What to do when a valve in use leaks? What are the main reasons for leakage?

1、 Leakage caused by the closing parts falling off the pipes

Reasons:

1. The poor operation causes the closing part to get stuck or exceed the top dead center which breaks and damages the connection.
2. The closing part is not firmly connected and falls off due to looseness.
3. The material of the connector is not suitable and therefore cannot withstand the corrosion of the medium and mechanical wear.

Maintenance methods:

1. Ensure the correct operation; do not close the valve too intensively; opening the valve should not exceed the top dead center; if the valve is fully opened the hand wheel should be slightly reversed.
2. The connection between the closing part and the valve stem must be firm. The thread connection must be provided with a stop piece.
3. The fastener used for connecting the closing part and the valve stem must withstand corrosion of the medium and have certain mechanical strength and wear resistance.

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

Reasons:

1. Improper selection of packing, improper corrosion resistance of the medium, high pressure or vacuum, high temperature or low temperature of a valve.
2. The packing is not installed correctly and there are some defects such as replacing the big with small, bad spiral winding joint, tightening and loosening.
3. The filler has aged and lost its elasticity due to wear and tear.
4. The accuracy of the valve stem is not high, along with bending, corrosion, wear and other possible defects.
5. The number of the packing rings is insufficient and the gland is not pressed tightly.
6. The gland, bolts and other parts are damaged. Therefore the gland cannot be compressed.
7. Improper operation, excessive force, etc.
8. The gland is skew and the gap between the gland and the valve stem is too small or too big, resulting in the wear of the valve stem and the damage of the packing.

Maintenance methods:

1. Materials and types of fillers 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 compacted one by one. And the joint should be at 30 ℃ or 45 ℃.
3. The packing should be replaced on time to avoid malfunctions due to aging, corrosion, wear and tear.
4. The valve rod should be straightened and repaired after bending and wearing. A seriously damaged valve rod should be replaced on time.
5. The packing should be installed according to the specified number of turns. The gland should be tightened symmetrically and evenly. And the pressing sleeve should have a pre-tightening clearance of more than 5mm.
6. Damaged gland, bolt and other parts should be repaired or replaced on time.
7. The operating procedures should be followed, except for the impact type hand wheel. The operation should be carried out 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 increased appropriately. If the clearance between the gland and the valve stem is too large, it should be replaced.

3、 Leakage of sealing surface

Reasons:

1. The sealing surface is grinded 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. The valve rod is bent or the assembly is not correct. Therefore the closing part is skewed or does not meet the center.
4. Improper selection of the sealing surface material or failure to select a valve according to the working conditions.

Maintenance methods:

1. According to the working condition, the material and type of the gasket should be selected correctly.
2. Ensure a careful adjustment and 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 big or small. There should be a certain pre tightening clearance between the flange and thread connection.
4. The gasket assembly should be centered and aligned and stress should be uniformed. The gasket is not allowed to lap and use double gaskets.
5. If the static sealing surface is corroded/damaged and the processing quality is not high, it should be repaired and checked for coatings 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.

4、 Leakage at the joint of a sealing ring

Reasons:

1. A sealing ring is not tightly rolled.
2. A sealing ring is welded with the body and the surfacing quality is poor.
3. The connecting thread, screw and pressing ring of a sealing ring are loose.
4. The sealing ring is corroded due to its connection.

Maintenance methods:

1. The leakage of seal rolling should be fixed by injecting adhesive and rolling.
2. The sealing ring should be re-welded according to the welding specifications. If the repair of a welding cannot be carried out at the surfacing position, the original surfacing and processing should be removed.
3. Remove the screw and pressure ring, clean and replace the damaged parts, grind the sealing and connecting seat sealing surface, and reassemble. The parts with large corrosion damage can be repaired by welding, bonding and other methods.
4. If the joint 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.

5、 Body and bonnet leakage:

Reasons:

1. The casting quality of iron castings is not high and there are sand holes, loose structure, slag inclusion and other defects on the valve body and bonnet body.
2. Cracks caused by sudden extreme low temperatures in cold weather situations.
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 methods:

1. Improve the casting quality and carry out the stress test in strict accordance with the regulations before installation.
2. If operating under 0° temperature conditions, the valves should be insulated or heated and the water should be pumped out when the valves are out of service.
3. The welding seams of the valve body and valve cover composed of welding should be carried out according to the relevant welding operation procedures. Flaw detection and strength tests should also be carried out after welding.
4. Do not push or place heavy objects onto valves. Likewise, do not use hammers on cast iron and non-metallic valves. Large diameter valves should be installed with supports.