The reason for valves sealing face's leakage and solution ways

Valve is one kind of the most used control part in flow systems, can be used for opening & closing, or controlling the flow direction, or adjusting. From the simplest function of cutting off, the valve's seal in machinery is to prevent the medium leaking out or preventing the external substances into the pipeline. The sealing part are called as seals or sealing structures; the two joint surface which contact with seals and have sealing function are called as sealing surface.

The sealing face is the core part for valves, the situation for its leakage always has those kinds: the leakage for sealing face; the leakage for the sealing ring; the leakage caused by shedding of closure parts. One of the widest functions used in the pipeline and machine is cutting off the medium's flow, so, its sealing function is the main factor to judge the leakage or not. The sealing face consists of a pair of sealing pairs, one on the valve body, the other one on the disc.

The leakage for the sealing face always have below reasons:

1. The sealing surface is not smooth and can't form as a tight line;

2. The connection between stem and closing part is suspended, not straight or worn;

3. The stem is bent or improperly assembled, skewing the closing part;

4. The material for sealing the face is improperly or choosing the valves not refer as the working condition, so the sealing face is easy to be corrosive and worn;

5. Surfacing and heat treatment are not operated according to the rules, caused the worn due to excessively low hardness, caused the corrosion due to burning loss of alloying elements, caused the crack due to the excessive internal stress and so on;

6. The seals with surface treatment peel off, or because of the excessive grinding, it will lose the original function;

7. The sealing face don't close tightly or cause the thin seams due to the cold shrinkage after closing, will easy to cause corrosion;

8. Using the cut-off valves as regulating valves or pressure reducing regulator valves, the sealing face was damaged by erosion;

9. The valve has been fully closed position but continue to apply excessive closing force, including the incorrect use of long lever operation, the sealing surface will be crushed, extrusion deformation;

10. The sealing surface is corrosive excessively then causes the drop-off situation, so the sealing parts can't be very close.

The methods for the prevention and elimination of valve sealing surface leakage:

1. When grinding the sealing surface, the grinding tools, abrasives, emery cloth sandpaper and other objects should be selected reasonably, the grinding method should be correct. After grinding should do a colored inspection, and the sealing surface should not have indentation, cracks, scratched and other defects.

2. The connection between the stem and closing part should match the design requirement, if the top center doesn't meet the requirement, should be trimmed and have a certain active clearance, especially the axial clearance between the stem shoulder and closing part is not less than 2mm.

3. Stem should be straightened once bent, when adjusting the stem, stem nut, shutoff and seat, they shall be on a common axis.

4. Choosing the valve or changing the sealing surface should match the work condition, after processing the sealing surface, its corrosion resistance, abrasion resistance and other performance should be better.

5. The surfacing and heat treatment process should comply with the rules and specifications, checking the sealing surface after processing, not allowing any defects affecting the normal use.

6. Valves' opening or closing should have marks, repair it on time if can't close tightly. For high-temperature valves, some thin seam will exist after closing and cold shrinkage, it should be closed more than once at a certain time.

7. The cut-off valves can't be used as regulating valves or pressure reducing valves, the closing part should be at the position of fully opened or fully closed. If needed to adjust the medium flow and pressure should set the regulating valves or pressure reducing valves separately.

8. The force for closing the valve should be appropriate, when handwheel diameter is less than 320mm, only one person is allowed to operate; when handwheel diameter is equal to or larger than 320mm, allowing two persons to operate, or one person operates with a lever up to 500mm.

9. Should change the sealing surface which can't be adjusted.

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