Guide to Selecting and Classifying Air and Oil Filters in Industrial Systems
In most industrial plants, compressors, compressed air networks, lubrication circuits and oil systems run for years with very few stops. But when air and oil quality are not taken seriously, problems start to show up gradually: reduced efficiency, pressure losses, bearing failures and, at some point, unexpected downtime.
This introductory article answers three practical questions: What types of air and oil filters exist? – Which type is more suitable for each application? – and What should you look at when selecting a filter? The aim is to help engineers, maintenance teams and technical decision-makers make more deliberate, informed choices instead of treating filters as anonymous spare parts.
1. Why are air and oil filters so important?
At first glance, a filter looks like a simple consumable – something that has to be replaced every now and then. In reality, filters play three major roles in an industrial system:
- Protecting expensive equipment (compressors, pumps, bearings, precision valves, etc.)
- Preserving product quality (coatings, packaging, clean compressed air for instruments)
- Reducing unplanned downtime and maintenance costs
A poor filter choice might look like a small price difference on a purchase order, but in practice it can lead to costly failures and lost production. That is why treating filters as a strategic component, not just a commodity, is so important.
2. Basic classification of air filters in industrial systems
Depending on where they are installed and what they have to remove, air filters can be grouped into a few common categories. Here we focus on applications around compressors and compressed air systems.
2.1 Air intake filters for compressors
The intake filter protects the compressor against ambient dust and solid particles. If this filter is not selected or maintained properly, solids will enter the compression element directly and cause premature wear of internal components.
Key features to consider: initial pressure drop, dust holding capacity, filtration efficiency and the ability to cope with dusty environments without clogging too quickly.
2.2 Compressed air line filters
Downstream of the compressor and dryer, line filters are used to remove fine solid particles and oil aerosols. They usually come in several types:
- Coarse or pre-filters for larger particles
- Fine or coalescing filters for small particles and oil aerosols
- Activated carbon filters to reduce oil vapours and odours
The right combination depends on the air quality level required at each point of use.
2.3 Point-of-use filters
In sensitive areas such as paint lines, final packaging or instrumentation, an additional filtration stage is often installed close to the consumer.
These point-of-use filters help catch any remaining contamination picked up in the distribution piping before it reaches the critical equipment.
3. Basic classification of oil filters in lubrication and compressor systems
In oil circuits – such as lubricated compressors, gearboxes, hydraulic systems and central lubrication systems – oil filters remove solid particles and other contamination generated by wear, environment or the oil itself.
3.1 Compressor oil filters
These filters are installed in the oil circuit of the compressor to protect bearings and moving parts from wear particles and contaminants.
Choosing the correct filtration rating, temperature capability, compatibility with oil viscosity and sufficient dirt holding capacity is critical for compressor reliability.
3.2 Oil filters in hydraulic and lubrication circuits
In hydraulic and central lubrication systems, you typically find filters in the pressure line, return line and circulation loop.
Each position sees different operating conditions, so the filtration class and pressure rating must be matched to where the filter is installed, not just to pipe size.
3.3 Oil separators in lubricated compressors
Strictly speaking, the oil separator is a special type of filter element whose job is to separate oil from the compressed air in oil-injected compressors.
Separator performance has a direct impact on oil carry-over, oil consumption, outlet air quality and the overall pressure drop of the system.
4. Key criteria for selecting air and oil filters
When selecting a filter, looking only at thread size or overall dimensions is not enough. Some of the key criteria to consider are:
-
Type of contamination
Do you mainly need to remove solid particles, control moisture, or focus on oil and vapours? Each type of contamination requires a different filtration technology and efficiency level. -
Filtration class and efficiency
For compressed air, the required quality at the point of use determines which combination of filters is needed. For oil, the acceptable particle size (often expressed in microns or cleanliness codes) is crucial for protecting bearings, valves and servo components. -
Pressure drop
Every filter creates a pressure drop. If a filter is undersized, pressure drop will be excessive, forcing the system to work harder and consuming more energy. -
Dirt holding capacity
The filter must be able to hold contaminants for a reasonable service interval so that you are not replacing elements too frequently. -
Operating conditions (temperature, pressure, fluid)
Operating temperature, type of oil, system pressure and environmental conditions all influence media selection, seal materials and housing design.
5. Common filter selection mistakes to avoid
- Selecting filters based only on physical similarity or size, without checking filtration class and performance.
- Using very fine filters everywhere, without evaluating pressure drop and flow requirements.
- Replacing original filters with cheaper, non-equivalent elements purely on price, ignoring efficiency and capacity.
- Having no monitoring of pressure drop and waiting to change filters only when they are completely clogged.
- Using the same filter type for every point in the system, regardless of how sensitive the final consumer is.
6. Conclusion: a good filter is not a cost, it is an investment
When air and oil filters are selected correctly, they stop being a simple “running cost” and become a long-term investment in asset protection and production stability. Understanding how filters are classified, knowing what contaminants you are dealing with and paying attention to pressure drop and dirt holding capacity are the first steps towards a more reliable system.
To explore industrial filters for compressed air and oil circuits, you can visit the PowerSep products page and, if needed, share your system details with our technical team via the contact section.
Additional in-depth articles on fine filtration, oil separators and building a filtration chain for compressed air and oil systems will gradually be added to the PowerSep knowledge articles section.