What to do when the valve leaks,and what is the main reason?

First, The closure piece falls off and causes leakage

The reason:
1. Poor operation makes the closing part stuck or exceeds the top dead center, and the connection is damaged and broken;
2. The closing part is not firmly connected, loosened and falls off;
3. The material of the connecting parts is wrong, which can not withstand the corrosion of the medium and mechanical abrasion.

Maintenance method:
1. Operate correctly, do not use excessive force to close the valve, and open the valve not to 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 the threaded connection should have a backstop;
3. The fastener used to connect the closing part and the valve stem should withstand the corrosion of the medium, and have a certain degree of mechanical strength and wear resistance.

Second, External leakage at the packing

The reason:
1. Wrong selection of packing, not resistant to medium corrosion, not resistant to valve high pressure or vacuum, high temperature or low temperature application;
2. The packing is not installed correctly, there are defects such as replacing the big with small, bad spiral joint, tightening and loosening;
3. The packing has exceeded the service life, has aged and lost its elasticity;
4. The valve stem is not high in precision, and has defects such as bending, corrosion, and abrasion;
5. The number of packing rings is insufficient and the gland is not pressed tightly;
6. The gland, bolts, and other parts are damaged, making the gland unable to 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, causing the valve stem to wear and the packing to damage.

Maintenance method:
1. The material and type of packing should be selected according to the working conditions;
2. Install the packing correctly according to the relevant regulations;
3. The packing that has been used for a long time, aging, or damaged should be replaced in time;
4. When 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. The packing should be installed according to the specified number of rings, the gland should be tightened symmetrically and evenly, and the compression sleeve should have a pre-tightening gap of more than 5mm;
6. Damaged glands, bolts and other parts should be repaired or replaced in time;
7. The operating procedures should be followed, except for the impact handwheel, to operate at a constant speed and normal force;
8. The 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 increased appropriately; if the gap between the gland and the valve stem is too large that should be replaced.

Third, The leakage of the sealing surface

The 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 incorrectly assembled, which makes the closing part skewed or misaligned;
4. Improper selection of the quality of the sealing surface material or failure to select the valve according to the working conditions.

Maintenance method:
1. Correctly select the material and type of the gasket according to the working conditions;
2. Carefully adjust and operate smoothly;
3. The bolts should be tightened evenly and symmetrically, and a torque wrench should be used when necessary. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening gap between the flange and the threaded connection;
4. The gasket assembly should be aligned at the center, and the force should be even. The gasket is not allowed to overlap or use double gaskets;
5. The static sealing surface is corroded, damaged, and the processing quality is bad. Repair, grinding, and color inspection should be carried out to make the static sealing surface meet 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.

Fourth, Leakage at the joint of the sealing ring
The reason:
1. The sealing ring is not tightly rolled;
2. The sealing ring is welded to the body, but the surfacing quality is poor;
3. The sealing ring connection thread, screw and pressure ring are loose;
4. The sealing ring is connected and corroded.

Maintenance method:
1. The leak in the sealed rolling area should be injected with adhesive and then rolled and fixed;
2. The sealing ring should be repaired according to the welding specification. When the surfacing welding cannot be repaired, the original surfacing and processing should be removed;
3. Remove the screws and pressure ring to clean and replace the damaged parts, grind the sealing surface of the seal and the connecting seat, and reassemble. For parts with large corrosion damage, welding, bonding and other methods can be used to repair;
4. If the connecting surface of the sealing ring is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.

Fifth. Leakage of valve body and valve cover:

The reason:
1. The quality of iron castings is bad, and there are defects such as blisters, loose structure and slag inclusion on the valve body and the valve cover.
2. Weather freeze cracking;
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 at working temperature below zero degree Celsius, 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 bonnet composed by 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 welding;
4. It is forbidden to push and put heavy objects on the valve, and it is not allowed to hit the cast iron and non-metal valves with a hand hammer. The installation of large-diameter valves should be completed with brackets.

Post time: Jul-12-2021