itself known for example from the already cited document no ep 1946793a1 a first tubular connector 2 and a second tubular connector 3 both of which are normally made of a suitable moulded thermoplastic material axially joined together in a permanent way with the modalities clarified in what follows the first and second tubular connectors 2 3 define respectively an upstream passage or inlet passage 4 and a downstream passage or outlet passage 5 which can be connected to respective sections of tubing of the medical line set between the upstream passage 4 and the downstream passage 5 is a one way valve the open close element of which set within a widened portion 9 of the tubular connector 3 coaxially with the latter consists of a cup shaped element 6 which comprises a circular bottom wall 7 and a skirt or side wall 8 and is conveniently made of a single piece of soft elastomeric material for example silicone rubber the free edge 8 a of the skirt 8 rests on a radial array of transverse projections 10 formed at the base of the widened portion 9 and delimiting respective radial channels that communicate on one side with a restricted central passage 11 which is in turn in communication with the.