Compressor oil is composed of a mixture of high quality lubricating base fluids and high-performance additives that offers exceptional lubrication in compressors in various types of service. Compressor oil is designed to lubricate and seal the compression components as well as lubricate the bearings inside the compressor. In addition, the fluid helps to reduce the buildup of carbonaceous deposits in the compressor valves and downstream piping, thus increasing the compressor life. Compressor fluids are typically rust and oxidation inhibited antiwear products blended to standard ISO viscosity grades. They are often customized for the intended service (air, gas, or refrigeration) as well as the type of compressor to be lubricated (rotary screw, reciprocating, axial, etc.).
Compressors are used in a multitude of applications. The most common gas that is compressed is air, for use in everything from heavy industry to the home workshop. Rotary screw compressors are the most common type used for air compression. The next most commonly compressed gas is natural gas (methane), in very large reciprocating compressors found mostly in compressor stations along gas transmission pipelines. Another common type of compressor application is the compression of refrigerant gases, in places including home and automotive air conditioners, home refrigerators and freezers, and chillers and freezers in the food and beverage industry.
Properties of Compressor Oil
As with most lubricants, viscosity is the single most important property of a compressor oil. In general, rotary compressors require lower viscosity grade lubricants, while reciprocating compressors need higher viscosity products.
Compressor lubricants are designed to be inert and resistant to the gas being compressed. In the case of air compressor lubricants, this means that the lubricant must have excellent oxidation resistance. For that reason, synthetic fluids are often used as the basis of air compressor lubricants. Fluids for use in natural gas compressors need to resist dilution by the gas. Both mineral oil and synthetic hydrocarbon (polyalphaolefin or PAO) fluids are susceptible to gas dilution. Fluids based on polyalkylene glycol (PAG) fluids are preferred for compressors handling natural gas or other hydrocarbon gases. In refrigeration compressors, the type of refrigerant must be known. The compressor lubricant must be miscible with the refrigerant to a certain extent to provide the required lubrication of the compressor. In addition, the lubricant must be chemically compatible with the refrigerant, and must have a pour point lower than the minimum temperature to which it will be exposed in service. With any compressor system, it is important to follow the manufacturer's lubricant recommendation.
Since the compressors used in air conditioning, refrigerators, and freezers are completely sealed systems and the electric motors driving them are inside the enclosure, the oils used in them must have good dielectric strength and contain virtually no water.
Advantages of Compressor Oil
The main purpose of compressor oil is to lubricate the moving parts and seal the compression portion of a compressor. This can reduce maintenance requirements and improve the life of a compressor. The above properties of the compressor oil help it to achieve its purpose as discussed below
- Compressor oil protects the compressor's internal surfaces and components from rust and corrosion.
- Compressor oil separates air and resists the formation of foam, both of which can adversely affect its operation.
- Compressor oil protects against wear, which helps to minimize maintenance requirements and improve the service life of the compressor.
- Air compressor lubricants have high resistance to thermal and oxidative degradation, thereby minimizing carbon deposits in the compressor. Accordingly, the systems lifetime is enhanced and frequency of maintenance is reduced.
- Gas compressor lubricants resist dilution by the gas being compressed.
- Refrigeration compressor lubricants are miscible with the refrigerant, chemically inert, and able to function at low temperatures.
Other Applications for Compressor Oil
- Compressor oils can be used as rust and oxidation inhibited (R&O) oils.
- Some compressor fluids can also be used in vacuum pumps.
Precautions for Using Compressor Oils
- Common air compressor lubricants are unsuitable for the compression of breathing air or oxygen.
- Always follow the compressor manufacturer's lubricant recommendation.