Analysis of Leakage Problems in Cast Steel Globe Valves

Cast steel globe valves are essential devices used to control fluid flow by moving a valve disc. The flow rate is directly proportional to the disc's travel distance, making these valves suitable for cutting off, regulating, and throttling fluid flow. Widely used in industries such as oil, chemicals, and power generation, cast steel globe valves are valued for their reliability and efficiency. However, leakage issues can arise during operation, primarily categorized into internal and external leaks. Understanding the causes and solutions for these problems is crucial for ensuring valve performance and system safety.

Types of Leakage in Cast Steel Globe Valves

Leakage in cast steel globe valves is one of the most common failures, mainly classified into two types: internal leakage and external leakage. Each type has distinct characteristics and causes, and understanding these differences is key to effectively addressing and preventing leaks.

1. Cast Steel Globe Valve Internal Leakage

Internal leakage occurs when fluid passes through the valve even when it is in the closed position. Common causes include:
Damage to Sealing Surfaces: The sealing surfaces of the valve seat or disc may become damaged due to wear, corrosion, or prolonged use, leading to seal failure.
Solid Impurities: If the fluid contains solid particles, these can erode the sealing surfaces, compromising the sealing effectiveness.
Improper Valve Travel Setting: In electric or pneumatic valves, incorrect travel settings may prevent the valve from closing completely, resulting in internal leaks.

2. Cast Steel Globe Valve External Leakage

External leakage refers to fluid leaking from external joints or packing areas of the valve. Main causes include:
Aging or Wear of Packing: Over time, packing materials can deteriorate, leading to leaks.
Loose Connections: Flange connections or bolts may not be tightened properly, causing leaks at the connection points.
Corrosion of the Valve Stem: Corrosion at the contact point between the valve stem and body can lead to seal failure.

Solutions for Steel Globe Valve Internal Leakage

Addressing internal leakage is vital for the normal operation and safety of cast steel globe valves. Here are several common solutions.

1. Inspect and Repair Sealing Surfaces

Check the sealing surfaces of the valve seat and disc for damage. Professional grinding or welding can restore their sealing capability. If significant damage is found, replacing the entire component may be necessary.

2. Remove Solid Impurities

If solid impurities are suspected in the fluid, operating the valve multiple times may help dislodge particles stuck on the disc.

3. Adjust Valve Travel Settings

Ensure that the travel settings for electric or pneumatic valves are correct to avoid insufficient travel that can lead to internal leaks. Regularly check these settings to align with equipment requirements.

Solutions for Cast Globe Valve External Leakage

External leakage can result in fluid loss and safety hazards, making timely identification and resolution critical. Here are common methods to address external leaks.

1. Maintain Packing

Since external leaks often occur at the packing, adjusting the packing gland's tightness can resolve the issue. If the packing is severely worn, it should be replaced promptly to ensure sealing performance.

2. Check Connection Points

Regularly inspect the tightness of bolts at flange connections. Reinforce as necessary to prevent leaks due to looseness. In critical areas, consider using sealants or gaskets to enhance sealing effectiveness.

3. Protect the Valve Stem from Rust

To prevent corrosion, avoid direct exposure of the valve stem to moisture. Regular cleaning and application of anti-corrosive oil can help maintain its functionality.

Cast Globe Valve Usage Considerations

Implementing proper practices during the daily use of cast steel globe valves can significantly extend their lifespan and reduce leakage issues. Correct operation and maintenance are essential for ensuring valve performance and enhancing the overall safety and efficiency of fluid systems. Key considerations include:

1. Avoid Forceful Closing

If a valve cannot shut off flow, do not force it closed. Instead, open the valve to allow the fluid to flush through before attempting to close it again, preventing damage to the sealing surfaces.

2. Prevent Excessive Resistance

When opening the valve, if the stem encounters resistance, avoid forcing it further to prolong the life of the stem and sealing components. Regularly check the valve's operation to ensure it moves freely.

3. Conduct Regular Maintenance and Inspections

Perform routine maintenance on cast steel globe valves, including checking sealing components, cleaning the valve body and fluid pathways, and ensuring proper operation. Pay special attention to lubrication and sealing conditions for valves that have not been used for extended periods.

Conclusion

The widespread use of cast steel globe valves in industrial applications underscores their importance in controlling fluid flow. However, leakage issues should not be overlooked. By understanding the types, causes, and corresponding solutions for internal and external leaks, one can effectively extend the lifespan of these valves and ensure the safety and stability of fluid systems. Regular maintenance, proper operation, and prompt leak management will greatly enhance the overall performance of the system and reduce the likelihood of failures.