Compressed Air Filtering Basics – Contaminants, Filters & More!

Take a deep breath. Breathe out. Breathe in… Now, let’s talk about all the contaminants in that air you’re breathing!

Atmospheric air is naturally contaminated. In addition to oxygen, air also contains water vapor, dust and dirt, and a medley of other filthy particles depending on the surrounding environment. The average metropolitan area, for example, contains approximately 4 million dirt particles per cubic foot of air.

When air is compressed, some of those contaminants need to be filtered out. Contaminated atmospheric air can cause damage to air compressors and air tools, and isn’t acceptable for certain medical and industrial applications.

But atmospheric air isn’t the only source of contamination for compressed air. Air compressors contribute their own share of pollution from wear particles and, if the compressor is oil-lubricated, carbonized compressor lubricant.

Between atmospheric air contamination and air compressor system contamination, there’s a lot of particles dirtying up our compressed air. Fortunately, we have compressed air filtering to save the day.

A Bit of Dirt Never Hurt Anyone…

Don’t worry about that dirty air you’re breathing. Your lungs act as your body’s filtration system, removing contaminants after they’re inhaled. Air compressor systems obviously don’t have lungs, but they do filter out air contaminants in other ways. Better still, a little contamination is usually okay.

Contaminated particles are measured in microns. The bigger the particle, the bigger the micron. Most fine particle tests use 0.3 micron as the standard to measure liquid or solid particle filtration. If a filter tested on this particle size proves to be 100 % efficient, then it’s fairly safe to say this filter can remove any particle above this size.

Many compressed air applications can handle contamination levels well above 0.3 microns. Tire service, construction, and most other mobile air compressor applications tend to tolerate quite a bit of contamination without problem. Operators with these types of jobs can get away with a more basic filtration system, such as an intake filter, which eliminates contaminants in the 30 to 40 micron range.

Industrial air compressor applications tend to be less tolerant of contamination than mobile applications and up to 80 % of industrial contamination is smaller than 2 microns. Therefore, many industrial air compressors need better filtration than mobile air compressors. Industrial air compressor systems often utilize advanced dry particulate and coalescing filters that can clean air down to 0.01 microns. For applications that require super-clean air for OSHA purposes, an additional charcoal activated filter may also be used.

However, these industrial applications are the exception. Outside of massive factories and industrial enterprises, most people use mobile-style air compressors that can tolerate quite a bit of contaminants and don’t need to think twice about their air compressor’s filtration capabilities.

What Contaminants Are In Compressed Air?

Now that you realize just how contaminated our air is, let’s talk about what it’s contaminated with.

Compressed air contains three types of contaminants:

  • Dry particulates
  • Vapors
  • Aerosols

Dry particulates are exactly what they sound like: dirt and other tiny solid particles. Vapors are the gas-forms of particles that condense into liquids at lower temperatures—for example, water. (The gas state is what allows these “liquids” to exist in air.) Meanwhile, aerosols are very fine solid particles that get trapped in air or gas, becoming suspended. Airborne dust is one familiar example of an aerosol.

Each type of contaminant has its own unique characteristics and properties, requiring their own filtration methods.

There are two primary types of filtration that are used in compressed air systems:

  1. Dry Particulate Filtration
  2. Vapor & Aerosol Filtration

In the next couple sections of this article, we’ll talk about these filtration types and the filters used to eliminate dry particulates, vapors, and aerosols.

The Principles of Dry Particulate Air Filtration

Here’s where we get technical. We already know that most contamination in a compressed air system can be removed simply by filtration. However, it’s important that your air compressor systems use the correct type of filtration for the particles being filtered.

Dry particulate filters rely on three principles to separate contaminants from the air:

  • Direct interception
  • Inertial impact
  • Diffusion & Brownian movement

Direct interception affects the larger particles in an air stream, which are literally sieved out through a filter.

Inertial impact occurs when a particle traveling in an air stream is eventually unable to negotiate the torturous path between the filter fibers and cannot change direction as quickly as the air stream. The contaminants then collide with a fiber and become attached to it.

Diffusion or Brownian movement affects fine particles. With diffusion, small particles merge with other gas particles and begin to move erratically. This erratic movement is called Brownian movement. As these particles move separately from the compressed air flow, they are more likely to become trapped in the filter.

Air Filtering though diffusion

All three of these principles work together in a dry particulate filter to capture and trap contaminants from the compressed air.

If you’re interested in reading more about the principles and physics behind air filtration, check out this “Mechanism of Filtration For High Efficiency Fibrous Filters” report by TSI.

Vapor & Aerosol Filtration for Compressed Air

Vapors and aerosols slip past dry particulate filters, which may require their own filtration systems. In this case, there are two options that may be utilized:

  • Coalescing
  • Adsorption

Coalescing filters trap moisture and oil. The compressed air enters through the inlet port and travels down into the filter, passing through a filter media before it leaves through the discharge port. Moisture and oil droplets bond together during this process, forming larger droplets that then drip into a moisture trap below.


Coalescing filters are commonly used in oil-injected air compressors, such as rotary screw air compressors. In VMAC systems, these filtration methods include a couple types of dry particulate filters, as well as a coalescing filter.

Adsorption filters help eliminate vapors and lubricants, using activated charcoal or similar chemicals to bond with the vapor molecules. Adsorption comes into play when vapors must also be eliminated from a system. Adsorption filters are typically only used in specific industrial applications.

Filtration Systems of Rotary Screw Air Compressors

Reciprocating air compressors that don’t use oil can often get away with just a dry particulate filter. That’s because the contaminants in atmospheric air are negligible for most construction and automotive applications, travelling through the air compressor without causing much problem.

However, oil-injected rotary screw air compressors require additional levels of filtration. The oil used to lubricate the rotors is necessary for this style of air compressor, but that same oil needs to be cleaned and separated from the air.

Therefore, rotary screw air compressors require two types of filtration systems:

  • Dry particulate filters
  • Coalescing filters

In a typical VMAC air compressor, you’ll find both types of filters throughout the system:

  1. Air filter: atmospheric air entering the system goes through a dry particulate air filter.
  2. Coalescing filter: Air that leaves the rotors, now mixed with oil, goes through a coalescing filter, which separates the oil from the clean air. The oil gets recirculated while the air exits the system.
  3. Oil filter: The separated oil then goes through the oil filter, which is another dry particulate filter that separates particles from the oil.filters

It’s these same filters that occasionally need to be replaced and will be included with VMAC’s service kits. Replacing the air filter, oil filter and coalescing filter ensures the air compressors continue to trap contaminants and keeps your air compressor in tip-top shape.

Air Tool Pressure + 5 Reasons To Use The Right PSI For Air Tools

If your air tools struggle to live out their warranty or require more maintenance than the manufacturer’s guidelines state, there’s a good chance you are using too much air pressure. This is extremely common and many service operators over-pressurize their pneumatic tools as a standard operating procedure.

The assumption is you get more power out of a tool if you apply more pressure. While this is true some of the time, it doesn’t apply all of the time and—in almost all cases—leads to tool breakage or worse…

In this article, we’ve put together a list of reasons you should always use the proper pressure for your air tools:

5. Reduce Expensive Tool Repairs

Using too much pressure can cause your air tools to wear out or break a lot sooner than they should. Here are the most common pneumatic tool repairs caused by excessive air pressure:

Blown seals: The more pressure you use, the bigger the opportunity for blown seals. You might as well use your shop-vac to suck the extra cash out of your pockets if you don’t protect yourself from blown seals because they result in VERY expensive repair bills.

Anvil breakage: There couldn’t be a better example of “cutting off your nose to spite your face” than anvil breakage, and it’s far too common. Guys apply more pressure to their impact wrench to get more torque, which works. Everyone is happy, the job gets done faster. But then the anvil sees higher stresses and can crack or break and the tool is down for repairs, wasting any time you saved with extra torque and resulting in significant costs for repairs.

Bearing failure: In addition to blown seals and anvil breakage, using too much pressure is one of the most direct causes of bearing failure. If you’ve worked with air tools for awhile, you know bearing failure is an expensive repair and you probably also know that if the bearings go, you already have many more damaged parts to repair. It’s not a good situation!

Vane motor breakdowns: As little as 20 psi of excessive pressure in a vane motor system can half the life of an air tool. Most tools are rated at 90 or 100 psi, so using 120 psi regularly ensures you will be replacing expensive air tools in half the time you should have to.

4. Maintain Your Tools’ Efficiency

In many cases, a broken tool doesn’t happen in an instant. Instead, tools wear down over time until they reach a point of failure. The more a tool is worn down, the less efficient seals and other components become, even if it’s still working. This results in leaked air, which essentially means the tool needs even more air to run than it normally would.

By using the right pressure for your tools, you reduce wear and improve tool efficiency. If you care about getting the best performance out of your tools, stop using too much pressure.

3. Stop Overpaying For New Tools

Tools that break or fail and can’t be repaired will need to be replaced, and we don’t need to tell you that new tool costs add up quickly! It’s an unnecessary expense that could have been reinvested elsewhere.

Consider this: when you buy an air tool from a manufacturer or dealer, they give you a price, and you either agree to pay the price or negotiate a discount. You never ask them to take more money from you. Yet, if you don’t take proper care of your air tools, you might as well do exactly that.

Treat your tools with respect and save your money for better purchases.

2. Prevent Dangerous Accidents

Let’s put the financial impacts aside because you won’t be thinking about expenses when you or one of your employees suffers a devastating or fatal injury. It’s easy to shrug off safety regulations and assume a serious injury would never happen to you or your team, but pressure safety warnings exist in manufacturers’ guidelines for a reason.

We’ve heard stories about tool technicians being killed when an over-pressured grinder explodes, because it’s operating at speeds much higher than the manufacturer’s safety ratings. You don’t want your team to be the one that proves these urban legends are true.

But even if the stories are false, the pneumatic tool manufacturers are concerned enough to include pressure rating warnings in their manuals. For example, here’s what Central Pneumatic says in their ¼” air angle die grinder manual:

“Over pressurizing the tool may cause bursting, abnormal operation, breakage of the tool or serious injury to persons. Use only clean, dry, regulated compressed air at the rated pressure or within the rated pressure range as marked on the tool. Always verify prior to using the tool that the air source has been adjusted to the rated air pressure or within the rated air-pressure range.”

Protect your team and your business by keeping everyone safe. Follow the pressure guidelines and you can prevent serious consequences.

1. Lower Your Fuel Consumption

Last but possibly not least, using the proper pressure will lower your fuel consumption.

The higher the pressure, the higher the volume of air that’s consumed. This is a problem because higher air volumes require more energy, which means you are spending a lot of extra horsepower on wasted air. Further, higher horsepower equals higher fuel consumption, which increases operating costs and throws low emission targets in the trash.

The Real Reasons Your Tools Aren’t Performing

Manufacturing engineers create and test tools using the same psi ranges they publish in the tools’ manuals. If your tool isn’t performing as well as you think it should, the pressure rating isn’t the problem. Instead of cranking up the pressure, take the following steps:

  1. Reflect on your expectations: Is it possible that you simply want a tool that performs better than it’s supposed to? If so, it may be time to consider why you want more power and whether it’s something you really need…
  2. Check the power management switch: If your tool has a power management switch, you wouldn’t be the first person to overlook it. Double-check whether your tool has this switch and ensure it’s on the proper setting.
  3. Check the pressure at the tool: Attach a pressure gauge between the end of your hose and your air tool to confirm whether the air pressure is at the maximum recommended pressure. Each air compressor design is different, and some systems can lose pressure before the air reaches the tool. If the air is losing pressure before it meets the tool, you can try turning up the pressure a bit, but only until it reaches the manufacturer’s psi recommendation.
  4. Check the hose size: A hose that’s too small can cause pressure drops that are easily remedied by an upgrade. Make sure you’re using the right hose size for your application. We talk more about how hose size impacts airflow in this article.
  5. Check the size of everything else: Hoses aren’t the only air compressor component that might be too small. Also check the size of your connectors, fittings, filters, regulators, and lubricators, and ensure they are big enough to handle the task at hand.
  6. Confirm the air compressor’s CFM: An air tool needs the right psi and the right CFM to operate properly. Double-check that the CFM capabilities of your air compressor match the needs of your tools. You can learn more about the CFM needs for your air tools here.
  7. Consider your air compressor type: A reciprocating air compressor has to build up air and then quickly loses pressure. But if you require higher pressure because you’re trying to hit hard and fast to beat the clock, your air compressor type is likely the problem. Instead, upgrade to a rotary screw air compressor that can maintain CFM and PSI for significant periods of time. Find out more about rotary screw vs. reciprocating air compressors here.
  8. Call the tool manufacturer: If everything above checks out, call the manufacturer. Their support team will be able to help you troubleshoot performance issues with your tool.
  9. Upgrade your tool: If you’ve gone through the list above and your tool isn’t getting the job done, it’s likely time for an upgrade. Tools that have enough air and are powerful enough for a job will work properly and efficiently at their recommended psi setting. If your tool isn’t performing under the proper conditions, you need a better tool.

One last tip—don’t use sound when determining if a tool is working. We’ve met operators who think their tool or air compressor is too weak because their tools get quieter after the air has run for a few seconds, even when the tools are operating just fine! Instead of listening, look at how the tool is performing to determine whether it gets the job done in a normal amount of time.

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Use The Proper Pressure For Your Air Tools

At the end of the day, too much pressure for your air tools can be a costly mistake. From equipment failure and repair costs to health and safety risks for your team, there are a lot of reasons you should simply use the right pressure.

It’s unlikely all the terrible things in this article will happen to your team and equipment if you use too much pressure. However, it’s probable you’ll encounter at least some of the issues, including the frustration that goes along with them.

By contrast, eliminating the issues caused by too much pressure is easy to do. Use the proper pressure for your air tools and rest assured you’re getting the most out of your tools.

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Fanelli Equipment Repair Upgrades to VMAC DTM70-H

Located in Hilmar, CA is Fanelli Equipment Repair. Owned by Phil Fanelli, this company has been operating in the Central Valley area for over 12 years, repairing and servicing all types of Caterpillar equipment, including landfill, recycling, and compost equipment for waste management companies, as well as servicing equipment used in the dairy industry.

Phil Fanelli has successfully grown his equipment repair business to include seven service trucks, each which puts on thousands of operating hours and up to 50,000 miles every year. “I work my trucks hard, and so I rotate through them every five years, to ensure there’s no downtime,” says Fanelli. “Because of this, I expect any piece of equipment to last me five years as well.”

Up until recently, Phil’s service truck was equipped with a reciprocating air compressor. This reciprocating air compressor resulted in a lot of challenges, the first and foremost being weight. The compressor was terribly heavy on his truck, which at the time was a Peterbilt with a 14-foot service body. Phil also found himself waiting for compressed air to be produced, resulting in downtime as his compressor tried to catch up to him. This slowed down his work.

When it was time to bring in a new service truck to the fleet, Phil seized the opportunity to “right-size” his truck. Because he’s often travelling to visit his technicians on different job sites, he chose to downsize to a Ford F550 truck. He also needed to address the weight and air supply concerns associated with reciprocating compressors. For this truck build and upfit, he went straight to Spencer Hinson, owner and GM of Lodi Truck and Equipment, located in West Sacramento.

“I’ve been getting Spencer at Lodi to build my trucks for over 10 years now, and I wouldn’t go anywhere else,” says Phil. “I go in, tell him what I want, and he keeps me involved in every step of the build.”

At first, Phil was interested in an UNDERHOOD™ 70 air compressor, which fits neatly in the engine compartment of the truck, supplies up to 70 CFM of air continuously, and weighs just 150 lbs, saving up to 260 lbs. But when it was time to start the truck build, Spencer recommended a different product: the newly released VMAC DTM70-H, a direct-transmission mounted PTO driven air compressor with hydraulic pump. The DTM70-H is the best choice for customers like Phil who are concerned with saving weight on their service truck, and who also need compressed air and hydraulic power at the same time.

“Spencer knows I’m really concerned about weight. It seems like I’m always overloaded, and he thought this set up would be the best fit,” explains Fanelli. And the weight savings were significant: “The VMAC DTM70-H saved 500 lbs, which is a big deal when you’re trying to set up an F550. With these weight savings, it was the only way to go. We were looking at aluminum doors and aluminum fuel tanks, but to save 500 lbs with one change tFinelli-VMACo the DTM70-H was a no-brainer.”

The VMAC DTM70-H weighs only 180 lbs, which frees up hundreds of pounds of weight, and allows customers like Phil to downsize their trucks, and at the same time load the truck up with more supplies. “I added more tools, a drawer set, tool boxes, and an oil tank, thanks to the weight savings,” says Fanelli.

It’s been several months since Phil picked up his new F550 truck from Lodi, and he’s been using the DTM70-H to power his air tools and crane simultaneously. Spencer’s expertise and recommendation was key in this new truck build and was exactly what Phil needed. “When I got the truck, it was show room quality, detailed, everything worked. It was exactly the way I wanted it.” And as for the DTM70-H? “It’s lightweight, which is what I needed, but it also produces the air I need, when I need it. It’s bulletproof.”

Subscribe to the VMAC blog to continue reading about Fanelli Equipment Repair’s experience with the VMAC DTM70-H, and to learn more about Lodi Truck & Equipment, located in West Sacramento, CA.

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