Pressure

Pressure is the driving force of filtration—applied as overpressure, vacuum, or a combination that creates transmembrane pressure (TMP). According to Darcy’s law, flux increases with pressure but is limited by medium and cake resistance as well as fluid viscosity. In practice, two regimes exist: constant-pressure operation (flow decreases as cake resistance increases) and constant-rate operation (pressure rises to maintain flow). Compressible cakes can lose porosity under excessive pressure, reducing permeability. Proper instrumentation—accurate pressure taps, temperature compensation, and calibration—is essential to ensure readings reflect the filtration zone, not piping effects. Specifications must define allowable ranges, pressure limits of media and housings, and safety interlocks. Optimising pressure means achieving clarity, washing efficiency, and dryness at minimal energy input without damaging media or seals.