The leakage rate standards of swing check valves vary significantly according to valve type, size, application scenario and compliance standards. The specific classification is as follows:
1. International general leakage level standard (ANSI/FCI 70-2 / ISO 5208)
| Leakage level | Maximum allowable leakage rate | Applicable scenarios | Test conditions |
|---|---|---|---|
| Ⅱlevel | ≤0.5% × rated flow capacity of valve | Common industrial systems (such as cooling water) | Water or air, 3.5 bar pressure |
| Ⅲ level | ≤0.1% × rated flow capacity of valve | Chemical, oil and gas medium pressure pipelines | Same as above |
| Ⅳ level | ≤ 0.01% × rated flow capacity or ≤0.0005 ml/min·psi·inch (liquid) / ≤1.5 SCFH·inch (gas) | Harsh working conditions (high temperature steam, hazardous media) | High pressure gas/liquid testing |
| Ⅴlevel | ≤ 5×10⁻¹² m³/s·mm(gas) | Nuclear energy, ultrapure fluid systems | Helium Mass Spectrometry Leak Detection |
2. Relationship between size and leakage
Small-diameter valves (NPS ≤ 2):
Liquid test: Zero visible leakage (0 drops/minute);
Gas test: Zero bubble leakage (such as natural gas pipelines).
Medium- and large-diameter valves (NPS 2.5-6):
Liquid leakage rate: ≤0.18 in³/min·inch (≈3 cm³/min·inch);
Gas leakage rate: ≤1.5 standard cubic inches/hour·inch (≈0.042 m³/h·inch).
3. Test methods and standards
Liquid sealing test:
API 598: Test pressure = 1.1 times the nominal pressure, pressure holding time ≥ 60 seconds;
Qualification standard: Leakage ≤ corresponding grade limit (such as no visible dripping for grade IV).
Gas sealing test:
ISO 5208: Use nitrogen or air, pressure = 0.6MPa;
Detection method: bubble counting method or flow meter measurement (such as DN100 valve IV level leakage ≤ 15 ml/min).
4. Actual working conditions leakage control
| Influencing factors | Leak rate change | Solution |
|---|---|---|
| Solid particle containing media | Wear of sealing surface will increase leakage by 2-3 times | Use carbide valve disc (such as STL cladding) |
| High temperature (>300℃) | Thermal deformation of metal causes leakage rate to increase by 30%-50% | Chromium-molybdenum-vanadium steel valve body |
| Installation direction incorrect | When installed horizontally, gravity fails and the leakage may exceed the standard by 10 times. | Ensure that the medium flows from bottom to top |
