What is an Air Compressor?
An air compressor is a device used to compress and pump air. There are several common uses for air compressors, including inflating tires and sports equipment, blowing dust or dirt off of surfaces, or using it as an air supply for painting, sandblasting, and general cleaning.
The term "compressors" may also be used to describe compressors intended for industrial use. These industrial models are typically either gear driven, or in the case of screw compressors, they drive themselves via a motor which spins a screw inside a closed housing. The screw compresses the fluid or gas.
The CFM rating of a compressor indicates the amount of air the compressor is capable of producing per minute. Higher CFM numbers are better for faster air production, such as inflating tires, while low CFM numbers are better suited for smaller jobs.
It's important to consider the CFM requirement of a given project when shopping for an air compressor, as multiple CFM ratings are available for various uses. The following chart is a rough guide for different air compressor CFM ratings, which can help you determine how powerful an air compressor you need.
What Does CFM stand for in Relation to an Air Compressor?
CFM stands for “cubic feet per minute.” In other words, CFM refers to the capacity of air your air compressor is capable of producing. This is a big deal when it comes to air-powered equipment, because the more CFM an air compressor produces, the more air your tools can suck in at once.
This can help you accomplish a few things. A smaller CFM air compressor might give you enough air to power a nail gun, but it won’t be able to keep up with high-end nail guns like finishers, which require far more air.
CFM can also help you regulate how much air your tools use. That’s because the higher the CFM, the more air your tools will use. So if you want to avoid blowing through your air tank too quickly, you might want to look for a lower CFM rating.
Remember, too, that CFM will help you determine how you can power these larger tools. For example, if you want to power a pneumatic nailer up to a 3” framing nailer, you’ll need at least a 4” hose. You might even want to consider a 3” hose when using a lower CFM option on a high-end tool.
How to Determine the Correct CFM
Many homeowners end up choosing a portable air compressor for a variety of reasons. If you’re thinking of purchasing one yourself, you need to learn what size compressor you should get.
Here’s a quick overview of how you can determine the correct CFM of portable air compressor that will work in your workspace:
If your air compressor will be used for light work and relatively rare projects, then a smaller HP air compressor is going to be more than enough. Typically, these are the small compressors that are about the size of a table.
If your compressor is going to be used on a daily basis or you have continuous and heavy duty projects, then a more powerful air compressor will be necessary.
Determining the CFM (cubic feet per minute) of an air compressor is the first step in determining what size you need. CFM is an indication of how much airflow a compressor will provide. It’s a versatile measurement, because it can indicate the airflow that will be provided by a compressor, or the output of an air tool. Air compressors are rated by CFM, so you also need to know the CFM needs of the tools that will be used with your air compressor.
Calculating the real CFM of your Air Compressor
When you hear that a air compressor has a "CFM", that number is only the maximum CFM of the motor. You cannot get a pressure reading until after the motor has reached that speed and has pulled a vacuum, so you really never know how many CFM's you will get.
Depending on the tank size of the compressor, you will see somewhere between 2-5 CFM difference between what the manufacturer says and what you get. In the chart above, the manufacturers rated CFM of the compressor is actually lower than what you will get when you are pumping a vacuum, and this is typical.
To figure out what you are really getting, figure out the tank size in gallons, and fill it with water at a known pressure and measure the time it takes to reach 10 lbs of pressure loss from the tank. Once you do this and fill out the chart above, you will have a much better idea of the actual CFM your air compressor is pumping.