1、 Leakage of valve body and valve cover:

Reason:

1. The casting quality of cast iron parts is not high, and there are defects such as sand holes, loose structures, and slag inclusions on the valve body and cover body

2. Cold weather and frost cracking;

3. Poor welding with defects such as slag inclusion, lack of welding, and stress cracks;

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

Maintenance method:

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

2. Valves with temperatures between 0 ° C and below should be insulated or heated, and valves that are no longer in use should be drained of accumulated water

3. The welds of the valve body and valve cover composed of welding should be carried out in accordance with relevant welding regulations, and after welding, flaw detection and strength testing should also be carried out;

4. It is prohibited to push or place heavy objects on the valve, and it is not allowed to hit cast iron and non-metallic valves with a hammer. The installation of large diameter valves should have brackets.

2、 Leakage at the packing area (valve leakage, the proportion of the packing area is large)

Reason:

1. Improper selection of fillers, not resistant to medium corrosion, and not resistant to valve high-pressure or vacuum, high or low temperature use;

2. The installation of the filler is incorrect, with defects such as replacing the large with the small, poor spiral wound joints, and loose upper and lower parts;

3. The filler has exceeded its service life, aged, and lost its elasticity

4. The valve stem has low accuracy and defects such as bending, corrosion, and wear

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

6. The gland, bolts, and other components are damaged, making it impossible to tighten the gland;

7. Improper use, excessive force, etc;

8. The gland is tilted, and the gap between the gland and the valve stem is too small or too large, resulting in valve stem wear and packing damage.

Maintenance method:

1. The materials and types of fillers should be selected according to the working conditions;

2. Install the packing correctly according to relevant regulations, the packing should be placed and pressed tightly one by one, and the joint should be at 30 ℃ or 45 ℃;

3. Fillers with long service life, aging, or damage should be replaced in a timely manner;

4. After the valve stem is bent or worn, it should be straightened, and those that are severely damaged should be replaced in a timely manner;

5. The filler 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 gap of more than 5mm;

6. Damaged glands, bolts, and other components should be replaced in a timely manner;

7. The regulations should be followed, except for the impact handwheel, with 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 appropriately increased; The gap between the gland and the valve stem is too large and should be replaced.

3、 Leakage of sealing surface

Reason:

1. The sealing surface is ground unevenly and cannot form a sealing line;

2. The top center of the connection between the valve stem and the closing part is suspended, misaligned, or worn;

3. The valve stem is bent or improperly assembled, causing the closing part to be skewed or out of alignment;

4. Improper selection of sealing surface material quality or failure to select valves according to operating conditions

Maintenance method:

1. Correctly select the material and type of the gasket according to the working conditions;

2. Carefully adjusted and stable;

3. The bolts should be tightened evenly and symmetrically, and a torque wrench should be used if 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 at the flange and threaded connection;

4. The gasket assembly should be centered and aligned, with uniform stress. The gasket should not overlap or use double gaskets;

5. The static sealing surface is corroded, damaged, and of low processing quality. Repair, grinding, and coloring inspection should be carried out to ensure that the static sealing surface meets relevant requirements;

6. When installing the gasket, attention should be paid to cleanliness, and the sealing surface should be cleaned with kerosene. The gasket should not fall to the ground.

4、 Leakage at the connection of the sealing ring

Reason:

1. Sealing ring not tightly rolled

2. The sealing ring is welded to the body, and the welding quality is poor;

3. Loose sealing ring connection threads, screws, and pressure rings;

4. The sealing ring is corroded due to connection.

Maintenance method:

1. Leakage at the sealing rolling point should be fixed by injecting adhesive before rolling;

2. The sealing ring should be re welded according to the welding specifications. When it is not possible to repair welding at the welding site, the original welding and processing should be carried out;

3. Remove screws and pressure rings for cleaning, replace damaged components, grind the sealing and connection seat sealing surfaces, and reassemble. For components with significant corrosion damage, welding, bonding, and other methods can be used;

4. The connecting surface of the sealing ring is corroded, and methods such as grinding and bonding can be used. If not possible, the sealing ring should be replaced.

5、 Leakage caused by the detachment of the closing part:

Reason:

1. Poor use, causing the closing part to jam or exceed the top dead center, and damage or fracture of the connection;

2. The connection of the closing component is not secure, and it falls off due to looseness;

3. The material of the selected connector is incorrect, and it cannot withstand medium corrosion and mechanical wear.

Maintenance method:

1. Correctly use, do not use excessive force to close the valve, do not open the valve beyond the top dead center, and after the valve is fully opened, the handwheel should be slightly reversed;

2. The connection between the closing part and the valve stem should be firm, and there should be a retaining part at the threaded connection;

3. The fasteners used for connecting the closure part and valve stem should withstand the corrosion of the medium and have a certain degree of mechanical strength and wear resistance.