The issue of replacing butterfly valves – urgent! !

Eccentric butterfly valves generally have a longer service life; another advantage is their ability to withstand high temperatures, but the key factor is still the former!

Even in foreign countries, medium-line soft-seal valves have a long service life; it’s probably a difference in manufacturing standards. One of our devices has been using such valves for 5-6 years without any problems, while the domestic valves we bought break down frequently

The main considerations are pressure and lifespan issues

It is recommended not to replace it, as there is a reason for choosing a three-eccentric design in the first place; the price difference between a three-eccentric valve, a valve with a central axis, and a two-eccentric valve is similar to the difference between Mercedes-Benz, Chery, and Qori. Centerline butterfly valves are used in applications where a tight seal is not absolutely necessary; they are valves used for controlling flow in intermediate pipelines. Single-ear and double-ear designs represent new valve types developed to overcome some of the shortcomings of centerline valves, reducing wear between the valve seat and the butterfly disc and thereby extending their service life. But the sealing remains a compression deformation seal between metal and a soft valve seat. The triple-eccentric valve completely overcomes the shortcomings of the aforementioned valves; it features a metal-to-metal seal (similar to that of globe valves) and can withstand higher temperatures. The issue of high differential pressures remains unsolved by butterfly valves; however, they can replace ball valves in many cases, especially for large diameters.

Differences among several types of butterfly valves: 1. Centerline butterfly valve (concentric butterfly valve). The structural feature of a centerline butterfly valve is that the axis of the valve stem, the center of the butterfly plate, and the center of the valve body are all in the same position. It has a simple structure and is easy to manufacture. Common rubber-lined butterfly valves fall into this category. The disadvantage is that the butterfly plate and the valve seat are constantly in a state of compression and scraping, resulting in a large flow resistance and rapid wear. To overcome compression and scraping and ensure sealing performance, the valve seat is generally made of elastic materials such as rubber or polytetrafluoroethylene; however, the sealing materials are limited by temperature in terms of their usability, which is why butterfly valves are traditionally considered unsuitable for high-temperature environments. II. Single-eccentric butterfly valve: The structural feature of the single-eccentric butterfly valve is that the axis of the valve stem is offset from the center of the butterfly plate; as a result, the upper and lower ends of the butterfly plate are no longer the rotation axis, which reduces the excessive pressure exerted on these ends by the valve seat. This approach solves the problem of compression between the butterfly plate and the valve seat that occurs in concentric butterfly valves. However, due to the fact that the scraping between the butterfly disc and the valve seat does not disappear throughout the entire opening and closing process of the valve in a single-eccentric design, and its application range is similar to that of concentric butterfly valves, it is not widely used. III. Double-eccentric butterfly valve: The double-eccentric butterfly valve is an improved version of the single-eccentric butterfly valve, and it is the most widely used type. Its structural feature is that the axis of the valve stem is offset from both the center of the butterfly plate and the center of the body. The effect of dual eccentricity allows the butterfly disc to quickly separate from the valve seat once the valve is opened, significantly reducing unnecessary excessive compression and scraping between the butterfly disc and the valve seat, decreasing the opening force, minimizing wear, and extending the lifespan of the valve seat. Scratching is significantly reduced, and this also allows dual-eccentric butterfly valves to use metal seats, thereby enhancing the applicability of butterfly valves in high-temperature environments. However, because its sealing principle relies on a positional sealing mechanism – that is, the sealing surfaces of the butterfly plate and the valve seat are in line contact, and sealing is achieved through the elastic deformation of the valve seat caused by the pressure exerted by the butterfly plate – high requirements are placed on its closed position (especially for metal valve seats), and its pressure resistance is low. This is why traditionally it has been believed that butterfly valves cannot handle high pressures and suffer from high leakage rates. IV. Three-eccentric butterfly valves: They need to be able to withstand high temperatures, require hard-sealing, but have 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. Its structural feature is that, in addition to the double eccentricity of the valve stem axis, the conical axis of the butterfly valve’s sealing surface is also tilted relative to the cylindrical axis of the valve body; in other words, after the third level of eccentricity, the sealing cross-section of the butterfly valve is no longer circular but elliptical, and as a result its sealing surface becomes asymmetric – one side being inclined relative to the center line of the valve body while the other side remains parallel to it. The most significant feature of this third type of eccentric design is that it fundamentally changes the sealing mechanism: it is no longer a position-based seal but rather a torque-based seal. In other words, sealing is achieved not by relying on the elastic deformation of the valve seat, but entirely through the pressure at the contact surface between the valve components. This approach solves the problem of zero leakage in metal valve seats. Moreover, since the contact surface pressure is proportional to the medium pressure, high pressure and high temperature conditions can also be handled with ease.

If there are no strict requirements regarding the leakage rate of the valve, a regular butterfly valve can be used as a substitute.

Butterfly valves with eccentric soft seals have a much longer service life than ordinary centerline butterfly valves. Since the friction coefficient of the three-eccentric or two-eccentric soft seals is low, their sealing rings are less likely to get damaged. Moreover, centerline butterfly valves have a relatively low pressure resistance – typically up to PN20 at most, and they can temporarily reach PN25, but not for long periods of time. In contrast, butterfly valves with eccentric soft seals can withstand pipeline pressures of PN25–50! The main advantage is indeed their longer service life! :)

The eccentric butterfly valve is easy to operate and has a long service life

Ordinary butterfly valves, if free from quality issues, generally last for about two years, as that is the lifespan of the rubber components inside them; eccentric butterfly valves, on the other hand, have a much longer service life

The butterfly valves we use are primarily applied in circulating water and tap water systems; they are rarely used in process pipelines where high sealing performance is required. Having learned the above information, one can consider expanding the scope of use for butterfly valves in the future.

I’m not aware of the specific operating conditions of your valves, such as the requirements regarding sealing performance or whether the switching frequency is high If it is only the case where \"the temperature range is below 80 degrees Celsius and the pressure level is 16 kilograms,\" I think a regular centerline butterfly valve can be used, but the material should be at least carbon steel or better. Additionally, it is necessary to clarify the pressure requirements with the manufacturer at the time of purchase, as some manufacturers’ centerline butterfly valves cannot achieve a pressure of 16 kilograms.

I’m not very familiar with butterfly valves; I’ve come to learn about them* – the one on the 6th floor is great