Introduction to the Main Types of Air Filters in Screw Compressors
The screw compressor is the heart of many modern compressed air systems. It often runs for years, day and night, with very little attention – until something goes wrong: efficiency drops, oil consumption increases, or a critical line suddenly loses pressure. In many of these cases, the story starts with one simple topic: air filtration.
One of the most effective tools you have to keep a screw compressor healthy is a set of well-selected and well-maintained air filters. In this introductory article, we will look at the main types of air filters used around screw compressors, what each of them does and what you should keep in mind when selecting and maintaining them.
1. The screw compressor and the air path – a quick overview
In a typical oil-injected screw compressor, ambient air enters through an air intake filter, is compressed together with oil in the screw element, then passes through an oil separator and the cooling stage before going out to the plant’s compressed air network. On the way out, you will usually find in-line compressed air filters and, near sensitive equipment, point-of-use filters.
Each of these filters has a specific role. Removing one of them from the chain is effectively accepting extra risk for downstream equipment and for the quality of your final product.
2. The air intake filter – the first line of defence
The first and often most critical barrier against contamination is the air intake filter. Its job is to stop dust, airborne particles and general environmental contamination from entering the screw element. If this filter is not doing its job, all of that contamination goes straight to the rotors, bearings and oil.
A few simple but important points about the intake filter:
- In dusty environments, you need a higher-efficiency filter with more surface area to cope with the load.
- The initial pressure drop should be low enough so the compressor does not waste energy just pulling air through a restrictive element.
- Cleaning or replacing the filter too late directly affects energy consumption and the lifetime of the oil and compressor.
In short, the cleaner the inlet air is, the easier the job becomes for the separator and downstream air treatment equipment.
3. In-line compressed air filters in the discharge line
Even with a good oil separator and cooler, the air leaving a screw compressor still contains some solid particles, moisture and oil aerosols. This is where in-line compressed air filters come into play.
3.1 Coarse or pre-filters
The pre-filter is usually the first filter after the compressor. It is designed to remove larger particles and part of the oil aerosols. This stage reduces the contamination load on finer filters and extends their service life.
Correctly sizing the pre-filter has a big impact on pressure drop, operating cost and how often you need to change downstream elements.
3.2 Fine / coalescing filters
Fine or coalescing filters are used to capture small solid particles and fine oil aerosols. They are one of the key elements for achieving higher compressed air quality for production lines and tools.
When selecting these filters, you should pay close attention to the filtration grade, allowable pressure drop and expected element lifetime under your actual operating conditions.
3.3 Activated carbon filters
In applications where odour and oil vapours matter – for example in food, pharmaceutical or some high-end painting processes – activated carbon filters are used.
These elements are mainly for final polishing of the air and should always be installed after particle and coalescing filters to avoid early saturation.
4. Point-of-use filters – the last protection before sensitive equipment
Even if you have a complete filtration chain in the compressor room, additional contamination can be picked up in the distribution piping: rust, scale, condensate and so on.
That is why, close to sensitive consumers such as:
- final painting and coating lines,
- final packaging machinery,
- instrumentation and precision measurement equipment,
it is strongly recommended to install point-of-use filters. These are usually a combination of a fine particulate/coalescing filter and, where needed, an activated carbon stage so that the air meets the required quality level right before entering the critical equipment.
5. Practical tips for selecting and maintaining air filters on screw compressors
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Do not judge filters by appearance alone.
Two elements with similar size can have very different efficiency and capacity. Always check filtration class and pressure drop data. -
Take the compressor environment seriously.
A compressor located in a very dusty area needs a stronger intake filter and a shorter service interval than one in a clean room. -
Monitor pressure drop.
Rising differential pressure across a filter is a clear signal that the element is becoming loaded. High pressure drop means higher energy consumption and potential quality issues. -
Think in terms of a filtration chain.
The intake filter, in-line filters and point-of-use filters complement each other. Removing one stage makes the whole system more vulnerable. -
Ask for technical support when in doubt.
A poorly chosen filter on a screw compressor can cost many times its price in failures and lost production. A short discussion with an experienced team is often worth it.
Over time, more specialised articles on screw compressor intake filters, filtration chain design and compressed air quality monitoring will be added to the PowerSep knowledge articles section.