Contra-rotating Fans for Commercial Buildings – Uses, Benefits & Setup & Maintenance

Contra rotating fan

Contra-rotating axial fans are a modification of the axial-flow fan. They consist of two impellers with aerofoil shaped blades that rotate in opposite directions. The drive is by means of a single motor through differential gears, or two separate motors, one for each impeller. They are placed in the airstream and act as streamlined hubs.


Contra-rotating is a technique whereby parts of a mechanism rotate in opposite directions about the same axis, minimising the effects of torque & vibration.

Contra-rotating fans have a number of uses including:

  • Provide fresh air underground in the mining industry, ensuring the safety of staff and production
  • Aircraft
  • Torpedoes
  • Helicopters

More commonly, and where our experience lies, these are used in commercial air extraction, particularly in canopy hoods for commercial kitchens.

Compared with the conventional fans, the contra-rotating axial flow fan raises the pressure ratio of the inlet to outlet within the limited space, thus improving the aerodynamic performance.


Contra-rotating & Benefits:

There are a number of benefits from using these fans:

  • More power can be transmitted for a given radius due to the nature of the contra-rotation
  • Efficiency is increased by recovering energy from the rotational flow of the leading propeller
  • IP65 insulation – this ensures that these fans are “dust tight” & protected against water injected via a nozzle, making them robust  & suitable for many applications
  • High pressure – contra-rotating fans have two complimentary impellers which gives a duplication of air pressure from the same volume
  • Corrosion-resistance – in order to handle their environments, they need to be corrosion-resistant. Rolled-steel casings are often covered with a corrosion-resistant primer & paint & stainless steel screws are used


Installing a contra-rotating fan:

Before installing a contra-rotating fan, ensure that:

  • Installation is carried out by a qualified person
  • Make sure that the installation complies with mechanical and electrical regulations
  • Once ready to use, the apparatus must fulfil the following standards:
    • Standard for Low Pressure Instalments 2006/95/CE
    • Machinery Standard 2006/42/CE
    • Standard for Electromagnetic Compatibility 2004/108/CE
  • Ventilators installed in high risk areas that are accessible to users must be adequately protected in order to comply with standards.
  • Ensure that they are not to be used in explosive or corrosive atmospheres.
  • If the apparatus is going to be used in atmospheres with over 95% relative humidity, consult with our team first.
  • If a ventilator is going to be installed to extract air from premises where a boiler or other combustion apparatus are installed, make sure that the building has sufficient air intakes to assure adequate combustion.


Starting a contra-rotating fan for the first time

Before starting a contra-rotating fan, ensure that:

  • The apparatus is well secured and the electrical connections have been carried out correctly.
  • Safety devices have been adequately connected.
  • No loose material or fitting remains surrounds the ventilator. If the ventilator has been mounted in a duct, make sure it is clear of loose material.
  • The earth fittings are adequately connected.
  • Electrical safety devices are correctly connected, adequately adjusted and ready for use.
  • Electrical connections are correctly sealed and water-tight.
  • The propeller turns in the correct direction.
  • There are no abnormal vibrations – our impellers are dynamically balanced according to ISO 1940 standards & should be vibration-free.

If any of the electrical safety devices blow, the apparatus must be quickly disconnected from the mains supply. The whole installation should be carefully checked before trying to start up the machine again.


Contra-rotating Fan Maintenance:

  • Before servicing the fan, make sure it is disconnected from the mains supply even if it has previously been switched off. Prevent the possibility of anyone else connecting it while it is being serviced.
  • The apparatus must be regularly inspected. These inspections should be carried out with the machine’s working conditions in mind, in order to avoid dirt or dust accumulating on the propeller, turbine, motor or grids. This could be dangerous and shorten the life of the unit.
  • Whilst cleaning, care should be taken not to tamper with the propeller or turbine.
  • All maintenance and repair work should be carried out in strict compliance with health & safety regulations.


If you are trying to find the right extraction solution for commercial kitchen, please free to call or contact us. We have some of the most experienced extraction engineers in the country who will help to ensure that your installation is compliant & safe.