What are the causes of valve leakage and what are the solutions?

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What are the causes of valve leakage and what are the solutions? I. Leakage caused by the detachment of the closing element. Reasons: 1. Improper operation, which causes the closing element to get stuck or go beyond its upper dead center, leading to damage and breakage at the connection points; 2. The connection between the closing element and other components is not secure, resulting in its detachment due to loosening; 3. The material used for the connections is inappropriate, and it cannot withstand corrosion from the medium or mechanical wear. Maintenance methods: 1. Operate correctly – do not use excessive force when closing the valve, and do not open it beyond its upper dead center; after the valve is fully open, turn the handwheel slightly in the opposite direction. 2. The connection between the closing element and the valve stem must be secure, and a stop device should be present at the threaded connection. 3. The fasteners used to connect the closing element to the valve stem must be resistant to corrosion by the medium, as well as possess sufficient mechanical strength and wear resistance. II. Leaks at the packing area (external leaks of the valve, with the packing area accounting for the largest proportion) Causes: 1. Incorrect selection of packing – it cannot withstand corrosion by the medium, nor high pressure or vacuum, high or low temperatures; 2. Improper installation of the packing – issues such as using packing that is not suitable for the application, poor winding of the packing, or uneven tightening; 3. The packing has exceeded its service life and has lost its elasticity; 4. The valve stem is not precise enough, with defects such as bending, corrosion, or wear; 5. Insufficient number of packing rings, or the gland is not tightened properly; 6. Damage to the gland, bolts, and other components, preventing proper tightening of the gland; 7. Improper operation, such as applying excessive force; 8. The gland is misaligned, resulting in either too small or too large a gap between the gland and the valve stem, which leads to wear of the valve stem and damage to the packing. Maintenance methods: 1. The material and type of packing should be selected based on the operating conditions; 2. The packing should be installed correctly in accordance with relevant regulations – the packing rings should be placed and compressed one by one, with the joints at an angle of 30° or 45°; 3. Packing that has been in use for too long, has aged, or is damaged should be replaced promptly; 4. If the valve stem is bent or worn, it should be straightened or repaired, and if the damage is severe, it should be replaced immediately; 5. The packing should be installed in the specified number of rings, and the gland should be tightened symmetrically and evenly; there should be a pre-tightening gap of at least 5 mm; 6. Damaged glands, bolts, and other components should be repaired or replaced as soon as possible; 7. The operating procedures must be followed – except for impact-type handwheels, the valve should be operated at a steady speed with appropriate force; 8. The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, it should be increased appropriately; if the gap is too large, the gland should be replaced. III. Leakage at the sealing surface
Causes:
1. The sealing surfaces are not properly ground, preventing the formation of a tight seal;
2. The connection between the valve stem and the closing element is uneven, misaligned, or worn;
3. The valve stem is bent or not assembled correctly, causing the closing element to be misaligned;
4. The material used for the sealing surfaces is inappropriate, or the valve was not selected based on the operating conditions.

Maintenance methods:
1. Select the appropriate material and type of gasket based on the operating conditions;
2. Adjust carefully and operate smoothly;
3. Tighten the bolts evenly and symmetrically; use a torque wrench if necessary. The preload should be appropriate – neither too high nor too low. There should be a certain pre-tightening gap at the flange and threaded connections; 4. The gaskets should be aligned properly when installed so that the load is distributed evenly – overlapping gaskets or the use of multiple gaskets is not allowed; 5. If the static sealing surface is corroded, damaged, or of poor quality, it should be repaired and ground, and a color inspection should be carried out to ensure that the static sealing surface meets the relevant requirements; 6. Care should be taken to keep the area clean when installing gaskets – the sealing surface should be cleaned with kerosene, and the gaskets should not be dropped on the ground. IV. Leakage at the seal ring connection Causes: 1. Inadequate pressing of the seal ring. 2. Poor quality of welding or cladding between the seal ring and the main body. 3. Looseness of the threads, screws, or clamping rings used to connect the seal ring. 4. Corrosion at the connection point of the seal ring. Maintenance methods: 1. For leaks at the sealed rolling area, apply adhesive and then roll to fix it; 2. The sealing ring should be rewelded in accordance with welding specifications without removing it. When it is not possible to weld repairs at the surfacing area, the original surfacing and any work done there must be removed; 3. Remove the screws and retaining rings, clean them, replace the damaged components, grind the surfaces where the seal meets the mounting base until they fit properly, and then reassemble everything. For components that have suffered significant corrosion damage, they can be repaired using methods such as welding or bonding. 4. If the connection surface of the seal ring is corroded, it can be repaired by grinding or bonding; if repair is not possible, the seal ring must be replaced. V. Leakage in the valve body and valve cover: Causes: 1. Poor quality of cast iron casting, with defects such as sand holes, loose structures, and slag inclusions in the valve body and valve cover; 2. Frost cracking; 3. Poor welding, resulting in defects such as slag inclusions, unwelded areas, and stress cracks; 4. Damage to the cast iron valve due to being struck by heavy objects. Maintenance methods: 1. Improve the casting quality and conduct strength tests strictly in accordance with regulations before installation; 2. For valves operating at temperatures of 0° or below, insulation or heating measures should be applied, and water accumulation should be removed from valves that are not in use; 3. The welds between the valve body and the valve cover, which are formed by welding, must be carried out in accordance with relevant welding procedures, and flaw detection and strength tests should also be conducted after welding; 4. It is prohibited to place heavy objects on the valves, and hammers must not be used to strike cast iron or non-metallic valves. Large-diameter valves should be installed using supports.