**Abstract:** This paper analyzes the common failure causes of safety valves in boilers, including valve leakage, body leakage, and issues with the main safety valve not operating properly after the impulse safety valve actuates. It also discusses problems such as delayed reseating of the main safety valve, low back pressure, frequency hopping, and flutter. The study identifies the root causes of these failures and provides practical solutions for maintenance and troubleshooting. The keywords include: Safety Valve, Impulse Safety Valve, Main Safety Valve.
**1. Introduction**
Safety valves are critical components in boiler systems, serving as essential protective devices that prevent overpressure scenarios by releasing excess media when system pressure exceeds safe limits. These valves automatically open to release pressure and then close once the system returns to normal operating conditions. Their reliable operation is crucial for both equipment integrity and personnel safety. Any malfunction in a safety valve can lead to catastrophic consequences, making regular inspection, maintenance, and timely repair vital for safe and efficient boiler operation.
**2. Common Failure Causes and Solutions for Safety Valves**
**2.1 Valve Leakage**
Valve leakage occurs when there is an unacceptable level of seepage between the valve disc and seat under normal operating pressure. This can result from dirt or debris on the sealing surface, wear and tear, or improper assembly. To address this issue, it is important to clean the sealing surfaces, inspect and replace damaged parts, and ensure proper alignment during installation. In cases where the sealing surface has been worn down due to long-term use, re-machining and re-welding may be necessary to restore the required hardness and smoothness.
**2.2 Body Leakage**
Body leakage refers to seepage at the junction between the upper and lower parts of the valve body. This is often caused by insufficient bolt tension, poor gasket quality, or uneven surfaces. Corrective actions include tightening bolts in a diagonal pattern, using standard gaskets, and re-grinding the mating surfaces if they are damaged or contaminated. Ensuring proper flatness and cleanliness of the joint surfaces is essential for maintaining a secure seal.
**2.3 Impulse Safety Valve Does Not Move After Main Safety Valve Actuation**
This issue, known as "main safety door refusal to move," can be dangerous and must be addressed promptly. The problem typically arises due to jamming in moving parts, excessive leakage in the piston chamber, or mismatched sizes between the impulse and main safety valves. Proper maintenance includes cleaning internal components, replacing worn-out parts, and ensuring that all dimensions meet manufacturer specifications. Adjustments to the throttle valve or flow area may also be necessary to improve performance.
**2.4 Delayed Reseating of the Main Safety Valve After Impulse Safety Valve Recoil**
Delayed reseating can occur when steam remains trapped in the piston chamber, keeping the valve open longer than necessary. This can be resolved by increasing the throttle opening to allow faster venting of steam, reducing the pressure inside the piston chamber. Additionally, checking and adjusting the clearance between moving parts can help the valve return to its seat more quickly.
**2.5 Low Back Pressure of the Safety Valve Seat**
Low back pressure can cause unnecessary emissions and energy loss. This issue is often linked to improper sizing of the impulse safety valve or excessive flow through the guide sleeve. Reducing the flow rate by throttling or adjusting the gap between the valve core and guide sleeve can help increase back pressure and ensure the valve seats properly.
**2.6 Frequency Hopping**
Frequency hopping occurs when the safety valve repeatedly opens and closes due to unstable pressure conditions. This can be mitigated by adjusting the throttle valve to reduce the pressure rise rate, thereby preventing frequent activation. Proper calibration and monitoring of the system pressure are also essential to avoid this issue.
**2.7 Flutter**
Flutter is a vibration phenomenon that occurs during the discharge process, potentially leading to mechanical fatigue and damage. It is commonly caused by oversized discharge capacity, small inlet pipe diameter, or high resistance in the discharge line. Solutions include selecting a valve with appropriate discharge capacity, increasing the inlet pipe size, and reducing discharge resistance.
**3. Conclusion**
This paper has analyzed the common failure modes of boiler safety valves and provided practical solutions for their prevention and correction. Although modern boiler systems incorporate dual protection mechanisms (main and impulse safety valves), understanding the root causes of failures and having effective repair strategies is essential for ensuring the safe and reliable operation of industrial equipment. Regular maintenance, proper installation, and prompt troubleshooting remain key to avoiding serious incidents.
**References**
1. Pan Waves. *HG-670 / 140-9-type boiler valve repair process specifications*. Jilin Thermal Power Plant, 1998.
2. Wang Chunnian. *Industrial boilers and pressure vessels with safety valve*. Ministry of Labor Boiler and Pressure Safety Journal, 1994.
3. *Valve Manual*. Machinery Industry Press, 1992.
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