What is Micron Rating in Filtration?
A micron rating indicates the particle size, in micrometers (µm), that a filter element is designed to capture. One micron equals one millionth of a meter. Hydraulic filters typically range from 1µm for servo valve protection to 150µm for coarse suction strainers. The rating must be paired with a beta ratio to be meaningful.
Absolute vs. Nominal Micron Ratings
An absolute micron rating means the filter has been multi-pass tested per ISO 16889 and achieved a beta ratio of 200 or higher at that particle size. A nominal micron rating indicates the filter captures some percentage of particles at that size, but without standardized efficiency testing. Absolute-rated filters provide predictable, repeatable performance while nominal ratings cannot be compared between manufacturers.
Size Comparisons
A human hair is approximately 70µm in diameter. The smallest particle visible to the naked eye is about 40µm. Particles as small as 5µm cause significant wear in hydraulic components with tight clearances. Servo valve spools typically have 1–4µm clearances, which is why fine filtration is critical for these systems.
Selecting the Right Micron Rating
The correct micron rating depends on the most sensitive component in the hydraulic circuit. Filter the system to the tightest clearance component. Over-filtering wastes energy through excessive pressure drop, while under-filtering causes accelerated wear and premature component failure.
Reference Table
| Micron Rating | Application | Typical Components |
|---|---|---|
| 1–3µm | Servo valve protection | Servo valves, EHC systems, aerospace |
| 5–6µm | Precision hydraulics | Proportional valves, CNC machine tools |
| 10–12µm | General industrial | Gear pumps, piston pumps, motors |
| 25µm | Return-line filtration | Low-pressure circuits, tank returns |
| 40–150µm | Coarse pre-filtration | Suction strainers, tank breathers |
Frequently Asked Questions
What micron filter do I need for a hydraulic system?
What is the difference between 10 micron absolute and 10 micron nominal?
Related Specifications
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