How Air Blowers Work: The Principle

An air blower uses a rotating impeller/rotor to create a vacuum. This vacuum causes air to rush into the blower. The air enters the centre of the impeller and is divided by the rotating blades. Centrifugal force increases the speed of the air and volume of the air stream within the housing.

Effectively, the kinetic energy of the impeller is transferred to the air. Pressure builds up as the volume of the airstream increases inside the housing. The air is then discharged from the housing towards a defined point.

This targeted channelling of the air is what differentiates an air blower from a simple fan. Air blowers, designed in as part of an air knife system, will create a balanced airflow – reducing wasteful over-generation of excess volume and pressure.

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Why Specifying The Right Type Of Air Blower Is So Important

Air blowers may look and sound simple enough at headline level. But it’s very important to specify the correct type for your application – otherwise you risk compromising blower performance and/or paying for more energy than you need.

These are the various types of air blower, based on their impeller design:
• forward curved centrifugal
• backward curved centrifugal
• backward inclined aerofoil
• radial
• axial fans.

And here are the advantages of each type…

Forward Curved Centrifugal Air Blowers

Centrifugal air blowers can move high volumes of air at low pressure – making them up to 90% cheaper than compressed air. Here’s how and why…

The air velocity (in metres/second) in a blower is fixed. But the mass flow rate (the number of kilograms of air passing a defined point per second) is not fixed. Centrifugal air blowers operate at lower pressure because they can use less air to create the required high-velocity airstream.

Lower pressure equals lower energy bills – for the same (or better) performance.

The impellers in forward curved centrifugal air blowers look a lot like hamster wheels. And as risible as that may sound, it’s probably the best visual description. It’s not one you’re likely to forget.

These are some of the most common air blowers – delivering medium levels of pressure from a medium level of power. The impellers can be either left- or right-handed to suit the application.

Which is better? Left- or right-handed? It depends on the application and where it is most advantageous for the motor to sit in relation to the discharge.

View our range of forward curved centrifugal fans. Our catalogue features more than 550 fans to meet the requirements of a broad spectrum of industrial applications.

Range of Forward Curve Fans

Backward Curved Centrifugal Air Blowers

Backward curved blowers offer ‘medium power, medium pressure’ performance – just like the forward curved variety. But backward curved blowers have a more robust impeller and fewer sloping blades.

Backward -curved blades flick the air – rather than cut it. So size-for-size, they deliver higher volumes of air at lower pressure. This means greater performance for less power (should the application demand it). Centrifugal? ‘Centri-frugal’ more like.

They’re not just more energy-efficient, they’re also quieter. So you’ll find them used in a lot of air conditioning systems and for data centre cooling. Some were also used to help create special effects in Walking With Dinosaurs – The Arena Spectacular, based on the BBC’s multi-award-winning TV mini-series.

View our range of backward curved centrifugal air blowers. Direct mounting of the impellers and low motor speeds deliver high-pressure performance with minimal noise levels.

Backward Curved Centrifugal Fan for Air Knife application

Backwards Inclined Aerofoil Blowers

Backward inclined aerofoil blowers such as the belt-driven EP10A have a different type of impeller. The rotor in this type of blower is much flatter, making them more compact.

But don’t underestimate their small size – they’re designed to blast out medium volumes of air at high pressure. The EP10A in particular has state of the art impeller design and superior belt technology, creating less friction. The belt’s tension is lower too – putting less load on the bearings so they last longer.

You’ll find EP10A blowers in our LNL (Low Noise Level) fully enclosed air knife systems and our EL partially enclosed air knives.

Belt driven blower for air knife enclosure


These are very tough blowers. They’re particularly recommended for marine/offshore applications or hot/cold environments. They’re not quite ‘fit and forget’ but they are very hard-working blowers.

The impeller blades radiate from the centre to the outside edge like the paddles on an old Mississippi steamboat. These blades are usually sandwiched between protective layers – resulting in greater strength and more efficient air movement.

ACI’s range of radial fans offers flow rates of up to 212,000 m³/hr (360,000CFM) and pressures up to 300 Mbar (120 In.Swg).

Range of ACI Radial Fans


The impellers on these high volume, low pressure units look like desk fans. They’re best suited to cooling large volumes of air cost-effectively.

You’ll find them in wind tunnels and some HVAC systems (not big ducted systems though because they’re low-pressure fans). They’re also good for destratification in buildings – mixing air to help stop stratified layers of heat becoming trapped near the ceiling.

ACI offers Euroventilatori axial fans with flow rates of up to 75,000 m3/hr (44,143 CFM) and static pressures up to 3 In.Swg (75 mmWG)

ACI Range of Axial Fans

Why It Pays To Get Expert Technical Advice

Impeller and housing design can have a huge impact on the performance of an air blower. Important factors to consider include:

  • The type and size of the impeller – the shape, angle and configuration of the blades. Larger diameter impellers create more pressure; wider (deeper) impellers give greater airflow.
  • The distance between the impeller and the cut-off point (the location where the air begins to exit the housing). This is crucial to performance.
  • How much heat the air blower gives off (due to the higher pressure of the air) – the temperature differential can range from 3°C to 20°C.
  • Where will the air blowers be used – what is the climate like? How hot/cold is it? At what altitude will the blowers be used? (Thinner air is harder to move).
  • Configuration of multiple blowers – will they be used in series (stacked) or parallel (side by side)? Stacking fans in series creates more pressure.

Furthermore, there is the issue of how the blowers are wired in. A blower is not a pump – so if you get it wrong, you’ll only get around 60% of the performance at best.

Our field engineers occasionally come across blowers that have been mis-wired in a three-phase supply – significantly affecting their airflow output.

See How ACI Air Blowers Solve Technical Challenges

It pays to partner with a world-class air delivery specialist like ACI. Read how our air blowers are used in a wide range of applications.

View our Case Studies page and click the Fans And Blowers tab to find out more.

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