5 major causes of valve leakage and repair methods

Leakage caused by falling off of the closure

Reason:

1. Poor operation makes the closing part stuck or exceeds the critical point, and the connection is damaged and broken;
2.  The closing part is not firmly connected, loose, and fall off;
3.  The material of the selected connecting parts is incorrect, and it is not resistant to the corrosion of the medium and the wear of the machinery.

Maintenance method:

1. Operate correctly, do not use excessive force to close the valve, and open the valve not to exceed the critical point. After the valve is fully opened, the handwheel should be reversed 1/4 turn;
2.  The connection between the closing piece and the valve stem should be firm, and there should be a stop at the threaded connection;
3. The fastener used to connect the closing part and the valve stem should be resistant to corrosion by the medium, and have a certain degree of mechanical strength and wear resistance.

Leakage at the packing (external leakage of the valve, the proportion of the packing is the largest)

Reason:

1. Packing is not selected correctly, it is not resistant to the corrosion of the medium, and it is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;
2. Packing is not installed correctly, there are defects such as replacing the big with the small, the joint of the spiral disc system, and the tightening and loosening;
3. Filler has been used for too long, has been aged, and has lost its elasticity
4. Valve stem is not high inaccuracy, too low in strength, and has defects such as bending, corrosion, and wear.
5. Number of packing figures is insufficient, and the gland is not compressed;
6. Gland, bolts, and other parts are damaged so that the gland cannot be compressed;
7. Improper operation, excessive force, etc.;
8. Uneven force in all directions of the gland or a too small or too large gap between the gland and the pole can lead to abrasion of the valve stem or damage to the packing.

Maintenance method:

1. Material and type of filler should be selected correctly according to the working conditions;
2. Install the packing correctly according to the regulations, the packing should be evenly placed and compressed round by round, and the joint should be 30° or 45°.
3. Packing that has been used for a long time, is aging, or is damaged should be replaced in time;
4. After the valve stem is bent or worn, it should be straightened and repaired. If it is seriously damaged, it should be replaced in time;
5. Packing should be installed according to the specified number of turns, the gland should be tightened symmetrically and evenly, and the gland should have a reserved compression gap of more than 5mm;
6. Damaged glands, bolts, and other parts should be repaired or replaced in time;
7. Operating procedures should be followed, except for the impact handwheel, operate at a constant speed and normal force;
8. Gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; the gap between the gland and the valve stem should be replaced if it is too large.

Leakage causes of sealing

Reason:

1. Sealing surface is ground unevenly, and the sealing line cannot be formed;
2. The top center of the connection between the valve stem and the closing part is suspended, out of alignment, or worn;
3.  Valve stem is bent or the assembly is not correct, which makes the closing part skew or not concentric;
4. Improper selection of sealing surface material or failure to select valve sealing type according to working conditions;

Maintenance method:

1. According to the working condition, the material and type of sealing gasket should be selected correctly;
2. Careful adjustment and smooth operation;
3. The bolts shall be tightened evenly and symmetrically. If necessary, a torque wrench shall be used. The pre-tightening force shall meet the requirements and shall not be too large or too small. There should be a certain pre tightening clearance between flange and thread connection;
4. The valve sealing gasket assembly shall be concentric with the valve stem, and the stress shall be uniform. The sealing gasket shall not be overlapped or double gaskets shall be used;
5. If the static sealing surface of the valve is corroded, worn and the light intensity of the valve stem is not high, repair, grinding, and coloring inspection shall be carried out to make the static sealing surface meet the relevant requirements;
6.  Pay attention to keep clean when installing valve sealing gasket, and the sealing surface shall be cleaned with kerosene.

Leakage at the joint of the sealing ring

Reason:

1. Sealing ring is not tightly pressed.
2. Contact surface of the valve sealing ring is uneven or too rough;
3. Sealing ring connection thread, bolt, and pressure ring are loose:
4. Connecting surface of the sealing ring is corroded.

Maintenance method:

1. If the sealing ring is leaking at the compression point, you can refill the adhesive and then press and fix it;
2. The sealing surface should be re-welded according to welding specifications.
3. Remove the bolts and the sealing pressure ring for cleaning, and replace the damaged parts, grind the sealing ring and the joint surface of the connecting seat, and reassemble. For parts with large corrosion damage, welding, bonding, and other methods can be used to repair;
4. The connecting surface of the sealing ring is corroded, and it can be repaired by grinding, bonding, and other methods. If it cannot be repaired, the sealing ring should be replaced.

Leakage of valve body and bonnet

Reason:

1. The casting quality of iron castings is not up to standard, and there are defects such as blisters, loose tissues, and squeezes on the valve body and bonnet body.
2. The temperature is too low and the valve body is frozen and cracked.
3. Poor welding, there are defects such as slag inclusion, non-welding, stress cracks, etc.;
4. The cast iron valve is damaged after being hit by a heavy object.

Maintenance method:

1. Improve the casting quality, and carry out the strength test in strict accordance with the regulations before installation;
2. For valves whose temperature is below 0° and 0°, they should be kept warm or mixed with heat, and the valves that are out of service should be drained of stagnant water.
3. The welding seam of the valve body and the bonnet composed of welding should be carried out in accordance with the relevant welding operation regulations, and the flaw detection and strength test should be carried out after the valve is welded;
4. It is forbidden to push and put heavy objects on the valve, and it is not allowed to hit the cast iron valve and non-metal valve with a hand hammer. The installation of the large-diameter valve should be provided with a bracket.