The scratches on the sealing surface of the gate valve are a common cause of internal leakage and shortened service life of the valve. To solve this problem, efforts should be made from four aspects: design selection, material processing, usage maintenance, and repair techniques.
The following are the specific solutions:
1. Design and Selection Optimization (Source Prevention)
Choose the "avoid rubbing" structure:
In the traditional parallel type gate valve, during the closing process, there is sliding friction between the gate plate and the valve seat, which easily causes damage to the sealing surface. An elastic gate plate or a double gate plate structure can be selected. These structures can reduce the wedge force during the closing process and lower the risk of damage.
Adopting the "floating" or "force-reducing" design:
Some new types of gate valves (such as some vacuum valves or soft-sealing gate valves) adopt special linkage or elastic component structures, enabling the valve plate to automatically align during closure and maintaining a small distance from the sealing surface during the opening and closing process, thus avoiding direct mechanical friction and abrasion.
Correct selection:
If the working conditions contain solid particles (such as sand and welding slag), the parallel gate valve should be preferred. The gate plate of the parallel gate valve slides between the valve seats, and its sealing surface is usually automatically positioned and less likely to be clogged by the particles. Compared with the wedge gate valve, it is more resistant to wear.
2. Upgrade of materials and surface treatment (enhanced resistance)
Appropriate selection of materials:
Select materials with higher hardness and better corrosion resistance based on the characteristics of the medium.
Particle-containing medium: The sealing surface is made of hard alloy (such as Stellite) that has been welded, to increase hardness and resist erosion.
Corrosive medium: Select materials such as acid-resistant stainless steel and Hastelloy alloy.
Surface coating technology:
Carry out special surface treatment on the sealing surface to form a protective layer.
Spraying ceramic/nano coatings: Forming a hard ceramic or nano-particle coating on the sealing surface, significantly enhancing wear resistance and erosion resistance.
Laser cladding: Using a laser beam, alloy powder is fused onto the surface of the sealing surface to form a metallurgically bonded cladding layer. This layer has high hardness and a strong bond with the base material, effectively enabling the repair and strengthening of the sealing surface.
3. Standardized Use and Maintenance (Operational Support)
Do not attempt to open under pressure!
If the valve is opened forcefully while there is still medium pressure inside, it will cause the sealing surface to be eroded by the high-speed fluid or result in severe friction due to the pressure difference. It is essential to operate after the pressure is released or after balancing the pressure through a bypass.
Avoid excessive force:
When closing the valve, do not use an extension rod to apply excessive torque. Excessive closing force will crush the microstructure of the sealing surface, causing deformation or cracks in the sealing surface.
Maintain the cleanliness of the medium:
Install a filter upstream of the valve to prevent welding slag, rust, sand, and other hard impurities in the pipeline from entering the valve chamber. These impurities are the "killers" that can damage the sealing surface.
4. Repair techniques after damage
If the sealing surface has already suffered scratches, the following repair measures can be taken depending on the extent of the damage:
1. Degree of injury: Minor abrasion (depth < 0.05mm
Repair method: Grinding (Lapping)
Explanation: By using grinding paste (coarse grinding, medium grinding, fine grinding) in combination with grinding tools, surface scratches can be removed and the smoothness restored. This is the most common and economical method.
2. Degree of damage: Moderate wear (spots, deep scratches)
Repair method: Electrocladding + Machining
Explanation: By using grinding paste (coarse grinding, medium grinding, fine grinding) in combination with grinding tools, surface scratches can be removed and the smoothness restored. This is the most commonly used and cost-effective method.
3. Degree of damage: Severe damage (large area of peeling and erosion)
Repair method: Laser cladding repair
Description: Utilizing laser cladding technology, large-area damages can be precisely repaired, restoring the geometric shape and hardness of the sealing surface. The heat affected zone is small and the repair quality is high.
