other by a hollow flow guiding device 9 starting from the second chamber 4 the flow guiding device 9 extends substantially coaxially with a longitudinal axis 15 of the casing 1 through the first chamber 3 and up to the third chamber 6 a first end region 10 of the flow guiding device 9 which is disposed between the first chamber 3 and the third chamber 6 is formed as partition 11 which on the one hand holds the flow guiding device 9 within the casing 1 and on the other hand separates the first chamber 3 from the third chamber 6 to create a substantially fluid tight seal therebetween a second end region 12 of the flow guiding device 9 which is disposed between the first chamber 3 and the second chamber 4 is formed as a funnel portion 13 an annular gap 14 is formed between a funnel edge and a casing inner wall 8 a spacing of the annular gap 14 between the funnel edge and the casing inner wall 8 varies around a circumference of the funnel portion 13 in the embodiment shown the annular gap 14 forms a flow path for the oil refrigerant mixture from the first chamber 3 to the second chamber 4 the funnel portion 13 facilitates a flow of a refrigerant.