Why PAG-Based Oils Resist Oxidation and Carbon Formation in Compressors​

As is well known, common compressor oils on the market include mineral oils, PAO (polyalphaolefins), Polyalkylene Glycol(PAG), and synthetic esters. Among them, compressor oils formulated with PAG as a base oil possess superior lubrication performance,  low friction, high flash points, high viscosity indexes, excellent oxidation resistance, and thermal stability. They are widely used in applications such as high-temperature chain oils, compressor oils, refrigeration oils, and textile manufacturing.

 

What is an air compressor?

 

An air compressor is a versatile machine that converts mechanical energy into gas pressure energy, primarily used in industrial production. Common types include reciprocating (piston), screw, and centrifugal compressors, with screw compressors developing the fastest. Its specialized lubricant, known as air compressor oil, serves to lubricate, cool, seal, and prevent rust by forming a protective film on friction surfaces. It must possess resistance to carbon deposition, coking, and oxidation to ensure the smooth operation of the equipment.

The oil's excellent oxidation resistance and carbon deposition resistance are imperative for delaying sediment formation, ensuring stable system operation, and extending service life. In high-temperature, high-pressure environments, air compressor lubricants are prone to oxidation, leading to oil degradation. This manifests as increased viscosity and acid value, darkening of color, and insoluble matter-chemical changes that finally trigger coking.

 

Key Indicator Changes During the Operation of PAG Compressor Oil

 

Item	Operating Time / h
	0	100	920	1860	4362	8000
Kinematic Viscosity (40°C) / (mm²·s⁻¹)	47.48	49.9	50.39	51.45	54.62	61.24
Kinematic Viscosity Change Rate / %	-	5.09	6.13	8.36	15.04	24.5
Acid Value (as KOH) / (mg·g⁻¹)	0.03	0.32	0.47	0.53	0.7	1.11
Acid Value Increase / (mg·g⁻¹)	-	0.29	0.44	0.5	0.67	1.03
Water Content / (mg·kg⁻¹)	4318	5293	1487	3166	6363

 

Key Indicator Changes During the Operation of Mineral Compressor Oil

 

Item	Operating Time / h
	0	100	920	1860	4362
Kinematic Viscosity (40°C) / (mm²·s⁻¹)	46.2	48.95	52.1	55.8	68.5
Kinematic Viscosity Change Rate / %	-	5.95	12.77	20.78	48.27
Acid Value (as KOH) / (mg·g⁻¹)	0.05	0.45	0.85	1.15	2.2
Acid Value Increase / (mg·g⁻¹)	-	0.4	0.8	1.1	2.15
Water Content / (mg·kg⁻¹)	120	350	850	2100	6800

 

At the same time, oxidative decomposition is also the primary cause of carbon deposit formation. Harmful deposits, such as carbon deposits and coking, can trigger equipment overheating, clog oil passages, reduce lubrication efficiency, and even pose safety risks.

 

To lower costs, a plant attempted to use an alternative oil. However, after 2,000 hours of operation, an electrical fault alarm was triggered on the air compressor. The underlying cause was identified as severe carbon deposition, which led to motor overcurrent. Strict adherence to operating procedures-specifically avoiding the mixing of different oils-is essential to prevent such failures.
PAG not only possesses excellent high-temperature stability, but also demonstrates superior chemical resistance. Meanwhile, its ultra-high viscosity index and excellent low-temperature fluidity ensure that the oil consistently maintains effective lubrication and high fluidity over a wide temperature range, thereby supporting long-term equipment operation.

 

Comparison of Key Parameters for Different Types of Base Oils at Equivalent Kinematic Viscosity

 

Item	Mineral Oil	PAO10(Synthetic Hydrocarbon)	Chorus PAG 68(Synthetic Polyalkylene Glycol)
Base Oil Type	High-quality Mineral Oil / Hydrogenated Oil	Polyalphaolefin (PAO)	Polyalkylene Glycol (PAG)
Kinematic Viscosity at 40°C, mm²/s	68	64.85	68
Kinematic Viscosity at 100°C, mm²/s	9	10.01	13
Viscosity Index (VI)	105	139	200
Flash Point, °C	240	242	220
Pour Point, °C	-18 to -12	-59	-40
Acid Value, mgKOH/g	≤0.05	<0.01	≤0.05
Water Content, ppm	≤50-100	30	≤0.1

 

In addition, the product has good detergency, which helps reduce the formation of deposits. Due to its fully saturated ether bond molecular structure, Polyalkylene Glycol (PAG) lubricant exhibits superior inherent detergency. Its decomposition products are clean and can be volatilized and discharged; moreover, it can dissolve and disperse initial oxidation products, thereby significantly inhibiting the generation of carbon deposits, varnish, and sludge at the source. This provides compressors with core advantages, including extending the service life of core components, maintaining heat exchange efficiency, achieving ultra-long drain intervals, and enhancing system reliability.

Combined with low hygroscopicity, it also effectively prevents system corrosion and deposit formation, further ensuring lubrication performance and cleanliness during long-term equipment operation.

CHORUS offers a wide variety of PAG base oils and a range of air compressor oil additive packages, earning unanimous praise from our cooperative clients. Contact us today for a current quotation.