Variable or fixed speed compressors


One size does not fit all when it comes to the world of air compressors, and knowing how you will use your compact, portable compressor day to day is important when selecting the right machine.


When it comes to compressors there are two different drive types – variable speed drives (VSD) and fixed speed drives (FSD).  Essentially the difference is in the drive motor, but it can be worth taking a minute to think through how you will use the compressor and the demands placed on it before taking the plunge and investing in a new machine.


Fixed speed compressors

Traditionally, air compressors were designed as fixed speed, meaning that no matter the technology inside they ran at a constant and consistent speed, producing a fixed air flow per minute and cycled between two set pressure points.

These compressors are still used in many applications.  In a fixed speed compressor, the motor runs at the same speed or RPM regardless of the air demands placed on it.  These compressors are ideal for applications where there is a constant air pressure and flow requirement, with minimal fluctuations in demand, for example powering equipment such as co-ordinate measuring machines (CMM), or where there is a large receiver/buffer tank.


Variable speed compressors

A variable speed compressor works very differently, with the motor modulating its speed depending on the air demand of the application.  This type of compressor is ideal for situations where the air pressure and flow requirement changes over the period of operation.  Applications such as fibre optic cable installation is a good example of an application where a variable speed compressor offers an advantage.  As fibre optic cable flows along the installation ducts and around bends, the demands on the compressor blowing the fibre changes. With a variable speed drive the compressor unit is able to adjust its output to the demand needed, thereby providing the right quantity and pressure of air at the right time, rather than a constant flow of air.


Benefits of variable speed compressors

VSD compressors offer a number of benefits to the user

  • Energy use is optimised as it is closely matched to the demands placed on the compressor. A fixed speed compressor will always draw the same amount of energy required to produce the maximum compressed air demand, whereas a VSD will lower its speed and therefore power consumption when air flow and pressure requirements reduce.
  • The noise of the compressor is reduced when running at a slower speed
  • Wear and tear on the compressor is minimised as the unit isn’t constantly switching on and off.
  • The operator has more control over the air output levels

Which compressor should I choose?

If your compressed air needs are constant with minimal variations in demand then a fixed speed compressor will be sufficient, however if your application demands a range of pressure and flow requirements during its period of operation then a variable speed drive may be more suitable.


If you are unsure whether a fixed or variable speed compressor is right for your application then get in touch with the team at Vert who will be happy to identify the right compressor for your job.