column 48 is thereby promoted after the switch over the functions of the adsorber columns 38 and 48 are transposed now the fresh air flows from the throttle 34 through the 3 way valve 64 the adsorber column 48 and the 3 way valve 56 to the particulate filter 40 and from there to the control room 4 however the discharge air from the control room 4 flows from the throttle 74 through the 3 way valve 52 the 3 way valve 58 the adsorber column 38 and the 3 way valve 66 to the fan 46 and from there to the outlet 72 the previously charged adsorber column 38 is now backwashed by the discharge air while the adsorber column 48 is available for cleaning the fresh air and accordingly for repeated charging in order to control the switch over operations by using the 3 way valves 52 56 58 64 66 there is provided the control unit 30 which advantageously also controls the two fans 12 and 46 and optionally other positioning members for throughflow and pressures it will be self evident to the person skilled in the art that the switch over functionality can also be brought about by using other line topologies and positioning members in an equivalent manner as indicated by the broken peripheral lines the ventilation system 2.