The translation is like this or something similar.

The wood shavings/chips are collected on the outside of large tube shaped filters.

Here is how it works:

The suction draws air through the tube shaped filters, thereby accumulating/collecting the dust/shavings/chips etc. on the outside of the filter surface. The advantage of this technology lies in the ease of the cleaning and maintenance of the filter, because it can simple be shaken to clean it or the collected dust can be blown off by reversing the vacuum and blowing pressurized air through the bag.

See also the following link which has a good description of what I just said:

http://www.bumerangs.de/bw-archiv/93/93417.htm

Hope this helps !!