ISO 4406 Cleanliness Code

ISO 4406:1999 is the international standard for reporting hydraulic fluid contamination levels. It uses three numbers representing particle counts at different size thresholds:

ISO Code = X/Y/Z (particles >4um / >6um / >14um per mL)

Code Scale Ranges

Each code number represents a range of particle counts per milliliter:

• Code 1 = 1 to 2 particles
• Code 10 = 500 to 1,000 particles
• Code 15 = 16,000 to 32,000 particles
• Code 20 = 500,000 to 1,000,000 particles
• Each increment doubles the count range

Component Sensitivity

Different hydraulic components require different cleanliness levels:

• Servo valves: 15/13/10 or cleaner
• Proportional valves: 17/15/12
• Vane pumps: 18/16/13
• Piston pumps: 17/15/12
• Gear pumps: 19/17/14
• Cylinders: 18/16/13

Beta Ratio (Filtration Efficiency)

Filter efficiency is measured by the beta ratio at a specific particle size:

Beta(x) = Particles upstream / Particles downstream at size x

• Beta 2 = 50% efficiency
• Beta 75 = 98.7% efficiency
• Beta 200 = 99.5% efficiency
• Beta 1000 = 99.9% efficiency