the pressure system 1 after the required pressure difference is obtained the compressor 5 is stopped and the first closing device 10 is again opened at this time the fourth closing device 13 either can be closed or can remain opened due to the established pressure difference the low boiling medium flows in a liquid state through the drawing off conduit 3 until again the pressure difference is eliminated wherein after the compressor 5 is again started the first closing device 10 is closed the fourth closing device 13 insofar as it was not maintained opened is opened and the whole cycle is repeated until all low boiling medium is drawn off the residue of vapors of the low boiling medium is suctioned off by opening the first closing device 10 closing the closing devices 11 and 13 starting the compressor 5 and opening the third closing device 12 so that by way of the condenser 7 the liquefied low boiling medium is forced into the storage vessel 2 in general closing devices which do not perform a particular function during the course of individual stages are normally closed and the closing device 8 of the pressure system 1 and the closing device 9 of the storage vessel 2 are opened during the course of the drawing off of the low boiling medium the drawing off of the.