In industrial operations, air compressors often demand a substantial percentage of energy usage onsite. In some cases, the plant’s air compression system is even considered the beating heart that keeps the operation performing. As a result, when an air compressor ceases to function correctly, a facility can experience higher maintenance and energy costs and drop in productivity.
Fortunately, such unwanted circumstances are avoidable by properly lubricating air compressors. Effective lubrication can help air compression systems run more efficiently and dependably to minimise maintenance and repair costs, system downtime and increased energy costs.
What does the term “proper lubrication” refer to?
The definition of proper lubrication will depend on multiple factors. These include operating conditions present, application and the type of air compressor in use.
Air compressors can vary considerably, with multiple types available to choose from including reciprocating, rotary vane, rotary screw and centrifugal, to name just a few. For each type of compressor, the function of the compressor lubricant can differ to a greater or lesser extent.
For instance, with reciprocating compressors, the lubricants main jobs are to minimise wear on rings and cylinders and to decrease or eradicate carbon build-up on the valves, which helps to prevent the issue of overheating. In centrifugal units, however the focus shifts to resisting bearing and gear wear while preventing the formation of varnish. Compressor lubricants for rotary screw compressors must help absorb heat for effective and subsequent dissipation inside the oil cooler, provide outstanding sealing and lubricate bearings. Rotary screw compressor lubricants must also be resistant to water contamination, as this unwanted inclusion can reduce lubricity and cause additives in the lubricant condensate, meaning the lubricants lose their effectiveness.
All the factors listed above affect whether or not the formulation of base oils and additives will provide maximum performance, service life and protection for the air compressor.
Desired characteristics that dictate proper lubrication
Proper lubrication is designed to minimise friction activity within the compressor. Friction increases heat and, as a result, demands greater levels of energy use to cool the unit adequately for safe operation. Therefore, proper lubrication means reduced power usage and, consequently, lower energy costs too.
In general, air compressor lubricants should have the following attributes to deliver proper lubrication:
• They must have sufficient viscosity and an appropriately high viscosity index (VI). As air compressors are commonly exposed to extreme operating temperatures, lubricants with a high VI are essential. The higher the lubricant’s viscosity index is, the more stable its viscosity will remain over a wide spectrum of temperatures
• Sufficient flash points and pour points are also key. These make sure that the lubricant maintains proper flow and operates safely across the full temperature range of the application
• High oxidative stability and thermal stability are vital for compressor oils. These attributes help support a lengthy active service life for the compressor lubricant. Without these properties, rapid oxidation usually occurs, curtailing oil lifespan. The issue of oxidation can also promote the formation of both varnish and sludge in the system. This build-up can hamper compressor operation and lead to frequent repairs and maintenance, increasing costs and operational downtime. While all compressor oils will eventually degrade because of oxidation in time, the slower this process is, the better for businesses
• Good wear protection is another core requirement. Robust anti-wear properties are critical to keep compressor components like bearings, rotors, sliding vanes, gears and cylinders moving efficiently and smoothly, and in correct condition. This property is particularly important for air compressors working under extreme pressures, loads, and shocks. Minimising wear on parts can keep them running for longer and reduces the threat of system breakdowns, and the frequency of operational downtime for expensive repair work
• Another sought-after property is low oil carryover. In many industrial applications, a minimal amount of compressor oil carrying over in the compressed air supply is rarely problematic. However, excessive carryover is a scenario that should be avoided. This is because it leads to increased lubricant consumption and more frequent topping off, which results in wasted oil and money for companies.
Selecting an oil with specific properties can reduce the issue of oil carryover and promote proper lubrication. Compressor oil selected should have efficient water separation attributes. Many compressor applications are prone to significant water production through condensation. Good water separability is essential because when oil and water separate poorly, the water can increase foaming and oxidation, shortening oil lifespan but also impeding its load-carrying capacity and viscosity. Excessive water in the system also increases the likelihood of corrosion on compressor components. Good demulsibility makes the process of removing water easier, effectively mitigating the risk of water-related issues.
To summarise, to achieve proper lubrication, operators must select an air compressor lubricant designed to answer the unique challenges of the type of compressor in use, as well as the operating conditions present and the application involved.