A valve assembly (10) comprising two valve portions, an upper and lower valve portion (12, 14), each having a valve housing indicated generally at (16, 18), a valve seat (28, 28′) and a valve closure member (20, 20′) moveable between a first position in which the valve closure member is displaced from the valve seat and the valve is open, and a second position in which the valve closure member cooperates with the valve seat and the valve is closed, wherein the assembly has a first configuration in which the first and second valve portions engage with one another, the valve closure members being closed, and the valve closure members being disposed at a distance apart defining, with the housing, a chamber (29) therebetween, which is capable of being sealed from the surrounding environment, having an inlet (44, 44′) and an outlet (45, 46′) through which sterilizing medium may pass, and a second configuration in which the valve closure members engage with one another and are moveable from their first to their second position, and a third configuration in which two valve portions are disengaged from one another.