This disclosure relates to the art of pressure vessels, more particularly of the type having a cylindrical container, one end of which is closed having a port, and the other end of which defines an open mouth. The container has a deformable bladder of resilient material positioned therein, said bladder having a large mouth with a thickened rim portion in which is molded the lower edge of an annular metal supporting member which extends outwardly from the rim with the free edge portion of said supporting member being secured to the rim of the mouth of the container which is closed by a suitable cover. The thickened rim of the bladder on the inner surface thereof has an inwardly extending annular bead molded integrally therewith in a plane below that of the lower edge of the supporting member to permit folding of the bladder without formation of a sharp pleat.