Closure caps for vessels

A closure cap for insertion into an opening in a vessel, comprising an attachment component with attachment means operative to enable the cap to be releasably secured in the opening and a sealing component separately formed from the attachment component, said sealing component being of a flexible and resilient plastics material formed as a unitary whole and comprising a support and including an inner seal integral with said support for engagement with an inner seating around the opening and an outer seal integral with said support for engagement with an outer seating around the opening, at least one of said seals comprising an outwardly directed flange integrally supported at its inner edge by the support and capable of yielding resiliently when it engages its associated seating so that the flange is urged towards the seating due at least in part to the innate resilience of the material, said closure cap having a duct leading from a space inwardly of the inner seal and communicating with a space outward of at least the inner seal, and a valve for closing the duct and comprising a valve member integral with the sealing component and openable in use in response to a pressure differential across the valve, the higher pressure being in the duct.