Determination of Air Release Value of Lubricating Oil (ASTM D3427 / ISO 9120)
🔹 Purpose of the Test
The air release value measures how quickly entrained air is released from a lubricating oil after being subjected to aeration. This property is critical for:
✅ Hydraulic oils – Prevents air bubbles that affect hydraulic performance
✅ Turbine oils – Ensures proper lubrication in high-speed rotating equipment
✅ Gear oils – Reduces foaming and improves gear protection
✅ Compressor oils – Minimizes cavitation and oxidation risks
📌 Entrained air in oil can cause cavitation, foaming, loss of lubrication, and performance issues.
🔹 Test Equipment & Materials
✔ Air Release Tester – Consists of a thermostatic bath, air supply system, and measuring setup
✔ Graduated Cylinders – To collect and observe air bubbles
✔ Thermometer – Maintains precise test temperature
✔ Stopwatch – Measures air release time accurately
✔ Oil Sample – Preheated and tested under controlled conditions
✔ Compressed Air Source – Delivers air at a specified pressure and flow rate
🔹 Step-by-Step Test Procedure
Step 1: Sample Preparation
1️⃣ Heat the Oil Sample – Preheat the lubricating oil to the test temperature (typically 25-75°C, based on application).
2️⃣ Fill the Test Chamber – Pour the oil into the air release apparatus.
📌 Why? Proper heating ensures consistent viscosity and test accuracy.
Step 2: Aeration Process
3️⃣ Introduce Air Bubbles – Inject air at 50 mL/min through a diffuser for a fixed time (typically 5 minutes).
4️⃣ Observe Foaming – The oil will form air bubbles due to the aeration process.
📌 Why? This simulates real-world conditions where lubricants are exposed to air.
Step 3: Air Release Time Measurement
5️⃣ Stop Air Injection – After aeration, stop the air supply.
6️⃣ Monitor Air Bubble Dissipation – Use a stopwatch to measure the time taken for entrained air to drop to 0.2% volume in the graduated cylinder.
📌 Why? Faster air release indicates a well-formulated lubricant with good anti-foam and air release properties.
🔹 Interpretation of Results
| Air Release Time (min) | Lubricant Performance |
|---|---|
| ≤ 2 min | Excellent (Ideal for high-speed machinery) |
| 2 – 5 min | Good (Acceptable for most applications) |
| 5 – 10 min | Moderate (May cause aeration issues) |
| > 10 min | Poor (High risk of foaming and cavitation) |
📌 Lower values mean better air release performance!
🔹 Factors Affecting Air Release Time
✅ Viscosity of the Oil – Higher viscosity = slower air release
✅ Additives in the Oil – Anti-foam agents improve air release
✅ Oil Contamination – Water and oxidation products slow air release
✅ Test Temperature – Warmer oil releases air faster due to lower viscosity
🔹 Common Issues & Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| Slow air release | High viscosity or poor formulation | Use anti-foam additives or reformulate oil |
| Bubbles remain after test | Contaminants in oil | Filter oil and check for oxidation |
| Inconsistent results | Temperature fluctuations | Maintain strict temperature control |
| Excessive foaming | Oil contains surfactants | Adjust anti-foam additive levels |
🔹 Applications in Industry
✔ Hydraulic Systems – Prevents aeration that leads to loss of efficiency
✔ Turbine Oils – Ensures smooth operation and prevents oxidation
✔ Gear Lubrication – Avoids foaming that can reduce lubrication effectiveness
✔ Compressor Oils – Reduces air entrapment, lowering wear and oxidation risks