If the butterfly valve is required to be used as a flow control, it is mainly to select the correct size and type of the valve. The structure principle of the butterfly valve is especially suitable for making large diameter valves. Butterfly valves are not only widely used in general industries such as petroleum, gas, chemical, water treatment, etc., but also used in cooling water systems of thermal power stations.Commonly used butterfly valves include wafer butterfly valves and flange butterfly valves. Wafer type butterfly valve is to connect the valve between two pipe flanges with stud bolts. Flange type butterfly valve is with flange on the valve, and the two ends of the valve are flanged to the pipe flange with bolts.The strength performance of the valve refers to the ability of the valve to withstand the pressure of the medium. The valve is a mechanical product that bears internal pressure, so it must have sufficient strength and rigidity to ensure long-term use without cracking or deformation.


With the application of anti-corrosion synthetic rubber and Teflon,the performance of butterfly valves can be improved and meet different working conditions. In the past ten years, the metal hard seal butterfly valve has developed rapidly. With the application of high temperature resistance, low temperature resistance, strong corrosion resistance, strong erosion resistance, and high strength alloy materials in the butterfly valve, the metal hard seal butterfly valve has been used in high temperature, low temperature and strong It is widely used under working conditions such as erosion, and partially replaces globe valves, gate valves and ball valves.

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