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.
Clean the sealing surface in oil, use a professional cleaning agent, and check the damage of the sealing surface while washing. Fine cracks which are difficult to find with the naked eye can be carried out by the dye penetrant inspection method. After cleaning, check the sealing performance of the valve with a red pen or a pencil for inspection. For example, use a pencil to draw a few concentric circles on the valve flap and the sealing surface of the seat, then rotate the valve flap and the valve seat tightly to check if the circle is wiped off. If the valve is not sealed well, use a standard plate to inspect the valve flap or the sealing surface of the disc and valve body, and determine the grinding position.
The grinding process is essentially a cutting process without a lathe, and the pitting or small hole depth on the valve head or the valve seat is generally within 0.5 mm. The grinding method can be used for inspection and divided into rough grinding, medium grinding, and fine grinding.
Rough grinding is to eliminate the defects such as scratches, indentations and pitting on the sealing surface, so that the sealing surface has a higher flatness and a certain degree of smoothness, which lays a foundation for the medium grinding. The rough grinding uses the grinding head or the 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. Because of that, the rough grinding can be performed by simply removing the pitting of the valve head or the valve 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.
Fine grinding is the last step in valve grinding, mainly to improve the smoothness of the sealing surface. Generally, when grinding, it should be rotated clockwise by 60-100 degrees, and then rotated 40-90 degrees in the opposite direction. After the valve is polished and shiny, a fine circle and black surface can be seen on the valve head and valve seat, then grind it gently with oil and clean it with gauze. After the grinding, eliminate other defects and assemble as soon as possible, so as not to damage the polished valve head.
The inspection process runs through the grinding process all the time. And the purpose is to grasp the grinding situation at any time so that the quality of the grinding can meet the technical requirements. It should be noted that different valves have to be ground with grinding tools suitable for various sealing surfaces to improve grinding efficiency and ensure grinding quality.
Clean the sealing surface in oil, use a professional cleaning agent, and check the damage of the sealing surface while washing. Fine cracks which are difficult to find with the naked eye can be carried out by the dye penetrant inspection method. After cleaning, check the sealing performance of the valve with a red pen or a pencil for inspection. For example, use a pencil to draw a few concentric circles on the valve flap and the sealing surface of the seat, then rotate the valve flap and the valve seat tightly to check if the circle is wiped off. If the valve is not sealed well, use a standard plate to inspect the valve flap or the sealing surface of the disc and valve body, and determine the grinding position.
The grinding process is essentially a cutting process without a lathe, and the pitting or small hole depth on the valve head or the valve seat is generally within 0.5 mm. The grinding method can be used for inspection and divided into rough grinding, medium grinding, and fine grinding.
Rough grinding is to eliminate the defects such as scratches, indentations and pitting on the sealing surface, so that the sealing surface has a higher flatness and a certain degree of smoothness, which lays a foundation for the medium grinding. The rough grinding uses the grinding head or the 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. Because of that, the rough grinding can be performed by simply removing the pitting of the valve head or the valve 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.
Fine grinding is the last step in valve grinding, mainly to improve the smoothness of the sealing surface. Generally, when grinding, it should be rotated clockwise by 60-100 degrees, and then rotated 40-90 degrees in the opposite direction. After the valve is polished and shiny, a fine circle and black surface can be seen on the valve head and valve seat, then grind it gently with oil and clean it with gauze. After the grinding, eliminate other defects and assemble as soon as possible, so as not to damage the polished valve head.
The inspection process runs through the grinding process all the time. And the purpose is to grasp the grinding situation at any time so that the quality of the grinding can meet the technical requirements. It should be noted that different valves have to be ground with grinding tools suitable for various sealing surfaces to improve grinding efficiency and ensure grinding quality.
