Jiangsu Changyueda Metal Products Co., Ltd. , https://www.goodstainlesssteel.com
The main safety valve may experience jamming due to improper assembly, dirt, or corrosion. Additionally, poor surface finish of the piston chamber or damage such as grooves can increase friction between moving and fixed parts, leading to a situation where f1 < f2 + f3 + fm, causing the main safety door to fail to move. For example, during an overhaul of furnace No. 3 in 2001, a major safety door failed to operate during a run-in test due to rust and impurities in the piston chamber, preventing the piston from moving. After cleaning, repairing the chamber, and reassembling with proper lubrication, the system functioned correctly during subsequent tests.
Another common issue is excessive leakage in the piston chamber. If too much air escapes, the force acting on the piston (f1) becomes insufficient, again resulting in f1 < f2 + f3 + fm. This can be caused by worn-out piston rings, incorrect clearance, or poor sealing. In one case, inspection revealed that the piston ring gaps were larger than specified, and the piston chamber had significant surface defects, leading to excessive steam leakage. The solution involved replacing the piston rings, repairing the chamber, and adjusting the throttle valve to improve steam intake and ensure proper operation.
Mismatch between the main safety valve and the impulse safety valve can also cause problems. If the impulse valve has a smaller diameter, it may not provide enough steam flow to activate the main valve. For instance, after replacing heavy hammer-type valves with smaller ones, the main valve failed to open properly. Adjusting the impulse valve’s flow area resolved the issue, emphasizing the importance of matching valve sizes.
Delays in the main safety valve returning to its seat after the impulse valve recoils are often due to high pressure in the piston chamber or excessive friction. Increasing the throttle opening allows steam to escape faster, reducing pressure and enabling the valve to close promptly. Additionally, ensuring proper clearances between moving parts helps prevent sluggish movement.
Low back pressure on the safety valve seat can lead to unnecessary emissions and energy loss. This often happens when the impulse valve discharges continuously, maintaining pressure in the system. Throttling the discharge reduces the flow, allowing the valve to return to its seat more effectively. Checking and adjusting the clearance between the valve core and guide sleeve also helps maintain proper pressure dynamics.
Safety valves may experience "frequency hopping" when they repeatedly open and close due to high back pressure or operator error. Adjusting the throttling valve can reduce the force on the piston, minimizing unnecessary activation. Similarly, flutter—caused by improper valve sizing, inlet restrictions, or excessive discharge resistance—can be mitigated by selecting the right valve size, increasing inlet diameter, or reducing discharge resistance.
In conclusion, understanding the causes of boiler safety valve failures and their solutions is essential for safe and efficient operation. Although modern systems use dual protection mechanisms, addressing issues promptly based on known failure patterns ensures reliability and prevents serious equipment damage. Regular maintenance, proper assembly, and attention to design specifications are key to maintaining the integrity of these critical safety components.