LUBRICATION GUIDE
Oil Analysis Limits: Water PPM, ISO 4406 Cleanliness, TAN and TBN
By the PCG Technical Desk · Updated 27 September 2026
Quick answer: There is no single universal limit. Set targets by component sensitivity and OEM guidance. Common practice: keep water in hydraulic oil to a few hundred ppm or less, with no free water. Keep the ISO 4406 code at or below the target for your most sensitive component. Watch TAN (acidity from oxidation) rise and TBN (engine-oil alkaline reserve) fall.
ISO 4406 cleanliness code chart
ISO 4406 reports three numbers for particles ≥4, ≥6 and ≥14 µm(c) per mL, for example 18/16/13. Each code number represents a range. Moving up one number roughly doubles the particle count.
| Code | Particles per mL (more than – up to) |
|---|---|
| 13 | 40 – 80 |
| 14 | 80 – 160 |
| 15 | 160 – 320 |
| 16 | 320 – 640 |
| 17 | 640 – 1,300 |
| 18 | 1,300 – 2,500 |
| 19 | 2,500 – 5,000 |
| 20 | 5,000 – 10,000 |
| 21 | 10,000 – 20,000 |
| 22 | 20,000 – 40,000 |
Typical cleanliness targets (guidance)
| Most sensitive component | Typical target |
|---|---|
| Servo valves | 16/14/11 or cleaner |
| Proportional valves | 17/15/12 |
| Piston / vane pumps | 18/16/13 |
| Gear pumps, general hydraulics | 19/17/14 |
These are common industry starting points. Use the component OEM's target where one is published.
Water in oil
Water speeds up oxidation, depletes additives, promotes rust and cuts bearing life. Levels are reported in ppm (by Karl Fischer). Hydraulic and turbine systems generally aim for a few hundred ppm or less. Visible haze means you are beyond the oil's saturation point and need to act.
TAN and TBN
- TAN (total acid number), mg KOH/g: rises as the oil oxidises. Trend it against the new-oil value.
- TBN (total base number), mg KOH/g: an engine oil's reserve for neutralising combustion acids. It falls in service. IOCL lists TBN 8.5–11.5 for Servo Pride TC 15W-40.
Outside Karnataka? The technical information on this page applies anywhere in India. PCG Business Solutions supplies SERVO in seven Karnataka districts. If you are in another state, send us your requirement and we will point you to IndianOil's authorised channel for your area, or answer any technical question about the grade.
