spring 63 is then active as a sealing force between the mouth edge 71 of the fluid duct 35 and the sleeve end edge 73 of the sleeve body 33 in other words the coupling connection of the connecting unit is automatically established when the device is shifted into the operating state by screwing the cover part 3 onto the housing 1 containing the pertinent filter element 9 the interacting regions of the sleeve body 33 and the fluid duct 35 which in the coupling state form the seal arrangement are designed such that one of the annular surfaces which are pressed against one another by the pretensioning of the spring forms a continuous radial plane the other ring surface forms a radial plane with a sealing edge projecting out of it in these embodiments the ring surface 75 on the fluid duct 35 is continuously level the ring surface 77 along its peripheral edge forms a slightly projecting sealing edge 79 the sealing edge 79 with the radially outer edge of the ring surface 75 forms a seal in interaction with its surface edge additionally the edge enclosure of the mouth edge 71 of the fluid duct 35 also forms centering ensure that extremely precise alignment of the coupling connection of the connecting unit necessarily takes place when the cover part 3 is screwed on since the filter element 9 aside from the compression spring 63 can be made without.