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Leakage prevention and elimination method of valve sealing surface

Posted by Bundor valve
Bundor valve reminds you that to understand the leakage prevention and elimination method of the valve sealing surface, we must first understand why the valve sealing surface leaks.
 
The valve sealing surface is generally composed of a pair of sealing pairs, one on the valve body and the other on the valve disc
 
 
The main reasons for the leakage of valve sealing surface are as follows:
 
1、 The sealing surface is unevenly ground and cannot form a close line;
 
2、 The top center of the connection between the valve rod and the closing part is suspended, incorrect or worn;
 
3、 The valve rod is bent or assembled improperly, so that the closing part is skewed or out of alignment;
 
4、 Improper selection of sealing surface material or failure to select valves according to working conditions, the sealing surface is prone to corrosion, erosion and wear;
 
5、 Weld overlay and heat treatment are not carried out in accordance with the procedures, wear occurs due to low hardness, corrosion occurs due to burning of alloy elements, cracks and other defects due to excessive internal stress;
6、 After surface treatment, the sealing surface peels off or loses its original performance due to excessive grinding;
7、 The sealing surface is not closed tightly or there are fine seams due to cold shrinkage after closing, resulting in the phenomenon of corrosion;
8、 When the cut-off valve is used as a throttle valve or a pressure reducing valve, the sealing surface will be eroded and damaged;
9、 When the valve has reached the fully closed position and continue to apply excessive closing force, including the incorrect use of long lever operation, the sealing surface is crushed and squeezed out of shape;
10、 When the sealing surface is worn too much, resulting in the phenomenon of wire dropping, that is, the sealing pair can not be tightly closed;
Prevention and elimination methods of valve sealing surface leakage:
 
First, when grinding the sealing surface, the grinding tools, abrasives, abrasive cloth, sandpaper and other objects should be selected with a reasonable grinding method. After grinding, coloring should be performed to check that the sealing surface should be free of indentations, cracks, scratches and other defects;
 
Second, the connection between the valve rod and the closing part should meet the design requirements. If the top center does not meet the requirements, it should be repaired. The top center should have a certain movable clearance, especially the axial clearance between the valve rod shoulder and the closing part should not be less than 2 Millimeter;
 
Third,the bending of the valve rod should be straightened., and after adjusting the valve rod, valve nut, closing piece and valve seat, they should be on a common axis;
 
Fourth, when selecting a valve or replacing the sealing surface, it should meet the working conditions. After the sealing surface is processed, its corrosion resistance and scratch resistance should be good;
 
Fifth, the overlaying welding and heat treatment process should meet the technical requirements of the regulations and specifications. After the sealing surface is processed, it should be accepted without any defects affecting the use;
 
Sixth,the processes of flame, nitriding, shed and plating on the sealing surface must be carried out in strict accordance with the technical requirements of the procedures and specifications. The penetrating layer of the grinding sealing surface should not exceed one third of the layer. If the coating and penetrating layer are seriously damaged, the coating and penetrating layer should be removed and the surface treatment should be carried out again. The sealing surface of high frequency sudden fire on the surface can be repeatedly repaired by falling fire ;
 
Seventh, the valve should be marked closed or opened, and should be repaired in time if it is not tightly closed. For high temperature valves, some of them appears slits after cold shrinkage, should be closed more than once at a certain time interval after closing;
Eighth, the valve used as a cut-of 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. If the flow and pressure of the medium need to be adjusted, a throttle valve and a pressure reducing valve should be separately installed.
 
 
Ninth, the front opening and closing of the valve should conform to the section "operation of the valve". The valve closing force should be appropriate. The diameter of the hand wheel should be less than 320mm, and only one person is allowed to operate. For the hand wheel with the diameter equal to or greater than 320mm, two people are allowed to operate, or one person operated with the help of a lever within 500mm;
 
Tenth, when the water line falls off, it should be adjusted, and replace the sealing surface that cannot be adjusted.
 
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