An one way valve comprising: a conical shaped valve seat (1); and a membrane (2) having a hole (3) that is located around the conical valve seat (1), such that a surface (60) of the valve seat (1) seals onto an inner periphery (61) of the hole in the membrane (2), wherein, in use, the membrane (2) is deflected from the surface (60) of the valve seat (1) to provide a fluid path across the membrane (2) and allowing fluid to flow from one side of the membrane (2) to the other.