Differential Pressure (DP) Flow

DP Flow Technology

Differential pressure (DP) flow measurement is a well-known and common technology for measuring flow in a closed pipe. DP flow solutions are made up of two elements to measure flow, a primary element, which introduces a pressure drop, and a secondary element (a DP flow transmitter) to measure the differential pressure flow. This technology uses Bernoulli’s equation to calculate the flow of the medium in the pipe.

Yokogawa offers a complete solution for measuring DP flow with a range of technologies. These include integral orifice plates, averaging pitot tubes (VERIS Verabar®), and nozzle type (VERIS Accelabar®).

Advantages of DP Flow Measurement

  • Simple devices with no moving parts
  • Less expensive compared to other flow technologies
  • Installation can be in any orientation
  • Can be used for most gases and liquids
  • Maintenance is similar to that of pressure transmitters
  • Draft Pressure instruments are a unique type of differential transmitter that is designed to measure small differences in very low static pressure environments.

Volumetric Flow Rate

Volumemetric flow rate is the volume of fluid which passes per unit of time. Common units of measaure are litres / sec (l/s) or Cubic feet per second (ft3/s).

Differential pressure flow meter uses a variation of Bernoulli’s principle to infer the volumeetric flow rate in a pipe. For our application of the principle, it states that the velocity of the flow increases and the pressure decreases as the flow moves through a restriction in the pipe; therefore, the pressure is higher before the restriction than after. Knowing this differential pressure, the flow rate can be determined. The square root of the differential pressure across the restriction in the pipe is proportional to flow.

Mass Flow Rate

Mass flow rate is the amount of mass of a substance which passes per unit of time. Common units of measaure are Kg/s or lbs/min.

This type of measurement needs more detailed input than just differential pressure. It also needs temperature, static pressure of the line, the composition of the fluid, and more information of the primary element. 


Differential Pressure Flowmeters consist of a Primary Element, a Secondary Element, and possibly Tertiary Elements

Primary Element: The Primary Element generates the differential pressure in the fluid. Primary Elements can be an averaging pitot tube, an integral flow orifice (IFO), or any number of DP producing devices.

Secondary Element: The Secondary Element is the pressure transmitter that is used to measure the DP. The secondary element may or may not include a flow computer with temperature and static pressure input.

Tertiary Element: The Tertiary Elements consist of flow computers, gas chromatographs, static pressure transmitters, or temperature transmitters.

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