Oil Vs Oil-Free Air Compressors

This guide explains everything you need to know about the differences between oiled and oilless / oil-free air compressors, from how they work, to the pro’s and con’s of each which I have summarized at the end of the article.

How Do Air Compressors Work?

To choose between oil-free air compressors or oil-injected compressors, it helps to have a rudimentary idea of how an air compressor works.

The downstroke of the piston draws air into the compressor, while the upstroke of the piston compresses the air and stores it in the storage container.

It is important not to mistake the operation of this piston with that of an automobile. But even with little lubrication, both pistons are required to avoid any friction or seizing between the wall of a cylinder and the metal-on-metal action of the piston. Read our guide for more details on what an air compressor is and how they are used.

Oil-Free Air Compressors

The piston chamber of such air compressors has been pre-lubricated and is coated with a permanent lubrication coating to ensure long-term performance. Teflon is the most common material used for this kind of coating. It protects the piston components during operation by creating a smooth frictionless surface on which they may operate. Over time, this coating has a tendency to disintegrate more slowly (essentially a self-lubricating design that will last for thousands of hours).

There is a sealed gearbox with a protective coating that protects the moving parts of the compressor, which is related to pre-lubricated components. Note: Occasionally, oil-free compressors may operate at a slightly lower RPM than usual in order to reduce the potential of overheating. I’m sure you have a general concept of what it implies, but it’s important to remember that oiling is necessary on a regular basis here.

With regards to the many forms of lubrication, there is a big range of oil on the market – see our comprehensive article on air compressor oil for more info on that.

Pressure System Compressors

Due to the high-pressure oil that is driven through the compression chamber by the oil pump, this kind of compressor is often seen in industrial compressors as well as rotary compressors. This flowing stream of oil (which operates in a similar way to how your car’s lubrication system works) is more effective at keeping the piston head from becoming too hot while functioning.

Splash System Compressors

This is the most common system. It makes use of an Oil Dipper, which is located on the piston’s connecting rod, to do this. From there, it travels into the oil pump and, with each rotation, distributes oil over the bearings, including the piston chamber.

How Do Oil-Free Compressors Work?

Explaining how oil-free compressors operate and why they last as long as they do is best accomplished by going through each function in a step-by-step manner. Consider the steps that an oil-less air compressor takes to get up and running and offer you with the compressed air that you need.

Drawing in Air

Oil-less air compressors begin by drawing in fresh air from the outside via their unloader valve and passing it through an input air filter (or filters) to guarantee that the air is clean. The filter will help to keep your compressor and its internal components from becoming damaged. Filters of this kind are normally tiny enough to keep out dust, dirt, and other minute particles.

In order for the compressor to pump air into its chamber, the unloader valve must be opened, putting it in the “loaded” position. After closing the valve, the compressor enters the “unloaded” state and starts to operate. (See illustration.) When your compressor is functioning and actively supplying compressed air, it is unlikely that it will be able to pull in any more air.

You should know that when you turn on your compressor and it begins to pull in air from a closed unloader valve, the first place that the air will end up is the low-pressure compressor element.

First Compressor Element

Most likely, you’ve observed that your air compressor generates heat. This is most typically due to the low-pressure compressor element, which is operating without the usage of oil.

Typically, the compressor element will work at 2.5 bar, and just compressing air may cause the machine to function at temperatures as high as 180 degrees. Because there is no flowing medium to remove heat from the compressor, the temperature may be more than twice as high as the temperature reached by oil-lubricated compressors.

In order for the air to be usable in your applications, oil-free components will begin compressing it and then circulating it through the compressor to cool it.

Intercooler Access

Following the first compression, pistons will force the air through an intercooler, where it may cool before being crushed even more. It will either be moved to the second compression phase or the final compression phase, depending on the kind of compressor you are using.

Compressing air releases heat, which reduces the amount of oxygen in the air, resulting in a reduction in its density. When an air compressor is used in conjunction with a combustion engine, cooling the air serves primarily as a straightforward technique of enabling denser and more oxygen-rich air to be recycled into the engine, which in turn supplies more fuel and increases the engine’s power output.

Intercoolers are necessary for a few of reasons. First and foremost, they lower the temperature of the air to a safe level in order to reduce the danger of heat-related harm. First and foremost, intercoolers enable air to be compressed at considerably greater PSIs in two-stage pumps, and the cooling process implies that the second stage will experience less wear as a result.

Condensation may occur as a result of the cooling of air, and intercoolers will be equipped with conventional filters that are meant to remove moisture and water from the air. This filter is often referred to as a moisture trap in the industry.

After the air has been cooled, it is returned to your compressor where it will be compressed again.

The Second Chamber Higher Pressure Compression

According to the design of your air compressor, the air will return to the main chamber or the second chamber, where it will be further compressed by a high-pressure element. The greatest pressure you’ll be able to reach is normally between 116 and 145 psig. Because of the absence of lubrication in the surrounding elements, the air gets very hot once again, necessitating the need for cooling once more.

Air Preparation and Aftercooler Access

During the second phase of compression, the air will reach temperatures of around 150 degrees, necessitating the usage of further cooling before the air can be utilized in other pieces of machinery. It is the aftercooler’s job to cool air after it has completed its final compression steps, which enables it to be properly stored.

As air is drawn into the aftercooler, it will pass through a check valve that is meant to prevent any backflow, ensuring that air is compressed and pumped into your tank. Backflow will cause harm to your equipment and may even cause the air compressor to fail completely.

There are pulsation dampeners installed on many compressors, particularly reciprocating compressors. These dampeners are positioned directly before the aftercooler on many compressors. Designed to lessen the pulsations and vibrations created by the air compressor while it is in operation and when the discharge valves are opened, the dampener is installed in the air compressor.

Pulses may echo throughout the piping system, and the resulting vibrations will make it difficult for your instruments and machines to accurately monitor and utilize the air pressure.

The process is now complete, and the compressed air is ready to be used.

Pressure Switches

The amount of air in your air compressor tank will be monitored by detection devices installed in the tank. When the pressure in the tank falls below a certain level, the air compressor will come back on and begin working to re-pressurize the tank to its original pressure. The pressure switch is what is used to monitor and control the compressor‘s operation, including turning it on and off.

Pressure switches are normally linked to the unloader valve, however the valve may also be internal in certain cases, like in this case.

Pressure switches are calibrated in the manufacturer and are calibrated to predetermined values upon arrival.

Type of Air Compressor

When it comes to choosing an air compressor, it’s crucial to grasp the differences between the three primary kinds of compressors. Compression methods may have an influence on their capacity to produce at a greater power level, be more portable, or maintain a more constant level of pressure.

Rotary Screw Compressors

Rotary screw air compressors employ displacement as well as compression to create air compression. They do this by operating a set of interlocking screws that pull in air and then pressurize it in a limited region.

Oil-free rotary screw compressors use non-contacting carbon ring seals to help in cooling, as opposed to contacting rubber seals. These seals are responsible for preventing any oil from entering the air stream inside the air compression unit. Coolant is utilized that has been sectioned off and is stored on the opposite side of the seal for simple cooling.

Oil-free rotary screws might have heat buildup over time due to the fact that they often lack the capacity to throttle the intake, which is why individuals with high needs will choose for the flooded variants.

Scroll Compressors

Scroll technology is an innovative air compression system that consists of two spirals, one of which is movable and the other of which is fixed. The two spirals work together to deliver air into the chamber for compression. By lowering the volume of air in the spiral, air is compressed inside the compressor, and then the compressed air is directed to the center of the compressor where it is cooled.

The most significant benefit of this technique is that there is no residual friction or wear on the system as a result of the spirals never coming into touch with one another. In many situations, these compressors also operate more smoothly, resulting in a sound that is distinct from that of traditional compressors. Some versions may need lubrication, however many popular types are designed to work without the use of oil.

Reciprocating Compressors

Positive displacement air compressors, such as reciprocating air compressors, create air pressure via two sides that may be used for either suction or discharge. Positive displacement is well suited for compressing tiny volumes of air at high pressures because it dissipates the heat generated by the compression process fast.

Reciprocating compressors have a smaller output than other types of compressors, but they are capable of producing quite high pressures. In the absence of oil, non-lubricated reciprocating compressors would normally use a Teflon piston ring as opposed to an iron piston ring. It is possible to eliminate the requirement for lubrication for the pistons, rings, and cylinders due to the Teflon ring’s wear-reduction capabilities. These units also prefer to use aluminum parts rather than cast iron in order to extend their service life.

Even though Teflon rings will need to be changed on a regular basis, they pose minimal danger of contamination to the compressor.

Certification – What is it and Why is it Important?

The International Organization for Standardization (ISO) establishes global standards for proprietary, industrial, and commercial applications around the globe. The ISO standards for compressed air are distinct from those for other types of compressed air. In accordance with the ultimate air purity (as measured by the number of particles per cubic meter of air, which is a function of particle size), compressors are classified into ISO Classes 0-5.

It was the filter manufacturers that created the first edition of the ISO compressed air purity standards in 1991, which was referred to as “made by and for.” The standard identified five classifications of oil concentration, with Class 1 being the highest and most concentrated. Class 1 stipulates an oil concentration of 0.01 mg/m3 at 1 bar(a), 14.5psia, and 20oC (68F), and compliance to these conditions is referred to as “a technically oil-free solution.” A solution that meets these criteria is referred to as “a technically oil-free solution.” These criteria, on the other hand, were revised in 2001 and were further revised in 2010. The present standard establishes limits for total oil content (aerosol, liquid, and vapor), and a new standard was established for the measurement of oil vapor in order to improve accuracy. A new class (Class 0) was created in order to accommodate more strict quality standards. For its oil-free manufacturing plant in Antwerp, Belgium, Atlas Copco has been given the ISO 8573-1 CLASS 0 (2010) accreditation and also possesses the ISO 22000 certification for the same site.

How to Choose Between an Oil-less or Oiled Air Compressor

When purchasing any piece of equipment, the first step is to assess how it will be utilized before analyzing other factors such as price and durability. As a result, we’ve become so used to hearing about oil-less compressors in the context of compact, portable models that it’s easy to forget that they are also available as fixed, single-stage piston compressors.

When it comes to selecting the most appropriate compressor, there are several things to consider. This is determined by the sort of work you will be doing with it and which type is the most appropriate for you. Oil-free compressors may be less expensive in the long term, but they will not have the same amount of output power. Oil air compressors utilize oil and may not need as much periodic maintenance as other types of compressors, but they may be more expensive in the long term.

How Much Will It Be Used?

Oiled air compressors are designed for heavy-duty and long-term use, and they need regular maintenance in order to keep the operation running smoothly and efficiently. Oil-free compressors, on the other hand, are designed for infrequent and intermittent usage. As a result, you won’t have to worry about keeping an eye on the upkeep as much.

As you can see, there are two sorts of use, which are regular and irregular, in this case. The oil-injected compressor may be the best option for you if your routine use is really demanding, in terms of effort, e.g. in industrial or commercial situations.

Oil-free compressors are more suitable for home users that need to utilize the compressor for non-professional, do-it-yourself operations. Because they are pre-lubricated, you won’t have to bother about doing any maintenance on them when they arrive.

How Much Noise Can You Handle?

Even though it is not directly connected to performance and capacity, it is very important when deciding between an oil free air compressor and an oil compressor. Whenever you’re operating a compressor someplace where it’s vital to keep the noise level minimal, oiled air compressors are your first and best option.

Due to the fact that oil-free air compressors are rather loud for their size, you must either use them outside or in a soundproof area while they are in operation. There are new models available which are both oil-free and at the same time almost as quiet as oil air compressors, which is a welcome development.

How Much Maintenance Can You Do?

Whenever machinery such as air compressors are used in industrial operations, there is always someone on call to maintain and run them. As a result, it is their responsibility to ensure that the compressor operates at peak performance. As a result, the lengthy checklist of oil compressor maintenance tasks is not a source of concern for them.

However, if you are the only person using it, it is possible that you will not have sufficient time for its maintenance. Due to this, the compressor‘s lifespan and performance could well be reduced.

So investing in an oil-less air compressor may be a wise decision in this situation due to the much easier and less regular maintenance they require.

Value For Money

Whether you purchase a compressor for $150 or $3,000, you’re going to expect a certain level of value for your money. However, this  value for money varies from model to model – there are some great compressors in the $150 – $250 price bracket, and some terrible ones (for the money!) in the $3000 – $5000 bracket.  Before buying a sophisticated item such as an air compressor, you should do thorough research.

You might begin by estimating how much work a compressor will do during its lifespan. Dividing it by the overall cost of the compressor may provide you with a good estimate.

A compressor’s true costs include the following:

  • Cost of equipment and installation.
  • The expense of maintenance and repairs.
  • The cost of electricity and oil.

How Good is The Warranty?

Top-tier air compressor manufacturers are likely to provide a certain and free repair/replacement service for their product, depending on the brand.

In this respect, major manufacturers such as California Air Tools, DeWalt, Makita, Campbell Hausfeld and others have a good record and are often willing to repair or replace defective machines within reason. Smaller or newer companies may provide a lower retail price, but you may not get the guarantee that you would from a more established brand.

I would say a good solid warranty is critical if you are planning to purchase an air compressor for industrial purposes. A unexpected fault in the system might cost you big time in terms of production and repair costs. In this sense, having a speedy warranty policy (together with on-the-spot servicing) is even more vital.

Advantages & Disadvantages of Oiled & Oil-Free Air Compressors 

Below we will summarise the various pro’s and con’s of both oiled and oil-less air compressors, to hopefully enable you to make a quick decision on which to invest in.

The Advantages of an Oiled Air Compressor:

  • Excellent for industrial or professional applications
  • Usually more powerful than oil-free compressors
  • Increased RPM means higher PSI/CFM ratings
  • It can be operated in hot weather but struggles in cold weather
  • Quieter than Oil-Free compressors

The Disadvantages of an Oiled Air Compressor:

  • They are heavier and less portable than oil-free alternatives
  • Frequent maintenance required
  • The is an air contamination risk

The Advantages of an Oil-Free Air Compressor:

  • There is no risk of oil contamination
  • They are often lighter and more portable
  • Almost zero maintenance required
  • No oil changes required
  • No oil filter needed
  • Runs cooler and more efficiently
  • Operate well in cold weather

The Disadvantages of an Oil-Free Air Compressor:

  • Not as powerful as oiled
  • Not suitable for running all day
  • Often louder than oiled compressors
  • Not suitable for industrial or commercial purposes

Hopefully this guide has provided you with every bit of information you need in order to make an informed decision on the right machine for you! Let me know in the comments below if you have any further questions.

Jeff Stelling

Jeff Stelling is an air compressor obsessive who has been working with compressors for over 25 years, since he was an apprentice engineer in the mid 90’s. He designed Aircompressorcompare.com to offer technical guidance and buying advice for compressors.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.