Complete Guide to Valve Leakage Classes (Class I–VI)
05.01.2025 | Valve Standards & Specifications
Get a complete guide to understanding valve leakage classes, Class I through VI, including what valve leakage classes are, a quick reference chart for maximum allowable leakage rates, how each class is defined and tested, and real-world applications by leakage class across different industries and their recommended classifications, outlining how they are applied across different system requirements.
Overview
Valve leakage classes define how much fluid or gas a valve is allowed to leak when fully closed. These standards are critical in selecting control and isolation valves for applications where tight shut-off or minimal leakage is essential.
In this guide, you'll learn:
- What Are Valve Leakage Classes?
- Valve Leakage Class Chart (Quick Reference)
- Understanding Each Leakage Class (I–VI)
- How Are Leakage Classes Tested?
- Real-World Applications by Leakage Class
- Related Resources
- Conclusion: What Class Do You Need?
What Are Valve Leakage Classes?
Valve leakage class is a standardized rating that defines the maximum allowable internal leakage through a valve when it’s fully closed.
These ratings range from Class I (least strict) to Class VI (most stringent). They're governed by standards such as:
- ANSI/FCI 70-2
- IEC 60534-4
- API 598 (for testing)
Valve Leakage Class Chart (Quick Reference)
| Leakage Class | Maximum Allowable Leakage | Test Medium |
|---|---|---|
| Class I | No test required | No test required |
| Class II | 0.5% of rated capacity | Air or water at 50-125°F (10-52°C) |
| Class III | 0.1% of rated capacity | Air or water at 50-125°F (10-52°C) |
| Class IV | 0.01% of rated capacity | Air or water at 50-125°F(10-52°C) |
| Class V | 0.0005 ml/min/in of port diameter per psi differential | Water at 50-125°F(10-52°C) |
| Class VI | 0.15 to 0.3 ml/min (air/water) | Air or nitrogen at 50-125°F(10-52°C) |
Understanding Each Leakage Class
Class I – No Leakage Test Required
Assumes inherent seat tightness. Common in utility-grade valves.
Class II – Low Leakage
Slight leakage allowed under test conditions. Typically metal-to-metal seated valves.
Class III – Moderate Leakage
Tighter than Class II, but not bubble-tight. Used in non-critical process controls.
Class IV – Tight Shut-off for Process Control
Often called “industrial tight shutoff.” Requires metal-to-metal sealing. Common in chemical plants and refineries.
Class V – Very Low Leakage
Used in clean service, high-pressure applications. Fluids: water, air, steam at 100 psi. Tested with water, not air.
Class VI – Bubble-Tight Shutoff
Tested with air or nitrogen. Common in soft-seated valves (e.g., PTFE, TFM 1600). Required in gas service, pharma, and food-grade systems.
How Are Leakage Classes Tested?
Leakage class testing is typically done per ANSI/FCI 70-2 or IEC 60534-4.
Common Test Parameters:
- Test media: water, air, or nitrogen
- Test pressure: ~3.5 bar (for Class V)
- Test duration: 60–120 seconds
- Temperature: ambient
Note: For valves like API 608 ball valves, testing may also follow API 598.
Real-World Applications by Leakage Class
| Industry | Recommended Class |
|---|---|
| HVAC & Water Systems | Class II or III |
| Oil & Gas (Upstream) | Class IV–V |
| Chemical Processing | Class IV–VI |
| Food & Beverage / Pharma | Class VI |
| Steam Isolation | Class III–IV |
Related Resources
Conclusion: What Class Do You Need?
For most industrial applications, Class IV or V will be sufficient. But for pharmaceutical, food-grade, or hazardous gas systems, only Class VI bubble-tight shut-off is acceptable.
Need help selecting the right valve or testing method?
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