What is CFM?
CFM is an acronym for “cubic feet per minute”. It’s used to describe how many cubic feet of air can be drawn into the compressor. It is generally measured in CFM. A higher CFM means the compressor can draw more air into the tank to fill the tank each minute.
The better CFMs are beneficial if you are filling a tank with a lot of cubic feet of air. For example, you may have a compressor that is described as having 2.5 CFM. This is a useful description if you’re using a compressor to pressurize your car tires or if you’re using it for something with a high CFM requirement.
The official way to measure CFM is to grab the air line and exert pressure on it. The higher the pressure, the higher the CFM rating. As an example, a standard air hose measures at 3 PSI.
Why is it Important?
CFM stands for cubic feet per minute and measures the amount of air a compressor can pump. The higher the CFM, the more air a compressor can pump. The more air you can pump, the faster your tool will run.
The higher the CFM, the less likely you are to have to wait for the compressor to catch back up with you after an interruption. A larger CFM also means that while you are waiting for the compressor to catch up, it will be pumping less air than a smaller CFM because it can recharge faster.
This is especially important when it comes to pneumatic tools. These tools, like air nailers or brad nailers, depend on air pressure to operate. A nailer that is forced to wait on a compressor to catch up is slowing down the user. This issue can be addressed by starting with a larger CFM compressor. After that, you can purchase a higher PSI rated nailer.
How to Increase CFM on an Air Compressor?
Grab a power screwdriver and some PVC pipes. It is going to be a good day.
Unplug and remove the cover to your air compressor. Generally, the screws will be on the top edge. This is where the positive and negative wires will be. Disconnect both of those. Unscrew the current discharge pipe. It's a 90 degree connector. Once it's disconnected, pull it back to make room for your modification.
You will need to put a Y-fitting to the discharge pipe. A Y-fitting is a piece of PVC pipe that has a T piece coming out of it. Then, cut your T piece down to size so it will fit into the 90 degree connector.
You will also need to install a Tee fitting to the discharge pipe. One side of the Tee will connect to your discharge pipe. The other side of the Tee will go back to the unit. The side that goes back to the unit will be the end where the noise reduction valve is.
Place a cover on the exposed discharge pipe after the modification.
Can you Decrease CFM?
The short answer to this question is “yes”. However, you can only decrease CFM on a shop air compressor if you also decrease HP. You cannot increase CFM without increasing HP because an electric motor is the pump. CFM can only be reduced by increasing the motor speed (rpm). Increasing speed (rpm) increases pressure in the pump. Increasing speed also creates a lot more heat and vibration inside the pump casing. Temperature and vibration increase until the pump is near shut down.
I don’t recommend decreasing CFM on a shop air compressor. If used for its intended purpose, a 55-gallon, 7.5 HP, 20 gallon per minute (gpm) ASME-rated shop air compressor isn’t too loud. The larger the tank, the quieter the compressor can be. The lower the CFM, the slower the compressor runs. You can run a compressor slower by partially filling the tank. The disadvantage is the time to build pressure in the tank. Also, to prevent valves from binding, you should top off the air in the tank to its max pressure rating.