Differentialtrycket

Differentialtrycket, or differential pressure, is the difference in pressure between two points in a fluid system. It is denoted ΔP and defined as ΔP = P1 − P2, where P1 is typically the upstream pressure and P2 the downstream pressure. The sign convention follows the direction of flow: a positive ΔP indicates a pressure drop as fluid moves from the first point to the second.

Differential pressure is measured with devices such as manometers and differential pressure sensors. A U-tube or inclined manometer uses a liquid column to compare two pressures. Modern instrumentation often uses sensors with a diaphragm that senses the pressure difference and outputs an electrical signal (for example 4–20 mA) to a control system. Differential pressure transmitters and gauges are common in process plants, HVAC systems, and laboratory setups.

In many applications, ΔP is used to infer flow or to monitor system health. For incompressible flow through a restriction or orifice, the flow rate is related to the square root of ΔP (Q ∝ sqrt(ΔP)), modulo discharge coefficient and fluid density. In pipe networks, the pressure drop due to friction can be described by relations like the Darcy–Weisbach equation, ΔP = f (L/D) (ρ V^2 / 2). Accurate interpretation requires knowledge of fluid properties, temperature, and the measurement location.

Applications include monitoring filter or membrane fouling, ensuring proper operation of burners and heat exchangers, and safeguarding process equipment. Proper calibration, installation, and temperature/density compensation are important for reliable differential pressure measurements.