<p>The collapsible safety element has a polygonal end and a star-shaped end which are interconnected by flat triangular sections. The triangular sections are disposed relative to one another so that the points of the star-shaped end are in line with the corners at the polygon-shaped end. Consequently, when the safety element is closed, the triangular sections extending from the star-shaped end are disposed in parallel relation to each other. This improves and increases the sealing effect of the safety element at high pressure.</p>
