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Determine the maximum allowable closure test leakage per ISO 5208:2015 (Table 4) for leakage rates A through G. Evaluate pass/fail based on measured leak rate for liquid and gas testing.
Results
ISO 5208:2015 Closure Test Leakage Rates
ISO 5208:2015 (Table 4) defines ten closure test leakage rates — A, AA, B, C, CC, D, E, EE, F and G — for industrial valve testing. The maximum allowable leakage is directly proportional to the valve size DN and does not depend on the test pressure. The closure test pressure itself is fixed by the standard (see note below).
| Rate | Liquid (mm³/s) | Liquid (drops/s) | Gas (mm³/s) | Gas (bubbles/s) |
|---|---|---|---|---|
| A | No visually detectable leakage for the duration of the test | |||
| AA | 0.006 × DN | 0.0001 × DN | 0.18 × DN | 0.003 × DN |
| B | 0.01 × DN | 0.00016 × DN | 0.3 × DN | 0.0046 × DN |
| C | 0.03 × DN | 0.0005 × DN | 3 × DN | 0.0458 × DN |
| CC | 0.08 × DN | 0.0013 × DN | 22.3 × DN | 0.3407 × DN |
| D | 0.1 × DN | 0.0016 × DN | 30 × DN | 0.4584 × DN |
| E | 0.3 × DN | 0.0048 × DN | 300 × DN | 4.5837 × DN |
| EE | 0.39 × DN | 0.0062 × DN | 470 × DN | 7.1293 × DN |
| F | 1 × DN | 0.016 × DN | 3000 × DN | 45.837 × DN |
| G | 2 × DN | 0.032 × DN | 6000 × DN | 91.673 × DN |
Formulas
For liquid testing (water), the maximum allowable leakage in mm³/s:
For gas testing (air/N₂), the maximum allowable leakage in mm³/s (or bubbles/s):
where qL and qG are the unit leakage rates from Table 4 above (e.g. 0.1 mm³/s per DN for Rate D, liquid) and DN is the nominal valve size. 1 mm³/s = 0.06 ml/min.
Practical Example
Given: DN = 100 mm, leakage Rate D, liquid test
Qmax = 0.1 × 100 = 10 mm³/s (= 0.6 ml/min, ≈ 0.16 drops/s)
If measured leak = 2 mm³/s → PASS (within limit)
ℹ️ Test Duration (ISO 5208:2015, Table 2, closure test): DN ≤ 50: 15 s, DN 65–150: 60 s, DN ≥ 200: 120 s (isolation valves). For check valves the minimum closure test duration is 60 s up to DN 150 and 120 s for DN ≥ 200.
ℹ️ Test Pressure: The closure test pressure is set by ISO 5208, not chosen freely: at least 1.1 × CWP for liquid testing, and 1.1 × CWP or 6 bar ± 1 bar for gas testing. The Table 4 allowable leakage does not vary with the applied pressure.
⚠️ Note: Rate A does not mean mathematically zero — it means no visually detectable leakage during the specified test duration. Rates A, B, C, D, E, F and G correspond to the leakage values of EN 12266-1; API 598 acceptance values correspond to Rate A (DN ≤ 50), Rate AA (gas) and Rate CC (liquid) for other than metal-seated check valves, and to Rate EE (gas) / Rate G (liquid) for check valves (ISO 5208:2015, Table 4, Note 4).
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Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
