Abstract: A fluid flow meter that includes a flow tube having a fluid flow input and a fluid flow output, the tube also having a peripheral wall that defines a generally circular flow cross-section. A round measuring orifice is provided in the tube and between the input and the output. A contoured plug is slidably mounted in the orifice on an axial slide, the plug being normally biased toward the inlet so as to close the orifice. The plug is of a curvilinear tapering cross-section, the curvature of which is such as to produce a linear relationship between differential pressure across an annulus formed by the coincidence of the plug and the orifice and between the flow through the annulus. A fluid flow indicator serves to indicate the fluid flow through the flow tube.

Abstract: A fluid flow meter comprising a flow tube of generally circular cross section in which is mounted a pair of generally semicircular vanes arranged for pivotal movement about a common diametral axis, said vanes being biased by resilient means into positions so as to close the tube and fluid flow indicating means for measuring gas flow rates in the range including flare gas flows and furnace combustion air flows.