The Importance of Using the Correct Compressor Oil Grade
Compressor oil does far more than lubricate moving parts—it seals, cools and protects the entire air system. Selecting the correct grade is one of the simplest ways to extend equipment life, reduce energy costs and maintain manufacturer warranty. This UK-focused guide explains oil grades, specifications, and how to choose the right lubricant for ABAC, Atlas Copco, FINI, NUAIR, HPS and dental compressors.
1. Why Oil Grade Matters
The wrong oil thickens or thins under temperature extremes, leading to bearing wear, valve deposits and higher running temperatures. Correct viscosity ensures a stable film between metal surfaces and transfers heat away efficiently. In rotary screws, oil also seals the compression chamber and prevents internal leaks between rotors.
2. Understanding ISO Viscosity Grades
| ISO Grade | Viscosity (cSt @40 °C) | Typical Application |
|---|---|---|
| ISO 32 | 32 cSt | Low-temperature environments, small screws |
| ISO 46 | 46 cSt | Standard UK ambient 5–35 °C; most screw compressors |
| ISO 68 | 68 cSt | High-temperature or heavy-duty sites |
| ISO 100 | 100 cSt | Piston compressors (non-detergent) |
3. Mineral vs Synthetic Oil
- Mineral Oil: Cost-effective for light-duty or low-hour operation; change every 500–1 000 hours.
- Synthetic Oil: Superior oxidation stability, wider temperature range, extended 2 000–4 000 hour intervals.
- PAO (Poly-alpha-olefin) Blends: Used by Atlas Copco and HPS for long-life performance and minimal varnish.
- Food-grade Oils: NSF H1 approved lubricants for compressors supplying food, beverage or breathing air.
4. Brand-Specific Recommendations
- ABAC Genesis / Spinn: ISO 46 synthetic or OEM ABAC Oil LT; change every 2 000 hours.
- Atlas Copco GX / GA: Roto Xtend Duty ISO 46 or equivalent full-synthetic.
- FINI / NUAIR Piston: ISO 100 non-detergent mineral; change every 250–500 hours.
- HPS Screw Range: ISO 46 synthetic with anti-oxidant additives for 4 000 h life.
- Dental Oil-Free: No lubricating oil in compression chamber—only bearing oil per OEM spec.
5. Oil Change Intervals (Typical UK Use)
Running hours, ambient temperature and load factor determine change frequency. The table below offers general guidance:
| Compressor Type | Oil Type | Change Interval (Hours) |
|---|---|---|
| Piston | ISO 100 mineral | 250 – 500 |
| Rotary Screw (mineral) | ISO 46 mineral | 1 000 – 2 000 |
| Rotary Screw (synthetic) | ISO 46 synthetic | 2 000 – 4 000 |
| High-temp duty | ISO 68 synthetic | 2 000 – 3 000 |
| Food grade | NSF H1 ISO 46 | 2 000 – 3 000 |
6. Common Oil Problems
- Milky Oil: Water ingress – check condensate drain and after-cooler.
- Dark or Burnt Oil: Overheating – clean coolers and verify airflow.
- Foaming: Overfilling or wrong grade – maintain level mid-sight glass.
- Carbon Deposits: Using automotive oil – always use compressor-specific blends.
7. Measuring and Topping Up Oil
- Check level daily via the sight glass while unit is off and pressure released.
- Maintain level midway between “min” and “max.”
- Never mix different brands or mineral/synthetic types – flush system before switching.
8. Environmental & Safety Responsibilities
Used compressor oil is classed as hazardous waste under UK Environmental Regulations. Collect it in a sealed container and send it to an approved recycler. Never discharge oil-contaminated condensate to drains—fit an oil-water separator.
9. Storage and Shelf Life
Store sealed containers indoors between 5–35 °C. Avoid freezing or direct sunlight. Mineral oils typically last 2 years; synthetics up to 5 years. Mark the opening date on each container.
10. Choosing the Right Oil for UK Conditions
Most of the UK has a moderate climate; ISO 46 suits 90 % of installations. Switch to ISO 68 during sustained ambient temperatures > 35 °C (summer factory floors) or ISO 32 for cold, unheated workshops.
11. Typical Oil Capacities
| Compressor Model | Oil Capacity (L) |
|---|---|
| ABAC Genesis 7.5 | 4 L |
| Atlas Copco GX 7 | 3.5 L |
| HPS 15 Screw | 8 L |
| FINI MK102 Piston | 0.6 L |
| NUAIR NB7/500 | 1 L |
12. Cost vs Longevity
Switching from mineral to synthetic oil may double the price per litre but usually halves energy losses and doubles service intervals—often saving hundreds of pounds annually in electricity and downtime.
13. Practical Tips for Engineers
- Warm engine before draining oil—hot oil flows and removes sludge.
- Replace the oil filter every time you change oil.
- Record hours and next due change on a tag attached to the sight glass.
- Keep one spare litre sealed near each compressor for emergency top-ups.
14. Special Notes for Dental & Oil-Free Compressors
Oil-free systems use sealed bearings; never attempt to add oil unless specified. Only use OEM bearing grease or lubricant identified in the manual. Replace bacterial and carbon filters annually to protect air quality.
15. Recommended Products (Internal Links)
FAQs
Can I use car engine oil in my compressor?
No. Automotive oils contain detergents that create carbon build-up and damage valves. Always use compressor-specific non-detergent or synthetic oil.
How much oil should I put in after a change?
Fill until the sight-glass is halfway. Overfilling increases separator pressure drop and oil carry-over.
Can I mix mineral and synthetic oils?
Never. They may be chemically incompatible—flush the system before switching.
Do oil-free compressors need oil?
Only for gearbox bearings, not for the compression chamber. Check manufacturer instructions before adding any lubricant.