Pressure regulators (monostats) actively maintain a set output pressure through automatic adjustment and are classified here. Pressure-relief valves open only when pressure exceeds a safety threshold and are classified under the heading for taps, cocks, valves, and similar appliances. The key distinction is whether the device continuously regulates pressure or merely provides a safety release.

Both mechanical and electronic pressure controllers performing an automatic regulating function fall within this heading. The presence of a digital display or electronic sensing element does not move the article to a different heading, though it may affect the applicable subheading. Importers should verify the subheading based on the device's operating principle and construction.