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What is Air Compressor CFM and How do I Calculate what I need for Different Tools?

The acronym CFM stands for Cubic Feet per Minute. In air compressor terms, this means what volume of air the compressor is capable of pumping out each minute. If the output is rated at 40 CFM, then 40 cubic feet of air volume is moved every minute the unit is in use.

With an air compressor that has inadequate CFM, your tools will not run reliably. If the CFM is too high then you run the risk of damaging your tools, and you will almost certainly have spent too much on your compressor to match your application!

What’s the difference between PSI & CFM

Both air pressure (air compressor PSI) and airflow (air compressor CFM) are important considerations when buying an air compressor. CFM is not to be confused with PSI. PSI stands for Pounds per Square Inch and relates to pressure. The PSI (normally written as ‘psi’ in lowercase in specifications) is the power element of the compressed air.

If an air-powered tool is to operate to optimum efficiency, there must be sufficient CFM and PSI. An output rating of 50 psi indicates that the unit delivers 50 pounds of pressure per square inch. Air gauges on compressors usually display PSI readings, not CFM.

For compressed air systems, pressure impacts directly on the rate of flow.

This is demonstrated by Boyle’s Law:

P1 X V1 = P2 X V2

P1 represents initial pressure and V1 initial volume. P2 and V2 represent final pressure and final volume. Boyle’s Law demonstrates that the pressure increases in inverse relation to the volume of the container.

What size air compressor do I need

If you are investing in an air compressor to run air tools, it is important to know the CFM requirement. This will be listed in the technical specification for the tool.

Calculating the required CFM requirements

When you have found the CFM for your equipment (usually in the manufacturer’s guidelines or technical specification), you need to multiply this by 1.5.

 So if your CFM is 10, then you need an air compressor capable of delivering at least 15 CFM.

If you plan to run more than one air tool from the same air compressor at the same time, then you need to add together the CFM requirements of each tool and calculate accordingly.

Large commercial air compressors are capable of running multiple air tools simultaneously. Smaller compressors for DIY applications are usually designed to run just one at a time.

Calculating the required tank size

You also need to calculate the required tank size for your chosen air compressor. The tank is used to store the compressed air.

To establish the minimum tank size for your compressor, you need to take the CFM and multiply this by 6.

So if your tool has a CFM of 6, then you need a minimum of a 36-litre compressor tank. A larger tank will improve the performance of the tool.

Continuous or intermittent use?

So you know the manufacturer’s specifications for your air tool. How you use these tools will also impact performance, longevity and compressor requirements.

Is your application continuous, or does your air tool, use and environment dictate that you operate in a more staccato style, which will allow your air compressor to keep up with your usage?

If you are running tools continuously and for longer periods during the working day, then you should consider buying an air compressor with a 100% duty cycle. The duty cycle is the ratio between run time and rest time. A 100% duty cycle rating means your compressor is capable of delivering consistent CFM and PSI the whole time it is in use.

If your use is intermittent in quick bursts, then you may be able to save money by buying a cheaper and smaller size air compressor. As long as it is still capable of matching your application requirements.

Will you be using multiple air tools at once?

If your application means you may want to run more than one tool at any given time from your air compressor, then that will affect your CFM requirement too.

To determine what that could be, then you must add together the CFM requirement of all the tools you plan to run simultaneously.

Different types of tools have differing requirements. Impact tools typically use less air than rotary or spraying tools because the air is flowing all the time they are in use. So impact tools can be often used together more successfully on smaller compressors.

Generally speaking, the larger the air tank on your compressor, the better your air tools will run and the more efficiently they will operate. Running multiple tools from one air compressor can be an efficient and cost-effective way to operate.

How air compressors with air receiver tanks might affect your CFM requirements

Not all air compressors require an air receiver tank, which is a pressure vessel designed to take air from a compressor and maintain this under pressure until it is required for operational use.

All reciprocating compressors require an air receiver tank to accommodate peaks in demand. A larger air receiver tank can mean a smaller, lower CFM air compressor is capable of delivering on increased CFM demand, and can therefore save money.

Air receiver tanks are available in a wide range of sizes. Choosing the right tank size is dependent on how long you plan on using your air tools. In continuous applications, the tank will deplete more quickly, so you will need a larger volume. For more sporadic applications, a smaller tank will suffice.

Example air flow values for given applications

Air tools used with portable air compressors have a lower CFM requirement (typically 5) than larger tools and equipment used with fixed compressors, which usually require well in excess of 10 CFM.

Angle grinders

For general metalwork and car maintenance, angle grinders are efficient and necessary tools that can perform a wide range of tasks. They do consume a quantity of air, typically 5 to 8 CFM.

Drills

If you need power, speed and accuracy, then a pneumatic drill provides the ideal solution and is even capable of drilling into rock and metals quickly and effectively. Air-powered drills have a typical CFM of 3 to 6.

Nailers

For construction applications, a nailer is a must-have tool, and a lightweight air-powered nailer has a very low CFM of less than 0.5.

Sanders

An air-powered sander will create an extremely smooth finish with very little effort on a range of surfaces including hard materials like metal and wood. Buffing down in just seconds, air-powered sanders have a CFM requirement of 11 to 13.

Cutting

Air-powered cutters using spinning discs make short work of cutting metals and other materials, with a CFM requirement of 4 to 10, dependent upon capacity.

Grease guns

Air-powered grease guns offer fully automatic and continuous operation and grease flow, the perfect partner for effective lubrication. They have a relatively low airflow requirement at just 4 CFM.

Air chisels

Heavy-duty air-powered chisels are a perfect match for the force needed to cut metal, stone or wood, requiring an airflow of 3 to 11 CFM.

Spray painting guns

Designed to achieve the perfect finish, spray paint guns need a clean and consistent paint flow. The pneumatic option allows accurate layering of paints and coatings, requiring a CFM of 3 to 11.

Saws

Fast and efficient pneumatic saws are accurate and clean, with a reduced airflow requirement of around 5 CFM.

Unscrewing

Faced with a tricky bolt or screw, reach for the impact wrench! For reverse and forward applications, and dependent on nozzle sizes, these tools have a CFM of between 2.5 to 10.

Wrapping up on CFM

Whatever your application and your operational requirements, matching your air compressor capability to the tasks in hand can speed up the processes and save you money.

Investing time and energy in choosing the right air compressor with sufficient airflow will also help increase the life of your air tools and improve results.

Take the time to check CFM and PSI requirements – it will be worth the effort.

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