here , as in the following , the same or similar reference numerals are given to the same or similar elements , so that their description to some extent is not repeated . fig1 shows a cylinder head cover 1 according to the invention which is attached onto a cylinder head 2 of a combustion engine . such a combustion engine produces so - called blow - by gases which are led away from the crank housing ( crank case ) and are led back into the intake line of the combustion engine . these crank housing gases contain finely distributed oil or oil spray which must be separated from the gas before leading back into the intake line of the combustion engine . the valve cover according to the invention which contains the tubular separator comprises a housing lower part 7 which extends over the cylinder head 2 of the combustion engine and defines a plane which extends in the longitudinal and transverse direction of the cylinder head cover 1 . the housing lower part 7 with a housing upper part 8 encloses a chamber which is subdivided by an intermediate wall 9 , into two parts , specifically an inlet chamber 5 and calming chamber 6 ( oil tank ). in the intermediate wall 9 two flow - through tubes 10 a , 10 b extend from one side to the other , which are installed inclined at an angle α to the previously mentioned plane . these flow - through tubes comprise inlets 12 a , 12 b and outlets 13 a , 13 b for the crank housing gases . within the cylinder head cover the flow - through tubes 10 a , 10 b represent the only ( single ) passage between the inlet chamber 5 and the calming chamber 6 . the housing of the cylinder head cover 1 comprises a gas inlet 3 for the crank housing gases which may flow into the inlet chamber 5 . in this , they are still charged with oil and oil spray . furthermore the housing of the cylinder head cover 1 comprises an outlet 4 out of the calming chamber 6 via which the crank housing gases purified of oil or oil spray may be led to the intake line of the combustion engine . two worm - like segments 20 a , 20 a ′ and 20 b , 20 b ′ are located in the flow - through tubes 10 a , 10 b after one another and arranged at a certain distance to the inlet 12 a and 12 b respectively . at the same time the worm - like elements 20 a and 20 a ′ or 20 b and 20 b ′ have opposite revolving directions . alternatively several segments revolving in each case in opposite directions to one another are possible . it must be noted that the worm - like segments do not rotate themselves , but are fixed within the flow - through tubes . the crank housing gases which enter into the inlet chamber 5 via the opening 3 , now flow through the two flow - through tubes 10 a , 10 b into the calming chamber 6 . with this they are firstly set into one rotational direction by way of the worm - like segments 20 a ′, 20 b and subsequently are set into an opposite rotational direction by way of the worm - like elements 20 a , 20 b ′. by way of this the oil spray contained in the gas is separated on the wall of the flow - through tubes 10 a , 10 b and runs out along the wall via the openings 13 a , 13 b . the separated oil then collects in the oil tank or the calming chamber 6 . from there it may be led away via a return valve , via a valve to be opened periodically or also via a siphon . this is not shown in this drawing . the purified crank housing gases now leave the chamber 6 via the outlet 4 . the plane which is defined by the cylinder head cover and which corresponds to the x - y plane represented in fig1 b extends over the cylinder head 2 of the combustion engine . the middle axis of the flow - through tubes 10 a , 10 b runs inclined at the angle α with respect to this plane . this has the advantage that any separated water runs out by itself from these flow tubes 10 a , 10 b , even if motor is at a standstill , and thus an icing - up of these flow tubes 10 a , 10 b is prevented . the inclination must at the same time be selected such that also when the vehicle has been positioned obliquely , the running - away of water out of the flow tubes 10 a , 10 b is ensured . fig2 shows a flow - through tube according to the invention as an oil separator 10 with a wall 11 , with an inlet 12 and with an outlet 13 . fig2 a now shows the flow - through tube 10 which is cut open in the left part . one may recognise a fast worm - like segment 20 which has thread surfaces 21 twisted about the middle axis 14 . fig2 b shows a sequence of several worm - like segments 20 a to 20 d , which have a different rotational direction . the segment 20 a rotates in the clockwise direction , whilst the segment 20 b rotates in the anti - clockwise direction . the segment 20 c which is represented partly interrupted is in turn clockwise rotating and the segment 20 d anti - clockwise rotating . fig3 shows a further segment 21 as may be applied with the present invention . the segment 21 rotates clockwise and has two flow paths or two flights 22 a , 22 a ′. these flow paths in the axial direction are offset to one another ( mutually offset ) by half a pitch , a complete pitch is indicated with the reference numeral 27 . fig3 a shows this worm - like segment which extends over in total three pitches , in cross section . again the two flights 22 a and 22 a ′ are to be recognised , wherein a core 24 is formed in the middle axis of the segment 20 . this core , as is to be recognised in fig3 b , is removed at the beginning of the segment on the left side . at the same time this tore is removed from the segment in a conically converging shape . this has the effect that the pressure losses at the beginning of the segment are very greatly reduced . fig4 shows further worm - like segments in the part pictures a , b and c , which may be applied in the present invention . all of these segments rotate clockwise . in fig4 a , the diameter of the segment changes from the edge 23 a to the edge 23 a ′ so that such a segment may be applied in a tapering flow - through tube . the segment in fig4 b has a pitch which is uniform over its entire length , and an unchanged diameter . the segment in fig4 c has a pitch which reduces in the course of the rotation from the edge 23 a to 23 a ′. by way of this the total pressure loss in the segment is also reduced . fig5 in two different views in the fig5 a and 5b shows the sequence of two worm - like segments 20 a and 20 b . both segments have two flights 22 a , 22 a ′ and 22 b and 22 b ′. the segment 20 a at the same time rotates clockwise and the segment 20 b anti - clockwise . the front edge 23 b of the segment 20 b at the same time is offset to the rearward edge 23 a ′ of the segment 20 a by 90 °. by way of this the thread surface 21 b projects into the flow path which is formed by the flight 22 a . the same applies in a corresponding manner to the flight 22 a ′. the thread surface 21 b now for the gas which flows through the flight 22 a forms a impingement surface which further improves the separation of the oil . in order however to avoid an atomisation at the edge 23 b of the oil spray separated on the surface 21 b , a flange 26 b is attached along the edge 23 b opposite to the flow direction of the gas , i . e . in the direction of the flight 22 a , said flange as a web or raised part preventing the overflow of the oil in the direction of the edge 23 b . fig6 in a corresponding manner shows two segments which are arranged after one another , wherein in fig5 as well as in fig6 , for the part figure a , the flow direction of the gas is to be observed from the top to the bottom , and for the part figure b the flow direction from the bottom right to the top left . in fig6 again a clockwise rotating segment 20 a is followed by an anti - clockwise rotating segment 20 b . this embodiment example corresponds completely to that in fig5 , however the web 26 b is not present . in all further points , this embodiment corresponds to that in fig5 .