Cleanliness
Particle populations relate to component clearances and contamination control.
- ISO code
- Patch appearance
- Filter debris
Technical pillar
Hydraulic Fluid Analysis
Cleanliness, water, viscosity and varnish risk for precision fluid-power systems.
Reviewed Jul 2026 · Oil Testing Atlas editorial teamOrientation
From a fluid result to an equipment decision.
Cleanliness, water, viscosity and varnish risk for precision fluid-power systems. This pillar connects fluids, equipment, tests, abnormal findings and corrective actions.
Interpretation should distinguish specification testing, condition monitoring, troubleshooting and research analysis. The same method may support all four, but the sampling design, decision rule and strength of conclusion are different.
Reviewed Jul 2026 · Oil Testing Atlas editorial teamDiagnostic dimensions
Read the evidence as a connected system.
A result gains meaning when companion evidence predicts the same mechanism and the operating context is comparable.
Fluid health
Viscosity, oxidation and additives influence response and component protection.
- Viscosity
- Acid number
- FTIR
Contamination
Water, air and wrong-fluid mixing disrupt system performance.
- Water
- Foam
- Additive mismatch
Knowledge map
What to examine.
Use topics as investigation branches rather than isolated checkboxes.
01ISO cleanliness
Review the relevant fluid, equipment, test and abnormal-pattern evidence before selecting action.
02Water
Review the relevant fluid, equipment, test and abnormal-pattern evidence before selecting action.
03Viscosity
Review the relevant fluid, equipment, test and abnormal-pattern evidence before selecting action.
04Varnish
Review the relevant fluid, equipment, test and abnormal-pattern evidence before selecting action.
05Additives
Review the relevant fluid, equipment, test and abnormal-pattern evidence before selecting action.
Sampling and data quality
A representative sample is part of the measurement.
Poor sampling can make precise analysis misleading. Fix the location, operating state, flushing practice and supporting records before comparing trends.
Open sampling guide| Control | Recommended practice | Risk if uncontrolled |
|---|---|---|
| Control 1 | Sample upstream of filters where the objective is system condition | Bias, contamination or a non-comparable trend |
| Control 2 | Flush sample ports | Bias, contamination or a non-comparable trend |
| Control 3 | Use particle-clean bottles | Bias, contamination or a non-comparable trend |
Interpretation framework
Context before alarm.
| Question | Evidence required | Why it changes the conclusion |
|---|---|---|
| Is the sample comparable? | Location, interval, operating state and container | Sampling variation can mimic a condition change |
| Did the fluid system change? | Grade, make-up, filtration and maintenance | Dilution and discontinuities alter concentration |
| Is the signal corroborated? | Companion tests, inspection, filters and machine data | Independent agreement increases confidence |
| Which rule governs action? | OEM, product specification, contract and jurisdiction | Universal limits are rarely defensible |
Related tests
Browse all tests →Build a panel around the decision.
test
Kinematic Viscosity
Confirm grade and detect dilution, oxidation, shear or contamination. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- physical properties
test
Viscosity Index
Describe the temperature sensitivity of lubricant viscosity. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- physical properties
test
Elemental Analysis by ICP-OES
Screen wear metals, contaminants and additive elements. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- wear and elemental analysis
test
PQ Index
Detect the relative amount of ferromagnetic debris, including particles too large for ICP response. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- wear and elemental analysis
test
Analytical Ferrography
Examine wear-particle morphology when routine trends suggest abnormal distress. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- wear and elemental analysis
test
Particle Count
Quantify fluid cleanliness and support contamination-control decisions. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- contamination
test
Karl Fischer Water
Quantify dissolved, emulsified and finely dispersed water. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- contamination
test
Acid Number
Trend acidic constituents associated with oxidation, contamination or additive chemistry. Learn the method principle, sample controls, interpretation limits and related diagnostic evidence.
- tests
- chemical condition
The Oil Testing Atlas provides general educational information and does not replace laboratory review, engineering judgement, equipment inspection, OEM instructions or safety procedures.