Questions about butterfly valves
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I’ve just started working in the chemical industry and encountered a problem. During a recent maintenance period at our plant, all the ordinary soft-sealed butterfly valves in the circulating water system were replaced with triple-eccentric hard-sealed butterfly valves. I would like to know what the differences between the two are and what are their respective characteristics Under what circumstances are they used respectively? Thank you all for your answers; I’m extremely grateful! This post was last edited by yfq4308 on 2009-2-21 08:43.]
It can withstand high temperatures, is easy to operate, has no friction during opening and closing; when closed, the sealing is enhanced as the torque of the transmission mechanism increases, thereby improving the sealing performance of the butterfly valve and extending its service life
Replacing it with a triple-eccentric butterfly valve makes operation easier. By \"hard sealing\" is meant that the shape of the sealing surface is that of an inverted frustum; the sealing surface is formed by alternating layers of elastic metal and graphite, while the disc itself has a frustum-shaped design. Sealing is achieved by applying pressure from the medium on the disc. Therefore, this type of butterfly valve comes with a direction arrow, and the direction indicated by this arrow is what, in technical terms, is referred to as the \"pressure application direction.\" Only when the medium pressure acts in the direction indicated by the arrow can sealing be achieved at 100% with no leakage; otherwise, leakage is likely to occur: lol
If it’s not turned on and off very frequently, I personally don’t think it’s necessary. The cost is much higher, so it’s not worth it
The cost of the latter is three times that of the former!
If it’s not turned on and off very frequently, I personally don’t think it’s necessary
Currently, butterfly valves, as components used to control the on/off status and flow rate in piping systems, have been widely applied in many fields such as petroleum, chemicals, metallurgy, and hydropower. In the well-known butterfly valve technology, sealing is typically achieved through a sealing structure, with sealing materials such as rubber and polytetrafluoroethylene being used. Due to limitations in its structural properties, it is not suitable for applications requiring high temperature and pressure resistance, as well as corrosion and wear resistance. A relatively advanced type of butterfly valve is the triple-eccentric metal hard-seal butterfly valve, in which the valve body and the valve seat are integrated components, with the sealing surface of the valve seat being clad with heat-resistant and corrosion-resistant alloy materials. Multi-layer soft folded sealing rings are fixed on the valve plate; compared to traditional butterfly valves, this type of butterfly valve offers advantages such as high temperature resistance, easy operation, friction-free opening and closing. When closed, the sealing is enhanced as the torque applied by the actuation mechanism increases, which improves the sealing performance of the butterfly valve and extends its service life. However, this type of butterfly valve still has the following problems during use: First, since the multi-layered soft and hard gasket assembly is fixed on the valve disc, when the valve disc is in the open position, the medium exerts direct erosion on its sealing surface; the soft sealing strip located in the metal layer is affected by this erosion, which directly impacts the sealing performance. II. Due to structural constraints, this design is not suitable for valves with a diameter of DN200 or less, as the overall structure of the valve disc is too thick, resulting in high flow resistance. III. Due to the principle of the three-eccentric structure, the sealing between the sealing surface of the valve disc and the valve seat is achieved by the torque of the actuation mechanism, which presses the valve disc against the valve seat. In the forward flow state, the higher the medium pressure, the tighter the sealing compression. When the flow medium flows in reverse, as the pressure of the medium increases and the unit normal pressure between the valve plate and the valve seat becomes less than the pressure of the medium, leakage in the seal begins.
The sealing performance of ordinary butterfly valves is inferior to that of the latter
Butterfly valves can be divided into two types based on their sealing mechanism: soft-sealing type and hard-sealing type. Soft-sealed types generally use rubber rings for sealing, while hard-sealed types usually use metal rings for sealing. Three-eccentric butterfly valves need to be able to withstand high temperatures; hard seals must be used, but they result in high leakage rates ； To achieve zero leakage, soft seals must be used, but they cannot withstand high temperatures. To overcome the contradiction of the double-eccentric butterfly valve, a third eccentricity was applied to the butterfly valve.
The three-eccentric hard-sealed butterfly valve has good resistance to high temperatures, but its sealing performance is not particularly good, especially when it comes to sealing gases!
Butterfly valves are generally used in applications where leakage requirements are not high; hard-sealed butterfly valves are not necessary for circulating water pipelines