In this raw-air system, the impellor fan is located between the woodworking machines and the filter. Via the impellor, the AAS units take in the air with its dust and chippings (raw air). The raw air is then pressed into the filter, capturing the dust and releasing the cleaned air. The system has the advantage that it is relatively cost-effective due to the simple design. During this process, an overpressure is imposed on the dust extraction system. This can result in very fine dust being pushed through the filter and back into the working environment. It is therefore essential that AAS units are fitted with an optional fine dust filter if MDF dust is to be extracted.