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 seperate
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.
