Concentric: This type of orifice plate is most common amongst all the three types. In this design, the orifice is equidistant i.e. concentric to the inside wall of the pipe. A concentric orifice plate is generally employed for clean liquids, gases, and steam flows specifically in pipes under six inches, where Reynolds numbers range from 20,000 to 107.
Segmental: These types of orifice plates are almost the same as concentric orifice as far as their functioning is concerned. In a segmental orifice, the circular section is concentric with the pipe while the segmental part is mounted in a horizontal pipe. This installation helps in eliminating damming of foreign materials on the upstream side of the orifice. Based upon the type of liquid, the segmental section is positioned on either the top or bottom of the horizontal pipe. This arrangement results in better accuracy of the measurement. Another variation of segmental orifice is segmental wedge which is essentially designed to detect the flow of liquids containing solids. This unit is easy to design and capable enough to measure flows at low Reynolds numbers. Furthermore, the pressure drop through the unit is merely around half that of customary orifices.
Eccentric: Eccentric orifice plates are designed in such a way that the edge of the orifice is reallocated towards the interior of the pipe wall. Owing to this design upstream damming gets avoided. It is employed in the same manner in the segmental orifice plate as well.
All the three kinds of orifice plates are shown in figure below:
Concentric Orifice Plates