Compressed-air filters

What is a compressed air filter?

A compressed air filter is a component of compressed air treatment that removes particles, oil, water, and other contaminants from compressed air. The compressed air filter separates unwanted contaminants from the compressed air produced by the compressor. These include solid particles such as rust, dust, and abrasion, liquid and aerosolized oil, as well as water vapor and microbiological contaminants.

Through this comprehensive separation, the filter ensures the required compressed air quality for a clean compressed air supply and protects machines, tools, and pneumatic cylinders from damage and wear. Compressed air filters or line filters guarantee the highest level of cleanliness depending on the operator’s requirements or the equipment regulations of the respective industry.

The international standard ISO 8573-1:2010 defines purity classes for particles, water, and oil in compressed air. It serves as the globally recognized reference framework that manufacturers, operators, and testing laboratories use as a guide. It is supplemented by the ISO 12500 series of test standards, which specifies test procedures for filter elements in compressed air systems. In practice, compressed air filters are connected in series: First, a pre-filter captures coarse particles, followed by a fine filter or coalescing filter, and—for high-demand applications—an activated carbon or sterile filter. This multi-stage treatment is crucial, as a single filter cannot remove all contaminants with equal efficiency.

In short: A compressed air filter is a treatment element that removes particles, oil, water, and odors from compressed air to reliably protect tools, processes, and end products.

Application and Purpose of Compressed Air Filters

Compressed air filters are designed to provide oil-free compressed air to the greatest extent possible. As a result, they are used in a wide variety of applications. Typical applications include pneumatic tools, pneumatic systems, packaging machines, painting systems, the food industry, the pharmaceutical industry, and electronic manufacturing processes.

Many manufacturers specify the level of cleanliness and residual oil content of the compressed air required to operate their machines. To clearly define and distinguish between these categories, so-called compressed air classes were established in ISO 8573-1:2010.

These standards define the desired residual levels of particles, water, and oil:

What is the difference between a compressed air filter and a water separator?

A water separator primarily removes liquid condensate and larger water droplets from the compressed air. Cyclone separators are often used for this purpose. These do not require a filter element and are installed directly after the compressor. They remove a large portion of the water accumulated in the compressed air.

A compressed air filter performs comprehensive filtration, which includes solid particles, oil aerosols, oil vapors, and other contaminants. In modern compressed air systems, the compressed air filter is often used in combination with a water separator as part of a multi-stage compressed air treatment process.

What types of compressed air filters are available?

To achieve these compressed air quality classes, various compressed air treatment filters are available:

Pre-filters: Remove coarse contaminants such as dust and water droplets. They protect downstream filter stages and extend their service life.

Fine filters: Filter particles down to approx. 1 µm and reduce the residual oil content to approx. 0.5 mg/m³.

Microfilters (ultrafine filters): Achieve separation down to 0.01 µm with a residual oil content of approx. 0.01 mg/m³.

Superfine filters: Provide even finer filtration and are suitable for particularly demanding applications.

Activated carbon filters: Adsorbe odors and oil vapors and achieve residual oil levels as low as 0.003 mg/m³.

Sterile filters: Are used in the pharmaceutical and food industries, where sterile compressed air is required.

This is also where the order in which the pressure filters should be installed is determined. The prefilter protects the subsequent, finer filter stages and extends their service life. Depending on the industry and requirements, individual stages may be omitted or additional sterile filters may be added.

Depending on the industry, compressed air filters should only be designed by a specialist, taking into account existing equipment and specific requirements. Proper placement and installation within the system should also be carried out in consultation with experts.

Is a coalescing filter or a filter separator needed for paint booths?

In paint booths, the purity of the compressed air is crucial. Filter separators effectively remove water and coarse contaminants. In addition, coalescing filters separate even fine oil aerosols and the smallest particles. Many companies also use multiple filter stages to achieve optimal painting results and ensure the highest quality standards. For sensitive painting applications, filter elements without silicone are often used, as silicone can interfere with the painting process and cause surface defects.

What is the difference between a fine filter and an activated carbon filter?

A fine filter operates primarily mechanically and removes particles as well as liquid oil from the compressed air. An activated carbon filter, on the other hand, uses the principle of adsorption to capture gaseous oil vapors and odors. For applications requiring a very low residual oil content of up to 0.003 mg/m³, the activated carbon filter is indispensable.

Where are compressed air filters used?

Compressed air filters are typically installed after the compressor and before the compressed air consumer. Air filters, oil filters, and separators are installed in the compressor to ensure optimal compressed air quality after the compressor and to optimize the service life and efficiency of the entire system and the downstream machinery.

Compressed air filters can remove particles as small as 0.01 µm from the generated air. This also applies to oil vapors down to a residual oil content of 0.003 mg/m³. After the dryer and along the piping from the compressor to the consumer, minute amounts of water and oil droplets condense. In addition, contaminants may accumulate in the line.

For this reason, a pre-filter is installed upstream of the consumer, and—depending on the consumer’s requirements—additional fine filters, ultra-fine filters, super-fine filters, and activated carbon elements are also installed. These compressed air filters remove unwanted contaminants from the air. The housings of these compressed air filters are designed to last the entire service life of the system. The filter elements must be replaced annually or as indicated by the differential pressure gauge or differential pressure sensor.

What compressed air class do I need for my application?

The required compressed air class depends on your industry and application. In food and pharmaceutical production, Classes 1 through 2 according to ISO 8573-1:2010 are typically required. In general mechanical engineering, Classes 3 through 4 are often sufficient. Check the specifications provided by your machine manufacturers and feel free to contact us for personalized advice.

Which compressed air consumers require particularly clean compressed air?

Compressed air quality varies greatly depending on the application. Particularly high purity requirements apply to paint booths, pneumatic systems, packaging machines, and in the food and pharmaceutical industries. Even small amounts of particles, oil, or condensate can lead to quality defects, production downtime, or increased wear. Therefore, compressed air filters are selected based on the consumer and the required compressed air class and, in many cases, are designed as multi-stage compressed air treatment systems.

How does a compressed air filter work?

The contaminated air enters the compressed air filter through the raw air inlet, where it passes through the filter element. This results in separation of particles down to 0.01 µm. In the case of activated carbon filters, this reduces the residual oil content to as low as 0.003 mg/m³. The clean air is then fed into the system via the clean air outlet.

What are the functions of the individual filter types?

Different filtration mechanisms are used depending on the filter type. Particle filters remove solid contaminants, coalescing filters separate oil aerosols and moisture, and activated carbon filters adsorb oil vapors and odorous substances.

Design and Operation of Industrial Compressed Air Filters

An industrial compressed air filter typically consists of a filter housing, a replaceable filter element, and seals. Optionally, a differential pressure gauge or a differential pressure sensor may be added to monitor the maintenance status. Modern filter housings are often equipped with condensate drains, which are available in various designs. These can be float-type, electronically controlled, or level-controlled condensate drains.

How are compressed air filters maintained, and how long do they last?

Compressed air filters must be checked and maintained regularly to effectively remove contaminants; otherwise, these contaminants will increase pressure drop and reduce efficiency over time. A filter’s service life is influenced by compressed air quality, operating conditions, and maintenance intervals.

How can I tell if a compressed air filter is saturated?

A defective or heavily contaminated compressed air filter can be identified by increased pressure loss, declining system performance, rising energy consumption, or contaminants in the compressed air.

Why is there water in the compressed air filter?

Water is produced when ambient air is compressed. As the compressed air cools within the compressed air network, moisture condenses and collects in the filter housing or water separator.

In certain cases, water can still get through despite the presence of a water separator. Possible causes include an overloaded water separator, a defective condensate drain, a missing compressed air dryer, or an improperly designed compressed air treatment system.

Selection Guide for Compressed Air Filters

When selecting the right compressed air filter, the following aspects must be considered: subtype, filter unit, and specific specifications. Here is a detailed list to help you make the right choice:

1. Which subtype is suitable?

Particle filters for dust, rust, and abrasion (first filter stage) Coalescing filters for oil mist and water (industry standard) Activated carbon filters for odors and oil vapors (e.g., food industry) Sterile filters for sterility (pharmaceuticals, medical technology)

Good to know: In practice, filters are almost always combined in a multi-stage configuration.

2. What specifications do I need?

Selection checklist:

Airflow (m³/min) Operating pressure (bar) Connection (threaded/flanged) Dimensions (length, diameter) Seal type Filter rating (µm) Medium (air, oil, steam, etc.) Desired ISO class

What should you look for when purchasing a compressed air filter?

Several factors play a key role in selecting a compressed air filter. These include the air flow rate, operating pressure, and connection size. Equally important are the filter fineness and the compressed air class according to ISO 8573-1. The type of contaminants to be removed must also be taken into account. Furthermore, it is important to consider whether oil-free compressed air is required and what the specifications are for compressed air quality and residual oil content.

What are the best compressed air filters?

The best compressed air filters are not necessarily those with the finest filtration. The best compressed air filters are those that are optimally suited to the application. For many industrial applications, multi-stage combinations of pre-filters, coalescing filters, and activated carbon filters are used.

Frequently Asked Questions (FAQ)

How do you install a compressed air filter?

Compressed air filters are typically installed in the compressed air line after the compressor or after the compressed air dryer. It is important to ensure the correct flow direction, sufficient space for maintenance work, and proper sizing.

How do I identify the right connection or seal?

You can identify the right connection using technical data sheets or existing filter elements. The thread type, diameter, and seal type are important here.

Where can I buy compressed air filters?

You can purchase compressed air filters, line filters, and other replacement filter elements directly from our B2B store. Using the product selector or cross-reference search, you can find both exact-fit filters and suitable alternatives from numerous manufacturers for a wide range of applications.

What should I do if I only have a part number?

No problem! Simply enter the part number into the search, and you’ll see all technically interchangeable alternatives to your filter.

This makes it a breeze to buy exact-fit compressed air filters online!

Does ELSÄSSER Filtertechnik also offer consulting services for compressed air treatment?

Yes, our team of experts will be happy to advise you on selecting and sizing the right compressed air filters for your system. We take into account your existing equipment, your industry-specific requirements, and the desired compressed air quality class.

Contact us by phone at 07032 / 96 04-0 or via our contact form.