Brass non-return valves (NRVs), are automatic, one-way valves constructed from brass, designed to prevent backflow in plumbing, water, and fuel systems. They use a, typically spring-loaded, internal disc to allow forward flow and automatically close when pressure reverses, ensuring system integrity and preventing, for instance, contamination or pump damage. They function automatically without human intervention, opening at low cracking pressures and sealing tightly against reverse flow.