How do I choose the right screw compressor?

Navigating the jungle of screw compressors can seem overwhelming, but with a few tips we'll help you on your way.

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How do I choose the right screw compressor?

When choosing the right screw compressor, there are a number of things you need to consider. Proper sizing of the compressor is essential to ensure the operation of your compressed air system. It is also important to consider the type of screw compressor that best suits your business needs.  

The basic sizing of the compressor

First and foremost, it is important to consider the basic sizing to ensure that the screw compressor can supply you with the compressed air your processes require.

Air flow requirements

First of all, you need to check how much compressed air you need at the point of use. If you have several connections that use compressed air, it is important whether these are in operation at different times or all need to be able to run simultaneously.

You can often find the air flow requirements for individual connections in the data sheets on the equipment. Alternatively, you can have the system checked with the help of a compressed air specialist.

Working pressure requirements

Not all connections need the same working pressure, so you need to find the highest working pressure required. The working pressure of the compressor should typically be 1-2 bar higher than the pressure you actually need, at the point of use, as pressure drops in the air handling system and pipework must be taken into account.

Fixed or variable speed screw compressor?

Allegro 160 screw air compressor

Screw compressors are available with either fixed or variable speed, depending on the compressor technology.

In a fixed speed screw compressor, the motor runs continuously at the same speed in so-called load/unload cycles. In other words, the compressor is either running or at rest. A fixed speed screw compressor is often a cheaper investment, and therefore a good solution for companies with a stable air demand.

A variable speed screw compressor, also called a variable speed compressor, uses a special technology where a special drive controls the rotational speed (rpm) of the compressor. This ensures that the air supply is constantly adjusted to the required air volume at the point of use. A frequency-controlled screw compressor is much more energy efficient, as the motor runs at a reduced speed when air demand is low, thus avoiding energy wastage. In addition, efficiency is maximized and so are overall running costs.

Learn more about how a screw compressor works.

Oil-injected or oil-free screw compressor?

The choice between an oil-injected and oil-free screw compressor depends on your company's processes and the air purity requirements within them. An oil-injected compressor is a cheaper option, and therefore often the best choice for a wide range of businesses.

WisAIR 75V oil-free screw compressor

In oil-free compressors, oil is used for sealing and cooling the compressed air, as well as for lubrication. Oil contamination in the form of particles and aerosols will always to some extent end up at the point of use, and thus in the end product. For many companies, after-treatment of the air is sufficient to meet air cleanliness requirements.

However, for some businesses there are stringent air cleanliness requirements. If any oil contamination, regardless of quantity, is to be avoided in the process and end product, choose an oil-free screw compressor instead. These compressors are most often used in the food industry, laboratories, the pharmaceutical industry and the electronics industry.

There are different purity classes for compressed air, which you can read more about here.