Tagged: compressor

Oil Properties / Used Oil Analysis

Critical Condition Monitoring Tests for Compressor Oils

To ensure these oils remain healthy (and not contaminated or degraded), a few basic tests can be performed on all compressors, regardless of type (reciprocating, screw, refrigerant, etc.). These include:

  • Viscosity – this is key as some of the gases can easily affect the viscosity, which (if decreased) will not provide adequate separation for the interacting surfaces and cause wear. Generally, a ±10% limit is used (though OEMs may use different values).
  • Acid Number – if this begins increasing, then we have an accumulation of acids in the oil, which can be because of contamination. For most compressors, a 0.2 mg KOH/g increase is the warning limit, but for refrigeration compressors, the limit is tighter at +0.1 mg KOH/g. Always check with your OEM for these limits.
  • Water content – changes by OEM and refrigerant type, as the different gases will have varied tolerances.
  • Wear metals – these values will vary as per OEM, as well, since they are all designed with different types of metals. Users should look for trends or significant increases in these values to indicate wear.

Some specialty tests for compressors include:

  • MPC (Membrane Patch Colorimetry) – this helps to measure if there is any potential for the oil to form varnish. Given the high temperatures these types of equipment endure and the potential for contamination, the oil is at risk of forming varnish. While limits will vary by OEM, some general guidelines to follow are 0-20 Normal, 20-30 Warning, >30 Action required
  • RULER® (Remaining Useful Life Evaluation Routine) – this quantifies the remaining level of antioxidants in the oil. When oxidation occurs, the antioxidants get depleted. As such, by monitoring antioxidant levels, one can easily determine whether oxidation is happening in the oil. The general rule of thumb is that if the level falls below 25%, there are not enough antioxidants to keep the oil healthy and prevent degradation.
  • Air Release (DIN ISO 9120) – measures the ability of the oil to allow air to escape and not keep the air in the oil. If air bubbles remain in the oil, this can be devastating, as it can lead to micropitting, cavitation, or increased oxidation. Users can trend the values; if they increase, it indicates that the air is taking longer to be released, which means it is staying in the oil and in the system longer.
  • Particle Count – this can identify if there are any contaminants in the system. These oils must be kept clean, and OEMs typically specify target cleanliness levels.

Compressors are critical equipment, and we must understand how they work and the lubricant specifications required. Monitoring their health can also help us avoid unnecessary downtime and keep our facilities running.

References

  1. Mang, T., & Dresel, W. (2007). Lubricants and Lubrication. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.
  2. Totten, G. E. (2006). Handbook of Lubrication and Tribology – Volume 1 Application and Maintenance – Second Edition. Boca Raton: CRC Press.
  3. Shell Lubricants. (2025, November 08). The Shell Corena range. Retrieved from Shell Lubricants Compressor Oils: https://www.shell.com/business-customers/lubricants-for-business/products/shell-corena-compressor-oils/_jcr_content/root/main/containersection-0/simple_1354779491/promo_1484925192/links/item0.stream/1759302155345/17be2a9a74057f321bb209128933f68f8b88ca70/s
  4. ExxonMobil. (2025, November 08). Refrigeration Lubricant Selection for Industrial Systems. Retrieved from ExxonMobil Lubricants: https://www.mobil.com/lubricants/-/media/project/wep/mobil/mobil-row-us-1/new-pdf/refrigeration-lubricant-selection-for-industrial-systems.pdf
  5. Chevron Lubricants. (2025, November 08). Optimizing compressor performance and equipment life through best lubrication practices Chevron. Retrieved from Chevron Lubricants: https://www.chevronlubricants.com/content/dam/external/industrial/en_us/sales-material/all-other/Whitepaper_CompressorOils.pdf

Find out more in the full article, "Compressor Oil, Types, Applications and Performance Drivers" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

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January 7, 2026
Oil Properties

Refrigeration Lubricants

For industrial refrigeration systems, there are a couple of essential pieces of information to consider before selecting the most suitable oil. The user must know the refrigerant in use, the evaporator type (dry or wet; carryover < 15%), the evaporator temperature, the compressor type, and the outlet temperature.

The refrigerant fluids are classified as per the ASHRAE classification (ANSI-ASHRAE Standard 34-2001):

  • R717 — Ammonia
  • R12 — Chlorofluorocarbon (CFC)
  • R22 — Hydrochlorofluorocarbon (HCFC)
  • R600a — Isobutane
  • R744 — Carbon dioxide (CO2)
  • R134a, R404a, R507 — Hydrofluorocarbons (HFC)

It should be noted that CFCs were banned under the Montreal Protocol (1989) due to their Ozone Depletion Potential, and HCFCs are being phased out due to their Global Warming Potential.

Chevron provides some general guidelines for selecting the appropriate refrigerant, as shown in the table below.5

(But you should always follow the guidelines of your OEM when selecting the appropriate lubricant.)

Table 1: Refrigerants and their associated lubricant technologies

ExxonMobil classifies its refrigeration lubricants based on refrigerant type, evaporator temperature, and compressor type (Piston, Screw, or Centrifugal). This is very helpful when determining the best-suited lubricant for your refrigerant compressor.

Check out the pdf here.

 

Find out more in the full article, "Compressor Oil, Types, Applications and Performance Drivers" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

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January 7, 2026
Oil Properties

Industry Standards for Compressor Oils

Some other classifications which users may see when dealing with compressor oils (even though some of these standards may be dated) include:

ISO 6743-3, which uses the following acronyms for associated compressors:

  • DAA, DAB, DAG to DAJ: Air compressors
  • DVA to DVF: Vacuum pumps
  • DGA to DGE: Gas compressors
  • DRA to DRG: Refrigeration compressors

 

In this standard, the “D” family includes detailed classifications of lubricants used in air, gas, and refrigeration compressors. The second letter usually indicates the type of compressor, and the third letter indicates the application severity or type, especially for gas or refrigeration compressors.

For instance;

DAJ represents:

D -> Compressor Lubricant

A -> Air compressor

J-> Lubricant drain cycles of >4000 hours

DVB represents:

D-> Compressor Lubricant

V->Vacuum pumps, Positive Displacement Vacuum pumps with oil lubricated compression chambers, Reciprocating and rotary drip feed, Rotary oil-flooded (vane and screw)

B-> Low vacuum for aggressive gas (102 to10-1kPa or 103 to 1 mbar)

DGD represents:

D-> Compressor Lubricant

G-> Positive displacement reciprocating and rotary compressors for all gases, Compressors for refrigeration circuits or heat pump circuits, together with air compressors, are excluded.

D-> Gases that react chemically with mineral oil, usually synthetic fluids, HCI, CI2, O2, and oxygen-enriched air at all pressures. CO2 at pressures above 103 kPa (10 bar) with O2- and oxygen-enriched air: mineral oils are prohibited, and very few synthetic fluids are compatible.

DRB represents:

D-> Compressor Lubricant

R-> Compressors, refrigeration systems

B-> Ammonia (NH3), Miscible, Polyalkylene glycol, Commercial and industrial refrigeration, For direct expansion evaporators; PAGs for open compressors and factory-built units.

Another standard which is also used in this industry is DIN 51506, which defines:

  • VB, VC: Uninhibited mineral oils (no oxidation inhibitors)
  • VBL: Mineral oil-based engine oil (additives that protect from corrosion and oxidation and air compressor temperatures up to 140°C)
  • VCL: Mineral oil-based engine oil (additives that protect from corrosion and oxidation and air compressor temperatures up to 160°C)
  • VDL: Inhibited oils with increased aging resistance (additives that protect from corrosion and oxidation and air compressor temperatures up to 220°C, recommended for compressors with 2-stage compression)

One more standard is DIN 52503, which has these classifications:

  • KAA: Not miscible with ammonia
  • KAB: Miscible with ammonia
  • KB: For carbon dioxide (CO2)
  • KC: For partly and fully halogenated fluorinated and chlorinated hydrocarbons (CFC, HCFC)
  • KD: For partly and fully fluorinated hydrocarbons (HFC, FC)
  • KE: For hydrocarbons (e.g., propane, isobutane)

These standards are referenced when discussing certain compressor oils, and their definitions are helpful for navigating acronyms.

Find out more in the full article, "Compressor Oil, Types, Applications and Performance Drivers" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

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January 7, 2026
Oil Properties

Types of Compressors and Oils

Compressors are integral to many of our operations. They are used to compress gas, increasing its pressure, and to power tools. They can also be used as vacuum pumps or blowers, but each application is different. As such, they require various types of lubrication, particularly for applications that use specific refrigerants and come into contact with the lubricant.

In all these applications, the functions of the oil remain largely the same: it must lubricate the surfaces, prevent wear and corrosion, maintain the required viscosity, and provide proper sealing.

In this article, we will dive into the various types of compressor oils and explain why they are suited to these applications. We will also discuss monitoring the health of these oils and the tests that should be performed to ensure your compressor oils remain healthy.

Types of Compressors

Essentially, there are two main types of compressors: Displacement and Dynamic. For displacement compressors, gas is drawn into a chamber, compressed, and expelled by a reciprocating piston. On the other hand, for dynamic compressors, turbine wheels accelerate a medium, which is then abruptly accelerated.1

Positive displacement compressors include Reciprocating and Rotating compressors. These can be further subdivided as shown in Figure 1. For Dynamic (Turbo) compressors, these are further subdivided into Centrifugal, Axial, and Mixed types (also shown in Figure 1).

Figure 1: Types of compressors
Figure 1: Types of compressors

Depending on the type of compressor, the required lubricant will vary. For example, positive-displacement compressors use rolling or sliding motion and include bearing and sealing components within the compression chamber. On the other hand, dynamic compressors use hydrodynamic journal and thrust bearings, or rolling-element bearings, to support the main shaft, which is isolated from the compression chamber.

Working pressures, temperatures, and the type of gas being compressed also play a significant role in determining the appropriate lubricant.2

As with most applications, there can be a dry-sump or a wet-sump. Wet sumps are typically seen in reciprocating and rotary screw compressors.  In a wet sump, the gas usually contacts the oil, lowering its viscosity. This is where it is essential to note the gas’s solubility in the system oil. Natural gas and other hydrocarbons are more soluble in mineral oils and PAOs than in PAGs and diesters. Thus, PAGs may be preferred in some cases to avoid lubricant failure.

Compressor Oils

Most of the major global lubricant OEMs have classified their oils based on:

  • Rotary vane and screw air compressor oils
  • Reciprocating (piston) air compressor oils
  • Refrigeration compressor oils

As seen below in Figure 2, Shell Lubricants3 has a line of lubricants, particularly for air compressors, which are further classified into mineral oils, PAOs, and PAGs for Rotary vane and screw air compressors or Reciprocating (piston) air compressors.

Figure 2: Shell Lubricants for Air Compressors
Figure 2: Shell Lubricants for Air Compressors

In reciprocating air compressors, cylinder design dictates the lubrication type, as this is the most severe application. Compressing the gas usually results in high temperatures, which can easily lead to oxidation. The compressed gas must be free of contaminants, as contaminants can accelerate oxidation. Typically, for reciprocating air compressors, mineral oils or PAO- or di-ester-based lubricants in the ISO VG 68 to 150 range are preferred.

Rotary vane compressors can experience pressure extremes as the vanes slide to compress the gas, and oil is continuously injected into the compressor chambers. Typically, ISO VG 68-150 oils are used in this application.

Figure 3: Reciprocating Piston vs Screw Compressor Lubricant Needs
Figure 3: Reciprocating Piston vs Screw Compressor Lubricant Needs

For screw compressors, the oil must perform several functions, including lubricating the meshing rotors and the plain and roller bearings that form part of the geared coupling. ISO VG 46 mineral oils are usually used in these compressors, but the viscosity can be increased to ISO VG 68 or to synthetic PAO or PAG lubricants at higher ambient temperatures. Similarly, Group III base oils of these viscosities can be used in this area. Most screw compressor oils contain mild EP/AW performance additives and require an FZG failure load≥10.

Ideally, reciprocating piston compressors will use higher viscosities (ISO VG 100-150) with extremely low carbon residue and no or mild EP/AW additives. Conversely, screw compressors will use lower viscosities (ISO VG 46 or 68) with excellent oxidation stability and mild/high AW/EP additives1, as shown in Figure 3.

Find out more in the full article, "Compressor Oil, Types, Applications and Performance Drivers" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

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January 7, 2026