The different installation versions of the primary flow sensors (orifice plates, flow nozzles, venturis) of differential pressure flow meters commonly used in flow measurement are tabulated below:
|Primary Element||Type of Primary Element|
|Orifice Plates||Corner Pressure Taps|
|Flanged Pressure Taps|
|D and D/2 Pressure Taps|
|Flow Nozzles||ISA 1932|
The graph below shows the percentage pressure loss against beta ratio (beta = d/D) for orifice plates, flow nozzles and venturis:
(a) Orifice plates are universal in their use in differential pressure flow meters but have the basic disadvantage of high pressure loss.
(b) Flow nozzles are characterized by lower pressure drops compared to orifice plates
(c) Venturis (Venturi tubes and Venturi nozzles) are characterized by much smaller pressure drops compared to orifice plates and flow nozzles.
The table below summarizes the various application limits with respect to bore or throat diameters(d), internal diameter of pipes (D), beta ratio (β =d/D) and pipe Reynold’s number (Re) for orifice plates, flow nozzles and Venturi flow meters:
|Flow meter parameters||Orifice Plates||Flow Nozzles||Venturis|
|Corner Pressure Taps||Flanged Pressure Taps||D and D/2 Pressure Taps||ISA 1932||Long Radius||Venturi Tube||Venturi Nozzle|
|Re, Dmin||5,000 - 20,000||2,500 - 540,000||2,500 - 540,000||20,000||10,000||200,000||150,000|