Abstract: A reverse buckling disk has an annular retaining flange for mounting in a flow passageway. The annular retaining flange is integrally formed with a central domed portion having a concave side and a convex side. The disk has a predetermined material thickness and domed height for establishing a rated pressure at which the central domed portion reverse buckles. A metal cutting element or knife is fixedly attached to at least a portion of the convex side of the central domed portion in surface-conforming relationship. The metal cutting element has a thickness greater than the thickness of the disk material and has at least one knife point thereon for cutting the disk as the central domed portion reverse buckles at the rated pressure.

Abstract: A differential pressure flow sensor for use in a flow passageway of very low pressure flow lines and utilizing at least first and second conductive membranes in superimposed relationship having center portions constructed to create a discontinuity to allow a predetermined flow rate therethrough. A conductive strip is in juxtaposed relationship with the superimposed membranes and has a normally closed switch position. When the flow in the flow passageway exceeds the predetermined flow rate, the pressure against the flexible membranes opens the switch of the conductive strip and provides an electrical indication of the open switch.