To find the ideal compressor for you, we have to start with determining what its ideal size would be. The main reason why sizing is so important is the one major downside of compressing air: it requires quite a bit of energy.
In fact, energy expenses make up the vast majority of the costs of conventional compressors over their lifetime. The initial investment, on the other hand, only accounts for a fraction of this total cost of ownership.
And that is why properly sizing your compressor pays off in two ways: You can not only reduce your investment costs but also significantly lower your operating expenses when the compressor you choose meets your needs and doesn’t waste energy.
Obviously, picking a compressor that is too small is problematic because it will not be able to meet your demand.
So now you know why sizing is important. But how do you do that?
Pressure & flow
To properly size your compressor, you first need to know your flow and pressure requirements.
The pressure of the air can either be measured in pounds per square inch (psi) or bar (metric measure of pressure). If these technical terms do not help you much, think of it like this: Pressure refers to the amount of force needed to perform a certain amount of work at any given point in time.
If that still doesn’t help, think back to something you might have done as a child. The task was to move an object across a table without touching it. That is why you blow against it. Some objects might be easy to move while others require a lot more effort, i.e. air pressure. At the same time, it would be a waste to exert more energy than necessary to move it.
It’s just like that in the case of compressors. They have to provide enough pressure to perform a given task.
For example, if you need 100 psi to accomplish a task (like moving a piece of wood across a table), then anything less will not get the job done. That is why you have to understand which amount of pressure is needed to size the compressor properly. Otherwise, you either waste energy or run into performance problems.
That brings us to the flow, which is also referred to as free air delivery. Depending on your geographic location, it is measured in cubic feet per minute (cfm), liters per second (l/s) or cubic meters per hour (m3/h).
In simpler terms, flow is the ability of the compressor to continue performing a task within an acceptable time frame. The amount of flow that is required is determined by the length of time needed to complete a given task.
Going back to the example of the wooden block, let’s consider two scenarios. In the first, the block has to be moved a certain distance every hour. This will require less flow and can be achieved with a smaller compressor and a storage tank. The compressor will cycle on and off and refill the storage tank for the next time the wooden block has to be displaced.
However, if the block has to be moved constantly within a given time frame, a larger flow of air (or CFM) with continuous flow will be needed. This, in turn, means a larger compressor is required. If the flow is insufficient, then the process has to be interrupted frequently while the compressor builds up pressure in the reserve tank. This is a clear indication that the compressor might be undersized.
That is why you have to consider the amount of compressed air flow needed at a specific pressure to ensure that a process works properly.
So how do you find out the total flow needed? One way is to contact the manufacturer of the equipment that uses compressed air and request data sheets with the desired information.
However, it is even better to perform a “compressed air audit” to determine the optimal flow. For this, all you have to do is to contact an Atlas Copco compressed air sales professional.
To summarize, pressure is determined by the job you are performing. Flow, on the other hand, will require the understanding of how frequently the job has to be done, or how many jobs you are performing at the same time.
Keep in mind that undersizing a compressor will result in pressure drops and the inability to complete a task. Oversizing the unit not only wastes energy and needlessly increases costs but can also lead to future mechanical problems and a potential failure of the compressor.
