Orifice Plates
Orifice plates are the simplest and conventional method for the measurement of flow rate in the industries.
Because of its low price, low maintenance and high accuracy, it is commonly used in oil and gas services.It is the most common head type flow measuring device.
An orifice plate is inserted in the pipeline and the differential pressure across it is measured.
Types of Orifice Plates
The simplest form of orifice plate consists of a thin metal sheet,
having in it a square edged or a sharp edged or round edged circular hole.
There are three types of orifice plates namely
1. Concentric
2. Quadrant Edge
3. Conical Edge
4. Eccentric
5. Segmental type.
The concentric type is used for clean fluids and low velocity vapour flows.
It is a sharp, square-edged hole bored in a flat, thin plate. The ratio of the hole diameter, d, to the pipe diameter, D, defines the beta ratio.
For most application this ratio should be between 0.2 and 0.75.
When the pipe Reynolds number is below 10000, the upstream orifice plate shall be used either quadrant edge or conical edge.
These contours give a more constant and predictable discharge coefficient at lower Reynolds number.
It is really immune to the effect of corrosion, erosion and the deposit of solids at the surface of orifice.
In metering dirty fluids, slurries and fluids containing solids, eccentric or segmental type is used in such a way that
its lower edge coincides with the inside bottom of the pipe.
This allows the solids to flow through without any obstruction.