How Does an Air Compressor Filter Work?

Dec 07, 2019

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Air compressors supply power to a wide variety of machines in many different industries and applications. Machinery and tools used in construction work, like jackhammers and air sanders, are powered by air compressors, as are many types of pneumatic HVAC control systems. Compressed air has a variety of contaminants in it that require removal for the machine to function properly, reduce costly downtime and extend its life.

In this guide, we’ll discuss what an air compressor filter is, how it works, some commonly asked questions and how to choose the best filter for your air compressor.

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What Does an Air Compressor Filter Do?

Air compressor filters, or air line filters, protect air compressors by preventing liquids and solid contaminants from entering compression assemblies. Compressed air contains significant amounts of oil, water and dirt, as well as other particulates that may even include heavy metals such as lead or mercury.

Air compressor filters remove contaminants from the incoming air, keeping critical system components such as cylinders and valves working smoothly. They also prevent seals from swelling and wearing prematurely, extending your compressor’s longevity. These capabilities make air filtration essential to proper air compressor function, resulting in reduced downtime, clean air and lower energy costs.

Does My Air Compressor Need a Filter?

To keep your equipment in working condition, you’ll need an air intake filter for your compressor. Filters protect components from premature wear and tear and prolong the life of your compressor, helping you save money that might otherwise go to part replacements.

A water filter for an air compressor is another valuable component, as it can prevent toxins from entering sewer systems and bodies of water and support environmental preservation efforts.

Additionally, your industry may be subject to certain government regulations mandating the use of air filters. OSHA has specific air quality standards for different compressor types, and the EPA requires oil/water separators. As such, you risk hefty fines if you do not use an air compressor water separator with your equipment.

How Does an Air Compressor Filter Work?

Air line filters work by straining air to trap solid particles and separate liquids from compressed air. To clarify the process, it helps to identify the main components found in an air compressor filter:

  • Inlet: The air compressor intake or inlet is where air enters the filter. There is an internal cap that forces air downward into a spiral. It’s important to get the right size inlet rather than using a filter smaller than the line.
  • Filter cap: This component directs airflow through the filter. You can tell the direction of the air by the arrow on the outside of the filter, which also prevents you from installing it backward.
  • Air path: This is the actual path the air follows as it spins like a cyclone and passes through the air filter itself.
  • Filter discharge: This orifice allows air to leave the filter, and it should match the inlet size. If the filter discharge is too small, it will restrict the flow of air.
  • Filter element: The filter itself is what takes contaminants out of the air, catching particulates over time. Eventually, filters become clogged and must be cleaned or replaced.
  • Filter bowl: The bowl is the biggest part of the filter that you can see. It is connected to the cap and is threaded or twisted and locked into place.
  • Filter quiet zone: The contaminants, water and oil collected by the filter all end up in the quiet zone at the bottom of the filter. You will usually find a barrier hanging from the filter bottom, preventing debris from being reintroduced into the air.
  • Drain: Collected contaminants and debris have to be drained. Many filters must be drained manually, but others have float-operated or electric auto drains.

In the first stage of filtration, compressed air passes through a mesh filter. This creates a clumping effect where the larger particles are trapped by the filter, and the water condenses into bigger droplets then travels to the separation chamber.

The compressed air slows down, allowing particulates to condense on a pad with honeycomb-like qualities. This facilitates the movement of droplets to the drain. After entering the drainage system, droplets are discharged through the drain valve. This stage of filtration removes a majority of the oil, large particles and water droplets.

Micron Measures

Air compressor filters catch particles so small that they are measured in microns. One micron is one-millionth of a meter. For scale, the width of a human hair is usually at least 70 microns. Fine particulate filters can remove particles as small as five microns, while a general-purpose filter will catch particles down to 30 or 40 microns in size.

When using a fine particulate filter, the risk of immediate clogging is significant. To keep air flowing while still capturing minuscule particles, it’s a good idea to use a fine particulate filter in tandem with a general-purpose filter up-stream. That way, larger particles are caught before they can clog the finer filter.

Air Compressor Filtration: Frequently Asked Questions

Many people are curious about air compressor filtration and how to make sure they are maximizing their filters’ benefits. These are some of the most commonly asked questions about inline filters.

Do I Need a Filter on My Air Compressor?

Yes. Without a filter, your compressed air will retain millions of particles that will cause premature wear and tear, increasing your maintenance costs and shortening the life of your compressor.

What Is a Micron?

A micron, also called a micrometer, is a unit of measurement equaling 0.001 millimeters or around 0.000039 inches. The official symbol for a micron is μm. Air compressor filters are measured by the size of particles they can trap, which are measured in microns.

What Level of Air Quality Should I Have?

Air quality is defined by the international standard ISO 8573-1:2010. The standard uses class ratings for solid particles, oil and water condensate content, with scores in these classes ranging from one to nine. The lower the number, the lower the level of contamination, and therefore, the higher the air quality.

Your applications and processes determine how clean your air needs to be. Many pneumatic applications of compressed air need a standard dry particulate filter. Other processes may require OSHA-approved elimination of vapors and aerosols. Refer to factory recommendations and specifications to determine the air quality you need.

Where Are Inline Filters Located?

For the most part, inline compressor filters are found right after the compressor, before and after dryers and before drops. They should be installed upstream from valves, actuators, lubricators and regulators. Some applications or facility configurations have different or additional filter locations to suit unique needs.

Do I Need a Regulator on My Air Compressor?

In most cases, yes. The pressure regulator allows you to increase or reduce the pressure of the airflow coming out of the compressor tank. Being able to adjust the PSI is necessary to match tool specifications and have your tools function properly. Nearly all industrial air compressors have a built-in regulator.

When Should I Replace the Intake Filter?

If a compressor is used several days each week, then the air intake filter should be cleaned every week. When you start noticing that it is more difficult to clean out debris, or you notice holes or tears appearing, it’s time to replace the filter. The length of time between intake filter replacements varies significantly depending on the application.

Does My Air Compressor Need a Water Separator?

Yes. Water condensed from the ambient air will accumulate without a water separator, and will cause damage to the compressor and connected components if not removed by a water separator.

How Do Air Water Separators Work?

Water separators use one of two methods to remove condensate:

  • Centrifugal separators: These create a rotary motion that causes particles to radiate outward as they accelerate. As the particles reach the outside of the separator, they drain into the filter bowl. This works for solid particles larger than five microns and for water. The great advantage of centrifugal separators is that this process does not require maintenance.
  • Coalescing separators: These cause air to flow from the inside of the filter element to the outside. When using this type of water separator for air compressors, you have to replace the filter cartridges frequently, which results in a buildup of downtime due to maintenance.

Effects of Water in Compressed Air

Water in your compressed air system can cause costly damage very quickly, creating the need for compressed air dryers and filters that remove all moisture. Factory applications are a good example of this. Before the development of dryers and water separators, these common problems plagued manufacturing:

  • Eroded lubrication: A lack of lubrication leads to wear and tear or rust on the moving parts of the compressor.
  • Lack of consistency in spray paint applications: Results in a non-uniform tone, adherence and texture on painted products.
  • Formation of ice in control lines: Causes malfunctions in essential controls.
  • Corrosion of connected tools: Manufactures will experience everything from incorrect readings to failures in factory operations.

The presence of moisture in compressed air creates a domino effect for every connected component that requires pneumatic controls. When rust or clogging happens due to moisture, factories can be forced to shut down and lose profits in the process.

Water Damage and Pneumatic Equipment

When moisture and the oily contaminants it carries build up on pneumatic parts, cylinders wear down more quickly. This creates a more frequent need for repairs on bearings and seals. As water is a universal solvent, moisture degrades essential lubrication that keeps all the moving parts in air cylinders functioning smoothly, resulting in a heightened risk of malfunctions.

When vaporized air passes through to spools, pistons and valve diaphragms in pneumatic tools, it leads to hardening that causes these components to crack. No matter the application of the air, moisture in it will wear down cylinders and decrease efficiency at the very least.

When moisture-laden air is sent to transmitters, gauges or converters, these instruments can lose accuracy or stop working completely — creating chaos for all of the functions they control. Instrument air lines will also corrode due to residue moisture produces.

Water Damage and Finished Products

Any assembly line where products are put in jars or bottles uses compressed air to clean and dry the containers. When water is a component in that compressed air, containers may be contaminated by any toxins or bacteria present in the water. This also means that the food or drink packaged in the containers can become dangerously contaminated.

Other examples of products that require dry compressed air are as varied as carefully formulated cleaning products and paints, fabrics and garments and printed goods. Moisture has a variety of effects that can lead to lower quality products as well as damage to the manufacturing equipment.

Types of Inline Air Compressor Filters

Compressor systems may use a variety of inline filter types to ensure high-quality air. The following types of filters all have unique benefits for compressed air treatment systems:

1. Particulate Filters

A dry particulate filter is generally used to remove particles that come through after an adsorption dryer. They may also be used to remove corrosion particles from the air. A particulate filter captures particles and traps them within the material of the filter.

2. Activated Carbon Filters

These filters use surface-active adsorption to bond odorants, and oil vapors. Carbon filters are essential to ensure compressed air oil removal.

3. Coalescing Filters

A coalescing filter is used to remove water and aerosols from air. Smaller droplets get caught in the filter and coalesce into bigger droplets that are then removed from the filter and prevented from re-entering the air by a re-entrainment barrier.

The majority of material removed is comprised of water and oil, however coalescing filters also remove particulates. If the filters are not changed frequently, you may experience pressure drops due to the particulates trapped in the filter media.

This type of filter removes dirt, dust, water aerosols and oil down to 0.01 microns, making it an effective choice for air dryer pre-filters.

4. Cold Coalescing Filters

This variation of coalescing filter is operated at 35 degrees Fahrenheit. Operating them at low temperatures increases efficiency in moisture removal.

5. Compressed Intake Filters

The air compressor intake filter is essential as the first defense against contaminants. An intake filter can block particulates as small as 0.3 microns and helps remove chemical contaminants from the air.

6. High-Efficiency Filters

These filters are better than others at removing particulates and reducing air pressure drop. They also use less energy than regular filters while removing particles as small as 0.01 microns.

How to Choose the Best Filter for Your Air Compressor

Selecting the best air compressor filter for your system is one of the best things you can do to preserve efficiency and prevent unnecessary wear on your equipment. Choosing one or more air compressor filters can be a challenging task. If you’re not sure where to start, consider the following factors as part of your decision:

Compressor Type

Every type of air compressor has its own set of fittings, filtration and other requirements you must take into account. The only way to narrow down your options for air filters is to refer to the manual and instructions for your system. If you no longer have the manual, it’s a good idea to consult a reputable company that can help you track down the specifications for your particular type and model of compressor.

Micron Rating

You want to find a good balance between filtration rating and service intervals. Finding the exact air quality requirements for your application allows you to select a filter that removes enough contaminants but doesn’t filter excess particulates. The smaller the particles a filter can trap, the smaller the holes in the filter. Smaller holes result in needing to replace the filter more often, as it becomes clogged easily and quickly.

For most industrial applications, general-purpose particulate filters are rated for either 40 or five microns. The required micron rating is determined by the compressor’s downstream components. Pneumatic tools and the majority of industrial equipment use 40-micron filtration, while more sensitive instruments or components use the five-micron option. There are also applications where 20, 25 or 75-micron filters are appropriate.

Using a five-micron filter when only a 40-micron filter is adequate will result in high pressure drops in the filter and shorten its lifespan, requiring you to spend more time and effort on maintenance and increasing the compressor’s consumption of energy.

Flow Capacity

Different applications demand different levels of airflow. Filters are available in a wide array of sizes, and you can find some rated for flows up to 1,000 standard cubic feet per minute. Once you know the flow required for your application, you can make the proper-sized selection by figuring out the maximum pressure drop allowable.

Compressed air filter manufacturers usually provide a chart showing the supply flow versus pressure drop for their filters. These charts show how the filter will perform in response to different levels of intake pressure. When using a chart, find the inlet pressure of your application. If your operation comes in at a different pressure than the ones you see on the chart, interpolate between the curves shown to find the right flow performance and appropriate pressure.

The next step is to find out the acceptable pressure drop. If you find the flow is too low, you can reach the requirements by choosing a bigger port or body size. If the flow is higher than it needs to be, a smaller filter unit will make up the difference. You will likely be looking at multiple filters with a specific port size and different flow capacities, all from the same manufacturer.

Quality and Efficiency

Filters use a certain amount of energy based on how much they restrict flow. Filters made with attention to efficiency remove more water and particles while minimizing pressure drop. Like any product, there is considerable variation in production quality, and choosing a unit from high-quality compressed air filter manufacturers will improve your end result.

Filters that have the same flow and micron ratings can display dramatically different efficiency, based on what they are made of. The lower the filter quality, the higher the pressure drop and rate of clogging. Saving money on a filter upfront only ends up costing you more in the long run.

High-performance filters cost more initially, but their lower flow resistance and more advanced ability to trap contaminants with less of a pressure drop results in better efficiency and longer intervals between replacement.

Sorting out the quality of air filters can be a challenge because different manufacturers may be testing compressed air filtration under disparate conditions. If you are concerned with achieving optimal quality, it may be a good idea to purchase and test multiple filters side by side to more directly compare their performance.

Fluid-Aire Dynamics: Filtration You Can Trust

There is no overstating the importance of proper filtration in a compressed air treatment system. Inline air compressor filters are essential in facilitating smooth function of your air compressor and its associated components, and without them, you’ll struggle with costly downtime, frequent equipment failure and premature wear of entire systems.

Fluid-Aire Dynamics offers a selection of quality air compressor filters in addition to compressors and components themselves. If you’re interested in optimizing the performance of your air compressor, we invite you to take advantage of a free compressed air system review or free equipment service review and estimate. You can reach Fluid-Aire Dynamics by calling 610.913.9100, or filling out our contact form for more information.


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