When choosing a compressor, the size of the compressor is very important. In order for your machines to operate at their optimal capacity, you need to consider the required amount of compressed air and operating pressure. Another big choice you have to make concerns the type of compressor and here, we will take a look at the two most popular ones: piston and screw compressors. Depending on what your business’ needs are, one of these will be significantly better than the other.
The first question you have to ask yourself when designing your compressor setup is how much compressed air you need at the supply point. In case your system has multiple supply points, it is necessary to consider how the individual system components will work. Especially whether they are going to alternate in operation or if they will all be running at once. If you find the right balance in operation, you will be able to estimate your overall air requirements.
When talking about compressor air requirements, we typically use the term air flow or Free Air Delivery (FAD). Depending on your location, FAD can be measured in liters per second (l/s), cubic feet per minute (cfm) or cubic meters per hour (m3/h). When you want to supply enough air to a specific application, it is important to think about the air flow (CFM) needed at a specific pressure (PSI) required for the process to work properly. You will find more on the pressure in the second part.
In order to find out what your total flow should be, you could take a look at the datasheets of the equipment that uses the air and take a look at what FAD they require. A better way though is to perform an audit of your compressed air system. This can be done by a company sales professional. The compressor’s size has a big impact on its efficiency and longevity, undersizing it will result in pressure drops and in some cases even prevent the compressor from performing a task. Oversizing it, on the other hand, can lead to future mechanical issues and potential failure of the compressor altogether.
Not all equipment operates at the same operating pressure, so it is necessary to find out which one in your system requires the highest operating pressure and then determine the working pressure of the compressor accordingly. Pressure is usually measured in pounds per square inch (psi) or bar (the metric measure of pressure). The working pressure of the compressor should usually be 1-2 bars higher than what you actually need in your setup because it is necessary to account for the pressure drops in the drying equipment, filters and piping further down the compressed air system. To give you an idea on what are considered low and high-pressure compressors, low-pressure ones are capable of supplying air at a pressure of 4-13 bars, while high-pressure ones are capable of putting out air at pressures up to 400 bar (sometimes even higher).
When buying a compressor, it is easy to be overwhelmed by the number of compressor types there are, but you will likely be best off with either a piston or a screw compressor. Of those two types, the one you should actually choose depends on your workload and the consumption characteristics of your tools. For applications with short-time (discontinuous) consumption of compressed air, for example, tire services and packing machines, a piston compressor is the best choice. In operations with a continuous need of compressed air, a screw compressor is necessary. If your system needs a continuous supply of compressed air with irregular consumption, you should consider a screw compressor with a variable speed drive. Let us take a closer look at the two types and what applications they are best suited for.