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Pneumatic butterfly valve

by:Sure     2021-08-17
The butterfly valve is used for the control of solid materials, and is often used as a discharge valve at the bottom of the tank, such as the bottom of a cement tank, a stone powder tank, etc., for discharging and fast cutting. Because most of the dust materials contain large or small particles, there is no doubt about the wear of the valve sealing surface. Improper selection will greatly reduce the service life of the valve, or quickly cause internal leakage of the valve, affecting continued use. The butterfly valve is used for the control of solid materials, and is often used as a discharge valve at the bottom of the tank, such as the bottom of a cement tank, a stone powder tank, etc., for discharging and fast cutting. Because most of the dust materials contain large or small particles, there is no doubt about the wear of the valve sealing surface. Improper selection will greatly reduce the service life of the valve, or quickly cause internal leakage of the valve, affecting continued use. There is such a case: there is a batching weighing system, the whole batching process is fully automatic controlled by PLC, and the discharge valve of the batching trolley uses a pneumatic three-eccentric butterfly valve, and the medium is very fine stone powder. After using it for a period of time, the customer reported that the valve had internal leakage, which caused the stone powder to often leak on the workbench in piles. The valve returned to the factory for inspection, but there was no leakage, and the customer reported that this valve was used before, and that the same medium did not happen. In order to clarify the situation, the company sent people to the site and finally found out the reason: it turns out that this medium is very thin and a little viscous. Although the batching trolley is equipped with a vibration motor, a lot of materials will eventually adhere to the tank wall and valve parts. When the valve is closed, it gets stuck around the sealing surface, so that the valve cannot be completely closed, resulting in leakage after refilling the material. Over time, the sealing surface will wear out severely, and even grooves will appear. After finding out the reason, a solution is proposed: in the PLC program, extend the vibration time of the motor, try to oscillate all the materials out before closing the valve; adjust the zero point of the weighing instrument, and display zero after all the materials are out. At this time, the PLC sends a signal to close the valve; replace the triple eccentric butterfly valve with a double eccentric elastic hard seal butterfly valve (the center line seal rubber butterfly valve can also be used, considering that there are occasional large particles in the material, the rubber seal may not be durable-if It is a fine powder without particles, you can consider using a soft sealing butterfly valve), because the valve seat of the triple eccentric butterfly valve is an inclined sealing surface, that is, a surface seal, so the material is easy to accumulate on the sealing surface and cannot be discharged quickly. Single eccentric or double eccentric butterfly valves do not have this disadvantage. Even if there is a little material on the sealing surface, it is scraped off by the valve plate when the valve is closed, thus ensuring a good seal and the sealing surface is durable. After such a transformation, such a problem never happened again. In such a system, there are other factors that need to be considered, such as: the material cannot be directly rushed to the valve plate of the valve when it is placed in the trolley from above (this impact force will also prevent the valve from closing tightly), and the material The static pressure also needs to not exceed the design bearing pressure of the pneumatic butterfly valve, and so on. The difference between a control valve and an ordinary manual valve is that you cannot treat it as an isolated component, but must consider it as a part of the entire automatic control system. Many problems in the use of control valves are not the selection. And the problem of configuration, but because the user's insufficient understanding of the control valve causes the control valve to fail to debug and cooperate with the control system. As long as the key to the problem is recognized, the valve is correctly selected, and the control valve is debugged in the system debugging stage, the failure rate will be greatly reduced, and the automatic control system will operate stably for a long time.
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