Pneumatic butterfly valve in the operation of the powder system

Pneumatic butterfly valves are widely used in gas and liquid media, but their application in solid materials—such as dust or fine powder—tends to be less common. This makes the selection and usage of such valves in solid material systems a topic worth exploring in depth. Based on practical experience, I would like to share some insights on this subject. In many industrial applications, butterfly valves are often installed at the bottom of tanks, serving as discharge valves—for example, in cement silos or other storage containers. Their primary function is to control the flow and allow for quick shut-off. However, when dealing with solid materials, especially fine powders, the sealing surfaces of the valve are prone to wear. If not properly selected, this can significantly reduce the valve’s service life and eventually lead to leakage, affecting system performance. Here's an example: A component weighing system was fully automated using PLC control. The discharge valve for the ingredient car was initially chosen as a pneumatic triple-eccentric butterfly valve, handling very fine stone powder. After some time, the customer reported frequent leaks, with large amounts of powder accumulating on the workbench. Upon returning the valve to the factory for testing, no leakage was detected. However, the customer continued to report the issue, and similar cases had not occurred elsewhere with the same medium. To investigate, our team visited the site and discovered the root cause: the material was very fine and slightly sticky. Although the ingredient car was equipped with a vibrating motor, some material still clung to the tank walls and the valve components. When the valve closed, the material got stuck around the sealing surface, preventing it from closing completely. As a result, leakage occurred once the material was reloaded. Over time, the sealing surface became severely worn, even forming grooves. After identifying the problem, we proposed a solution: Adjusting the PLC program to ensure the vibration motor ran long enough to remove all material before the valve closed. Additionally, we calibrated the weighing system so that the valve only closed once the weight reading showed zero. Finally, we replaced the triple-eccentric butterfly valve with a double-eccentric elastic hard-seal butterfly valve (or a neutral rubber-sealed one, depending on the particle size). Since there were occasional larger particles in the material, a soft-seal valve might not be suitable. The triple-eccentric design has a conical sealing surface, which tends to trap material, while the single- or double-eccentric version allows for better self-cleaning during closure, reducing the risk of leakage and increasing durability. After these changes, the problem never occurred again. In such systems, other factors should also be considered, such as avoiding direct impact of material onto the valve disc from above, ensuring the static pressure does not exceed the valve’s design limits, and more. The key difference between a control valve and a manual valve lies in the fact that a control valve cannot be treated as an isolated component—it must be integrated into the overall automation system. Many issues arise not from the valve itself, but from a lack of understanding of how it interacts with the control system. Proper commissioning during the system integration phase is crucial to ensuring reliable and long-term operation. By recognizing potential problems early, selecting the right valve, and thoroughly testing the control valve during system debugging, the failure rate can be significantly reduced, leading to stable and efficient automatic control systems.

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