A filter advertised as “10 micron” is not fully specified. The buyer also needs to know how efficiently it captures particles at that size under a defined test method. Beta ratio is a way to express the upstream-to-downstream particle count across a filter element.
Read the ratio with its particle size
Beta is a count ratio, not a pore diameter. For a specified particle threshold x, beta at x is the number of particles at or above that size upstream divided by the corresponding number downstream in a controlled multipass test. A beta value of 200 means one particle leaves for every 200 entering at that threshold under the test conditions, or 99.5 percent capture by the formula (beta − 1)/beta. It does not mean that every particle smaller than x passes or that every larger one is captured in a live machine.
HYDAC’s element guide explains beta ratio using the ISO 16889 multipass method. If 200 particles of the specified size or larger enter and one leaves under the test conditions, beta is 200 at that size; calculated capture efficiency is 99.5 percent. That example does not guarantee an installed machine will maintain the same cleanliness, because bypass operation, dirt loading, fluid viscosity and ingress also matter. Compare beta values only when the stated particle size notation and test basis are the same. Ask for the complete element data sheet rather than a marketing micron label.
The installed circuit is not the laboratory rig
A filter can have impressive media efficiency yet deliver poor system cleanliness if oil bypasses the element, a seal is missing, the housing is undersized, or dirt enters downstream. Temperature changes viscosity and element pressure drop; flow surges can open a bypass valve. Particle counters also report size using a defined calibration convention, so comparing a beta value at “10 µm” with one at “10 µm(c)” without checking the test standard can mislead. HYDAC’s element data explains the ISO 16889 basis and gives worked count examples.
A purchasing comparison
Two elements are both sold as “10 micron.” One data sheet gives beta 75 at 10 µm(c); another gives beta 200 at 10 µm(c). Under the same multipass test convention, the latter captures a greater fraction at that threshold. But if the second element causes high pressure drop and the housing frequently bypasses during cold starts, its superior media efficiency may not translate into cleaner oil in service. Ask for the full flow-versus-pressure-drop curve, bypass arrangement and dirt-capacity data alongside beta. Then verify with oil samples at the sensitive part of the circuit after installation.
How to compare two proposals
Start with the cleanliness level required by the most sensitive component, then specify the particle size and beta ratio on the same test basis for both candidates. Compare peak-flow pressure drop at cold and hot viscosity, dirt capacity, collapse rating, fluid compatibility and the housing bypass arrangement. Ask for an oil-sampling plan to verify installed performance after commissioning. The filter element is only one part of contamination control; the reservoir, breather, assembly practice and maintenance procedure matter too.
Checks to put on the drawing or test plan
- Record the required cleanliness level at the most sensitive component.
- Compare beta ratio at the specified particle size, not at different sizes.
- Check element flow, pressure drop and dirt-holding data for the duty cycle.
Failure mode to avoid: Treating nominal micron labels from two manufacturers as proof that the filters provide the same efficiency.
Information to request before approval
- Fluid type and operating viscosity range.
- Target cleanliness and peak flow.
- Housing and element part numbers.
For a related explanation, see oil cleanliness codes.
技术参考： HYDAC filter element technical data. The cited manuals and product data describe their makers’ equipment; this article is independent engineering guidance and does not assign their ratings to Yongjian products.