The demand for highly efficient filtration systems has increased to meet the cleanliness expectations of rapidly evolving engine and hydraulic technologies. Donaldson engineers fuel, oil, coolant, bulk fluid and hydraulic filters to meet the exacting performance standards required by modern equipment manufacturers.
But how does industry measure filter performance? That's where Beta ratings come in.
Why Micron Size Isn’t Enough
We often hear about filters being rated by micron size; remember that 1 micron is one-millionth of a metre, or the smaller size range of bacteria. Simply knowing a filter stops 10-micron particles isn’t helpful without knowing how efficiently the filter performs at 10 microns.
For example, a roll of toilet paper might stop some 10-micron particles, but at what percentage? Without a consistent measure of efficiency, micron ratings alone can be of little value.
Enter the Beta Ratio
To reduce confusion, filter manufacturers use a Beta ratio to describe filter and media performance.
This ISO test uses particle counters and tests fluid dosed with ISO test dusts. Particles at specific sizes are counted before and after the fluid moves through a filter. The Beta ratio details the number of particles upstream on the dirty side of the filter in ratio to the number of the same-sized particles downstream on the clean side of the filter.
Simply, the higher the Beta ratio, the higher the efficiency of the filter at a specific micron size.
If someone asks for a "5-micron filter," the next question should be: “At what Beta ratio?”
For example:
- A 5-micron filter with a Beta ratio of 1000 is much more efficient than a filter with a Beta ratio of 2 on the same-sized particle.
ISO 16889 lists several common Beta ratios.
| Beta Ratio | How Many Particles of a Given Size Will Pass Through the Filter? | Actual Filter Efficiency |
|---|---|---|
| 2 | 1 out of every 2 particles | 50% |
| 10 | 1 out of every 10 particles | 90% |
| 20 | 1 out of every 20 particles | 95% |
| 75 | 1 out of every 75 particles | 98.7% |
| 100 | 1 out of every 100 particles | 99% |
| 200 | 1 out of every 200 particles | 99.5% |
| 1000 | 1 out of every 1000 particles | 99.9% |
| 2000 | 1 out of every 2000 particles | 99.95% |
Each Beta number tells us how well a filter traps particles of a specific size.
A Simple Analogy
Imagine your shirt sleeve filtering marbles. It might have a Beta ratio well above 2000 for marble-sized particles, but well below a Beta ratio of 2 for particles as fine as talcum powder.
Just as a micron size is of little value without knowing the efficiency at the given size, the efficiency or Beta ratio is of little value without knowing the particle size it relates to.
Based on the image above, the filter has only allowed 1 particle out of every 10 particles sized at 5 microns to pass through. Therefore, this filter will have a rating of Beta ratio of 10 against 5-micron particles.
Why It Matters
Matching the right micron rating and Beta ratio or efficiency to your application is critical. Here’s why:
- Using a tighter, more efficient filter than needed can shorten element life, increase pressure drop, or even strip important additives from fluids.
- Using a less efficient filter might extend element life, but at the cost of letting more contaminants through, potentially damaging critical components.
Final Thought
Understanding and specifying the right Beta rating ensures your filtration system performs as intended, protecting your equipment and maximizing longevity.
