How to maintain the sealing performance of valves?

Repairing the sealing surface is a large and important task because after long-term use, the sealing surface of the valve disc and the valve seat will wear and the tightness will be reduced. The main method of repair is grinding. Surface with severe wear needs to be first welded and then ground after lathe turning. The repairing process includes cleaning, inspection, grinding, and inspection procedures.

The grinding process is essentially a cutting process that does not require a lathe. Pitting or small hole depth on the valve head or seat is generally within 0.5 mm.The grinding methods can be divided into rough grinding, medium grinding and fine grinding.

Rough grinding is to eliminate the scratches, indentations, pitting and other defects on the sealing surface, so that the sealing surface has a high degree of flatness and a certain degree of smoothness, which lays the foundation for the medium grinding.The rough grinding is done with a grinding head or a grinding seat tool, and sandpaper or grinding paste with big grit size.Rough grinding has characteristics such as large cutting amount, high efficiency,  but the cutting grain is deep and the sealing surface is rough.Thus, rough grinding can be performed simply by removing pitting on the valve head or seat.

Medium grinding is to eliminate the rough lines on the sealing surface and further improve the flatness and smoothness of the sealing surface with fine-grained sandpaper or grinding paste. Its small cutting amount is beneficial to reduce roughness. The tools should be replaced correspondingly and kept clean. After the medium grinding, the contact plane of the valve should be bright. If you use a pencil to make a few strokes on the valve head or seat, turn around the valve head or seat, the pencil marking should be erased.

The fine grinding not only can help eliminate marks on the valves’ sealing surfaces, reduce the sealing gap, but also can improve the finish of the sealing surface as well as enhance the sealing performance of the valves. Generally, when grinding, it should be rotated clockwise by 60-100 degrees, and then rotated 40-90 degrees in the opposite direction.

The inspection process runs through the whole grinding process.Its purpose is to grasp the grinding situation at any time, so that the grinding quality to meet the technical requirements.It should be noted that different valves must be ground with grinding tools suitable for different sealing surfaces to improve grinding efficiency and ensure grinding quality.

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