Jet fan

What are impulse fans?

An Impulse fans (Jet fan) ísa a type of axial fan that is adapted for operation in tunnel environments by e.g. material selection and silencer. The tunnel fans create airflow through a fan wheel that rotates and moves the air axially. They are usually delivered as a complete unit consisting of fan wheel, motor, cover, silencer and mounting stand. The flow of tunnel fans can be regulated with a frequency converter.
In order to choose the right impulse fan for tunnel ventilation, one should start from operating data, tunnel design and whether there are any special requirements.
Contact us at FläktComp for support.

Where are impulse fans used?

Since the early 1960s, impulse fans have been used to ventilate road tunnels with longitudinal ventilation.
One of the earliest theoretical background reports was presented by a member of the Witt group.
This means that we have extensive experience with tunnels and tunnel fans.
Impulse fans are today placed in all types of tunnels that require some form of ventilation. It can be road tunnels, metro or train tunnels.
They are usually mounted visibly in the tunnel ceiling, but can also be located adjacent to the tunnel and function as supply or extract air fans.
Depending on requirements, the design of the tunnel ventilation can be completely adapted to the customer’s needs.
Correctly dimensioned, an impulse fan provides problem-free operation and high performance for many years, even in tough tunnel environments.

About our impulse fans

Our tunnel fans from Witt & Sohn is one of the leading brands for tunnel and metro ventilation systems with many projects around the world.
In Sweden, FläktComp has, among other things, supplied the tunnel fans to Citybanan in Malmö and Norra Länken in Stockholm.
Witt & Sohn maintains its position in the market through continuous development of:
• Jet fans
• Large axial fans for supply and exhaust air

The jet fans are available as
• Asymmetric design, developed for high efficiency with one flow direction
• Symmetrical design, with partially reversible operation (40%, 85%, 95%) in both flow directions.

The standard range includes jet fans with traction force from 35 N up to 3500 N (higher values ​​are possible on request).
With different muffler lengths, almost all required sound pressure levels can be reached.
With specially developed impellers (cast-in steel bolts, etc.), very high peripheral speeds and very high temperatures are possible.
X-ray of the impeller blades and impeller hub is not necessary, but can be done on request.

The jet fans are tested according to ISO 13 350, the axial fans according to ISO 5801. In addition, all fans must pass the factory test before delivery. The jet and axial fans are tested and certified according to EN 12 101−3.

Banana Jet®

Witt & Sohn has developed the patented Banana Jet® fan.
Depending on the tunnel design, the Banana Jet® generates 20-50% more effective thrust than a traditional jet fan of the same size.
This jet fan reduces the costs of new tunnel ventilation systems and enables the upgrading of tunnel systems (due to increased traffic load or new fire regulations) without high costs.

Reduced losses in tunnel installations
A significant part of the air flow in a regular jet fan gets stuck in the ceiling and thus the transmitted impulse is reduced considerably. To account for this effect, several tunnel installation loss factors (Kempf factor, etc.) must be applied.
This problem was previously overcome using Saccardo nozzles, which solved the problem by blowing air into the tunnel at a slight downward angle. As an extension of the Saccardo nozzle solution, the Banana Jet® was developed to be used where Saccardo nozzles are not practical.
Banana Jet® with the curved outlet flow directs the impulse jet slightly towards the center of the tunnel, therefore friction losses due to vortices in the ceiling are negligible. So with the Banana Jet® tunnel, loss factors such as Kempf factor can be ignored in most cases.

Benefits of Banana Jet®
• Fewer jet fans, lower investment costs for fans
• Lower power consumption, lower investment costs for the electrical system, especially cables (which can often be a larger part of the costs than expected).
• If niches are needed, they can be smaller and shorter, resulting in lower construction costs.
• Lower operating cost due to reduced power consumption and fewer fans to maintain
• Less turbulence from a layered layer of smoke in the ceiling

Speed ​​profiles

Selection table for consultants/tunnel designers