【Daily Question No. 301】November 03, 2018

The causes of safety valve leakage and the methods to resolve them are: ① When scale, rust, debris, etc. settle on the sealing surface, it can be cleaned using a manual steam purge； ②When the sealing surface is mechanically damaged or corroded, it can be repaired by grinding or by grinding after turning, or it can be replaced ； ③The spring should be replaced when it fails due to excessive loading or when its elasticity decreases as a result of corrosion ； ④When the valve stem is bent or deformed, or when the seating surface of the valve core is misaligned, the cause must be identified, and components such as the valve stem should be reassembled or replaced ； ⑤When the lever of a lever-type safety valve is skewed relative to its pivot, causing uneven stress on the valve core and the valve seat, the center line of the lever should be adjusted.

①When scale, rust, debris, etc. fall on the sealing surface, it can be cleaned using a manual steam blowout； ②When the sealing surface is mechanically damaged or corroded, it can be repaired by grinding or by grinding after turning, or it can be replaced ； ③The spring should be replaced when it fails due to excessive loading or when its elasticity decreases as a result of corrosion ； ④When the valve stem is bent or deformed, or when the seating surface of the valve core is misaligned, the cause must be identified, and components such as the valve stem should be reassembled or replaced ； ⑤When the lever of a lever-type safety valve is skewed relative to its pivot, causing uneven stress on the valve core and the valve seat, the center line of the lever should be adjusted.

1) There is dirt between the valve disc and the valve seat sealing surface; this dirt fills the sealing surface, creating a gap between the valve core and the valve seat, which leads to leakage in the valve. The method to eliminate this fault is to remove the dirt and impurities that have accumulated on the sealing surface; this is generally done during the maintenance work carried out when the boiler is prepared for shutdown or major repairs. 2) Damage to the sealing surface. First, the material of the sealing surface is of poor quality. The sealing surfaces of the safety valve spool and seat have generally been ground to a very low level, which reduces the hardness of these sealing surfaces as well; this leads to a decline in the sealing performance. The best way to address this issue is to machine away the existing sealing surfaces and then remanufacture them according to the specifications provided, thereby increasing the surface hardness of the sealing surfaces. Be sure to maintain high quality during the processing; if defects such as cracks or pitting appear on the sealing surface, they must be removed by turning before further processing is carried out. Secondly, the quality of maintenance is poor; the grinding of valve cores and seats does not meet the required quality standards. To address this issue, the sealing surfaces are repaired by grinding or by grinding after turning, depending on the extent of the damage. 3) The valve stem is bent or tilted, or the lever is offset from its pivot point, causing the valve core and valve disc to be out of alignment. The way to eliminate this fault is to reassemble or replace it. 4) The spring loses its elasticity or its resilience decreases. After long-term use, springs age and their elasticity decreases; either the material used for the springs does not meet the required standards, or the heat treatment process is inadequate, which leads to plastic deformation when exposed to heat. Additionally, the winding process of the springs is poor, resulting in springs of varying lengths and uneven end surfaces. The methods to eliminate this fault include replacing the springs with qualified ones and readjusting the opening pressure. 5) Improper assembly or inappropriate dimensions of related parts. During the assembly process, the valve core and seat may not be fully aligned, there may be light penetration at the joint surface, or the sealing surfaces of the valve core and seat may be too wide, which hinders proper sealing. The solution is to check the size and uniformity of the clearances around the valve spool, ensure that the hole at the top of the valve spool is aligned properly with the sealing surface, and verify that there are no gaps in any part that could cause the valve spool to lift ； Reduce the width of the sealing surface appropriately as required by the drawings to achieve effective sealing.

①When scale, rust, debris, etc. fall on the sealing surface, it can be cleaned using a manual steam blowout； ②When the sealing surface is mechanically damaged or corroded, it can be repaired by grinding or by grinding after turning, or it can be replaced ； ③The spring should be replaced when it fails due to excessive loading or when its elasticity decreases as a result of corrosion ； ④When the valve stem is bent or deformed, or when the seating surface of the valve core is misaligned, the cause must be identified, and components such as the valve stem should be reassembled or replaced ； ⑤When the lever of a lever-type safety valve is skewed relative to its pivot, causing uneven stress on the valve core and the valve seat, the center line of the lever should be adjusted.

①When scale, rust, debris, etc. fall on the sealing surface, it can be cleaned using a manual steam blowout； ②When the sealing surface is mechanically damaged or corroded, it can be repaired by grinding or by grinding after turning, or it can be replaced ； ③The spring should be replaced when it fails due to excessive loading or when its elasticity decreases as a result of corrosion ； ④When the valve stem is bent or deformed, or when the seating surface of the valve core is misaligned, the cause must be identified, and components such as the valve stem should be reassembled or replaced ； ⑤When the lever of a lever-type safety valve is skewed relative to its pivot, causing uneven stress on the valve core and the valve seat, the center line of the lever should be adjusted.

(1) Damaged sealing surface (common)； (2) Spring damage (usually due to severe corrosion by acids or alkalis, resulting in insufficient spring strength) ； (3) Stem deformation (rarely seen under normal circumstances)

The sealing surface is damaged, reducing the spring force

The main reasons for safety valve leakage are: (1) damaged sealing surface (quite common)； (2) Spring damage (usually due to severe corrosion by acids or alkalis, resulting in insufficient spring strength) ； (3) Stem deformation (rarely seen under normal circumstances)

(1) There is stolen goods stuck to the sealing surface, or the sealing surface is corroded or worn, resulting in pits and grooves； (2) The concentricity of components such as the valve disc and valve seat is compromised due to incorrect installation or other reasons ； (3) The spring loses its original elasticity due to prolonged exposure to high temperatures ； (4) Poor assembly quality of the safety valve, etc

The main reasons for safety valve leakage are: (1) damaged sealing surface (quite common)； (2) Spring damage (usually due to severe corrosion by acids or alkalis, resulting in insufficient spring strength) ； (3) Stem deformation (rarely seen under normal circumstances)