Leakage rating and sealing rating
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Help: Relationship between leakage rating and sealing rating
Both the leakage rating and the sealing rating refer here to the performance parameters of the valve seat. The leakage level of the soft-sealed valve seat is zero leakage (also known as Class 6 leakage) ； The typical leakage level for valves with a hard-sealed seat is class 4 leakage. Of course, there are also those that achieve zero leakage.
Leakage level: It is the amount of internal leakage that is acceptable for process operation when the system is shut down. Levels categorized by volume. Sealing grade: It refers to the amount of leakage that is acceptable under any given conditions, based on the physical and chemical properties of the medium. Levels categorized by volume.
The leakage ratings of commonly used control valves are divided into several grades: A, B, C, D, and E. Class A does not allow leakage ； Grade B: 0.5%C; Grade C: 0.1%C; Grade D: 0.01%C; Grade E: 0.0005%C. In the formula, C is the flow coefficient.
Each standard is different; you can take a look at the FCI 70-2 standard