Published: 22/12/2022
How to choose the right air compressor size
Choosing an air compressor can seem like a daunting task. There are different types of compressors, different ways of powering them, and now you have to think about what size you’ll need too. However, once you know what type of air compressor you want, choosing the sizing should come pretty easily.
Below, we have outlined some top tips to help you get started!
Airflow – CFM requirement
The first thing you need to be sure of is exactly what you’ll be using the compressor for. Once you’ve got this narrowed down you can then discover the airflow you’re going to need your compressor to deliver. This is can be measured in cubic feet per minute (CFM) which is the older denomination, or a more modern metric measurement IE Nm3/h (metre cubed per hour), Nm3/min or Litres/min
To find out the air flow you’re going to need, you’ll need to know how much the tool or machine you’re using requires to run, and how much air the compressor you’re looking at produces. If you’re planning on running multiple tools off the one air compressor, you’ll need to add together the flow of each tool. This will help you in choosing the right size compressor for the job.
A fixed speed compressor will always be the same size, so choosing one to cope with the maximum demand, but often using less air can be expensive on energy costs, if you have a varying air demand, the modern variable speed frequency controlled air compressors can have a very short payback over a fixed speed purchase, as these adjust their kW rating to match air demand
Working pressure
You’ll next need to know the pressure required for your tool or machine. This is most commonly measured in either BAR or the older imperial pounds per square inch (PSI). The minimum pressure that the tool will run at is the important number to look at NOT the maximum pressure of the compressor you may be considering, as compressors have a start pumping pressure that is typically 2 bars below their Max pressure, so as they are about to start, this is the system pressure you will see, also pressure drop over equipment like air dryers, line filter, and pipework distribution needs to be factored in.
Tank size
The tank (or Air Receiver to call it by its proper name) is there to regulate the stop/start, or load unload of the compressor, so the bigger the compressor is in kW, HP or CFM, then in turn the bigger the air receiver needs to be. As a rule, the receiver can only be too small, as a bigger receiver on a rotary compressor will keep the machine stopped for longer and save energy, and on a stop dead machine like a piston compressor, the pressure stays constant for longer, and allows for blasts of air to be used that exceed the compressor’s capabilities.
It is very important to note that air receivers do not give you any more air flow in anything other than a very short burst. You must ensure the compressor is filling the receiver at the same rate as your demand is taking it out for any length of time
Summary
Keeping in mind the CFM requirement, the working pressure, and the tank size, you should be able to work out how to size an air compressor for the jobs you want it for. However, finding these figures can also be tricky. Sometimes they are in the manuals of the tools you have, but other times they can be harder to find.
Here at Air Supply, we are experts in all things to do with compressed air. We have over 25 years of experience and our extremely talented and professional team can help you out with any query. If you’re still struggling to choose the right air compressor size for you, get in touch with us and we will happily assist!