Ask three suppliers for a “10 micron” filter and you may receive three different products. Nominal micron ratings are a marketing description; the β-ratio is a test result. For a buyer, the difference shows up in valve life, pump wear and the interval between element changes.
The definition
The β-ratio at a stated particle size is the number of particles of that size or larger upstream of the filter divided by the number downstream. A β(c) of 200 means that for every 200 particles of size c or larger entering the filter, one leaves it — an efficiency of 99.5 % at that size.
So “β10 ≥ 200″ and “99.5 % efficiency at 10 µm” describe the same performance. Our return-line and pipeline elements are quoted at β ≥ 100 with an overall efficiency of at least 99.5 %, verified with the ISO 16889 multi-pass method.
Why the number matters
Hydraulic components fail on clearances measured in single microns. A spool valve with a 3–5 µm clearance does not care that a filter is “nominal 10 µm” — it cares how many 5 µm particles pass. Two filters with the same nominal rating but β5 of 20 and β5 of 200 will give completely different component life on the same machine.
What to ask for
- The β-ratio at the size that matters to your component, not just the nominal rating.
- The test standard — ISO 16889 multi-pass is the reference for hydraulic elements.
- Dirt-holding capacity, because a high β-ratio with a tiny capacity means frequent changes.
- Collapse pressure, because a filter that deforms under differential pressure stops filtering.
When finer is not better
A finer element has a higher pressure drop and loads faster. On a suction line, going too fine causes cavitation and pump damage — which is why suction strainers are normally 80–180 µm while the return line does the fine work. Select the finest rating the circuit can afford in pressure drop, and change it on the differential-pressure indicator rather than on the calendar.