Design features 
Wolter air-extract boxes are used to extract more heavily polluted air, for example from professional kitchens.  A well-insulated housing keeps the noise level to a minimum.  The impeller is driven by a standard flange-type motor, single or 3-phase supply, mounted outside of the airstream.  Motors suitable for speed control are available.  Impeller and motor are mounted on a swivel door.  The impeller is easily dismounted for cleaning.
The permissible temperature range of the conveyed medium is -30°C to +120°C.

Motors
All fans are equipped with standard flange type IEC-motors. Protection class IP54, isolation class B.  Up to motor size 100, voltage-controllable motors can be supplied.

Impeller
Wolter air-extract boxes are fitted with either forward-curved or backwardcurved impellers.  Forward-curved impellers are manufactured of galvanised sheet metal, backward-inclined impellers are made of aluminium. The design of both impeller types guarantees high efficiency and minimal noise emissions. 
 KAT. - forward-curved impeller with scroll
 KAF. - backward-curved impeller without scroll

Casing
Wolter air-extract boxes have a torsion-resistant aluminium frame, joined by solid plastic corners.  All side plates are made of galvanised sheet metal insulated with noise-absorbing mineral wool.  The aerodynamically shaped scroll (KAT) guarantees high efficiency.  KAF type fans are fitted with a plug fan impeller without scroll. The fan inlet and outlet can easily be connected to standard air ducts.  Special connection clamps (RSV) are available.
Speed Control 
All KAT./KAF. type fans are speed-controllable by frequency converter.  All models marked "Stb." are also suitable for speed control by transformer.
Fan performance curves
The performance curves for these fan types have been established in mounting position B (installed on the pressure side and open on the suction side) and show the total pressure increase as a function of the volume flow.
Sound levels
The ascertaining of the sound level follows the enveloping surface method according to DIN 45 635 section 38.