About Primary Elements

Primary elements enable reliable accuracy, consistent DP flow measurement and long-term process performance.


Ensure Optimal Flow Measurement with the correct Primary Element

For trusted performance in differential pressure (DP) flow measurement, Rosemount and Daniel offer a wide variety of primary element options for a vast range of process conditions. These primary elements can reduce your process penetrations and pipe straight run requirements as well as enable routine maintenace and installation without shutting down your process. 

Primary Element Types

Orifice Plates are inserted into the flow path to create an increase in velocity and decrease in pressure. The difference in pressure is then measured and converted into a DP flow measurement for a simple measurement solution. Easy-to-install and resilient in extreme process conditions, this solution is widely used for gas, liquid and steam applications, including high temperature and high pressure environments.


The Rosemount Conditioning Orifice Plate is designed with four, equally spaced orifices that help resolve irregular flow profiles. Requiring only 2 diameters upstream and downstream of pipe straight-run, this element eliminates the need for separate flow conditioners and piping modifications. Options reduce the need for impulse lines or special flanges and are an ideal solution for applications with limited space.


Averaging Pitot Tubes, like the Rosemount Annubar™ primary element, obtain the flow rate in a pipe or duct by measuring the velocity pressure over a cross-section of the process, averaging the result. With several measurement ports over the length of the element, an averaging pitot tube obtains a highly accurate velocity average with minimal permanent pressure loss. It can be installed while the pipeline is under pressure (hot-tapped) and provides outstanding performance in steam applications.


Venturi Tubes are low-pressure-drop metering devices designed with a tapered inlet that creates a drop in pressure with a constricted middle section and restores pressure through a tapered outlet. This element provides low susceptibility to erosion, high-pressure recovery and installation at any angle. With low installation costs and virtually maintenance-free operation, Venturi tubes perform well in a range of conditions, such as carbon dioxide, wet gas and low pressure loss applications. 


Flow Nozzles feature an elliptical inlet that increases velocity, decreases pressure and leads into a cylindrical throat to DP measurements. This design allows sweep-through of particles in the flow stream, reducing risk of nozzle damage. Directly welded into the line to reduce potential leaks, this nozzle is also erosion- and corrosion-resistant and performs well in many high temperature and high velocity applications, including water, vapor, steam and gas.

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