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Oil-Free or Oil-Less?

The decision to purchase an Oil-Less compressor or an Oil-Free compressor is based on several factors whether this is a personal preference to maintain the efficiency and life of the compressed air network system, air tools, pneumatic equipment and processing equipment or to comply with industry standards, directives or guidelines. To narrow the choice several important questions need to be answered:

Do I need Oil-Less or Oil-Free compressed air?

There are several technologies available to provide the specific quality of air required however, there is some confusion to the class of air required and how the air quality is defined. Essentially Oil-Free air is generated without any lubricant (oil) coming into contact with the compressed air, whereas Oil-Less air is generated by conventional methods (where oil and compressed air is in direct contact) and then oil removal systems are applied to reduce the oil residue within the final product.

Oil-Free rotary screw compressors can utilise Dry Running Air Ends or Water Injection Systems (Fleming-SCROLL Series) or (NOBEL Series)

Oil-Less rotary screw compressors can utilise high efficiency filtrations (Compressed Air Filtration) and the choice will depend on the final quality of compressed air required.

The selection becomes much easier if the following questions are exactly defined.

What air quality do I require?

Most Original Equipment Manufacturers (OEMs) will normally specify the compressed air specifics to efficiently use their equipment. In additional to capacities, pressure, etc. and class of air will also be indicated in accordance with DIN ISO 8573-1. Although this section does not focus on particulate filtration and dew point, these values are also contained within this standard along with the oil residue content values. In addition to the specifics required by the manufacturer, it is important to overlap these with any standards, directives or guidelines that are advised or enforced by government or relevant industry bodies.

Compressed air quality classes to DIN ISO 8573-1

There are recommended compressed air quality classes for the different pneumatic applications to ensure trouble free function of equipment. In the table below the compressed air quality for each type of contamination is listed separately. The quality classes are recommended in DIN ISO 8573-1.

ISO 8573-1 Chart

This standard is very useful as it is common for an OEM or relevant body to insist on an ISO 8573-1 air quality class of, Specific Air Quality of 2, 3, 1. This for oil residue purposes provide compressed air containing an oil residue content of 0.01 mg/m3. The above class is referred to generally in the industry as clean, Dry Air¯ and the final compressed air quality is generated by most full feature rotary screw compressors. In some circumstances the dew point needs to be of a higher class along with the oil residue content for certain applications such as dental practices (HTM2022), however this will be explained later. Due to increasing demands for even greater purity and therefore elimination of oil residue any manufacturers are providing solutions to an improved standard:

Compressed air quality classes to DIN ISO 8573-1 Class 0 (2001)

Class 0 is the most pure and according to the standard, it describes compressed air that must be more pure than class 1. Classes 1 through 4 as shown cover the range from less than 0.01 mg of oil content per cubic meter of compressed air to less than 5 mg per cubic meter. Class 0 can be reached using dry air-ends, water injected systems or catalytic convertors.

MGF Icon  Piston Dry System - Medic+Air Series and MGF Range
Nobel Icon  Rotary Screw Dry System - NOBEL Series
Fleming Icon  Scroll Dry System - FLEMING Series

Do I need to comply with industry standards, directives or guidelines?

As explained the OEM will provide the specifics for the piece of machinery or tooling to operate efficiently, however, depending on the application a much better or purer quality may need to be attained to comply with industry or governments standards or guidelines. Although many applications and tooling need clean air and minimal oil residue values as low as Class 0 such as engineering processes, CNC machining, laser cutting, pharmaceutical processing, material conveying, irrigation, etc. there are several areas where improved air quality is required or recommended including:

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