Differential Pressure Flow

Differential Pressure Flow

Differential pressure (DP) flow measurement determines flow by measuring the pressure drop created when a primary element constricts or conditions the stream. The approach is used for continuous measurement in liquids, gases, and vapors, and remains a widely accepted solution where standardized primary elements, broad temperature/pressure capability, and established calculation methods are valued.

In a typical implementation, an orifice plate, pitot tube, or Venturi tube generates a differential pressure that is sensed by a DP transmitter. The transmitter converts the measured ΔP into a flow value using the selected sizing and calculation parameters, so the metering performance is a combined result of the primary element geometry, the transmitter accuracy, and the fluid property assumptions used for compensation.

DP technology scales effectively from standard services to demanding duties with elevated pressures and temperatures, provided impulse piping, manifold/valve block design, and wetted materials are matched to the service. Universal DP transmitters can support related measurements such as level and filter monitoring, and pre-assembled, pressure-tested valve blocks can simplify installation and commissioning while reducing field assembly variability.

Typical applications include steam and utility metering, burner and boiler control, compressed air and fuel gas monitoring, and flow measurement in chemical and petrochemical units. With appropriate primary elements and compensation, DP measurement also supports mass flow calculations and standardized volume reporting, and can be extended into filtration and exchanger ΔP monitoring where the same transmitter platform is leveraged for multiple process indicators.

Successful specification centers on primary-element selection and sizing (beta ratio, Reynolds number, allowable permanent pressure loss) and on the quality of installation details such as tapping geometry, impulse line routing, and condensate/plugging management. Because the measured signal is proportional to the square of flow, low-flow sensitivity and turndown are influenced by both transmitter range and the chosen primary element. Where density varies materially, integrating temperature and pressure compensation into the transmitter or flow computer is typically required to maintain mass or standardized volume accuracy and to avoid bias during transients.

George E. Booth Co., an exclusive authorized representative of sales and service for Endress+Hauser.