Compressed air is only as good as its purity. Oil exposures make it difficult to keep air clean, which increases costs. To address this concern, many companies use oil-free or oil-less air compressors. An oil-free air compressor is similar to an oil-injected compressor, but it doesn’t use oil for lubrication.
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Today, oil-free compressors are becoming more common because they offer cost savings, have a minimal environmental impact and provide dependable performance. Learn more about how these machines work and how they can benefit your application.
Oil-free air compressors either have no mechanical contact inside the compression chamber or use alternate materials to protect the mechanism without lubrication.
Most oil-free compressors utilize other materials like water or a Teflon coating to keep the mechanism running smoothly. Because the lubrication of bearings and gears is all external to the compression chamber, proper sealing prevents any oil from contaminating the compressed air. The result is a 100% oil-free air supply. Some oil-free designs have even removed metal-to-metal contact within the compression chamber, eliminating the need for oil-based and synthetic lubrication altogether.
These purity and environmental benefits will often translate into other savings that may reduce your overall ownership costs. Here are a few things to consider if you’re contemplating switching to an oil-free model:
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, how they compare to other types of models and in which applications they work best.
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The phrases oil-free and “technically oil-free” are often used to identify the purity of compressed air. These phrases correlate with different air compressor rankings, which ultimately depend on the worldwide standards set by the International Organization for Standardization (ISO).
Air compressors are ranked based on how clean the air is after compression, from ISO Class 0-5. Class zero air is the highest air quality possible and the cleanest choice for sensitive applications.
The best air compressor for your facility will depend on your specific application. Oil-free compressed air is critical for many applications where oil contamination can damage production equipment or cause product spoilage and recalls. These compressors are the perfect solution to ensure your processes meet the highest air purity standards. In contrast, oil-injected compressors typically have a more durable design and can last longer than oil-free models.
When the choice narrows down to an oil-free air compressor vs. oil-injected alternatives, the following considerations may be essential to helping you find the best fit:
An oil-injected air compressor might be the more cost-effective option for applications where the above advantages aren’t necessary to improve efficiency or maintain safety. However, in situations where the risk of oil contamination is too high, such as food processing or medical services, oil-free air compressors are required.
Understanding how oil-free 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.
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.
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.
Oil-free 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.
After it’s initially compressed, pistons will push the air through an intercooler, where the air can cool so it can be further compressed. Depending on your specific compressor, this step will either move it to the second compression phase or the final one.
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.
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.
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 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.
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.
Remember that air compressors contain oil that resides in the gearbox, never contacting the compressor.
The air compressor’s gearbox drives the two compressor elements with the electromotor. Gearboxes need lubrication to operate properly and can be costly to replace, so maintenance checks should review them on a regular basis. The oil in your gearbox lubricates the internal gears and bearings, as well as the bearing and timing gear located inside each compressor element.
An oil sump pumps oil from inside the gearbox. Then, an oil cooler and filter cool it before transferring it to cool the compressor and gearbox parts. The filters remove debris during this action.
Internal gearbox elements are treated with long-lasting lubrication. This puts more of a strain on the engine over time but helps oil-free models require less day-to-day air compressor maintenance.
Understanding the general pressurization of air compressors is pretty straightforward, as it often operates the same way across oil-injected and oil-free units.
For the oil-free compressors we’re looking at, there are two main methods for cooling the compressor itself: Water and air. Air-cooled compressors, which tend to be rotary screw compressors, use outside air to cool the compressed air and the oil used in the gearbox. Air circulates and moves heat away from internal components as well as from the parts that house the oil, which helps remove heat from your compressor elements.
Water-cooled machines will have a two-part cooling system. Water moves near each element, heats up and flows away from the components, condenses and cools and then moves back toward the equipment (often via gravity). These systems will have a water-cooling circuit used for the oil, intercooler and low-pressure element. The second circuit works to cool the high-pressure element and the aftercooler.
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Generally, an oil-free compressor will not last as long as an oil-lubricated model because its pre-lubrication will gradually wear away and degrade over time. Oil-free compressors also tend to use a universal motor, which won’t last as long as an induction motor.
The Teflon coating often used to lubricate the internal cylinder simply wears off over time, and this wear can increase when an oil-less compressor is used in extreme temperatures or for long durations. If you’re vigilant, you can have an oil-less compressor last for years, but this requires more time and money (typically) than an oil-lubricated air compressor.
If you want to extend how long your oil-less compressor will last, good maintenance is your best friend. Air compressors have a lot of moving parts that can cause significant wear, so ensure that you’re looking inside at least once a month. Check the permanently lubricated elements, such as the cylinder’s Teflon coating and either Teflon or carbon ring seals.
Part of how oil-less air compressors work includes a significant generation of heat. The more stress they’re put under or the higher the pressure you’re going for, the more likely it is that your air compressor will grind against itself or generate enough heat to burn out and/or warp components.
Oil-free air compressors tend to have a smaller clearance than their oil-injected counterparts, which means there may be less room for them to intake and move enough air to circulate and cool properly. To avoid this, you need to run the compressor only at its manufactured specifications and ensure that you’re providing plenty of space surrounding the unit to keep its exhaust and intake lines free from heat-causing dust and dirt.
When you’re ready to make your selection for an air compressor, it’s important to understand the three main types of compressors. The method of compression can impact their ability to output at a higher power level, be more portable or maintain more consistent pressure.
Reciprocating air compressors use positive displacement, which generates air pressure via two sides that provide either suction or discharge. Positive displacement is suitable for compressing small amounts of air at high pressures and can quickly dissipate the heat from compression.
Reciprocating compressors tend to have a lower output than others, but they can achieve relatively high pressures. Non-lubricated reciprocating compressors will typically use a Teflon piston ring instead of oil. The Teflon ring means there’s no need for lubrication for the pistons, rings and cylinders because the material reduces wear. To improve life, these units also tend to opt for aluminum pieces in place of cast iron.
Teflon rings will need to be replaced regularly, but they present little contamination risk to the compressor.
Rotary screw air compressors also use displacement and generate the air compression by running a system of interlocking screws that draw in air and then pressurize it in a small area.
Oil-free rotary screw compressors opt for non-contacting carbon ring seals to aid their cooling. These seals prevent any oil from entering the air stream inside of the air compression unit. Sectioned-off coolant is used and kept on the other side of the seal for easy cooling.
Oil-free rotary screws can see heat buildup over time since they typically lack the ability to throttle the inlet, which will see those with large demands opt for the flooded models.
Scroll technology is an advanced air compression system that includes one mobile and one stationary spiral, which work together to bring air into the chamber for compression. Air is compressed within the spiral by decreasing the volume of the air, then directing the air to the center of the compressor to be cooled.
The biggest advantage of this technology is that there is no residual friction or wear on the system because the spirals never contact each other. In many cases, these compressors also work more smoothly, producing a different sound from other compressors. Some may require lubricant, but many common models operate with an oil-free design.
Oil-free compressors have many advantages for users, such as:
No matter its application, an oil-free compressor has minimal effects on the environment and lowers your operational expenses.
Oil-free air compressors can meet the needs of many industries and applications, including:
Oil-free compressed air also contributes to many other industries not named here.
Oil-free air compressors are a more thoughtful choice and require careful consideration for your operations. The fundamentals of how oil-less air compressors do their work means you could be looking at lower costs, a better footprint and cleaner air.
If you’re in an industry that demands air purity at 100% clean levels, then a compressor that doesn’t rely on internal oil is a top bet. By not using oil, you’ll also be able to lower your carbon footprint, and these smaller units also tend to require less energy because they have more options for speed regulations.
Quincy Compressor offers a suite of oil-free air compressors and can make recommendations specific to industries such as electronics, pharmaceuticals, textiles and food and beverage applications. We stick to the ISO -1: standard to ensure that your air purity needs are always met.
When you’re ready, reach out to your local authorized Quincy Compressor distributor to get all of the information you need about specialty models, including the QOF oil-free scroll compressor, and to receive a no-obligation price quote for your application.
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Last Updated June 28, at 12:15 pm
As long as there has been “oil-free” certification there have been myths floating around. The one that’s used most is the claim that oil-lubricated compressors combined with filters are “technically oil free.” And, that air quality from those oil-injected compressors with the help of that filter can be better than oil-free. While filters can reduce the level of oil particles, filters do not reduce the risk of oil contamination. Renting temporary solutions based on incorrect information could cause inadvertent damage to sensitive applications, products, and the environment.
Air purity is critical for many applications where even the tiniest drop of oil, or air contaminated with oil, can cause product spoilage, product recall or damage production equipment and even environmental damage. Your specific application will determine which type of air compressor is best for you to use in your facility and the Atlas Copco Rental experts will guide you along the way.
Oil-free air compressors are not “better” than oil-lubricated compressors. The compressor you choose depends on your specific application requirements and the air quality that you need to achieve. In instances where the threat and consequences of oil contamination are too high, having an oil-free air compressor is a must such as in medical procedures, food processing, and bubble curtain applications. When the consequences of oil contamination are not as serious, such as general manufacturing and in industrial workshops, oil-injected air compressors are used.
First, let’s take a moment to break down some of the above vocabulary. Oil-free and is used to describe compressors that do not use any lubrication in the compression chamber. While it describes a type of compressor, Class 0 and “technically oil-free” express how clean the air is after compression. Though they are close in meaning, there are a few important differences between the two.
The International Organization for Standardization (ISO) sets forth worldwide standards for proprietary, industrial and commercial purposes. Compressed air has its own set of ISO standards. Depending on air ultimate air purity (determined by number of particles per cubic meter as a function of particle size), compressors can be ranked from ISO Class 0-5.
The original version of ISO compressed air purity standards () was ‘made by and made for’ the filter manufacturers. The standard defined five classes of oil concentration, the best of which was Class 1. Class 1 specifies an oil concentration of 0.01 mg/m3 at 1 bar(a) 14.5psia and 20oC (68F), and conformance to these criteria is sometimes called “a technically oil-free solution.”
However, these standards were edited in and were further updated in . The current standard sets limits on total oil content (aerosol, liquid and vapor), and a specific standard was introduced on measurement of oil vapor. A new class (Class 0) was added to cover more stringent quality requirements. Atlas Copco was awarded the ISO -1 CLASS 0 () certification and also holds the ISO certification for the oil-free production facility in Antwerp, Belgium.
Air compressors function based on a very simple principle: When the air is compressed, its volume decreases whereas the pressure increases. In that same vein, oil-free and oil-injected air compressors work in essentially the same way. Air compression is a two-stage process in which the pressure of air rises while the volume drops. There are, however, different oil-free air compressor technologies that work in different ways:
Oil-free air technology helps you avoid needing to purchase filter replacements because they are don’t have to filter any oil. This cuts the cost of oil condensate treatment and reduces energy loss from pressure decreasing filter pressure. There is also the environmental impact: By employing oil-free air, you help protect the environment and ensure better compliance with international regulations. Leaks and energy usage are minimized, and the need for condensate treatment (and the collecting/disposing of condensate) is eliminated.
What’s more, you will not risk contaminating your end-product or process with oil, so no risk of loss of reputation or negative impact to your bottom line. While our equipment is a temporary support of your own installation, you can expect the highest qualities and guaranteed absence of oil in the air you need.
Which industries and critical applications employ oil-free air:
The Part 2 test measures aerosols and liquids. Testing can be done through partial flow (B2) or full flow (B1) methods (see below). The Part 5 test measures vapors only. Both parts are necessary to obtain ISO CLASS 0 certification. This means that all three sources of oil contamination – aerosol, vapor and liquid – have to be measured.
Both methods are acceptable for aerosol and liquid measurement according to ISO -1 Part 2 The B2 method targets only the center of the air flow. Oil aerosols are registered but oil that sticks to the pipe wall (wall flow) is not detected. Most air compressor manufacturers still prefer this less stringent method. The B1 method examines the entire air flow to measure both aerosols and wall flow. This comprehensive test method was used on the Atlas Copco range of oil-free air compressors. Even so, no traces of oil were found in the output air stream.
This solution is often referred to as “technically oil-free air”. However, even under optimum conditions and with several stages of oil removal, the air quality with regard to oil is suspect.
To achieve even barely acceptable air quality with oil-injected compressors, it is necessary to have air cooling devices and several stages of oil removal with multiple components. A failure of any of these components or inadequate maintenance can result in oil contamination of a process.
With oil-injected compressors there will always be a risk of contamination and the possibility of severe consequences for the business.
One aspect influencing the efficiency and purity of air systems is temperature. When using oil-injected compressors with oil removal filters, oil carryover through filter media increases exponentially according to the temperature at the filtration interface.
If the ambient temperature in the compressor room increases to 30°C, the compressor outlet temperature could be 40°C with the oil carryover 20 times the specified value. Such temperatures are not unusual even in colder countries, where the compressor room temperature is substantially higher than that outside.
Temperatures also cause an increase in the vapor content of the air, some of which can carry through to the end product. Moreover, high temperatures shorten the lifetime of activated carbon filters. An increase in temperature from 20°C to 40°C can cut filter lifetime by up to 90%. Even worse, the activated carbon filter does not warn the user when it is saturated. It will simply allow oil to pass on to processes. For Atlas Copco’s oil-free compressors, air quality is independent of temperature.
Ambient air has very small traces of oil coming from vehicles and industrial sources. However, in contaminated areas, oil content does not normally exceed 0.003 mg/m3. This is borne out by tests conducted by the TÜV near a factory with heavy machining activity (including turning, milling, grinding and drilling). Heavy vehicular traffic and a garbage incinerator were in the vicinity. Aspirated by an oil-free compressor, this extremely low level of atmospheric oil is almost completely washed away by the condensate in the intercooler and aftercooler, resulting in pure oil-free air for your process.
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