Introduction to knowledge related to the use of butterfly valves

Thread Content

Introduction to knowledge on the use of butterfly valves 2020-07-20 Currently, in the world, butterfly valves with a diameter of DN300 millimeters or more are gradually replacing gate valves. Compared to gate valves, butterfly valves have a shorter opening and closing time, require less force for operation, need less installation space, and are lighter in weight. Taking DN1000 as an example, the butterfly valve weighs about 2 tons, while the gate valve weighs about 3.5 tons. Moreover, the butterfly valve can be easily combined with various driving devices, and it boasts good durability and reliability. ? The disadvantage of rubber-sealed butterfly valves is that when used for throttling, improper use can lead to cavitation, causing the rubber seat to peel off or get damaged. To this end, metal-sealed butterfly valves have been developed internationally, reducing the cavitation area; in recent years, China has also developed metal-sealed butterfly valves. In Japan, comb-toothed butterfly valves that are resistant to cavitation and feature low vibration and low noise have been developed in recent years. ? Under normal conditions, the service life of a standard seal seat is 15 to 20 years for rubber, and 80 to 90 years for metal. However, the proper selection depends on the operational requirements. 　　The relationship between the opening degree of a butterfly valve and the flow rate is essentially linear. When used for flow control, its flow characteristics are closely related to the flow resistance of the piping as well. For example, if two pipes have identical valve sizes and types, but different pipe loss coefficients, the flow rates through the valves will also differ significantly. ? If the valve is in a state with a large throttling range, cavitation can occur on the back side of the valve disc, which may lead to damage to the valve; therefore, it is generally used at angles other than 15°. ? When the butterfly valve is at a medium opening position, the shape of the opening formed between the valve body and the front end of the butterfly plate is symmetrical with respect to the valve shaft; on one side, the front end of the butterfly plate moves in the direction of the flow, while on the other side it moves against the flow direction. As a result, one side forms an opening similar to a nozzle, while the other side forms an opening similar to a throttle orifice. The flow velocity is much higher on the nozzle side than on the throttle side, and negative pressure is generated below the valve on the throttle side, which often leads to the detachment of the rubber seals. ? The operating torque of a butterfly valve varies depending on the degree of opening and the direction in which the valve is opened or closed. For horizontal butterfly valves, especially those with large diameters, the torque generated by the difference in water head above and below the valve shaft due to the depth of water cannot be ignored either. Additionally, when a elbow is installed on the inlet side of the valve, flow deviation occurs, resulting in an increase in torque. When the valve is at an intermediate opening, the operating mechanism needs to self-lock due to the hydrodynamic torque. https://www.shfm8.com/uploads/allimg/200717/1-200GG643300-L.jpg The Valve Knowledge Center will provide you with information on the problems and related knowledge related to various types of valves that you may need. This article provides an introduction to the knowledge related to the use of butterfly valves, in the hope of helping you gain a basic understanding of them.