Abstract: A variable orifice flow sensor includes a flow conduit member defining a flow orifice and fluidly connecting first and second fluid flow ports, a flapper of magnetizable sheet metal that is mounted in the conduit member by a hinge portion so that the flapper angularly deflects out of the plane of the orifice in response to fluid flow through the conduit member to vary the effective fluid flow cross-sectional area of the orifice in proportion to the flow rate of fluid through the conduit member, and a pressure sensing tap on either side of the flapper. A deflection-limiting surface is provided in the conduit member adjacent the hinge portion. The hinge portion abuts against the deflection-limiting surface when the flapper experiences an angular deflection at least equal to a predefined angle in response to a fluid flow rate that is at least equal to a predetermined value, whereby overstressing of the hinge portion is minimized.