Abstract: A reverse buckling disc having a central domed region, an outer flange and an integral transitional region interconnecting the flange and the domed central region wherein the included angle of the transitional region is greater than the included angle of the domed region, such that the reversing pressure of the disc is determined by the angle of the transitional region rather than by the height of the dome.

Abstract: In a device for detecting fluid flow, an elongated body, such as a wire, is supported so that when a substantial portion of its length is exposed to a flowing fluid with the longitudinal axis of said portion arranged substantially transverse to the fluid flow, said portion can be caused to vibrate by vortex shedding; an electromechanical transducer is coupled to the body so as to produce an electrical signal in response to the vibration; and either the presence of the electrical signal is detected, for operation as a safety switch, or the frequency of the vibrations is detected, for measurement of fluid flow rate, fluid velocity etc.