The Class 4C is similar to the Class 4 except that the convolution is molded in. The suggestions, pressures and other information, with regard to flange retention, listed under the “Description” of Class 4 in the design manual also apply to the Class 4C.
Because it is molded in the “as-installed” configuration, the Class 4C diaphragm need not be inverted at installation. The pre-convoluted design has a small spring gradient or centering effect, which tends to return the diaphragm to its “as-molded” or neutral plane position. The design can be fastened to the piston with a flat retainer plate.
The stroke of these diaphragms is limited since deep-molded convolutions are impractical to manufacture and are better suited for limited strike lengths.