Air compressors are a demanding application for any lubricant. The lubricant is subjected to high temperatures, contaminants, and often harsh environmental conditions. Air compressor lubricants must handle these tough conditions while providing the following critical functions.
Protection Against Wear and Friction
Like any lubricant, air compressor oil protects against wear and friction by separating moving surfaces, which helps prevent metal-on-metal contact. This separation layer is incredibly thin, often less than 4 µm (less than the thickness of a human hair).
A critical factor in maintaining this separation is the viscosity of the oil. If the viscosity is too low, the lubricant will not be able to separate the moving surfaces effectively. If the viscosity is too high, increased friction and heat will result. The correct viscosity of a lubricant is typically selected by the manufacturer of the compressor.
| Compressor Type | Typical Viscosities |
| Rotary Screw | 32, 46, 68 |
| Piston (Reciprocating) | 68, 100, 150 |
| Rotary Vane | 100, 150 |
| Centrifugal | 22, 32 |
| Rotary Lobe Blowers | 150, 220 |
Since compressors in high-temperature environments often operate at higher temperatures, it is typically recommended to use a higher-viscosity oil. This is because the viscosity of the oil decreases as the temperature rises.
Sealing
Air compressor lubricants can also increase compression efficiency by creating a seal. In a rotary screw compressor, the oil creates a seal between the rotating male and female rotors.
Heat Transfer
An air compressor lubricant must also transfer heat. A lubricant with poor heat transfer properties can lead to excessive temperatures, which can cause catastrophic equipment failure due to thermal expansion.
Fluid Life
The combination of air and high temperatures leads to the mortal enemy of any lubricant: oxidation. When oil oxidizes, it increases in viscosity and acidity. This higher viscosity increases friction, which results in higher temperatures. In addition, oxidized oil produces sludge and varnish. These deposits can become trapped in the oil cooler, reducing its effectiveness and leading to further increases in temperature.
This becomes a vicious cycle, as the higher the temperature, the faster the rate of oxidation. This is why selecting oil with a long fluid life not only allows for extended drain intervals but also improves operational efficiency.
As a general rule, for every 10°C increase, the lifespan of oil is reduced by half. Since most air compressor lubricants are rated for an oil life of 90°C, they are unlikely to meet their claimed oil life under today’s higher operating conditions, as their lifespan will likely be cut in half.
Next Lubricants are designed to provide superior resistance against oxidation. The oil life of all Next Lubricant air compressor oils is set at 100°C to help ensure our oils meet expectations.
In addition, Next Lubricant air compressor oils have been specially formulated to resist oxidation. Formulations like Aero XL are designed to provide a fluid life of between 8,000 to 12,000 hours. Next Lubricants’ air compressor oils are also much less likely to form sludge, especially when compared to competitive formulations.
