KEVOS® MAKEOS · Maintenance
Hydraulic Filter Selection (Beta Ratios, Cleanliness Code, Pressure Drop)
Will this filter bring the oil to my target cleanliness code, and is its pressure drop acceptable at my flow and oil viscosity?
Selection check of a hydraulic filter: particle counts per millilitre at 4, 6 and 14 µm upstream, the counts after a filter with your beta ratios at each size and its capture efficiencies (as the filter beta ratio tool), the ISO 4406 codes before and after (as the ISO cleanliness code tool) against the target, and the element pressure drop scaled from the maker’s rated value for your flow and viscosity against the allowable drop.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Upstream counts (per mL) | ||
| ≥ 4 µm | per mL | Particles of 4 µm(c) and larger per mL upstream (from an oil sample). |
| ≥ 6 µm | per mL | Particles of 6 µm(c) and larger. |
| ≥ 14 µm | per mL | Particles of 14 µm(c) and larger. |
| Filter beta ratios | ||
| β at 4 µm | Filter beta ratio at 4 µm(c) from the maker’s ISO 16889 data. | |
| β at 6 µm | Beta ratio at 6 µm(c). | |
| β at 14 µm | Beta ratio at 14 µm(c). | |
| Target code | ||
| Target at 4 µm | Target ISO 4406 range number at 4 µm (from the component maker’s requirement). | |
| Target at 6 µm | Target at 6 µm. | |
| Target at 14 µm | Target at 14 µm. | |
| Pressure drop | ||
| Element pressure drop at rated flow and viscosity | bar | Clean element pressure drop the maker gives at the rated flow and viscosity. |
| Rated flow | L/min | Flow at which that drop is given. |
| Rated viscosity | cSt | Viscosity at which that drop is given. |
| Actual flow | L/min | Flow through the filter in service. |
| Actual viscosity (coldest running) | cSt | Oil viscosity at the coldest running condition. |
| Allowable clean element drop | bar | Largest clean element drop you accept (well below the bypass setting). |
Method and formulas
- Downstream count = upstream ÷ β; efficiency = 1 − 1 ÷ β (as the filter beta ratio tool).
- ISO 4406 range number = ⌈log₂(count per mL ÷ 0.01)⌉ (as the ISO cleanliness code tool).
- Element drop ≈ rated drop × (Q ÷ Q_rated) × (ν ÷ ν_rated) for laminar flow through the media.
- Example: the oil goes from 21/19/17 to 18/12/9 against 18/16/13; the element drops 0.23 bar.
Limitations
- Single pass through the filter; a real system reaches a balance between ingression and filtration.
- Housing and bypass valve drops are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a filter rating for a target oil cleanliness
- Check a filter’s pressure drop with cold oil
- Explain an oil sample that misses its target code
Who it is for
- Maintenance engineers
- Hydraulic engineers
- Reliability engineers
What you get
- Downstream counts and efficiencies
- ISO codes before and after against the target
- Element pressure drop
Interpreting the result
- Code numbers fall by one for every halving of the count: a β of 200 drops the code by about seven.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2439–2442. Topic reference; no source tables or recommended settings are reproduced.
- ISO 4406 Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Hydraulic Filter Selection (Beta Ratios, Cleanliness Code, Pressure Drop) calculator
