Energising ring for a closure membrane

A closure for a container, which has a self-closing valve having a cup-shaped valve head ( 32 ) with a dispensing aperture defined therein. In response to increased pressure in the container, the head of the self-closing valve to flatten and partially invert, thereby opening the dispensing aperture ( 6 ). The closure ( 1 ) includes an energizing ring ( 5 ) arrange surrounding the valve head ( 32 ) and adapted to restrict the radial expansion thereof. The position and design of the energizing ring ( 5 ) relative to the valve head ( 32 ) may be adjusted to affect the performance of the valve allowing a single valve design to be used for a number of different applications. Alternatively the energizing ring ( 5 ) may be used to improve the performance of a particular design of valve.