What is Beta Ratio in Filtration?
Beta ratio measures filter efficiency per ISO 16889. It is the ratio of upstream to downstream particle counts at a specific micron size. A beta ratio of 200 equals 99.5% particle capture efficiency. Higher beta ratios indicate finer filtration and better contaminant removal from hydraulic fluid.
How Beta Ratio is Measured
Beta ratio testing follows ISO 16889, the Multi-Pass Test. A standardized test dust (ISO Medium Test Dust) is injected upstream of the filter while automatic particle counters measure particle concentrations on both sides. The formula is: βx = Upstream count at size x ÷ Downstream count at size x. The subscript denotes the particle size in microns. For example, β10 = 200 means the filter captures 99.5% of particles 10µm and larger.
Beta Ratio vs. Micron Rating
A filter’s micron rating is only meaningful when paired with its beta ratio. A “10 micron” filter could be β10 = 2 (50% efficient, nominal) or β10 = 200 (99.5% efficient, absolute). Always specify both values when selecting replacement filters to ensure equivalent performance. This is why cross-referencing by micron rating alone can be misleading and potentially dangerous to hydraulic system components.
Practical Application
Servo valves and proportional valves typically require β ≥ 200 or higher at 3–6 microns. Standard hydraulic pumps and motors may only need β ≥ 75 at 10–25 microns. Always match the OEM’s beta ratio specification when selecting a replacement filter element. Using a lower beta ratio than specified will degrade system cleanliness and accelerate component wear.
Reference Table
| Beta Ratio | Efficiency | Rating Type | Typical Application |
|---|---|---|---|
| β ≥ 2 | 50.0% | Nominal | Coarse pre-filtration |
| β ≥ 75 | 98.7% | Absolute | General industrial hydraulics |
| β ≥ 200 | 99.5% | Absolute | Standard servo/proportional valves |
| β ≥ 1000 | 99.9% | High-efficiency | Critical servo systems |
| β ≥ 2000 | 99.95% | High-efficiency | Aerospace, EHC turbine control |
Frequently Asked Questions
What does a beta ratio of 200 mean?
What beta ratio do I need for servo valves?
Is a higher beta ratio always better?
Related Specifications
Need Help Selecting the Right Filter?
Our filtration specialists can help you match specifications to your application. Search our database of 250,000+ filters or request expert assistance.