The primary purpose of an oil free compressor and oil compressor are identical, but the applications for which they will be used for will make a significant impact on your choice. Aside from size, CFM and bar rating, you must also consider oil vs oil free compressor when making your purchase.

This guide will help you decipher which type is best for your operation, so here’s how both compressed air systems function and the differences between them both.

How Does an Oil Free Compressor Work?

Source: © Atlas Copco

An oil free compressor isn’t technically oil free as oil is still used just not in the compression chamber. The cylinder is lubricated in order to protect the pump during operation, but an inter-cooler is used instead of oil to keep the level of heat down and debris is removed using a filter, so it is completely clean.

Here is the process of how oil free air compressors work in more detail:

1. Drawing in the Ambient Air

The operation begins with the valve opening and bringing outside air in and filtering it through to the compressor. The filter makes the air clean, limiting damage to the machine and, when the valve closes, the compressor starts to run.

2. Low-Pressure Compressor Element & Intercooler

The air then follows through to the low-pressure compressor element where the oil-free components will compress the air and cool it down. Further cooling and compression occur through an intercooler; the air becomes denser and more oxygen-rich through this process.

3. An Aftercooler & Compressed Air Storage

Once compressed again, cooling occurs once more and then the air will be stored ready for use. The valve that the air is passed through prevents any backflow, so the tank can fill up and be sent to equipment and accessories for use.

4. Pressure Switches

Pressure switches are used to monitor the levels of the compressor, so when the levels of air fall below a specific measure, the compressor will turn on to restore the air in the tank.

How Does an Oil Lubricated Compressor Work?

Source: © Atlas Copco

An oil lubricated compressor uses oil to cool the machine, provide adequate lubrication for the pistons and other moving parts, sealing the compressor chamber and storage, and to help with noise dissipation. Residual oil may be left in the compressed air, but it’s a small amount typically between 10–15 mg/m³.

Here is the process of how oil air compressors work in more detail:

1. Drawing in the Ambient Air

Oil lubricated compressors most commonly use a piston to pull the outside air in. They also utilise filters to clean the air of debris and, the compressed air system will begin to run immediately.

2. Compressed Air Storage & Cooling

The air is then compressed into storage using the upstroke of the piston and is cooled down through the use of oil. The amount of oil circulating the oil cooler is controlled by a thermostatic valve in order to maintain the optimum temperature.

3. Equipment Use

Once the storage tank reaches the maximum amount of air, the compressor will turn off and you will be able to use the compressed air for your equipment.

Air Compressor Oil FAQs

How Often Should You Change the Air Compressor Oil?

As a general guideline, oil should be changed a minimum once per year, however each air compressor will have specific instructions regarding oil changes. Also, remember to check the oil filters when you change your oil too.

What Kind of Oil Should You Use in an Air Compressor?

There are two types of oil used in air compressors: synthetic-based and mineral oil-based. Mineral oil-based is self-explanatory, synthetic-based lubricants are a more refined oil that has gone through a specific process and engineering.

Most standard compressor lubricants are made from an oil-based formulation and both can be used in most air compressors, however it depends on the type of compressor you use and amount of work you will use it for:

Light to Medium Duty Cycles: Mineral oil-based will be better if you won’t be using often as it is the more cost-effective choice.

Regular to Heavy Duty Cycles: Synthetic will be better if you will be using your air compressor more than 3 times a week as it protects against overheating whilst allowing your machine to run quieter and smoother.

What Operating Conditions Affect Air Compressor Oil?

Ambient Temperature: Temperature is the most important parameter and should be the priority when selecting the right oil. Element outlet temperature should be used as the primary parameter for oil selection, but if unavailable, ambient temperature will be suitable.

Air Quality: Air quality refers to elements affecting the quality of the ambient air surrounding the compressed air system. Commonly this will be dust contamination and the levels of dust that are created from your specific application environment which will need to be assessed.

Humidity: Depending on the location of your site and the weather it experiences, this could have an impact on the humidity levels in the ambient air. High humidity levels within intake air means that there will be a higher amount of water vapour.

What Happens If I Choose the Wrong Oil for an Air Compressor?

If you choose the wrong oil for your air compressor use, you can severely damage your equipment due to insufficient lubrication, therefore shortening its lifespan. Bearings, oil pumps, and other moving parts will not work properly, consequently causing increased internal pressure and energy consumption.

Oil Free Compressor vs Oil Compressor

Compressed Air Contamination

Unlike oil lubricated compressors, oil free compressors don’t contaminate the compressed air it produces. Even though air filters can be used to reduce contamination, choosing oil free systems gives you more peace of mind, especially with those industries where contaminant-free air is compulsory. Dentistry, pharmaceuticals, and the food and beverage sector do not tolerate air contamination.

Maintenance Requirements

As there is no oil used throughout the air compressing operation in oil free compressors, this maintenance is not required. The only thing you need to do is to drain the air compressor tank after each use and maintain the water- and air-cooling systems. You need to regularly change the oil, dispose of the oil, plus frequently change the oil filtration elements in an oil air compressor.

At Air Power East, we would still recommend maintenance checks and servicing on a regular basis though.

Life Span

For industrial purposes and longer working hours, oil lubricated air compressors are better suited due to their durability and longer life spans. Oil free compressors can only support small amounts of usage and have a shorter life span, so would be ideal for light applications.

Cost & Weight

An oil free compressor has less parts than an oil lubricated compressor so therefore is lighter in weight; this makes them easy to manoeuvre if necessary. Initially, oil-free air compressors typically cost less than traditional systems too. There are fewer parts in the machine, so there will be fewer repairs or replacements in general. Also, they are commonly built to include regulators which means they will only us energy when you need it, saving you more energy in the long run.

Noise & Heat

Due to the lubrication in oil lubricated air compressors, they make a lot less noise and also maintain a cooler temperature. Oil can help draw heat from the compression process while in operation, therefore oil free air compressors produce more heat as well as sound. However, oil free compressors have the ability to start quickly, no matter what the temperature.

Industrial Applications

Oil-powered air compressors are the finest option for construction and heavy-duty industrial applications that need power equipment. They may run for long durations and compress as much air as needed. If there isn’t any pressing necessity for a lubricant-free air compressor, as when air pollution must be deterred, a lubricant-based compressor is a more cost-effective option for large-scale operations.

Choose an Air Compressor with Air Power East

Choosing an air compressor isn’t an easy task, but you should never opt for the cheapest and easiest option without real consideration or speaking to an expert. Always consider your needs and requirements and, if you require further advice and guidance, talk to an expert to find the perfect one for your application.

At Air Power East, we have a wide range of air compressors to suit your needs. We also provide other services, such as Installation, Servicing and Maintenance, as well as Quality Testing. You can rely on us for all of your air compressor needs, so contact us today to discuss your requirements.

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