Is air harmful to lubricating oil?

The lubrication system is a critical component of various machinery and automobiles, with one of the key maintenance points being the prevention of impurities. We generally pay attention to contaminants such as dust, particulate matter, and moisture, often overlooking air. Indeed, air can indeed affect the performance of lubricating oil. Although lubricating oil inevitably comes into contact with air, the presence of air mixed into the oil—such as foam on the oil surface or trapped bubbles within the oil that cannot be released—can negatively impact lubrication.

Under normal circumstances, lubricating oil will slowly oxidize (contact with oxygen) when exposed to air, but this process is relatively slow and unavoidable, which is normal. However, if air enters the interior of the lubricating oil, the problem becomes much more serious.

Three forms of air mixing in lubricating oil

There are three main types of air mixed into lubricating oil:

1. Air dissolved in oil (invisible to the naked eye)

2. Bubbles suspended and trapped within the oil that cannot be released

3. Foam on the oil surface

Among these, the most harmful to machinery and lubricating oil are the bubbles suspended and trapped within the oil.

How to identify bubbles in lubricating oil

Foam will accumulate and float on the oil surface, with a relatively large volume. If foam appears, it generally indicates that bubbles may have already formed inside the oil. Bubbles are suspended and trapped within the oil, smaller in size but highly hazardous.

Bubbles can cause oil to become cloudy. If the oil appears turbid, you can take a sample. If the sample shows layering, then the cloudiness of the lubricating oil is caused by contamination from water or other liquids. If the sample clears up after standing for a while, it indicates that bubbles have been mixed into the oil.

The reason for bubbles in lubricating oil

Many factors can cause an increase in bubbles and foam in lubricating oil, with the most common being the ingress of water. When water mixes into the oil, the surface tension of the oil decreases, preventing the formation of large bubbles that would float to the surface. Instead, they break into tiny bubbles suspended within the oil.

1. Lubricating oil is contaminated

Other liquids, detergents, solvents, etc., are mixed into the oil.

2. Lubricating oil oxidation

Oil oxidation leads to a decrease in the oil's anti-foaming properties. Some oils may exhibit increased foaming after prolonged use, with oxidation being a common cause.

3. Additive depletion

The loss of antifoaming agents can also lead to increased foam. It's important to note that adding too much antifoaming agent can also cause foam issues. Some users, upon noticing increased foam or depletion of antifoaming agents, may add more, but excessive use can similarly result in foam problems.

4. Leakage

Air leakage at the oil pipe, seals, and other parts.

5. Poor fuel tank design

The fuel tank is too small, lacks a filter screen or baffle to remove air bubbles, the return pipe and suction pipe are too close together, and the oil flow rate is too fast to allow bubbles to dissipate.

6. Improper selection of lubricating oil viscosity

Excessive or insufficient viscosity can both lead to bubble issues.

The presence of bubbles and foam in lubricating oil is harmful.

Bubbles and foam are harmful to both lubricating oil and machinery:

Harm to lubricating oil:

• Bubbles accelerate the oxidation and deterioration of lubricating oil.

• Accelerated consumption of additives

• Affects heat dissipation

• Unable to form a complete lubricating oil film

• Bubbles in high-pressure systems can also cause localized high temperatures, leading to rapid oil deterioration.

Hazards to the equipment:

• Air is easily compressed; if there is gas in the lubricating oil, the oil film thickness will become thinner or even rupture, leading to direct friction between mechanical components and causing wear.

• Causes cavitation: Bubbles collapse under pressure, leading to cavitation damage on metal surfaces.

• Impact on mechanical operation: Bubbles can affect the stable operation of mechanical systems. For example, hydraulic systems may experience unstable operation, loss of control, varnish formation on valve cores causing sticking, and corrosion issues.

Methods for handling when excessive foam is detected

When there is an increase of foam in the fuel tank, how should it be handled?

1. Check moisture

Use a clean, dry sampling bottle to collect some oil from the drain port, and observe whether there is water in the discharged oil—free water, or if the oil appears cloudy, stratified, or emulsified and whitish. If water is present, the foam is likely caused by water ingress in the lubricating oil.

2. Check the system

If not caused by moisture, check for air leaks and oil level. If everything is normal, take an oil sample for fluid analysis to detect contamination by other chemicals or oils, additive depletion, or oil degradation.

3. Improve fuel tank design

If the fuel tank design is poor, consider increasing the tank volume, installing baffles and screens in the return oil and suction oil zones.

preventive measures

To ensure excellent mechanical lubrication, it is essential to prevent any foreign substances or other oils from entering the lubricant. The oil must be clean, dry, and free from contamination by any other materials.

• Regularly inspect seals to prevent air leaks.

• Keep lubricating oil clean to avoid contamination

• Rational design of the lubrication system

• Select lubricating oil with appropriate viscosity

• Regularly replace lubricating oil and additives

• Control the usage temperature of lubricating oil