June 2019

Brian Barnes, business line manager compressor technique service operations at Atlas Copco, outlines air compressor oil and additive properties and their functions: to seal, cool, clean and reduce wear. P What is the best air compressor oil? Just as a motor vehicle manufacturer will specify types and grades of lubricants to ensure optimum performance and maximum protection for the engine, so every type of compressor needs a specific lubricant. This article looks at how the choice of lubricant depends on the equipment and its application, and the relevance of the ambient conditions, flow patterns and maintenance intervals. Also covered are the risks of choosing the wrong type of oil, oil ageing, and running equipment for longer than the recommended oil drain interval. What makes air compressor oil special? Compressor lubricants comprise a base oil stock and specific synthetic, semi-synthetic or non-synthetic additives. Apart from providing lubrication and heat increases oxidation by exposing more of the surface area of the oil to oxygen. Without these additives, excessive foam will saturate the oil separator, decreasing its lifetime. A saturated oil separator will create an increased pressure drop; every 1 bar pressure drop increases energy consumption by 7%. Oil demulsification additives are designed for improved water separation, to protect the system from water/oil emulsions. This priority makes subsequent oil capture in oleophilic bags easier, and improves condensate disposal procedures. Equipment-specific lubricants Equipment users may ask ‘What’s wrong with using a generic lubricant?’ or ‘Can I use motor oil in my air compressor?’ But air compressors are mechanically complex machines, often required to operate in challenging conditions. That is why leading equipment manufacturers of compressors, in close collaboration with oil companies, apply extensive research, testing and expertise to developing unique additive packages designed to meet all the demands of their product solutions. In contrast, generic lubricants are produced for a broad range of unrelated equipment with undemanding lubrication requirements. As such, they will lack the essential properties to achieve optimum performance of air movement equipment. Users should also be aware that there are suppliers within the industry releasing lubricants, without specific selection properties or type testing, that lack any established link between oil design and compressor performance. What is the risk of choosing the wrong type of lubricant? The incompatibility of the wrong lubricant can shorten equipment lifetime, encourage formation of deposits within the oil circuit and Process, Controls & Plant Focus on: Compressed Air absorption, lubricants prevent corrosion, contamination and premature wear. The balanced mix of additives tailors them for the equipment requirements and the ambient conditions. These additions imbue the lubricant with properties such as oxidation resistance, viscosity at low temperatures, air release capability, demulsification, anti-foaming and anti-wear. Additive properties Anti-oxidant additives delay the oxidising process, as well as the formation of acids. They increase lubricant lifetime, protect equipment during standby periods and increase lubricant compatibility with a wide range of operating conditions. Surface activity additives optimise anti- foaming. When large air bubbles – above 1 mm diameter – in the lubricant/air flow rise to the surface, they produce foam. Foaming How to choose the right oil for your compressor 24 | Plant & Works Engineering www.pwemag.co.uk June 2019