Why is the pneumatic butterfly valve not closed tightly? Most of them are seals damaged. The damage to the sealing surface is generally caused by the erosion of the medium, which is the result of the abrasion, flushing and cavitation of the sealing surface when the medium is active. 　　　　

There is such a case: there is a batching weighing system, the whole batching process is fully automatically controlled by PLC, and the feeding valve of the batching trolley is a pneumatic three eccentric butterfly valve, and the medium is very fine stone powder. After a period of time, the customer reported that the valve leaked internally, causing the stone powder to often leak in piles on the workbench. The valve returned to the factory for inspection, but there was no leakage, and the customer said that this type of valve was used before, and the same medium had never happened. In order to find out the reason, the company sent people to the site and finally found out the reason: originally, this medium was very thin and a little sticky. Although the batching trolley was equipped with a vibration motor, there were many materials attached to the tank wall and the valve. When the valve was closed, it was stuck around the sealing surface, so that the valve could not be completely closed. As a result, leakage occurred after re installing materials, The sealing surface is also severely worn, and even shows grooves.
After finding out the cause, propose solutions: in the PLC program, extend the motor vibration time, try to shake all the materials out before closing the valve; Adjust the zero point of the weighing instrument, and it will not be displayed as zero until all the materials are out. At this time, the PLC will send a signal to close the valve; Replace the triple eccentric butterfly valve with a double eccentric elastic hard sealing butterfly valve (the central line sealing rubber butterfly valve can also be used. Considering that there are occasionally large particles in the material, the rubber seal may not be durable - if it is a fine powder without particles, a soft sealing butterfly valve can be considered), because the seat of the triple eccentric butterfly valve is an inclined sealing surface, that is, a face seal, As a result, materials are 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 good sealing and durable sealing surface.