Refrigeration Compressor Lubricants

Refrigeration compressors are a type of equipment used extensively in many different sectors and applications, including food preservation, HVAC (heating, ventilation and air conditioning), and other industrial cooling systems. To keep compressors protected and operating at optimum, refrigeration compressor lubricants have been designed which can meet the needs of equipment and keep it in top shape.

Over the years refrigeration compressor lubricants have evolved and been updated to answer the ever-changing refrigerant fluid design largely driven by legislation, but also operational demand and modern levels of output. For instance, hydrofluorocarbon systems are often served by synthetic polyol ester fluids, but there are multiple refrigerants and compressor lubricants that see continued use today.

Care must always be taken when choosing refrigeration compressor lubricants to ensure they are fully compatible with the refrigerant in use. As a result, users are always advised to check their equipment manual or original equipment manufacturer’s recommendation to select the best-suited product for any given application.

In applications where a refrigerant is vital to supply the cooling attributes of a refrigeration system, the refrigeration compressor oil is critical for the correct operation of the equipment. Lubricants designed for refrigeration compressors must perform multiple tasks. For example, they are relied upon to reduce friction but also prevent unwanted wear on compressor components. They must also be dependable to provide a robust seal between both the low and high pressure sides of a system and be compatible with materials used to manufacture components.

Requirements of refrigeration compressor lubricants

While the core function of a refrigeration oil will always be lubrication, it must also have the capacity to withstand the most extreme temperature differences experienced within the system and be compatible with the type of refrigerant being used. Below are some of the key requirements that refrigeration compressor lubricants must fulfil.

Thermal and chemical stability

Refrigeration compressor lubricants must function properly over a broad temperature range. This is because end compression temperatures inside refrigeration compressors can often reach peak temperatures as high as 180°C. For this reason, refrigeration oils must always have excellent thermal stability. Should the compressor lubricant include oil fractions that are volatile, the lighter ends will enter the compressor system in a vapour state where they will condense, causing a reduction in heat transfer efficiency while increasing the viscosity of the lubricant.

Refrigeration compressor lubricant must also be chemically stable. This property is vital to avoid any chance of an unwanted chemical reaction with the type of refrigerant in use.

Solubility

Refrigerant and compressor lubricant mixtures can be insoluble, soluble or partly soluble. Total solubility can help lubrication but can also lead to substantial drops in viscosity within the compressor. This can result in increased wear and friction on components.

To work properly, the mixture of refrigerant and lubricant should always have a viscosity that is adequately high to provide satisfactory lubrication and sealing within the compressor.

What types of lubricants are employed in refrigeration systems?

Polyalphaolefin (PAO) is a refrigeration lubricant that possesses both sound thermal and chemical stability. Additionally, PAO has impressive viscosity temperature properties. Its miscibility with refrigerants is low, however. For this reason, PAO is mainly used in refrigeration applications where the issue of miscibility is of no concern. Another downside to PAO is that it can make seals shrink, but this problem is often solved by mixing alkylbenzenes with PAO.

Alkylbenzenes, referred to commonly as AB, are refrigeration lubricants with solid thermal and chemical stability. Their miscibility with refrigerants is high and AB lubricants are entirely soluble with both PAO and mineral oils. As a result, it is possible to create mixtures with the aim of improving the lubricant’s properties, as mentioned above.

Polyalkyleneglycols (PAG) are refrigeration lubricants that possess a high viscosity index and excellent thermal stability. PAG however, is hygroscopic, meaning that it can draw water to it. PAG is also soluble with ammonia.

Polyol ester (POE) is currently the most common kind of synthetic lubricant utilised with hydrofluorocarbon (HFC) refrigerants such as R134a.

Mineral oils like naphthenic oils are also used as refrigeration compressor lubricants. Their key characteristic is their low pour point, making them especially suitable for systems operating at lower temperatures.

Choose the best refrigeration compressor lubricant for your equipment

Remember that selection of the right refrigeration lubricant will always depend on the specifications of your compressor and the type of refrigerant used by the system. The lubricant selected should be thermally and chemically stable and should never react with refrigerants in use. Another important factor is how the lubricant interacts with the refrigerant (for example, solubility qualities) and how when mixed they perform in the compressor. Problems related to lubricants can occur in compressors when the viscosity of the lubricant becomes too low and when an absence of lubricant exists.

For leading refrigeration compressor lubricants like those manufactured by leading brands like CPI Fluid Engineering, contact Oil Store now to find out more.

Explore our full range of refrigeration compressor lubricants

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