Oil vs Oil-Free Air Compressors: The Ultimate Guide

Air compressors are ubiquitous in many industries, from construction and manufacturing to pharmaceuticals and food processing. The dilemma emerges when faced with choosing between oil-lubricated and oil-free air compressors. Which is best for what you need? 

Let’s examine the crucial differences, benefits, and drawbacks of both.

The Basics: How Air Compressors Work

Several air compressor variations function on a simple principle: they compress air and then use it to power a wide array of tools and equipment. The pivotal role of lubrication in these machines is to reduce friction between moving parts, thereby decreasing wear and tear and preventing overheating.

Oil-Lubricated Air Compressors

Oil-lubricated air compressors use oil for lubrication and cooling.

These machines work by pulling in ambient air and compressing it within a confined space. The oil, typically housed in a sump, is precisely injected into the compressor at key friction points. This lubrication helps reduce wear and tear and dissipate heat produced in the compression chamber during the process.

For example, an Atlas Copco GA 37 VSD oil-lubricated air compressor uses a rotary screw mechanism. Its screws, revolving at speeds up to 3000 rpm, encounter immense friction, so lubricating oil is essential. The compressor’s inbuilt oil filters ensure minimal air contamination in the compressed air stream, retaining oil purity as low as 3 ppm.

Oil lubricated air compressors like the Atlas Copco GA 37 VSD, with a maximum working pressure of 13 bar (188 psi) and a motor size of 37 kW (50 hp), are designed to withstand demanding industrial applications, a testament to the resilience and performance of oil-lubricated air compressors.

The Advantages of Oil-Lubricated Air Compressors

• Heavy-duty performance: With their robust build and high-capacity motors, oil-lubricated air compressor variations, like the Atlas Copco GA series, can efficiently handle high-pressure industrial applications.
• Longevity: If maintained regularly, oil-lubricated compressors tend to have a longer lifespan, ensuring a good return on investment.
• Cooler operation: The oil in these compressors facilitates cooling and lubrication, minimising the risk of overheating during prolonged usage.

The Disadvantages of Oil-Lubricated Air Compressors

• Maintenance requirements: Oil-lubricated compressors generally require regular oil changes, filter replacements, and overall maintenance to ensure optimal performance.
• Risk of oil contamination: Oil may contaminate the compressed air if the oil separator fails or is not maintained correctly, which can be detrimental to some applications.
• Limited portability: Due to their size and weight, oil-lubricated compressors are not easily portable, which could pose challenges in situations where mobility is a factor.

Oil-Free Air Compressors

Oil-free air compressors, such as Atlas Copco’s ZT 15-22, ZR/ZT 30-45, ZR/ZT 22-37-55 VSD, employ oil-free technology, using materials like Teflon, water, or air for lubrication, and are ISO 8573-1 CLASS 0 certified.

These machines draw in ambient air and then compress it in a two-stage process. In the first stage, pre-compression occurs, where air is partially compressed and cooled. During the second stage, final compression takes place, leading to further cooling and the release of air at the desired pressure.

The lubrication in oil-free compressors is typically through self-lubricating materials, such as Teflon-coated cylinders, or other non-oil liquids, like water. These methods minimise friction and ensure that the compressed air remains free from oil contamination. Atlas Copco’s ZR/ZT55-VSD oil-free compressor, for instance, is available in water- or air-cooled versions and operates at a maximum working pressure of 8 bar (125 psi), with a motor power of 55 kW (75 hp). Their lower weight and more compact design make these machines highly portable and suitable for industries where air purity is paramount.

The Advantages of Oil-Free Air Compressors

• Low Maintenance: With no oil to change, oil-free compressors, like Atlas Copco’s ZR/ZT series, require less routine maintenance, saving time and costs.
• Air Purity: These compressors eliminate the risk of oil contamination, making them ideal for industries like pharmaceuticals, food processing, and electronics, where air purity is critical.
• Portability: Models like Atlas Copco’s ZT 15-22, ZR/ZT 30-45, and ZR/ZT 22-37-55 VSD are lighter and more compact, offering greater mobility than oil-lubricated compressors.

The Disadvantages of Oil-Free Air Compressors

• Lifespan: Oil-free compressors generally have a shorter lifespan due to increased wear and tear from technically oil-free operations.
• Limited Capacity: Although oil-free compressors can handle a wide range of applications, they may not be suitable for some heavy-duty industrial tasks due to their lower capacity for repetitive tasks.
• Noise Levels: The lack of oil can lead to louder operation, which might be a concern in some operating environments.

Oil vs. Oil-Free Compressors: The Air Quality Factor

Choosing between an oil-lubricated and an oil-free compressor isn’t just about power and performance; it directly impacts the quality of the air your system produces. This is a critical consideration, especially for industries with stringent purity requirements.

Oil-lubricated compressors, while robust and often more cost-effective upfront, carry the inherent risk of introducing oil aerosols into the compressed air stream. Even with efficient oil separators, trace amounts of oil can pass through, impacting product quality, damaging sensitive equipment, or posing health risks in applications where air comes into contact with products or people.

Oil-free compressors, as the name suggests, completely eliminate this risk. By using alternative lubrication methods (such as Teflon coatings or water), these compressors guarantee oil-free air, making them the preferred choice for:

• Pharmaceuticals: Where even minute traces of oil can compromise the integrity of medicines.
• Food and Beverage Production: To ensure compliance with strict hygiene standards and prevent product contamination.

Electronics Manufacturing: Where oil contamination can damage delicate electronic components.

Testing Methods for Compressor Air Quality

Ensuring compressed air purity is essential, particularly when choosing between oil-free and oil-lubricated air compressors. Various testing methods help maintain compliance with air purity standards:

• Dew Point Monitoring: For both oil-free and oil-lubricated air compressors, dew point sensors track moisture levels to prevent condensation, corrosion, and microbial growth. These sensors ensure the air supply meets industry standards.
• Particle Counters: Whether using oil-free or oil-injected air compressors, particle counters monitor airborne contaminants. This is particularly important in industries such as food processing, where maintaining air purity standards is critical.
• Oil Vapour Analysis: Oil vapour analysers detect hydrocarbons, helping identify air contamination in oil-lubricated compressors. For oil-free air compressors, this test verifies that the air remains clean and uncontaminated.
• VOC Detectors: Detecting volatile organic compounds (VOCs) ensures air quality in both oil-free and oil-lubricated compressors, helping businesses avoid contamination in sensitive environments.

Incorporating these testing methods ensures that compressed air solutions—whether oil-free or oil-lubricated—meet high air purity standards for any application.

Improving Air Quality in Oil-Free and Oil-Lubricated Compressors

Maintaining clean air in both oil-free and oil-lubricated air compressors is essential for optimal performance. Here’s how to enhance air quality:

• Aftercoolers: These systems cool compressed air, causing moisture to condense and separate. This is particularly important in oil-lubricated compressors to prevent mixing with oil and forming harmful byproducts.
• Dryers: Whether using oil-free or oil-lubricated compressors, incorporating refrigerant or desiccant dryers removes moisture from the air, ensuring a compressed air solution suitable for sensitive applications.
• Filtration Systems: Multi-stage filters capture solid particles and oil aerosols, which is crucial for oil-lubricated compressors. Regularly replacing filters and using oil-water separators helps maintain air quality and meet industry standards.
• Condensate Management: Automatic condensate drains are essential for removing water from aftercoolers, dryers, and air receivers, minimising the risk of corrosion and prolonging the lifespan of both oil-free and oil-lubricated compressors.
• Routine Maintenance: For oil-lubricated compressors, regular oil changes prevent contamination, while oil-free compressors benefit from periodic checks of self-lubricating components like Teflon coatings. Both types require consistent upkeep to sustain air quality.

Myths and Misconceptions

Contrary to popular belief, oil-free compressors are not necessarily much louder than their oil lubricated counterparts. Similarly, it is a misconception that oil-lubricated compressors are universally more durable. The durability of a compressor largely depends on their operating conditions, including the environment, and maintenance practices.

How to Choose Between Oil and Oil-Free

The decision between oil and oil-free compressors hinges on factors such as the intended application, industry requirements, and maintenance capabilities.

Consider the following typical use cases of Atlas Copco compressors:

Pharmaceutical Industry

In this sector, air purity is paramount to avoid contamination of medicines. An oil-free compressor such as Atlas Copco’s ZR/ZT series, which ensures oil-free compressed air, would be the ideal choice.

Food and Beverage Industry

Like pharmaceuticals, air purity is critical in food processing to maintain hygiene standards. Oil-free options, like the ZT 15-22, ZR/ZT 30-45 and the ZR/ZT 22-37-55 VSD, are suitable as they provide clean, uncontaminated air.

Heavy-Duty Manufacturing

In industries where high pressure and constant use are the norm, the resilience and power of oil-flooded air compressors, like the Atlas Copco GA 5-37 VSD, make them a solid choice.

Automotive Industry

Here, both types of air compressor can be beneficial. Oil-free compressors can be used in the painting process to prevent oil contamination, whereas oiled air compressors could be used in power-heavy tasks.

Construction Sites

Portability is a concern in this case and an oil-free compressor, being lighter and more compact, would be the preferred choice for easier transportation.

Ensure you take into account factors like the degree of air quality required, intensity of use, portability needs, and maintenance capabilities before making your choice. 

And don’t overlook space limitations. Most users typically place air compressors as close to their points of application as possible because it eliminates the need for long air hoses, which can significantly reduce energy efficiency.

Final Thoughts

In conclusion, when choosing between oil and oil-free air compressors, weigh up their pros and cons. Consider your specific requirements and find the perfect fit for your needs. Whether it’s the efficiency and durability of Atlas Copco oil compressors or the cleanliness and convenience of oil-free compressors, make an informed decision for the best results!

Contact the team at Anglian Compressors, for expert advice and help, when investing in new compressed air equipment.

FAQ

What are the key differences between oil-free and oil-lubricated air compressors?

Oil-free air compressors use materials such as Teflon for lubrication, whereas oil-lubricated compressors rely on oil to lubricate their internal components. Oil-free compressors provide cleaner air, making them ideal for industries like pharmaceuticals or food processing. On the other hand, oil-lubricated models offer greater durability for heavy-duty applications but require regular oil changes and maintenance.

Are oil-free air compressors better for certain industries?

Yes, oil-free air compressors are often considered more suitable for industries where air purity is critical, such as electronics, food production, and pharmaceuticals. They eliminate the risk of oil contamination in the air stream, ensuring compliance with strict air purity standards.

Do oil-lubricated compressors require more maintenance than oil-free models?

Yes, oil-lubricated compressors typically require more frequent maintenance, including oil changes and filter replacements. Oil-free compressors generally require less maintenance due to the absence of oil in the system, though periodic checks on self-lubricating components like Teflon coatings may still be necessary.