What is the ISO Cleanliness Code?

The ISO cleanliness code, defined by ISO 4406, expresses hydraulic fluid contamination using three numbers representing particle counts per milliliter at three sizes: ≥4µm, ≥6µm, and ≥14µm. For example, a code of 16/14/11 means 320–640 particles ≥4µm, 80–160 particles ≥6µm, and 10–20 particles ≥14µm per mL.

Reading the Code

Each number represents a range of particle counts per milliliter. Code “16” means 320–640 particles/mL. The three positions represent particles ≥4µm(c), ≥6µm(c), and ≥14µm(c). A system at ISO 16/14/11 has significantly more contamination than one at ISO 14/12/9. Lower numbers mean cleaner fluid.

Achieving Target Cleanliness

To achieve a target ISO code, you need a filter with an appropriate micron rating and beta ratio, properly sized for the system flow rate. A system targeting ISO 16/14/11 typically needs β6 ≥ 200 filtration. The ingression rate of contaminant and the filtration ratio together determine the steady-state cleanliness level.

Why Cleanliness Codes Matter

Studies show that 75–85% of hydraulic system failures are caused by fluid contamination. Maintaining proper cleanliness extends component life by 3–5x. Every ISO code number reduction (e.g., from 18/16/13 to 17/15/12) roughly halves the particle count and measurably extends equipment life.

Reference Table

Component	Target ISO Code	Required Filtration
Servo valves	14/12/9	β3 ≥ 200 (3µm absolute)
Proportional valves	16/14/11	β6 ≥ 200 (6µm absolute)
Vane/piston pumps	17/15/12	β10 ≥ 200 (10µm absolute)
Gear pumps	18/16/13	β12 ≥ 200 (12µm absolute)
Cylinders	18/16/13	β12 ≥ 200 (12µm absolute)

Frequently Asked Questions

What ISO cleanliness code should my hydraulic system be?

The target ISO code depends on the most sensitive component in the circuit. Servo valve systems should target ISO 14/12/9 or cleaner. General industrial hydraulic systems with gear pumps and cylinders typically target ISO 18/16/13. Check your component manufacturer’s recommendations.

How do I measure ISO cleanliness code?

ISO cleanliness is measured using automatic particle counters (laser-based) that count particles in a fluid sample at ≥4µm, ≥6µm, and ≥14µm sizes. Portable particle counters can test fluid on-site, or samples can be sent to a laboratory for analysis.

What does ISO 16/14/11 mean?

ISO 16/14/11 means the fluid contains 320–640 particles/mL at ≥4µm, 80–160 particles/mL at ≥6µm, and 10–20 particles/mL at ≥14µm. This is a common target for proportional valve systems and mid-criticality hydraulic circuits.

Related Specifications

Beta Ratio Micron Rating Filter Media Types

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