What CFM is required for Spray Painting?

CFM (Cubic Feet per Minute) is important to a spray gun as it determines the level at which the compressed air affects the outcome of the spray. Therefore, it’s important to ensure that you’ve got adequate volume and CFM in your air compressor tank to do the paint job consistently.

One thing you need to note though is that different spray guns require different CFM. So, before you get your hands on the project, you’ve to ask yourself; what CFM is required for spray painting cars?

Well, that’s one of the issues we’ll be looking at in this article.

First, let’s look at the definition and role of CFM in spray painting cars!

What’s CFM?

CFM is an acronym for Cubic Feet per Minute. By definition, CFM is a universal way of measuring airflow or the amount of air that a particular air compressor can deliver/ produce per minute at a given PSI.

In spray painting, CFM refers to the amount or volume of air moving through the air compressor’s ductwork per minute. In other words, it shows how fast an air compressor can compress air to catch up with the spray gun.

This will directly affect how fast you spray the paint to the surface as well as the results of the coat once it cures.

In addition, CFM tends to vary with the atmospheric pressure as it’s responsible for the air movement in the cylinder. For that reason, you’ve to ensure that the CFM specifications of your spray gun meet the CFM output of the air compressor you intend to use.

Most HVLP spray gun manufacturers recommend using the tool with a 3 to 5-HP air compressor. However, if you’re looking for the best air compressor for spray painting cars, the most important factor you should pay close attention to is the Cubic Feet per Minute (CFM) rate.

Taking us back to our main question; how much CFM do you need to spray paint a car?

Let’s find out!

How much CFM do you need to paint cars?

The volume of air you need to spray paint your car efficiently depends on the CFM rating of your sprayer and the CFM output of your compressor. As mentioned earlier, different spray guns require different CFM to deliver the perfect car paint finish.

Therefore, it’s essential to ensure the spray gun’s CFM requirements and the air compressor’s CFM output are in line.

Generally, you should use a compressor that generates more air volume than your spray gun requires. This helps to keep the CFM rate steady to ensure consistent paint atomization as you work.

As an example, you can use an air compressor that produces 6 CFM at 40 PSI with a spray gun that needs CFM to deliver the perfect car paint job.

Getting back to the issue of how to spray gun CFM requirements tend to differ from one model to another, smaller sprayers usually require lower CFM than bigger models.

If your spray gun has a lower rating than 10 CFM, choose an air compressor for spray painting with a rating of at least 12 CFM. A 12 CFM-rated air compressor means that 12 Cubic Feet of air flows through its system per minute at a given PSI.

A compressor with this rating provides adequate air to handle large applications like spraying large areas, needle scaling, and dual sanding. However, this may need to be higher for professional applications.

Whichever the case, the most important thing is to check the CFM requirements of the spray gun and choose an air compressor that exceeds that figure. Choosing an air compressor whose CFM rating is equal to or lower than the spray gun CFM requirements will lead to imperfect coverage due to volume loss and pressure drop.

Does CFM increase as Pressure (PSI) decreases?

Sometimes, power tools like power washers and spray guns require an increase in the Cubic Feet per Minute (CFM) for them to work efficiently. Therefore, taking measures to increase the CFM/ airflow will come in handy.

As you would expect though, increasing the CFM will automatically reduce the pressure (PSI).

Here’s why!

Every compressor has a unique power rating that is calculated by multiplying the airflow rate (CFM) by the PSI. While both variables are necessary for the air compressor to function, the airflow rate (CFM) determines how well the machine will perform in continuous projects like spray painting.

So, if you want the air compressor to work better, you have to find a way to make the airflow more consistent without increasing the power. For instance, you can accomplish this by reducing the output air pressure (PSI).  

As you know an air compressor works by taking in air into its tank and pressurizing it. It then forces the pressurized air through an opening in the tank, causing the pressure to build up to a specific output PSI.

This gives you a specific air volume until the compressor kicks back to refill it. Therefore, reducing the output PSI causes the pressure in the tank to increase, giving you more airflow to run your tool for longer!

Other ways to increase the CFM rate of an air compressor

Reducing the PSI output of the air compressor is one of the best ways to increase the CFM. However, there are other efficient ways of increasing the air compressor’s CFM to keep up with the needs of your project. Some of the methods include;

Connect 2 similar compressors

Connecting another compressor from the same brand, model, and CFM rating to your existing one will double the current airflow rate without causing control issues.

Moreover, you don’t have to worry about synchronizing the pressure switches of the machines as they’ve got the same cut-in and cut-out pressure presets.

Connect 2 similar air compressors but with different CFM

Buying a similar compressor to the one you already own seems too expensive, look for a smaller one from the same manufacturer, but with a different CFM. For instance, if you’ve got a 10 CFM air compressor, buy a similar tool with a 5 CFM rate.

That way, you’ll get a continuous airflow of 15 CFM when you connect them.

Add another air receiver/ tank to your air compressor

Adding an air tank to your air compressor allows the machine to fill up both at the same time. Consequently, the motor of the air compressor will run for much longer reaching its cut-out pressure.

In short, this will allow you to use your tools continuously for a longer period than you did before.

On top of that, more air storage will give the air compressor more time to cool off. However, the extra cooling time will only work if the device isn’t drawing more air than its pump can generate.

Final Word

Overall, airflow rate/ CFM is one of the most important variables when it comes to painting a car with spray fun. It will determine the outcome of the paint coat on the car surface as well as how long the compressor can run your spray gun.

However, you also need to consider the horsepower and PSI (air pressure) that the compressor can produce to determine the perfect airflow to run your spraying tools efficiently.

In most cases, spray gun manufacturers recommend a specific CFM that will allow their tools to run efficiently. For that, it’s important to choose an air compressor that will meet the CFM requirements of your spray gun.

As a general rule of thumb, you should use a compressor that produces a higher airflow rate (CFM) than your spray gun’s actual requirements. This will ensure that the spray gun runs continuously for longer before the air compressor cuts off to refill the air tank.

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