An introduction to differential pressure (DP) flow
From orifice plates to Pitot tubes, explore our full portfolio of DP flow solutions designed for accurate monitoring and control.
DP flow is a method of measuring fluid flow by detecting the pressure difference across a restriction in the pipe. Primary DP flow elements have a long history of achieving high accuracy readings and durability in a wide variety of industries. The selection of the correct primary element is affected by the process conditions as each element has ideal scenarios. Endress+Hauser offer a wide variety of primary elements that can be utilised across a vast range of process conditions.
Primary elements
Primary elements are the key components within DP flow, and they come in a wide variety. These elements can consist of many different designs and options to accommodate a diverse range of line sizes and flow conditions. Some examples of primary elements include orifice plates, Pitot tubes, Venturi tubes and flow nozzles. The main purpose of the primary elements is to create a restriction within the pipework to create a pressure drop that can be measured.
Flowmeters
Differential pressure flowmeters have three key elements: the primary element creates a pressure drop via a pipe restriction (e.g. plate or constriction), enabling flow rate calculation using Bernoulli’s equation. The secondary element, typically a DP transmitter, measures this drop. The tertiary element includes the rest of the system - connectors, impulse piping, and supporting components.
Flow calculations
Flow calculations are used to study and understand the characteristics of the flow in a pipe section. DP flow is proportional to the square root of differential pressure which means that pressure is a critical component in the calculations of DP flow. There are other factors that influence mass flow (Qm), including density, viscosity, temperature, pipe diameter and fluid type.
Qmass = NCDY1 Ed2 √DP(ρ)
N = Dimensional constant
CD = Discharge coefficient
Y1 = Expansion factor
E = Expansibility factor
d = Orifice diameter
V = Dimensional constant
