The terminology and jargon used on air compressors can be a bit confusing. The first problem most people encounter when comparing different air compressors is SCFM. What is SCFM on an air compressor, anyway? And adding to the confusion, tools are generally rated in CFM and PSI.
So, what does SCFM mean on an air compressor? Let’s break all of these critical measurements for air compressors to better understand what you need and what your compressor can do.
What is SCFM?
If you’ve ever shopped for or researched air compressors, you already know that SCFM is one of the essential terms to understand. Compressors are rating for a specific SCFM, and knowing what SCFM you need is vital to getting an air compressor suitable for the job.
What Does SCFM Stand For?
SCFM is the standard cubic feet per minute of air that an air compressor can process.
However, more important than simply defining what the letters mean is understanding why it’s so important. The SCFM is a vital measurement to understanding what your air compressor is capable of. Using the SCFM, you can figure out what sort of tools you can run and how many.
What Does SCFM Mean?
SCFM is a measure of volume. The bigger and more powerful your air compressor is, the higher the SCFM rating is.
The “standard” in SCFM refers to the standards against which the compressor is compared. You can’t compare two units to one another unless the air they are pumping is identical. The Compressed Air & Gas Institute (CAGI) and the American Society of Mechanical Engineers (ASME) have established “standard conditions” as 14.7 PSI, 68 degrees Fahrenheit, and 36 percent relative humidity at sea level.
Since SCFM is measured at these hypothetical standard conditions, chances are your real-world CFM is different. If you measure what the machine is actually doing, the measurement is known instead as ACFM, or actual cubic feet per minute.
What is CFM?
Cubic feet per minute are simply a measurement of the volume of air that passes through an appliance. For air compressors, SCFM is the agreed-upon measure of the overall power of a compressor. As described above, this standard helps you compare one compressor to another.
But inside of the actual compressor, things change. The CFM is a measurable value taken at the point where the air is pressurized usually to 90 PSI.
SCFM vs CFM
What is the difference between SCFM and CFM? The simplest way to think about it is to divide the two terms up. The SCFM comes before the air gets into the compressor, and the CFM is for the air that comes out of the compressor.
Since it comes after the air is pressurized, CFM is always a lower number than the SCFM.
In the real world, SCFM is the best indicator of how pressurized air will perform at the end application, while CFM is better to measure the air compressor’s internal capacity.
Air Tool SCFM Rating vs Air Compressor SCFM Rating
While the compressor is measured in how much air it can compress in a given minute, tools are rated by how much air they need to operate. Tools will be rated in both PSI (pounds per square inch of pressure) and in SCFM.
How Many SCFM Do I Need to Run Air Tools?
Once you understand the difference between the theoretical SCFM and CFM measurements, you might be left wondering what to do with all of this information. How does it help you get the right air compressor or the right tool?
In a factory setting, where near-continuous use of the pneumatic system is expected, the best policy is to add up the CFMs of all of the pneumatic tools used. You should then compare the total to what is available from the air compressor driving them.
Ideally, the air compressor should be providing at least 150 percent of the required CFM. That way, there will always be plenty of reserve power in the system.
For home use, you do not have to invest in quite so much reserve power. But you still need to compare the numbers to ensure that you can use the tools you want to, as often as you want to, without exceeding the compressor’s duty cycle.
Here’s an example. Your air nailer needs 4 to 6 CFM of compressed air flow at a certain pressure to operate correctly. Most nailers and air tools require between 60 and 100 PSI. The stated air consumption for the nailer is likely based on the air tool running continuously. If you need to use the air nailer continuously, you will need a compressor that will continuously deliver at least 4 to 6 CFM. But with air nailers, spot use is more prevalent than continuous use.
Compressor Discharge Pressure
The volumetric flow rate isn’t the only measurement you’ll need to pin down with your air compressor. It’s also important to understand PSI, or pounds per square inch.
Pounds per square inch (PSI) is the amount of air pressure or force that the air compressor can exert. Most pneumatic tools are rated from 40 to 90 PSI. The higher the pressure, the more power the tool has.
PSI and CFM have an inverse relationship. As the compressor’s pressure is increased, CFM goes down.
If your compressor specifications state that at a discharge pressure of 40 PSI, the compressor should continuously deliver 3 CFM of compressed air. This same compressor will deliver only 2 CFM of compressed air at a pressure of 100 PSI.
When figuring out the total required CFM and the PSI needed for a project, it’s important to keep in mind the compressor’s duty cycle. Many smaller compressors are not built to run continuously. Therefore, it cannot continuously deliver compressed airflow at the specified pressure and flow rate on a non-stop basis.
The terminology used in the air compressor industry isn’t as daunting as it might first appear. Keep in mind that everyone does different things with their air compressors, so the right compressor for someone else may not fit your needs.
Do you have a question about the difference between SCFM for tools and compressors or air flow rates? Please add your comment here (along with photos) to help others help you with your compressor and equipment problem!
Here are a few other links that help explain the overall concept of SCFM and CFM.