air compressor selector

Everything you ever wanted to know about oil free air compressors, variable speed air compressors and everything in between.

Most companies purchasing compressors will know exactly what application their air compressor will be required for - and they are either replacing or upgrading an existing piece of equipment. However, the plethora of options can be confusing - and add significant cost to your purchase which may not be necessary.

Here we will explain how to select what you need - and only what you need, starting with the rotary screw compressor and the oil free air compressor.

Air compressors convert power - generated by a motor -  into compressed air. As the compressor operates, air is forced into a storage tank where the pressure gradually increases. When the pressure reaches a pre-set limit, the air compressor shuts off, retaining the air in the storage tank until it is required.This compressed air can then be put to use in a variety of applications....... until the pressure in the tank drops - at which point the air compressor starts again. This basic theory remains the same with all air compressors, but the air compressors themselves vary vastly in their design. The advantages of air compressors over electrical tools can be significant. Generally lighter, more manoeuvrable, safer (due to no chance of overload or electric shock) and with a higher power-to weight ratio than their electrical or hydraulic counter-parts air compressors drive not just individual pieces of plant, but entire operating systems.

The rotary screw air compressor is ubiquitous in factories and workshops, supplying large quantities of compressed air. Dependable, it works tirelessly through periods of prolonged use, providing continuous 24/7 service for high volume applications. As such, it does not generally benefit pneumatic applications which are smaller in scale, such as drills or nail guns. Instead, it excels where the need for compressed air is high and may require subtle control (such as through the programming of a variable speed drive) in industries such as car assembly, (robotic tools and conveyor systems) construction, energy and manufacturing (drilling/ stamping / ventilation / bulk packing) where they ably and efficiently provide easily stored, safe, 'clean' energy.

Often they exist as combined units of air compressor and integrated dryer, such as the SCR Comp. complete C range. This allows an all-in-one solution to your compressed air requirements. With both units together, the footprint of the air compressor is reduced, making it ideal for locations where space is of paramount importance. These air compressors with integral dryer can result in a pressure drop in the system however, which will mean additional energy costs to maintain the required pressure in your system.

Variable speed drive air compressors - Variable speed drives with air compressors. Do you need to alter the speed of your air compressor to match fluctuating demands? Used correctly, vsd (drive) controlled air compressors can save you energy (and money) by matching the supply to the demand. Over time, this can save huge amounts of energy by allowing the pressurised air created to vary according to the actual requirement. These machines also possess all the benefits inherent in variable speed drives, and by allowing a controlled start up (thus reducing power surges) they also keep the compressor at a steady temperature (thus extending it's life-cycle as the equipment is not subject to sudden temperature changes). They are not suitable however where you require continuous high output, or continuous low output. In these instances the variable speed drive has nothing to do and will ultimately cost more to operate. It only excels where there is a requirement to control irregular demand. If your air compressor will be running at a continuous speed day and night, or if it runs only on an infrequent basis, or at a low volume, then the purchase of a fixed speed air compressor will be a far more cost-effective and viable solution.

Variable speed air compressors can, when sized properly, and in the correct application, make vast savings to you energy usage.

They can greatly enhance the control you have over your compressed air system. They can also be inefficient, power-hungry, expensive drains on your profits. How do you tell which scenario they will result in for your business?


The key in deciding whether a variable speed air compressor will be of benefit is to look at your whole system requirements. Taken in isolation, the ability to vary the speed of your supply is often deemed to be the best, most economical way forward: a logical if erroneous assumption. Only an energy audit on your compressed air system will show if your demand profile is best served by a vsd compressor. Without this information, not only is it difficult to correctly size the vsd compressor, it is almost impossible to accurately predict the demand fluctuations - the very fluctuations which decide which type of air compressor best suits your requirement.


scr compressor assembly line

The addition of a variable speed drive to the air compressor comes with its own set of potential drawbacks. It is only worth your investment if the advantages of the inverter control outweigh its corresponding shortcomings ie if your air demand is such that a fixed speed compressor is not coping adequately.

The ideal scenario for a variable speed compressor is one where the unit runs in tandem with a fixed speed compressor, generating the additional air required. A bank of fixed speed compressors, accompanied by a lesser number of variable speed compressors - which step in when short-term fluctuations occur - is likely to be a well planned and optimized system. This is a system which can grow and expand - and equally contract - as the requirement for compressed air varies.

For further information on selecting the correct air compressor for your particular application contact us at Not only will you be assured of the very best possible industry pricing for your compressor purchase, you'll also be sure of the best technical expertise in recommending the air compressor to suit your needs and those of your company. View our variable speed air compressor brochure here. Or view our range of variable speed drive compressors here.


oil free air compressorOil free air compressors -  Due to the manufacturing spec of oil free air compressors they are usually more expensive, noisier & less common than the lubricated (oil injected) variety. As the name suggests, they operate with a total lack of oil in the compression stage, & are put to use in specific industries where the oil - normally beneficial to the end product - is not required, or is detrimental to the process. The pharmaceutical, electronic & food industries all have processes and applications well suited to oil free air compressors. Here, oil would not serve its normal purpose of lubricating & protecting, but could contaminate the industrial process via the inevitable oil carry over present with all oil injected systems. As a result, oil free ranges of air compressor are suited to specific industries which can not afford to have anything but totally oil free, uncontaminated air. Their lubricated counterparts however, can be found in a multitude of applications where oil carry-over does not cause issues. These machines, due to the presence of oil, are quieter, less prone to breakdowns & less costly to run. However, it should be noted that in applications which require uncontaminated air at point of use, the ambient air itself must be of the highest quality - the air you put in is the air you get out). As such, high quality air filtration systems are often in effect in such plants, ensuring that only the highest quality, uncontaminated air is available for processing via the oil free air compressor (which itself contains no oil with which the air output by the compressor can be polluted). SCR now offers its own range of state-of-the-art oil free compressors. See our main menu to view our oil free fixed speed range, or the oil free variable speed drive controlled range of oil free air compressors, total oil free compressed air solutions for all your applications.