Differenialdruk

Differenialdruk refers to the difference between two static pressures within a fluid system, indicating the driving force that causes flow from the higher-pressure point to the lower-pressure point. It is usually denoted as ΔP and measured in pascals (Pa), kilopascals (kPa), or pounds per square inch (psi). Positive values mean that the upstream point has higher pressure than the downstream point.

Measurement and instrumentation: Differential pressure is measured with devices such as differential manometers (including U-tube and inclined types) or electronic differential pressure transmitters that output a signal corresponding to the pressure difference. The sensing elements are typically diaphragms or bellows, and must be compatible with the process fluid and temperature. Tappings are placed on upstream and downstream sides of a flow element, such as a valve, orifice plate, filter, or pipe section.

Applications: In HVAC, differential pressure across air filters indicates clogging or the need for maintenance. In process engineering, it is used to monitor and control flow by relating ΔP to flow through a meter or restriction via the element’s characteristic. In filtration and separation, ΔP reflects performance of membranes or filters. In fluid dynamics more generally, differential pressure is a key variable in equations such as Darcy–Weisbach and Hagen–Poiseuille, which relate pressure drop to flow rate, density, viscosity, and geometry.

Considerations: The measured ΔP depends on fluid density (and thus temperature and pressure for gases), viscosity, and compressibility. Proper installation, tapping, and isolation are required to avoid errors from vibrations, pulsations, or leaks.