Standard Industrial Valve inspection & Testing

1.Valve Leakage: Key Standards and Core Points.

Whether for daily equipment maintenance or procurement selection, mastering relevant standards and key points is essential. Here concisely summarizes the definition, classification, testing methods, and selection/acceptance criteria of valve leakage based on international standards such as GB/T 13927-2022, API 598-2023, ANSI/FCI 70-2, and ISO 5208.

2.What is Valve Leakage?
Valve leakage refers to the flow rate or volume of medium passing through the sealing pair (including the valve seat and closure member, body-bonnet joint, stem-packing, etc.) under specified test pressure, test medium, and duration. It is generally divided into visible leakage and micro-leakage. The former can be directly observed by the naked eye (e.g., liquid dripping, continuous gas bubbles), while the latter requires professional instruments for accurate measurement.

3.Introduction of Leakage Classes
Valve leakage is classified into six levels from I to VI, in order of increasing sealing capability. Each level corresponds to a different allowable leakage rate and suits different application requirements.

    · Class I – The lowest sealing level, with no quantitative leakage requirement, only basic sealing function. Suitable for non-critical applications (e.g., ordinary cooling water, atmospheric air conveyance). No special leakage test is required.

    · Class II – Allows small leakage: liquid leakage ≤ 0.1 × DN (drops/min), gas leakage ≤ 30 × DN (mm³/s). Suitable for general gate valves and globe valves in ordinary conditions.

    · Class III – Medium sealing requirement, leakage lower than Class II. Suitable for low-pressure chemical regulating, conventional water treatment, etc.

    · Class IV – Commonly used for metal-seated valves. Leakage ≤ 0.01% of rated flow. Suitable for harsh conditions such as high-temperature high-pressure steam, oil & gas pipelines.

    · Class V – Higher sealing precision, leakage one-tenth of Class IV. Suitable for dangerous media such as flammable or toxic substances.

    · Class VI – The highest sealing level, mostly for soft-seated valves. Requires zero leakage. For small bore (DN ≤ 50 mm), zero bubbles; for larger bore, a small number of bubbles allowed. Suitable for applications with extremely high sealing requirements, such as food & pharmaceutical, high-purity gases, LNG, etc.

4.To accurately determine valve leakage performance, standard test procedures must be strictly followed:

    · Sequence – Leakage testing shall be performed after successful shell strength testing.
    · Test medium – Priority given to clean, impurity-free water (for liquid test) or air/nitrogen (for gas test). For special conditions, corresponding media may be used with proper documentation.
    · Test pressure – High-pressure seat test: 1.1 times the valve’s nominal pressure. Low-pressure seat test: 0.4–0.7 MPa (mainly used to check micro-leakage). For valves with a backseat (upper seal) structure, an additional backseat test at 1.1 times nominal pressure is required.
    · Test duration – Adjusted according to valve size: Liquid test ≥ 60 seconds; Gas test ≥ 30 seconds; For large-bore valves (DN > 100 mm) ≥ 120 seconds. Readings shall be taken after the pressure is stabilized.
    · Measurement methods – Liquid leakage measured by counting drops or volume with a measuring cup. Gas leakage measured by submerging the valve in water and counting bubbles, or directly with a flow meter. For Class VI, the bubble method is mandatory.

We ZheJiang ZhengFeng Valve co.,ltd is a professional valve manufacturer. All valves we produce strictly adhere to the above testing standards. If you need any assistance or further information, please do not hesitate to contact us :sales@zfvalve.com