The leakage class rating in valve design refers to the allowable amount of leakage through the valve when it is closed or in the fully shut-off position. It indicates the level of tightness or sealing performance of the valve and is typically specified by industry standards or valve manufacturers.
Leakage class ratings are expressed using a numerical scale or classification system, with lower numbers indicating tighter sealing and minimal allowable leakage, and higher numbers indicating looser sealing with higher allowable leakage. The leakage class rating is determined based on standardized test procedures and criteria established by organizations such as the American Petroleum Institute (API), American Society of Mechanical Engineers (ASME), or International Organization for Standardization (ISO).
Common leakage class ratings used in valve design include:
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Class I: Also known as zero leakage or bubble-tight sealing, Class I valves have the tightest sealing performance, allowing virtually no measurable leakage when the valve is closed.
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Class II: Class II valves have very low leakage rates, typically allowing a small amount of leakage that is acceptable for most applications but may not meet the strict requirements of Class I.
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Class III: Class III valves have moderate leakage rates, allowing a higher level of leakage than Class II valves but still within acceptable limits for many applications.
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Class IV: Class IV valves have higher leakage rates than Class III valves, allowing a significant amount of leakage under specified test conditions. They are suitable for applications where leakage is permissible and does not affect system performance or safety.
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Class V: Class V valves have the highest leakage rates among the standard classes, allowing substantial leakage that may impact system performance or require additional measures to mitigate.
It's important to note that the specific criteria and test methods used to determine leakage class ratings may vary depending on the type of valve, application requirements, and applicable industry standards. Additionally, the leakage class rating is typically specified in conjunction with other performance parameters, such as pressure ratings, temperature limits, and material compatibility, to ensure that the valve meets the requirements of the intended application.
