The Class 1A Bellofram Rolling Diaphragm includes “O”-Ring type bead around the entire circumference of its mounting edge. It is designed for installations requiring minimum outside flange diameter.
This construction eliminates the need for wide flanges, and in some cases, also eliminates the need for flange bolts or flange studs. It requires no perforations or bolt holes through the flange of the diaphragm.
As in other top hat diaphragms, the Class 1A diaphragm requires inversion upon installation and a curved lip retainer is suggested to prevent the piston corner radius from returning to its “as-molded” shape.
In some special designs the Class 1A diaphragm can be provided as a pre-convoluted style with a permanently molded convolution. This pre-convoluted design is easier to assemble. However, it does have the small spring gradient and centering effect which is present in other pre-convoluted designs. A flat retainer plate can be used to retain the head portion of pre-convoluted Class 1A diaphragms.
The cross-sectional area of the bead groove and the hardware for retaining the bead should be equal to the cross-sectional area of the Bellofram bead itself. The corners of the groove should be machined square with minimum fillets. These practices are recommended to provide best retention of the bead without over stressing the elastomer and fabric in the bead. If the groove area is too small, it will cause excessive compression on the elastomer and subsequent damage to the rolling diaphragm. It is recommended that this design be used where differential pressures do not exceed 150 psi.