If leakage beyond the rated range occurs at the seal of the disc and seat of the double-acting pneumatic actuator safety valve, it will lead to media loss and further damage to the sealing material. Generally speaking, the sealing surface of a safety valve consists mainly of metallic material and should be as smooth and flat as possible. However, if the medium is extruded secondarily under pressure, it is not possible to require a complete seal without leakage. Therefore, safety valves with steam as the medium can only be detected by visual observation and by ear in a rated pressure environment. The main causes of valve leakage are as follows.

(1) Because of dirt and debris on the sealing surface, the original sealing surface is blocked and separated, resulting in a gap between the spool and the valve seat, leading to valve leakage. To solve such problems, the sealing surface should be usually cleaned. When a boiler is temporarily shut down for maintenance, the safety valve should first be tested for weight operation. In the event of leakage, a complete overhaul should be carried out. After complete cooling, run the weights at intervals of 20 minutes.

(2) Damage to the sealing surface. There are many reasons for this, such as unqualified sealing materials. After years of use, safety valves tend to weaken the strength of the sealing surface due to constant opening and closing, wear, and maintenance, thus weakening the sealing capacity. The recommended measure to address this problem is to spread the original sealing surface and to carry out secondary machining and welding according to the original drawings to improve the hardness and strength of the surface. Also, pay attention to damage to the surface and do not be careless.

(3) Quality of maintenance. Due to the poor level of maintenance, the grinding process of the core and seat cannot be achieved to a certain level. The solution is to use grinding or even turning to repair as many sealing surfaces as possible, depending on the severity of the damage.

(4) Improper assembly or incorrectly sized parts. Throughout the assembly process, the core and seat are not perfectly aligned, or there is a serious light transmission problem on the mating surface, or the seal between the core and seat may be too loose to truly seal. The solution is to rigorously check the length, thickness, and distribution of the gap next to the core and ensure that the core cannot be lifted through the gap in each part. The width of the sealing surface should be reduced appropriately to seal according to the data on the drawing.