1、 Body and bonnet leakage:

Reason:

1. The casting quality of iron castings is not high, and there are sand holes, loose structures, slag inclusions and other defects on the valve body and bonnet body

2. The weather is cold and cracked;

3. Poor welding, slag inclusion, no welding, stress crack and other defects;

4. The cast iron valve is damaged after being hit by heavy objects.

Maintenance method:

1. Improve the casting quality, and conduct the strength test in strict accordance with the regulations before installation;

2. Valves with air temperature below 0 ° and 0 ° shall be insulated or mixed with heat. Valves that are not in use shall be drained of water

3. The welds of the valve body and bonnet composed of welding shall be carried out according to the relevant welding operation procedures, and the flaw detection and strength test shall be carried out after welding;

4. It is prohibited to push or place heavy objects on the valve, and it is not allowed to hit the cast iron and non-metal valve with a hammer. The installation of large- diameter valve shall be equipped with a bracket.

2、 Leakage at packing (valve leakage, the largest proportion of packing)
Reason:

1. The packing is not selected correctly, is not resistant to medium corrosion, and is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;

2. The packing is not installed correctly, and there are some defects such as replacing the big with the small, bad spiral wound joint, loose tightening, etc;

3. The filler has aged and lost elasticity after the service life

4. The accuracy of the valve rod is not high, and there are defects such as bending, corrosion, wear, etc

5. The number of packing rings is insufficient, and the gland is not compressed;

6. The gland, bolt and other parts are damaged, so that the gland cannot be pressed tightly;

7. Improper operation, excessive force, etc;

8. The gland is skewed, and the gap between the gland and the valve rod is too small or too large, which causes the valve rod to be worn and the packing to be damaged.

Maintenance method:

1. Materials and types of packing shall be selected according to working conditions;

2. The packing shall be installed correctly according to relevant regulations, the packing shall be placed and compacted one by one, and the joint shall be 30 ℃ or 45 ℃;

3. The packing with long service life, aging and damage shall be replaced in time;

4. Straighten and repair the bent and worn valve rod, and replace the damaged valve rod in time;

5. The packing shall be installed according to the specified number of turns, the gland shall be tightened symmetrically and evenly, and the compression sleeve shall have a pre tightening clearance of more than 5mm;

6. Damaged glands, bolts and other parts shall be repaired or replaced in time;

7. The operating procedures shall be followed, except for the impact handwheel, which shall be operated at a constant speed and normal force;

8. Tighten the gland bolts evenly and symmetrically. If the gap between the gland and the valve rod is too small, increase the gap properly; if the gap between the gland and the valve rod is too large, replace it.

III. leakage of sealing surface
Reason:

1. The sealing surface is ground unevenly, and the sealing line cannot be formed;

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 materials or failure to select valves according to working conditions

Maintenance method:
1. Select the material and type of the bumping gasket correctly according to the working condition;

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 small. There shall be a certain pre tightening clearance at the flange and threaded connection;

4. The gasket assembly shall be aligned in the middle with uniform stress, and the gasket shall not be overlapped and double gasket shall not be used;

5. If the static sealing surface is corroded, damaged, processed or of poor quality, it shall be repaired, grinded and checked for coloring to make the static sealing surface meet the relevant requirements;

6. Pay attention to cleaning when installing the gasket. The sealing surface shall be cleaned with kerosene, and the gasket shall not fall to the ground.

IV. leakage at the joint of sealing ring
Reason:

1. The sealing ring is not rolled tightly

2. The welding quality of sealing ring and body is poor;

3. The connection thread, screw and pressure ring of sealing ring are loose;

4. The sealing ring is connected and corroded.

Maintenance method:

1. The leakage of seal rolling shall be fixed by injecting adhesive and rolling;

2. The sealing ring shall be repaired according to the welding specification. If the weld overlay cannot be repaired, the original weld overlay and processing shall be removed;

3. Remove the screws and press rings for cleaning, replace the damaged parts, grind the sealing surface of the seal and the connecting seat, and reassemble. The parts with large corrosion damage can be repaired by welding and bonding;

4. If the joint surface of 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.

V. leakage due to falling off of the closing parts:
Reason:

1. If the operation is poor, the closing part will be stuck or exceed the upper dead center, and the connection will be damaged and broken;

2. The closing parts are not connected firmly, loose and fall off;

3. The materials of the selected connecting parts are not correct, and they cannot withstand the corrosion of the medium and the wear of the machinery.

Maintenance method:

1. Correct operation, do not use too much force to close the valve, and do not open the valve beyond 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 rod shall be firm, and the threaded connection shall be provided with a retaining part;

3. The fasteners used for the connection between the closing part and the valve rod shall withstand the corrosion of the medium and have certain mechanical strength and wear resistance.