Hattersley Pressure Reducing Valves (PRVs) are devices used in plumbing and public health systems to automatically lower a higher inlet pressure (e.g. from boosted cold water supplies) to a stable, safe outlet pressure suited to site requirements. They are made in various materials such as DZR brass (e.g. Fig. 425) for smaller sizes or cast/ductile iron for larger sizes (e.g. Fig. M416/M425) include integral strainers to protect the control mechanism and are adjustable over a range of outlet pressures (often ~ 0.5–8 bar) depending on model