The present paper shows results of theoretical and experimental studies of the employment of liquid ring machines used in compressor-type heat pump cycles. Liquid ring machines distinguish oneself by their very simple and robust design. Owing to the intensive phase contact between the gas and the liquid ring, their employment allow to combine the isothermal compression with a physical and chemical cleaning of the sucked gas stream. In spite of the traditional low isothermal efficiency the using of liquid ring machines is now and then the most favourable version, because of the comparatively low investment and service costs. The investigated heat pump obtained performance figures from 3 to 8 in handling the working media combination water/heat-transfer oil in an evaporator temperature area from 40 degrees C to 80 degrees C and a range of temperature difference from 20 K to 40 K. The results of the investigations show, that the employment of liquid ring machines in compressor-type heat pumps allow performance figures of conventionally closed heat pump cycles. By using an open cycle it is possible to obtain supplementary effects for instance in the field of environment techniques. The results reached by simulating the operational behaviour of such compressor-type heat pump cycles, using a self-made mathematical module, could be confirmed by test series carried out at a heat pump combined with a single-stage liquid ring machine, That＇s why these mathematical module is suitable to estimate the operational behaviour in other conditions.