As people’s requirements for environmental protection are becoming more and more stringent, the requirements for valves are also increasing, and the requirements for the allowable leakage level of toxic, combustible and explosive media in petrochemical plants are becoming more and more stringent. Valves are indispensable equipment in petrochemical plants. , Its variety and quantity are large, and it is one of the main leakage sources in the device. For toxic, flammable and explosive media, the consequences of the external leakage of the valve are more serious than the internal leakage, so the external leakage requirements of the valve are very important. The low leakage of the valve means that the actual leakage is very small, which cannot be determined by conventional water pressure and air pressure sealing tests. It requires more scientific means and sophisticated instruments to detect small external leakage.

  Commonly used standards for detecting low leakage are ISO 15848, API624, EPA method 21, TA luft and Shell Oil Company SHELL MESC SPE 77/312.

  Among them, ISO class A has the highest requirements, followed by SHELL class A. This time, NSEN has obtained the following standard certificates;

ISO 15848-1 class A

API 641

TA-Luft 2002

  In order to meet the requirements of low leakage, valve castings need to meet the requirements of helium gas test. Because the molecular weight of helium molecules is small and easy to penetrate, the quality of the casting is the key. Secondly, the seal between the valve body and the end cover is often a gasket seal, which is a static seal, which is relatively easy to meet the leakage requirements. Furthermore, the seal at the valve stem is a dynamic seal. The graphite particles are easily taken out of the packing during the movement of the valve stem. Therefore, special low-leakage packing should be selected and the clearance between the packing and the valve stem should be controlled. The clearance between the pressure sleeve and the valve stem and stuffing box, and control the processing roughness of the valve stem and stuffing box.