Air Supply UK: Specialist Compressed Air Engineers

Published: 19/10/2021

Air compressor buyer’s guide: Oil vs oil free air compressors 

When choosing an air compressor for any purpose, knowing which type of compressor to buy for any application can be difficult. Two of the most popular types of air compressors are oil lubricated and oil free compressors. 

Although both types of air compressor both perform the same function (compressing air) they’re very different in the way that they work, the way they’re made and and the applications they’re designed for. 

Advancements in technology mean that oil free and oil lubricated compressors are still different but they’re not as widely separated now as they used to be. In this guide, we’ll take a look at how both types of compressor work, their differences and how to choose the right one for your application. 

How do air compressors work?

Air compressors work by drawing in air due to the downstroke of a piston inside. The upstroke of the piston compresses the air into storage. Piston compressors require some lubrication in order to prevent friction or seizing of the moving parts inside.

How do oil free air compressors work?  

In an oil free compressor no oil is used within the compression chamber. The compression chamber is pre-lubricated and equipped with a permanent lubricated coating (usually Teflon). This helps to create a smooth and frictionless surface and provides a shield for the piston parts when they’re working. 

Whilst this provides lubrication, the coating can degrade over time which makes oil free air compressors less durable than oil based air compressors. 

Different types of oil free compressors are available including: 

  • Oil free rotary screw compressors 
  • Oil free piston compressor
  • Oil free scroll compressor

Each type operates in a slightly different way but none of them require oil to work as they are already pre-lubricated. 

How do oil lubricated air compressors work? 

Oil lubricated (or oil lubed) air compressors use oil to protect the moving parts inside so they require re oiling on a regular basis to ensure that they keep working properly and to maintain their lifespan. 

There are different types of lubrication used within oil based air compressors:

Pressure system 

This lubrication system is used within industrial compressors and rotary compressors. High pressure oil is forced through the chambers of the compressor, using an oil pump. The steam of oil can also be more efficient in preventing the piston head from getting too hot while it’s working. 

Splash system 

This is the most common type of lubrication system. An oil dipper is used on the piston’s connecting rod. It reaches inside the oil pump and sprinkles oil across the bearings, including the piston chamber upon each revolution. 

Factors to consider when choosing between an oil free and an oil based air compressor 

There are several key differences between the two types of air compressor that should be considered before making your final choice. 

Maintenance 

Oil based air compressors need more maintenance than their oil free counterparts. 

The oil needs to be changed from time to time, depending on the type of compressor you have and amount of usage it gets. Each compressor has its own requirements for how often the oil should be changed so this is something to look out for when you buy your air compressor. The old oil will need to be removed and replaced with new oil to ensure continued effectiveness. 

Routine maintenance will be required when using an oil based air compressor. 

On the other hand, oil free air compressors are already lubricated with permanent solutions so you will never have to change the oil or lubricate them. As a result, they require much less maintenance in comparison. 

Air contamination 

One of the biggest problems that many businesses find with oil lubricated air compressors is the compressed air produced can become contaminated with the oil. Depending on the usage of the air compressor, this can be detrimental to the end product or equipment you’re powering. For many applications, this is not a problem so an oil lubricated air compressor will be the perfect solution. 

For example, if you run a car garage where a small amount of oil contamination will not be a problem for air tools or power tools, it doesn’t matter which type of air compressor you use. 

On the other hand, if your business is impacted by contamination in the compressed air, no matter how small, and it causes a serious issue, an oil free air compressor should always be used. An air filter can be applied to an oil lubed air compressor to prevent oil from coming through into the air but this could still cause problems within some applications. 

High purity air is required for machines that are used in food production, medicine, electronics and sensitive products so it’s imperative that an oil free compressor is used. 

Durability 

Oil based air compressors tend to be more durable and have a longer life expectancy than oil free versions because they have oil in the pump which means there is less friction and wear and tear taking place. 

If the oil runs out or goes bad, all you have to do is replace the oil and it will run effectively again. However, the permanent lubrication used in oil free compressors eventually wears out over time. Once the lubrication completely wears out, the compressor becomes noisier and will fall apart. 

This makes oil lubricated compressors more suitable for commercial applications where the compressor is used for long periods of time and by many people at once. The constant lubrication helps to reduce friction and keep the compressor cool during operation which reduces wear and tear significantly. 

Noise 

Oil free air compressors can be loud. As a result, they are usually kept away from the place of work to help reduce noise in the workplace. Newer oil free air compressors are now slightly quieter and will run 10-15 dBA quieter than older versions. 

Due to the added lubrication, oiled compressors run smoothly with very little noise – this is one of the key differences between the two types of compressor. 

If a noisy compressor will cause problems for your business and air contamination is not a problem, we recommend an oil based air compressor. Where noise is not an issue, either type of air compressor is recommended. 

Applications 

The main function of the two types of compressor is the same but the amount of air they compress and the equipment they will be used for can make a huge difference. 

Oil based air compressors are the best choice for heavy duty industrial and construction applications where power tools are needed. They can run for long periods of time and compress as much air as is required. If there is no great need for an oil free air compressor, such as where air contamination needs to be avoided, an oil lubricated compressor is a more economical option. 

Oil free air compressors are lighter which makes them an ideal option for applications where portability is required or needed for compressed air is less such as within the medical sector.

Cost 

Oil based air compressors can cost two or three times more to purchase than an oil free air compressor but they offer a longer lifespan and greater air capacity for powering larger tools and huge teams. 

Most oil lubricated air compressors provide a working life of up to 15,000 hours when properly maintained. Oil changes are recommended for every 200 to 500 hours to keep the machine running smoothly. Oil changes can help to extend the lifetime of the compressor and prevent replacements from being needed but the oil changes will need to be factored in to the overall lifetime cost of the air compressor. 

Oil free designs carry much lower costs of ownership over their lifetime because the initial purchase price is lower and these compressors do not require oil changes. While ongoing costs and initial costs are lower, oil free air compressors have a lower lifespan than oil lubricated compressors. 

Technology advancements in the manufacturing of oil free air compressors means that they have a much longer lifespan than older oil free air compressors. They now have a lifespan of up to 2,000 hours which is four times longer than the average oil free air compressor and is even comparable to some oil lubricated versions. 

If you’d like more advice on how to choose between an oil free or oil lubricated air compressor, please contact our expert team

 

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