Abstract: A rolling diaphragm not subject to the formation of cusps. The rolling wall of the diaphragm is made up of two regions, one region intended to engage the lateral wall of the piston of the rolling diaphragm device, and another region intended to extend from the lateral wall of the piston of the rolling diaphragm device to the diaphragm clamping region formed by the cylinder body of the rolling diaphragm device. In the first mentioned region the rate of change of diameter along the rolling wall is relatively small, or minimized. The second region is circularly shaped in cross-section. The radius of curvature of the cross-section of that portion is relatively large, so that the rate of change of diameter of the rolling wall in that portion thereof is relatively large.