In ventilation systems, the differential pressure can be used to determine the degree of contamination in a filter when the pressures are measured in front of and behind the filter. The more contaminated the filter element is, the more resistance there is against the medium flowing through it.
A common application of differential pressure is flow rate measurement in pipes. This differential pressure method requires a primary element to be installed in the pipe. Primary elements are available in various designs and taper the pipe cross-section at the measuring point. This results in a local increase in the flow velocity at the point of constriction, which in turn results in a change to the static pressure (p1 stat and p2 stat). The pressure connections for measurements are located directly in front of and behind the primary element. The pressure difference is an indirect measure of the flow.