The orifice plate flow meters use the principle of a flow restriction creating a differential pressure to measure the flow rate of liquids, steam and gases. The orifice flowmeters consists basically of the orifice plate that creates the flow restriction and device that measures the differential pressure created by the orifice plate.
The orifice plate calculations used nowadays still differ from one another, although various organizations are working to adopt an universally accepted orifice flow equation. Orifice plate sizing programs usually allow the user to select the flow equation desired.
The orifice plate meter can be made of any material, although stainless steel is the most common. The thickness of the plate used (1/8-1/2") is a function of the line size, the process temperature, the pressure, and the differential pressure.