Can top or bottom - has protruding dome pulled inwards by vacuum and snapping out on release

摘要

The top and/or bottom is for a cylindrical can, which is evacuated after filling. It has one or more domes (4) protruding outwards, and which are pulled inwards by the vacuum in the can (1), snapping outwards again on the entry of air etc. The dome can be in the centre of top or bottom, and of truncated-cone section in two parts, the cone angle of that joining directly onto the top or bottom being >= that of the one further out. The greater of the cone angles can be only slightly less than 180 deg.