Orifice Plates

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The orifice plate is an instrument used for measuring flow rate. Either a mass or volumetric flow rate may be defined, depending upon the calculation linked with the orifice plate. It uses the principle namely Bernoulli’s principle which says that there is a relation between the pressure and the velocity of the fluid: when the pressure of the fluid increases, the velocity of the fluid decreases and vice versa.

Description of the Orifice plate

An orifice plate is a thin metal plate with a hole in the middle.  The orifice plate is placed in a pipe in which fluid flows. When the fluid arrives at the orifice plate, the fluid is forced to assemble to go through the small center hole; the level of maximum convergence occurs soon downstream of physical orifice, at vena contracta point. 

By calculating the difference in fluid pressure across tappings downstream and upstream of the plate, the mass and volumetric flow rates can be obtained from Bernoulli’s equation.

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Orifice plates are used to measure flow rates in pipes, when the flow is continuous instead pulsating, the fluid is well-mixed and single-phase, the fluid fills the entire pipe, the flow profile is even and the fluid and flow rate satisfy certain other conditions. Under these conditions when the orifice plate is constructed and installed as per appropriate standards, the flow rate can easily be determined using published formulae based on substantial research in industry, following national and international standards. 

Plates are made with sharp edged circular orifices and placed concentrically with pipe and with pressure tappings at one of three standard pairs of distances downstream and upstream of the plate; these are covered by ISO 5167, ASME MFC-3M, and different major standards. 

Different sizes

There are many other possibilities. The edges may be conical or rounded, the plate may have an orifice a similar size as the pipe excluding a segment at the top or bottom which is obstructed, the orifice may be set eccentric to the pipe, and the pressure tappings might be at other positions. Each combination leads to different coefficients of discharge which can indicate as long as various conditions are met, conditions which may vary from one type to another. 

When the orifice plate is designed and installed, the flow rate can be indicated with an acceptably low uncertainty only by taking the square root of the differential pressure across the orifice’s pressure tappings and using an appropriate constant. Even compressible flows of gases that vary in temperature and pressure may be evaluated with acceptable doubt by simply taking the square roots of the absolute pressure or /and temperature, depending upon the goal of the measurement and the costs of ancillary instrumentation.

Regular orifice plates, also sometimes referred to as paddle type orifice, are the simplest designed type of primary flow elements. We machine these in various stainless steel grades from AISI 316 to Hastelloy, Inconel or any exotic material needs you might have. They are easily installed and easy to replace. Installation of orifice plates required orifice flanges ASME B16.36

We also manufacture orifice plates with built in tappings, whether it is single pressure tappings or annular chamber (piezometer rings), thus eliminating the need for orifice flanges.

All our orifice plates assemblies and meter runs are designed according to ISO 5167-2 ensuring accuracy and durability. These are ideal for remote mounting of DP transmitters.