This type of cover consists, on the one hand, of the main supporting features in a curve shape that are deployed radially in a ring around the crown, forming a ribbed framework and, on the other, of the secondary supporting features that span the remaining openings or areas between the main supporting links.

The area of the ring of the central crown is
covered by a special plate. With this cupola-shaped design the main supporting links absorb the loads of the very light secondary supporting features and transfer them to the rim or wall of the tank, which has to absorb major vertical and horizontal stresses. This means that it has to be thoroughly inspected insofar as concerns its supporting role.