Differential Pressure Flow

Differential Pressure Flow

Differential Pressure Flow Measurement infers flow rate from the pressure drop created by a primary element installed in a pipe. Orifice plates, Pitot tubes, and Venturi tubes generate a differential pressure that increases with flow; a DP transmitter measures that differential and calculates the flow rate. The method is broadly applied to gases, vapors, and liquids and remains a reference approach where standards-based design and calculation transparency are priorities.

Versatility under demanding mechanical conditions is a major advantage. DP elements and transmitters can be specified for high process pressures and elevated temperatures, supporting steam service and harsh process environments. A single DP transmitter family can also address adjacent measurement tasks - level measurement via hydrostatic head and filter monitoring via differential pressure - reducing hardware diversity and simplifying spare parts strategies.

The measurement chain is explicit: primary element geometry, impulse connections, and transmitter characterization. Compensation for pressure, temperature, and density can be applied when mass or standardized volumetric flow is required, while square-root extraction can be handled in the transmitter or control system. When paired with pre-assembled, pressure-tested valve blocks and disciplined impulse-line practices, DP installations can be maintainable and stable over long operating intervals.

Typical applications include saturated and superheated steam distribution, boiler and burner control, natural gas and process gas measurement, and general-purpose liquid service where permanent pressure loss is acceptable. DP is also common on large pipe sizes and in retrofit situations where a primary element can be installed without replacing long spool sections. In utility headers, consistent element selection supports balancing and allocation across parallel runs.

Design tradeoffs include permanent pressure loss, straight-run requirements, and sensitivity to erosion, fouling, or impulse-line plugging in dirty services. Accuracy depends strongly on installation geometry and primary element condition, so inspection and documentation become part of the lifecycle plan. Where extremely wide turndown or ultra-low flow sensitivity is critical, alternative technologies may be preferred, but DP remains a proven, economical option when engineered to the process conditions.

Forberg Smith, an exclusive authorized representative of sales and service for Endress+Hauser.