Compressor air filters are installed in condensed airlines to block the ingression of water, solid, and oil contaminants into the air compressors.

A cubic meter of compressed air contains millions of dirt particles.

Of course, this is together with a significant quantity of water and oil in the form of vapor as well as heavy metals.

If you do not remove these contaminants using compressor air filters, then they will compromise the operation of very crucial process components.

Contaminants in compressed air

Understanding the nature of contaminants present in compressed air enables you to select the best treatment and filtration systems for your application.

The contaminants can originate from the atmospheric air you are compressing.

Alternatively, it may come from within the system through compressor and system wear or process fluids.

Some of the most common types of contaminants include:

· Solid Contaminants

The size of solid particles ranges from tiny particles that are imperceptible to the human eye to particles as big as 1 mm thick.

A cubic meter of untreated atmospheric industrial air can contain between 140-150 million particles.

Approximately more than 85% of these contaminants are less than 2 microns.

Similarly, rust and metal particles generated from the distribution and pipework as a result of the ingression of water and corrosive fluids in the system are common.

Carbon contamination can also come from the wear of carbon piston rings found in oil-free compressors or the activity of compressor heat on lubricating oil.

Mechanical fixing of components and pipework is also another pathway of system generation of solid contaminants.

· Water and Vapor

The compression of atmospheric air produces a lot of heat, which warms up the air and increases the amount of water vapor it can hold.

When you compress the air, the amount of water per cubic meter increases multiple folds compared to ambient air.

When the air cools, it produces condensate water because compressed cold air cannot hold so much water.

For instance, atmospheric air can hold 28.3 g/M² of water at 30°C and 90% relative humidity but will only 3.8 g/M² when compressed to 7 barg.

The condensate can wash out lubricants from pneumatic components or corrode the metals.

It can also solidify when temperatures drop beyond 0°C and damage piping and other components or block the air supply due to expansion.

· Oil Contaminants

Oil contamination is common in compressed air systems because of lubricating oil used in moving parts of the compressor or atmospheric hydrocarbon oil.

The oil aerosols find their way into the system as fine vapor or mist.

When the compression process subjects the oil to high temperatures, it becomes acidic and oxidized.

This makes it an aggressive contaminant.

Atmospheric oil getting into the system as a vapor will condense into a liquid when it cools.

Consequently, risking tainting of manufactured products or blockage of pipes.

Filtration of compressed air occurs in two stages.

In the first stage, the filter removes more than 95% of the water, oil, and large particle contaminants.

The air passes through a tube-shaped mesh filter and experiences a coalescence effect.

The mesh removes larger particles and condenses the larger droplets into a honeycomb-like pad.

They then go to the separation chambers.

Condensation takes place when the velocity of air slows down.

The condensate moves to the waste collection area of the bowl where they get discharged through the manual, automatic, or electric drain.

In the second stage, the air goes through a fibrous material that produces disturbance and numerous small vortices that distribute air unevenly.

The uneven distribution increases the probability of the contaminants making contact with the surface of the medium.

Compressed air filtration

The medium captures and retains the fine particles because of their inability to go through the small pore sizes in the filter medium.

The process generates a small amount of pressure drop as a result of resistance subjected to the airflow.

Compressor air filters are mandatory in all industries that use compressed air in their process applications.

Some of the industries that require compressor air filters include:

• Manufacturing industries
• Agricultural industries
• Pharmaceutical industries
• Energy exploration industries
• Dry cleaners
• Food and beverage industries
• Home applications
• Hospitals
• HVCA in schools
• Sea exploration through scuba diving
• Business areas, both small, medium and large businesses among others

Compressed air filter element

A good compressor air filter should possess the following features:

• Easy to install and remove
• High efficacy in contaminant removal
• Have a low-pressure drop
• Support a high flow rate
• Resistant to corrosion
• Meet the industrial quality requirements
• Long-lasting and reliable performance
• High dirt holding capacity
• Capable of withstanding high temperature and pressure

An air compressor filter comprises:

• Inlet: The inlet port is the point of air entry. It has an internal cap that forces the air downwards. Ensure that the size of the inlet port fits into your system piping.
• Filter cap: it is responsible for directing the airflow inside the filter. An arrow located on the outside of the filter will show you the direction of airflow to aid in filter installation.
• Filter element: The element is composed of fibrous material that is responsible for trapping and removing the contaminants from the compressed air stream.
• Outlet port: It discharges clean air out. The size must match the inlet port to avoid airflow restrictions.
• Housing: It is also known as the bowl. The main function of the bowl is to host the other components of the filter in place.
• Sump/quiet zone: The zone is located at the bottom of the housing and collects the removed contaminants. It has a barrier to avoid recontamination of air.
• Drain: The drains can be manual or automated. It removes the filtered contaminants out of the filter.

There are several types of compressor air filters used to remove different types of contaminants.

They include:

· Particulate Filters

Particulate compressor air filters remove solid contaminants from the air.

They remove the contaminants using different mechanisms such as direct interception, inertial impaction, and diffusion.

The filter elements trap and store the contaminants when air passes through the filter.

Also, the medium gets filled as more dirt sticks on it, the pressure drop increases, and so is the amount of contaminants that go through it.

Therefore, you have to replace the filter elements after a predetermined pressure drop level, which is indicated by a differential pressure gauge and alarm.

· Coalescence Filters

You will use this filter to remove oil, oil vapor, and moisture suspended compressed air.

They remove contaminants by amalgamating the tiny droplets into large drops that can drain through gravity into a collection chamber.

These filters can also remove tiny solid particles

· Activated Carbon Filters

Activated carbon filters remove hydrocarbons, odors, and oil vapor.

The air coming into activated carbon filters must be free of all liquid and solid contaminants.

The filters maintain extremely pure airflow and protect sensitive components such as fiber optics, instrumentation, and other susceptible equipment.

· High-efficiency Filters

These filters are better in particulate removal and reduction in pressure drop.

They can remove particles down to 0.01 microns and utilize less energy compared to regular filter

· Cold Coalescence Filter

The filters can operate 2°C making it more suitable for removal of moisture.

· Compressor Intake Filters

They are the very first filters you will use to remove contaminants down to 0.3 microns.

They are fundamental for removing chemical impurities from the air.

A cubic meter of compressed can harbor hundreds of millions of particulate, water and oil contaminants.

If these contaminants all find their way into the system, they will greatly hinder the operations of system components such as cylinders and valves.

They will make the seals bulge and wear prematurely, resulting in high energy, maintenance, and downtime costs.

Selecting the best compressor air filter will go a long way to guarantee system efficiency while avoiding undesirable component wear and tear.

You can consider the following factors when selecting a compressor air filter:

Compressed air filter system

· Type of Application

Different applications require different types of compressor air filters.

Each filter has a different set of filtration requirements and fittings.

You should refer to the requirements of your filtration or consult a reputable company before settling for a given type of filter.

· Filter Micron Rating

Similarly, the cleanliness required for the compressed air will determine the micron rating of the filter you select.

You should select a filter that will achieve the desired level of cleanliness and still maintaining good service intervals.

· Flow Rate

The size and of the filter you select will depend on the application level of airflow.

Understanding the maximum allowable pressure drop will assist you to decide on the best size of a filter to select.

The manufacturers will provide a chart showing the pressure drop versus the supply flow.

These charts indicate the performance of a filter at a given intake pressure.

Look through the chart and select the models whose port size and other features meet your system requirement.

· Efficiency and Quality

You should choose a filter that will effectively remove the contaminants at the desired level of efficiency at a minimum pressure drop.

Note that filters might have similar micron and flow rate rating but significantly differ in their effectiveness in removing contaminants.

High-performance filters might cost you more initially but will give you better results compared to ordinary filters.

To ascertain the quality of a filter, you can purchase several brands from different manufacturers and test them side by side for performance comparison.

There are different parameters considered when rating a compressor air filter.

These parameters include:

· Micron Rating and Extraction Efficiency

The micron rating of a compressor air filter indicates the size of particles the filter will be able to remove from the stream of compressed air supply.

General-purpose filters usually remove contaminants that measure between 40 and 50 micron.

On the other hand, the high-efficiency filters can remove particles down to 0.01 microns.

The efficiency of a filter depicts the percentage of contaminants at a particular micron that the filter is capable of removing from the air.

For example, a filter rated at 99.997% is a high-efficiency filter that retains almost all the particles at the specified micron.

· Flow Rate

The flow rate helps you select the correct size of a filter for a given application.

Applications with higher flow rates need bigger filters with a higher flow rate rating.

Choosing a filter that has a lower flow rate rating than that of the process application will tremendously increase the pressure drop of the filter.

ISO 8573-1:2010 contains the requirements for rating compressed air based on the class rating of three kinds of contaminants.

The classes include the number of solid particles, water, and oil content.

Air quality rating classes range from 1 through 9.

The rating indicates the maximum allowable contamination levels and particle sizes for the respective quality classes.

Also, the lower the class rating, the cleaner the air is.

The compressed air filters operate under very demanding conditions such as high temperature, pressure and humidity variations, and chemical attacks.

Other factors that degrade the air compressor filter media are:

• Acids and oils
• Varying humidity conditions for particulate filters

Additionally, high-velocity particles constantly bombard the filter media when in operation.

Eventually, the constant bombardment weakens and damages the element.

A damaged filtration media will fail to provide the desired filtration efficiency for the compressed air.

As a result, it gives the filter element finite service life.

Yes, you can clean and reuse elements which have been manufactured and labeled as cleanable.

The frequency of cleaning will depend on how often you are filtering.

The service life of a compressor air filter depends on the process flow rate and level of contamination of the process air.

The dirt-holding capacity of a filter will also influence how long it will last.

Conducting regular system checks daily for indications like oversaturation and wear will help you determine the expected life span of the filter.

You should also use an automatic differentials pressure gauge to alert you when the elements are due for replacement.

Compressor air filter element

You can construct the filter elements using a wide variety of selective fiber material to ensure that you achieve the desired level of filtration.

Among the wide selection, you can choose the following materials for making a reliable compressor air filter medium.

· Cellulose

This material is suited for the removal of solid particles.

The cellulose fibers have wide diameters, and therefore not conducive for filtering out liquid aerosols.

· Fiberglass

You can use fiberglass to construct a high-efficiency coalescence filter element.

You can vacuum form the filter media.

So that, the downstream layer enhances coalescence filtration while the upstream layer removes particulate contaminants.

Elements made using this product can achieve extended service life, high contaminants removal efficiency, and low differential pressure.

· Activated Carbon/Molecular Sieves

You will use these materials for constructing adsorption filter media for the removal of hydrocarbons, odor, and other gas-phase impurities.

The materials can be manufactured into beds or contained in a carrier such as polyester fabrics.

Consequently, you can roll the polyester into cylindrical filter elements.

Elements made from the materials are located downstream after coalescence filters to protect the medium from any liquid aerosols or water.

· Wrapped HEPA Paper

You can use this material to construct elements that can remove both particulate and liquid aerosols at the same time.

You can use binders on the glass papers to construct the material to increase the strength of the filtration tube or enhance its filtration efficiency.

You can also use binderless media but with caution.

Prolonged exposure to liquid contaminants weakens and disintegrates or delaminate the media.

Pressure spikes are also known as pressure pulse and occur as a result of rapid drop or rise in compressed air pressure.

The spike can emerge from sudden starting or stopping of the pump.

The sudden shift of a valve from fully opened to fully closed can also cause pressure spike.

If left unchecked, strong spikes can cause system malfunction and damage sensitive components exposed to the pressure spikes.

Specifically, they can instantaneously rupture the elements enabling unfiltered air to flow into the system.

To avoid the occurrence of pressure spikes, ensure that you set slow opening and closing of the isolation valves when pressurizing systems.

You will follow the guidelines provided in ISO 12500 standards to test the effectiveness of a compressor air filter.

The test will vary depending on the type of filter you are testing.

If you want to test the performance of the coalescence compressed air filter, you will use the guidelines provided for under ISO 12500-1 as follows.

• You should start your experiment using a clean and reliable source of compressed air.
• Control the testing conditions, setting the inlet air pressure at 7 bars; inlet air temperature at 20°C and ambient temperature at 20°C.
• Record the initial (dry) pressure drop
• Using a Laskin nozzle, generate aerosols ranging from 0.1 to 0.3 microns and inject them into a clean stream of compressed air.
• Ensure that the mixture adheres to the aerosol challenge of 10 mg/m3 or 40 mg/m3 using a white light scattering photometer.
• Record the measurement once the filter reaches equilibrium, that is, the wetted condition to determine its performance.

Record the pressure drop.

Also, measure the penetration of aerosols through the elements by using a photometer scattering white light.

• Have at least three sets of reading and find the average from the three tests.
• The test will give you the penetration of oil aerosols in mg/m³, the filtration efficiency in (%) of the aerosols captured, and the pressure drop.

ISO 12500 standards provide international guidelines on production and rating of compressed air filters by manufacturers.

The standard comprises three multi-parts that deal with different types of contaminants.

ISO 12500-1 provides guidelines for testing the efficiency of coalescence filters in removing oil aerosols.

In the second part, ISO 12500-2 concerns the removal of vapor by adsorption filters.

While ISO 12500-3 gives the requirements for testing solid removal efficiency of particulate filters.

You can choose different types of drains for your compressor air filter.

They include:

• Manual drains: You remove the contaminants manually by twisting the drain plugs regularly, i.e., once per shift
• Semi-automatic and normally open drains: Immediately you shut off the compressed air, the drain will open.
• Full automatic and normally open: It will release the contaminants when the contaminants reach a certain level in the housing or the compressed air shuts off.
• Full automated closed: The drains will open when you switch on the compressed air, and the condensates reach a certain level in the bowl.
• Electric drains: An electric signal will remotely close and open these kinds of filters.

Air filter system

Dryers remove the water vapor that remains after passing the air through the micro coalescence filters.

They are classified based on pressure due point (PDP), which is the temperature at which you can cool the compressed air without the content water condensing.

When the temperature falls below PDP, condensates form and will remain and erode the materials even if you increase the temperatures.

There are different types of dryers including:

• Refrigeration dryers
• Membrane drier
• Adsorption driers

As you can see, there are many aspects you should consider when choosing a suitable compressor air filter.

The best part of this guide has outlined everything you need when choosing these types of filters.

Still, if you have any questions or inquiries, feel free to contact the Filson team.