COMPARING THE MOJET® How does the MoJet® compare with deflection vanes?

Deflection vanes can be installed on one or both sides of a jet fan, in order to deflect the flow from the tunnel soffit or walls, overcoming the Coanda effect and purporting to enhance the in-tunnel thrust. However, they suffer from the following disadvantages compared to the MoJet®:


The jet fan bench thrust is reduced by deflectors

by between 5% to 20%, depending on their degree of turning, distance from the silencers and whether they are installed on one or both sides of a jet fan.

Deflectors kill the discharge swirl and this significantly extends the jet throw.

The extended jet throw can present a hazard to pedestrians and emergency responders in the tunnel, if the local air velocities are excessive (e.g. greater than 11 m/s). During traffic flow, the extended jet may cause buffeting of heavy goods vehicles, which also presents a life safety risk.

The extended jet throw from deflectors

can cause the jet to adhere to the tunnel floor or to stationary traffic (especially onto heavy good vehicles in road tunnels and trains in rail tunnels), increasing aerodynamic shear and reducing the in-tunnel thrust.

Deflector vanes cause regenerated noise

due to vibration of the vanes and vortex shedding, which can add between 1 to 3 dB to the sound power level.

Deflector vanes

can suffer from fatigue-induced failure, which could cause the vanes to fall onto the tunnel traffic, causing injury or death.

Power consumption is increased due to deflectors

by up to 12%, due to the additional pressure drop caused by the vanes.

Installation of deflectors presents an additional installation step

which costs time and money on site.

TechnologyDeflect jetCompactNo jet throw extensionNo noise regenerationNo deflector metal fatigue riskNo additional power
No loss of bench thrustNo risk of bearing damage



Slanted silencers

None of these drawbacks are present with the MoJet®, which is the most modern jet fan technology available for enhancing in-tunnel thrust.

Read our technical paper on the performance of deflection vanes

Discover the benefits of the MoJet®

The reversible MoJet® tunnel ventilation system can increase the in-tunnel aerodynamic thrust by up to 100%