Oil-Free vs. Oil-Flooded Air Compressors – What’s the Difference?

Air compressors play important roles in many commercial and industrial systems. There are two main types: oil-free air compressors and oil-flooded air compressors. Both see wide use in a variety of industries, but which is suitable for your application? Is an oil-free air compressor best in every situation?

How and where you intend to operate a compressor varies significantly across different facilities and lines of work. Here’s a breakdown of the various applications for each type of compressor.

Oil-Free Air Compressors

Oil-free air compressors don’t rely on oil for lubrication. Industries that cannot risk any contamination from lubricating oil often use these types of compressors. Hospitals are among the primary users, along with water treatment and other sensitive manufacturing operations.

The demand for these air compressors is constantly rising, driven by the rise in applications that require incredibly clean air. The separation in various industries is clear, but what actually sets apart oil-free and oil-flooded air compressors? And is an oil-free air compressor best?

Oil-Flooded Air Compressors

In the case of oil-flooded compressors, the compression chambers are directly lubricated. This allows for air and oil to mix and must later be separated. The main problem that prohibits their use in some industries is that the oil can mix with water as it condenses out of the air. This mixture can then work its way into downstream processes, causing any number of potential issues.

This oil carryover is an anticipated effect. Compressor manufacturers disclose the oil carryover for their compressors, letting facilities determine if it’s within their tolerance. These values are generally in the range of parts per million, with newer models constantly improving.

Because oil-free air compressors have no oil at all, the oil carryover is zero, making them the only viable choice for some applications due to zero tolerance for oil in the final product or within the process, such as in medical gas systems.

How Oil-Free Air Compressors Work

Compressors require lubrication to allow for moving parts to move freely and to remove heat from the compressor. So how does an oil-free compressor work without having oil inside the compression chamber?

Air is drawn into the first air compressor element, compressing the air to around 2.5 bar. This compression heats the air to 180°F, significantly higher than the temperatures inside oil-flooded compressors.

The air then moves to an intercooler for cooling. The chilled air goes to the next compressor element, which could be the final one or just another step in a multi-stage compressor. Cooling between elements is absolutely necessary as further compression continues to raise the temperature. In most applications, attempting to reach full compression in one stage without lubricating oil to remove heat could present serious fire hazards.

Of course, an oil-free air compressor does have some oil. The oil is never in contact with the compressed air instead of serving to allow the gearbox to function. The compression chamber itself is oil-free.

Other Factors When Choosing the Right Air Compressor

Oil-free air compressors are often used in applications even where they are not strictly required. There are many factors to consider when choosing a compressor, and it isn’t uncommon for oil-free to be the best choice after weighing all the available options.

Any process that uses oil-flood air compressors needs to have some way of collecting and disposing of oil-ladened condensate. This means more equipment, more resources, and more time dedicated to that aspect of the process. You can also eliminate downstream filters. This further reduces initial and ongoing costs.

Downstream filtration also adds resistance to flow, and not having to deal with that pressure drop means less energy used. There will also be no need to continue purchasing oil to refill the compressor.

Ask the Pros at The Severn Group

The Severn Group provides design services for many industries. Reach out to our team today to find the right air compressor for your medical gas system or other applications. For more tips, make sure to check out our blog and follow us on Facebook.