Class 3 Bellofram Rolling Diaphragms employ a beaded flange. The flange is similar to an “O”-Ring and seals the diaphragm via axial compression of the “D” shaped bead.
The bead is installed in a housing having mating groove. This design eliminates the need for any perforations in the diaphragm flange, since it is retained by squeezing the bead into its mating groove.
Because the “D” shaped bead loses some of its effectiveness at high pressures as a result of sidewall stress, this design is not recommended where differential pressures exceed 150 psi.
The convolution is formed by inverting the top head corner radius around its entire periphery during installation. To insure that the piston corner radius does not return to its “as-molded” shape, a curved lip retainer plate is generally recommended.