Generally, valves are mechanical devices used in plumbing water supply systems to control, regulate, or stop the flow of water in the system. They work by opening, closing, or partially obstructing an internal passage, allowing users to start/stop flow, isolate sections of piping, or adjust flow rate and pressure as needed. Valves are critical for both normal operation and maintenance, enabling individual fixtures or system segments to be serviced without shutting down the entire system. Common types include shutoff valves, like ball valves and supply stops; hydrants that offer freeze protection, needle valves, and specialty valves such as thermal expansion or mixing valves. Valves are typically manufactured from brass, or engineered plastics, and are configured to suit specific applications.