Abstract: In cryogenic applications a compression device circulates a fluid, such as helium, in a closed cooling circuit. The compression device includes at least one compressor, preferably a helical compressor, with a bypass valve connected in parallel thereto, which serves to decompress the compressed fluid. The suction pressure is measured with a pressure measuring device and is supplied to a control device, which controls the position of a powered valve spool of the compressor and also the position of the bypass valve. In order to achieve a high control performance with small bypass losses for load cases which are hard to predetermine, the positions of bypass valve and power valve spool are adjusted so that a fluid flow flows as a control reserve through the bypass valve and is on the order of a fraction of the total fluid flow.