Causes and maintenance methods of valve leakage


What should I do when the valve in use leaks? What is the main reason?
1. The closing parts fall off and cause leakage
reason:
1. The operation is poor, so that the closing part is stuck or exceeds the top dead center, and the connection is damaged and broken;
2. The connection of the closing part is not firm, and it falls off loosely;
3. The material of the connector is incorrect, and it cannot withstand the corrosion of the medium and the mechanical wear.
Maintenance method:
1. Correct operation, close the valve can not be too forceful, open the valve can not exceed the top dead center, after the valve is fully opened, the handwheel should be reversed a little;
2. The connection between the closing part and the valve stem should be firm, and there should be a stopper at the threaded connection;
3. The fasteners used to connect the closing part and the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance.
2. Leakage at the packing (outside leakage of the valve, the proportion of the packing is larger)
reason:
1. The 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. The packing is installed incorrectly, and there are defects such as replacing the big with the small, the spiral coiled joint is bad, and the upper is tight and the lower is loose;
3. The filler has aged and lost its elasticity after it has exceeded its service life.
4. The accuracy of the valve stem is not high, and there are defects such as bending, corrosion and wear
5. The number of packing circles is insufficient, and the gland is not pressed tightly;
6. The gland, bolts, and other parts are damaged, so that the gland cannot be compressed;
7. Improper operation, excessive force, etc.;
8. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, resulting in wear of the valve stem and damage to the packing.
Maintenance method:
1. The material and type of packing should be selected according to the working conditions;
2. The packing should be installed correctly according to the relevant regulations, the packing should be placed and pressed one by one, and the joint should be at 30°C or 45°C; 3. The packing that has been used for too long, aged and damaged should be replaced in time;
4. After the valve stem is bent and worn, it should be straightened and repaired, and if the damage is serious, it should be replaced in time;
5. The packing should be installed according to the specified number of turns, the gland should be tightened symmetrically and evenly, and the pressure sleeve should have a pre-tightening clearance of more than 5mm;
6. Damaged glands, bolts and other components should be repaired or replaced in time;
7. The operating procedures should be followed, except for the impact handwheel, operate at a constant speed and normal force;
8. Tighten the gland bolts evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; if the gap between the gland and the valve stem is too large, it should be replaced.
3. Leakage of sealing surface
reason:
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 improperly assembled, causing the closing part to be skewed or out of alignment;
4. The quality of the sealing surface material is improperly selected or the valve is not selected according to the working conditions
Maintenance method:
1. Correctly select the material and type of the gasket according to the working conditions;
2. Careful adjustment, smooth operation;
3. The bolts should be tightened evenly and symmetrically. If necessary, a torque wrench should be used. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening clearance between the flange and the threaded connection;
4. The gasket assembly should be aligned at the center, the force is uniform, and the gasket is not allowed to overlap and use double gaskets;
5. If the static sealing surface is corroded, damaged, and the processing quality is not high, it should be repaired, ground, and checked for coloring, so that the static sealing surface meets the relevant requirements;
6. Pay attention to cleaning when installing the gasket, the sealing surface should be cleaned with kerosene, and the gasket should not fall to the ground.
4. Leakage at the joint of the sealing ring
reason:
1. The sealing ring is not rolled tightly
2. The sealing ring is welded with the body, and the quality of surfacing is poor;
3. The connecting threads, screws and pressure rings of the sealing ring are loose;
4. The sealing ring is connected and corroded.
Maintenance method:
1. The leakage at the sealing and rolling place should be injected with adhesive and then fixed by rolling;
2. The sealing ring should be re-welded according to the welding specification. When the surfacing weld cannot be repaired, the original surfacing welding and processing shall be removed;
3. Remove the screws, clean the pressure ring, replace the damaged parts, grind the sealing surface of the seal and the connection seat, and reassemble. For parts with large corrosion damage, it can be repaired by welding, bonding and other methods;
4. The connecting surface of the sealing ring is corroded and can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.
5. Leakage of valve body and bonnet:
reason:
1. The casting quality of iron castings is not high, and there are defects such as sand holes, loose structure and slag inclusion on the valve body and valve cover body.
2. Day freeze cracking;
3. Poor welding, there are defects such as slag inclusion, unwelding, stress cracks, etc.;
4. The cast iron valve is damaged after being hit by heavy objects.
Maintenance method:
1. Improve the casting quality, and carry out the strength test in strict accordance with the regulations before installation;
2. For valves with air temperature below 0° and 0°, they should be kept warm or heated, and the valves that are out of use should be drained of water.
3. The welding seam of the valve body and the bonnet composed of welding should be carried out according to the relevant welding operation regulations, and the flaw detection and strength test should be carried out after welding;
4. It is forbidden to push and place heavy objects on the valve, and it is not allowed to hit cast iron and non-metallic valves with a hand hammer. The installation of large-diameter valves should have brackets.

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