The screens are fitted in descending order of perforation size into the fibre classifier. The paper filters are placed in the suction housings under the container, which is then closed. When the start button is pressed, water flows into the units. As soon as the last container is full, the start button is pressed again. The flow of water through the classifier stops and the sample is added to the uppermost container. After the filling time, the agitators and water flow starts automatically, and the classification process begins. After this period has elapsed the agitators come to a standstill and the addition of water stops. Opening the fasteners and starting the vacuum pump extracts the suspension. During rinsing the rest of the fibres collect in the filter. It can then be removed, dried and weighed.