COMPARING THE MOJET® How does the MoJet® compare with slanted silencers?

Slanted silencers can be installed on 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®:

Slanted silencers typically require 24% more headroom than MoJets®

If additional head room is available in a tunnel, then additional thrust can be produced by specifying larger-diameter jet fans, or simply by moving the jet fans away from the bounding tunnel surfaces (soffit and side-walls).

The jet fan thrust is reduced by slanted silencers

This is due to flow separation at the junction between the slanted silencers and the fan housing, and because of horizontal reaction forces generated at the downstream silencer due to flow impingement and aerodynamic friction.

Premature fan bearing failure

Vibration due to flow separation within slanted silencers can cause premature fan bearing failure.

Additional power consumption

Due to internal flow separation, impingement and friction losses, jet fans with slanted silencers absorb more power than conventional jet fans.

Restricted silencer length

Due to the requirement not to encroach upon the tunnel traffic gauge, silencer lengths are limited with slanted silencers. This restricts the sound attenuation that can be achieved.

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.

View our technical paper on jet fan technology

Discover the benefits of the MoJet®

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