ABSTRACT
Head-type flow meters comprise a class of devices for fluid flow measurement including orifice plates, venturi tubes, weirs, flumes, and many others. They change the velocity or direction of the flow, creating a measurable differential pressure or “pressure head” in the fluid. Two fundamental characteristics of head-type flow measurements are apparent from the basic equations. First is the square root relationship between flow rate and differential pressure. Second, the density of the flowing fluid must be taken into account both for volume and for mass flow measurements. For a large proportion of industrial processes, which seldom operate below 30% capacity, a device with pointer or pen motion linear with differential pressure is generally adequate. Readout directly in flow can be provided by a square root scale. The basic equations of flow assume that the velocity of flow is uniform across a given cross section.
