Abstract: A plurality of coaxially arranged, nested tubes (1, 2, 3, 4) are retained between distributor heads (8, 45). The heads and the outermost tube (1) are coupled to one another in a media-tight manner by fitting flanges to provide releasable axial connections. Each distributor head (9, 45) has two walls (9, 10, 46, 47) concentric to one another as well as one end chamber (17, 50) communicating with an annular chamber (11, 48, 49) formed between the walls. The outer wall (9) is joined to the outer tube (1), and the second tube (2), located inside the outer tube, is inserted into the inner wall (10) against an axial stop (24). A sleeve (26, 58, 59) is connected to a third, inner tube (3) located inside the second tube (2). The sleeve (26) is also braced against an axial stop (28) of the inner wall (10) close to the end chamber. The interior (34) of the sleeve communicates via an opening (19, 55) with the end chamber (17, 50).