Differential Pressure Flow

Differential Pressure Flow

Differential pressure (DP) flow measurement determines flow by measuring the pressure drop created when a primary element is installed in the line. Devices such as orifice plates, pitot tubes, or Venturi tubes generate a differential pressure that is sensed by a DP transmitter, which then calculates flow from the measured value.

A key advantage of DP flow is broad applicability across gases, vapors, and liquids, including services with high pressures and elevated temperatures. This approach remains widely applied because it is grounded in well-established fluid dynamics and standardized design practices, and can be engineered around demanding materials and mechanical constraints.

DP flow assemblies are often selected when line sizes are large, when very high temperatures exceed sensor limits, or when an engineered primary element is already specified by project standards. In energy and utility services, DP-based measurement supports saturated and superheated steam, compressed air, and fuel gas metering, particularly where density compensation and energy calculations are handled in a flow computer or control system.

Installation and performance depend heavily on correct primary-element sizing, pressure-tap arrangement, and available straight-run conditioning to manage swirl and asymmetry. Because the flow relationship is non-linear (square-root), turndown and low-flow sensitivity must be evaluated carefully, and impulse line design should be addressed to avoid plugging, freezing, or condensation errors. Proper materials, manifolds/valve blocks, and maintenance access typically drive lifecycle reliability.

Selection should balance required uncertainty, allowable permanent pressure loss, and the operational cost of lost head versus installed capital. DP measurement is often the most economical path for large pipe sizes and extreme process conditions, while still providing stable, continuous indication when engineered, installed, and maintained as a complete system.

Miller Mechanical Specialties, an exclusive authorized representative of sales and service for Endress+Hauser.