With just 2 counter-rotating, in-series axial flow fans, static pressures up to nearly 5000 Pa can be achieved. The multi-stage unit consists of 2 or more counter-rotating single-stages in series with lefthand and righthand impellers, without guide vane. The spin of the first stage is transformed into an additional static pressure by the following stage. This way, the system produces an excellent airstream profile and 2,7 to 3 times the pressure of a single-stage version.

All parts of the multi-stage version can be taken from the single-stage fan and therefore can be produced at a low cost. Each stage has its own separate motor. If one stage fails or is switched off, the second stage still produces 65% of the air volume, while consuming only 40 % of the energy. This system is ideal for exhausting in carpark-buildings. It works in accordance to the regulations for carpark-exhaust systems in Germany and other countries, which require two independent stages, so that the fan will still be operating in case of a failure of one stage.

The airstream of the first stage will automatically turn the impeller of the switched-off second stage in the opposite direction, so that it supports the airflow instead of disturbing it. This also saves energy compared to similar systems. Besides, the impeller is already rotating in the right direction when the second stage is switched on. As another advantage, this is an inexpensive way of adjusting the air volume.