The valve is a control component that is widely used in fluid systems. It can be used to switch or control the flow direction and adjust the function. From the simplest cut-off function, the valve is sealed in the machine. Its function is to avoid the medium. The joint between the parts along the cavity where it is located, leaks outwards or prevents internal materials from entering the inside. The collar and parts that play a sealing role are called seals or sealing structures, or seals for short. The two joint surfaces are in contact with the seal and play a sealing role. The appearance is called the sealing surface.
The valve sealing surface is the central part of the valve, and its leakage can be divided into the following types, namely, leakage of the sealing surface, leakage of the sealing ring joint, leakage of the sealing part falling off, and leakage of foreign objects embedded between the sealing surfaces. One of the most common uses of valves in pipelines and equipment is to cut off the flow of media. Therefore, the tightness of the exhaust valve is an important factor in determining whether internal leakage occurs.
Leakage inspection method for the sealing surface of the exhaust valve
1. The sealing surface is unevenly ground and cannot form a tight line;
2. The top center of the connection between the valve stem and the closing part is suspended, incorrect or worn;
3. The valve stem is bent or incorrectly assembled, which makes the closing part skewed or misaligned;
4. Improper selection of the sealing surface material or failure to select the valve according to the working conditions, the sealing surface is prone to corrosion, erosion, and wear;
5. Surfacing and heat treatment are not operated in accordance with the regulations, due to low hardness, wear, corrosion due to burning of alloy elements, cracks due to excessive internal stress and other defects;
6. The surface-treated sealing surface peels off or loses its original performance due to excessive grinding;
7. The sealing surface is not closed tightly or the slits appearing due to cold shrinkage after closing, resulting in the phenomenon of intermediate corrosion;
8. The shut-off valve is used as a throttle valve or a pressure reducing valve, and the sealing surface is eroded and damaged;
9. The valve has reached the fully closed position and continued to apply excessive closing force, including incorrect use of long lever operation, and the sealing surface is crushed and squeezed;
10. Excessive wear of the sealing surface results in disconnection, that is, the sealing pair cannot be tightly sealed;
The prevention and elimination method of the leakage of the valve sealing surface of the exhaust valve:
1. When grinding the sealing surface, the grinding tools, abrasives, emery cloth, sandpaper and other objects should be reasonable and accurate. After grinding, the coloring review should be carried out. The sealing surface should be free of defects such as indentation, cracks, and scratches;
2. The connection between the valve stem and the closing piece should meet the design requirements. If the top center does not meet the requirements, it should be trimmed. The top center should have a certain movable clearance, especially the axial gap between the valve stem shoulder and the closing piece is not less than 2 Mm;
3. The twists and turns of the valve stem should be straightened. After the valve stem, valve stem nut, closure, and valve seat are adjusted, they should be on a common axis;
4. When selecting a valve or changing the sealing surface, it should meet the working conditions. After the sealing surface is processed, its corrosion resistance, resistance, abrasion resistance and other properties should be good;
5. The surfacing welding and thermal solution process should conform to the regulations and standard skills. After the sealing surface is processed, the sealing surface should be checked and accepted. There are no shortcomings that may affect the use;
6. Processes such as firing, nitriding, infiltration, and plating on the surface of the sealing surface must be carried out strictly in accordance with the technical requirements of its regulations and standards. The impregnated layer of the sealing surface should not exceed one-third of this layer to damage the plating and impregnated layer. If it is serious, the plating layer and the soaking layer should be removed and the surface should be cleaned up. The sealing surface of the external high-frequency smashing fire can be repeatedly fired and repaired;
7. The valve should be marked when it is closed or opened, and repaired in time if the valve is not tightly closed. For cryogenic valves, some of the slits that have emerged from cold shrinkage after being closed, should be closed more than once after being closed;
8. The valve used as a shut-off valve is not allowed to be used as a throttle valve or a pressure reducing valve. The closing part should be in the fully open or fully closed position. When it is necessary to adjust the flow and pressure of the medium, the throttle valve and reducing valve should be set independently. Pressure valve;
9. The front opening and closing of the valve should be in accordance with the section "Valve operation", the valve closing force is appropriate, the diameter of the handwheel is less than 320mm, only one person is allowed to operate, and the handwheel with a diameter equal to or greater than 320mm is allowed to operate by two persons, or one person Operate with leverage within 500 mm;
10. After the water line is dropped, it should be adjusted, and the sealing surface of the sealing surface that cannot be adjusted should be changed;