The 250D is the basic model with an optimized filter cartridge, which ensures maximum air flow rate. The 250D "Pharma" was specifically developed for the pharmaceutical industry, which prescribes a contamination-free disposal of suction waste (in other words human contact with the suction waste has to be avoided at all times).
Therefore the cardboard cartridge with the integrated filter is disposed of together with the waste, whenever the whole unit is full. Different filter types are available, to enable a larger spectrum of applications. For security reasons a secondary absolute filter is placed downstream. For the prevention of unpleasant gases or smells, an activated charcoal filter can also be installed as an option.