Compressed air is only as good as its purity. When your process is exposed to oil, it becomes increasingly difficult to keep air clean, increasing the costs you’ll face — especially as you use more and more air. To address this concern, many companies are turning to oiless or oil-less air compressors. Today, oiless compressors are becoming more common because they offer cost savings.

These purity and environmental benefits will often translate into other savings that may reduce your overall ownership costs. Here are a few of the things to consider if you’ve been wondering: “How do oiless air compressors work?”

1. There’s no need to collect or dispose of oil-ladened condensate.
2. Downstream filters have reduced replacement needs, because they’re not filtering oil.
3. Energy costs are minimized because there’s no need to increase force — some fluid-flooded units can see a downstream pressure drop due to filtration.
4. Reduced oil costs, because there’s no need to continually refill your compressor.
5. Typically, these units can unload within two seconds of the command to unload, and will use about 18% of their full load horsepower when unloaded.

 

Those savings can be very tempting. To see if you can make use of the oil-less compressors, you’ll need an understanding of how the compressors work and in which applications they work best.

 

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Functional Steps of How Oiless Air Compressors Work

Understanding how oiless air compressors work and why they last as long as they do is best illustrated by reviewing each function in a step-by-step method. Let’s walk through how an oil-less air compressor starts working and provides you with the compressed air that you need.

1. Drawing in Air

Oil-less air compressors start by bringing in outside air through their unloader valve and passing it through an inlet air filter (or filters) in order to ensure that the air is clean. The filter will limit damage to your compressor and its internal components. These filters are typically fine enough that they keep out dust, dirt and small debris.

The unloader valve opens to help the compressor pump air into its chamber, placing it in the “loaded” position. When the valve closes, the compressor enters the “unloaded” condition and begins running. When your compressor is running and actively delivering compressed air, it typically won’t be able to draw in any more air.

When you turn on your compressor and it starts to draw in air through an open unloader valve, the first destination for the air is the low-pressure compressor element.

2. First Compressor Element

You’ve probably noticed that your air compressor can create heat, and this often has to do with the low-pressure compressor element, because it’s working without any oil.

The average compressor element will operate at around 2.5 bar, and compressing air alone can make the unit operate at a temperature of up to 180 degrees. That can be more than twice as high as the temperature that oil-lubricated compressors reach, due to the lack of a flowing medium that whisks away heat.

Oiless elements will begin compressing the air and then move it through your compressor to cool the air down so it can be used in your applications.

3. Intercooler Access

After it’s initially compressed, pistons will push the air through an intercooler, where the air can cool so it can be further compressed. This will either move it to the second phase of compression or the final one, depending on the nature of your compressor.

Compressing air generates heat that limits the oxygen content of the air, thus reducing its density. Cooling the air essentially acts as a simple method for allowing denser and more oxygen-rich air to be again used by the engine, which in turn provides more fuel and improves the power output when the air compressor is working with a combustion engine.

Intercoolers are essential for two reasons. First, they cool the air down to a proper temperature to minimize the risk of any damage related to heat. Second, intercoolers allow air to be compressed at much higher PSI’s in two-stage pumps, and the cooling process means the second stage will face less wear.

Cooling air can lead to some condensation, and intercoolers will come with standard filters designed to remove moisture and water from the air. You’ll typically see this filter listed as a moisture trap.

After the air is cooled, it’s returned to your compressor for additional compressing.

4. Second, Higher-Pressure Compression

The air will move back into the main chamber of your air compressor — or the second chamber, depending on its design — and will be further compressed by a high-pressure element. The maximum pressure you’ll achieve typically ranges from 116 to 145 psig.

The air again becomes very hot due to the lack of lubrication in the surrounding elements, so it will need to be cooled once more.

5. Air Prep and Aftercooler Access

During its second phase of compression, the air will reach temperatures of around 150 degrees, requiring additional cooling before it can be used in other equipment. The aftercooler is the destination for air after its final compression stages, and this cooling allows it to be properly stored.

As air flows to the aftercooler, it will pass through a check valve that is designed to prevent any backflow, ensuring that air continues to compress and fill your tank. Backflow will damage your equipment and cause a major failure of the air compressor.

Many compressors — especially reciprocating compressors — are fitted with pulsation dampeners, and these are located just before the aftercooler. The dampener is designed to reduce pulsations and vibrations caused by the air compressor when it uses suction and opens discharge valves.

Pulsations can reverberate through the piping system, and these vibrations will make it difficult for your tools and machinery to measure air pressure and use it properly.

The air is finally stored or sent to your equipment for use.

6. Pressure Switches

Detection equipment in your air compressor tank will monitor the level of air you have. When it falls below a specified level, the air compressor will turn back on and start working to rebuild the pressurized air in the tank. The pressure switch is what is used to monitor and turn the compressor off and on.

• Pressure switches are typically attached to the unloader valve, though sometimes the valve is internal.
• Pressure switches are set by the factory and arrive at predefined levels.