In the industrial field, low-temperature globe valves are essential equipment widely used in various low-temperature medium systems. Their primary function is to cut off or regulate the flow of media, ensuring the normal operation of the system. However, due to the unique nature of their working environment, low-temperature globe valves may encounter various issues during use. This article will provide a detailed overview of common faults, their causes, and preventive and troubleshooting methods, helping you better maintain and use this vital equipment.
A low-temperature globe valve is used for low-temperature media (such as liquid hydrogen, liquid oxygen, LNG, etc.) and is mainly employed to cut off or connect media in pipelines. It can also regulate and control the flow of fluids. Key design features include flexible operation, reliable sealing, anti-static properties, and pressure resistance. The proper functioning of low-temperature globe valves in systems like air separation devices and LNG transport vessels is crucial for ensuring the safety and efficiency of the entire system.
During operation, low-temperature globe valves may encounter various issues that not only affect normal operation but may also pose safety risks. Understanding these common faults and their causes is critical for timely identification and resolution. Below are some typical faults and their cause analysis.
The valve top (head) is connected to the valve stem, allowing for automatic alignment of the sealing surfaces when the valve closes. However, after prolonged use, the anti-backlash washer may be damaged, leading to loosening of the locknut. When opening the valve, the valve top may detach, causing the valve to lose its sealing function. Furthermore, if the locknut material is unsuitable, such as using brittle metals, it may also lead to damage.
Valve leakage is a common fault in low-temperature globe valves. The primary causes include:
Damaged Sealing Surfaces: Hard materials (such as silicone, metal shavings, or welding slag) may damage the valve top and seat sealing surfaces, leaving indentations. In such cases, excessive force may be used to close the valve, worsening the damage.
Misalignment of Valve Stem and Seat Sealing Surface: If the valve stem's centerline is not perpendicular to the seat sealing surface, or if the valve top and seat are worn due to long-term use, leakage can occur.
Wear of Threads on Valve Stem and Bushing: The threads on the valve stem and bushing are prone to wear, especially on the female threads of the bushing (usually made of brass). This can prevent proper closure of the valve, often caused by excessive force when opening or closing the valve or continuing to force the valve after it reaches its limit.
The valve stem packing is typically located in the packing chamber near the cold box wall. If the packing is uneven or loose, or if the valve stem is not straight or round, low-temperature liquids or gases can leak from the packing. Due to the transmission of cold, moisture in the air can freeze on the packing, causing the valve stem to freeze. In such cases, steam or hot water is often required to heat the packing to open or close the valve. However, after the valve is operated, the water accumulated in the packing may freeze again, making the valve difficult to operate and potentially leading to valve stem breakage or handwheel fractures.
Common causes of flange leakage include uneven or rough sealing surfaces, insufficient pipeline compensation, uneven tightening of bolts, or the use of inappropriate bolt materials. The threaded ends of the valve stem bushing are connected with tin solder, which may crack after long-term use, leading to leakage. During pressure testing and leak testing, if such leakage is detected, it is recommended to remove the valve stem, reapply solder, tighten, and use silver brazing for repair.
After understanding the common faults and causes, let's explore how to prevent these issues and effectively resolve them when they occur. Correct preventive measures and timely solutions can extend the valve's lifespan and ensure the stable operation of the system. Here are some practical preventive and troubleshooting methods.
Avoid Excessive Force: When opening or closing the valve, do not use excessive force. If the valve cannot move, do not force it open or closed. This can prevent damage to the valve stem and bushing threads and reduce wear on other components.
Regular Inspection and Maintenance: Periodically inspect all valve components to ensure proper operation. Focus on critical parts such as the valve stem packing and flange sealing surfaces.
Packing Installation: After servicing the valve, ensure the packing is installed evenly and tightly. Tighten the packing gland nut securely to ensure the quality of installation and prevent leakage caused by uneven or loose packing.
Heating and Thawing: If the valve stem is frozen, steam or hot water can be used to heat the packing. However, after the valve is operated, it is essential to remove any accumulated water in the packing to prevent re-freezing.
Sealing Surface Inspection: Regularly check the cleanliness and smoothness of the flange sealing surfaces. If any damage is found, repair or replace the surfaces promptly.
Bolt Tightening: Ensure bolts are evenly tightened to avoid leakage due to loose bolts. Select appropriate bolt materials to prevent damage from inappropriate materials.
Tin Solder Thread Maintenance: Regularly check the tin-soldered threads at both ends of the valve stem bushing. If cracks are found, repair them promptly. During pressure and leak testing, if leakage is detected, remove the valve stem, reapply solder, tighten, and use silver brazing for sealing.
Anti-Backlash Washer Inspection: Periodically inspect the condition of the anti-backlash washer. If damaged, replace it promptly to prevent the locknut from loosening.
Sealing Surface Protection: Avoid allowing hard materials to enter the valve to prevent damage to the sealing surfaces of the valve top and seat. If damage occurs, repair or replace the sealing surfaces promptly.
A reasonable structural design and appropriate material selection are the foundation for ensuring the performance and reliability of low-temperature globe valves. These factors are essential for increasing the equipment's service life and reducing maintenance costs. Here are key considerations for the design and material selection of low-temperature globe valves.
The design of low-temperature globe valves should account for their performance in low-temperature environments. For example, the connection between the valve top and stem allows the sealing surfaces to automatically align when the valve closes, enhancing sealing performance.
Selecting the appropriate insulation method is crucial for the performance of low-temperature globe valves. A good insulation design can reduce heat transfer, preventing issues like packing freezing.
Locknut Material: Avoid using cold-brittle metals for locknuts. Choose suitable materials to enhance durability and reliability.
Valve Top and Seat Sealing Materials: Select wear-resistant and corrosion-resistant materials to reduce leakage caused by damage from hard materials.
Valve Stem and Bushing Materials: Since the valve stem threads are less prone to wear, but the bushing (usually brass) threads are more susceptible to damage, selecting appropriate materials and designs can increase the bushing's durability.
Ensuring good sealing performance is critical in the design of low-temperature globe valves. Reducing heat leakage is also essential for improving system efficiency. During design, seal materials and techniques should be selected carefully to address these issues.
Rigorous testing and inspection during the design and manufacturing process are essential. This ensures the valve's quality and performance, providing reliable products to the users.
Now let's explore how effective maintenance and repairs can ensure long-term stable operation. A reasonable maintenance plan and professional repair procedures are key to maintaining the performance of low-temperature globe valves. Below are some practical maintenance and repair suggestions.
Establish a Maintenance Plan: Based on the valve's usage frequency and operating environment, establish a regular maintenance plan. Inspect all valve components periodically to identify and address issues promptly.
Record Maintenance Activities: Keep detailed records of each maintenance session and any issues found. This helps analyze and summarize findings to improve maintenance efficiency and reduce faults.
Choose Professional Technicians: When performing repairs, select experienced technicians who are knowledgeable and capable of diagnosing and solving problems accurately.
Use Professional Tools: Ensure the use of professional tools and equipment during repairs to guarantee high-quality and efficient work.
Spare Parts Inventory: Maintain a certain number of spare parts based on the valve's usage. This ensures prompt replacement in case of failure, reducing downtime.
Spare Parts Quality: Choose high-quality spare parts to ensure compatibility and performance with the original equipment.
Low-temperature globe valves play a critical role in industrial systems. By understanding their common faults, causes, and preventive and troubleshooting methods, we can better maintain and use this equipment. Proper operation, regular maintenance, professional repairs, and reasonable spare parts management are essential for ensuring the normal operation of low-temperature globe valves. Additionally, careful consideration of design and material selection, taking into account the characteristics of low-temperature environments, can improve the valve's performance and reliability. It is hoped that this article will provide valuable reference to help you better manage and maintain low-temperature globe valves, ensuring the safety and efficient operation of your system.
