the evaporator chamber 36 a valve 42 is opened so that a connection is opened between the lower part of the treatment chamber 10 and the evaporator chamber 36 via the tube 38 the valve 42 and the tube 40 the valve 42 is kept open as long as required for all free liquid carbon dioxide in the treatment chamber 10 to leave for the evaporator chamber 36 if the treatment chamber 10 is located above the evaporator chamber 36 the transfer of liquid carbon dioxide from the treatment chamber to the evaporator chamber can take place by means of gravitation otherwise a pump will be necessary to transfer the liquid carbon dioxide the evaporator chamber 36 now contains dirt mingled washing liquid and liquid carbon dioxide from the treatment chamber 10 and in its upper part gaseous carbon dioxide to separate the dirt from the liquid carbon dioxide a process of distillation will follow where gaseous carbon dioxide with aid of the compressor 46 will be sucked from the evaporator chamber 36 through the condenser or heat exchanger 44 and conveyed to the supply tank 18 where the carbon dioxide again reaches its liquid state now the valve 42 closes and the valves 33 and 54 open while the valve 64 and a valve 65 are activated to regulate the pressure in the tube upstream the valves and compensate for the pressure in the compressor 46 and in the supply tank 18 the compressor 46.