Differential Pressure Flow Measurement

• Measurement of gases, steam, liquids and slurries
• Many options for materials of construction*
• 3.1 or 3.2 Materials Traceability & NACE Compliance
• ¼”NB 48″NB [DN8 to DN1200]
• ASME, API, PN Rated Process connection to suit all requirements
• Design Pressures & Temperature to customer requirements
• Non-Destructive Testing
• Calibration
• PED / PE(S)R Compliance

Differential pressure or DP flow meters work by introducing a restriction to the pipe flow. The partial restriction on the flow increases the velocity of the fluid as it passes through and consequently, the pressure reduces. The difference in pressure between the upstream and downstream is measured by a differential pressure transmitter and using Bernoulli’s principles, the flow rate is calculated.

DP flow meters are split into two elements, a primary element that introduces the pressure drop, and a secondary element that measures the difference in pressure. Orifice plates, for example, are referred to as a primary flow element and the DP flow transmitter is referred to as the secondary element. EMI specialise in the specifying and manufacture of primary differential flow elements.

Orifice plates are used in a piping system to measure the flow of a liquid or gas. They are a primary DP flow element that restricts the flow via an orifice or bore. Paddle type, concentric orifice plates are the most common type consisting of a machined disc with a precise concentric bore and a tab handle. However, other designs exist depending on the application. Orifice plates are mounted concentrically using a pair of orifice flanges or a purpose-built carrier. Their design and limits of use are largely covered in ISO 5167-2 or ASME MFC-3M. Each orifice plate, as with all differential pressure devices, require at least one pair of pressure taps, one upstream, and one downstream of the plate, to measure the difference in pressure caused by the bore. Pressure taps are typically located within the orifice flanges or the carrier.

This is a relatively simple piece of technology which can provide a high level of accuracy without the need for additional time-consuming calibration.