outlet 13 comprises an additional control element 3 u2033 which may open or close respectively the oil outlet 13 to the oil collection vessel in a further non illustrated embodiment the oil outlets 13 of at least two oil separating elements 1 arranged in parallel open into a dedicated oil collecting vessel which is connected to the crankcase by a check valve in this case the check valves also have the function of the additional control element 3 u2033 mentioned above fig7 of the drawing illustrates an embodiment for the cyclone 1 in a cross section with a control element 3 in form of a valve 31 arranged upstream the valve 31 in this case is mounted as a prefabricated unit in a pipe connection piece which is arranged in the course of the partial stream 22 to the gas inlet of the cyclone 1 the prefabricated unit is pressed in by means of a spring a valve plate it is biased in a closing direction the valve plate may be raised from the valve seat against the force of the spring by the partial stream 22 as soon as this partial stream 22 is large enough such that the partial stream 22 gets through the control element 3 to the gas inlet 11 of the cyclone 1 and thereafter flows through the cyclone 1 in the center of the cyclone 1 a part of.