What does a control valve do in a water-based system?

• A. It increases water pressure.
• B. It filters impurities from water.
• C. It sounds alarms when water moves.
• D. It allows the system to be isolated for maintenance or testing and to control water flow.

Answer: (D)

Control valves regulate and isolate the movement of water in a system. They can be opened, closed, or throttled to set the flow rate and pressure in different parts of the system, and they provide a way to shut off a section for maintenance or testing without draining the whole system. This combination of controlling flow and enabling isolation for service is what makes this option the best choice.

Increasing water pressure is not the primary role of a control valve (pumps or pressure-regulating devices handle pressure changes). Filtering impurities is done by filters, not valves. Alarms are the job of sensors and monitoring equipment. The ability to isolate for maintenance or testing while controlling water flow captures the essential function of a control valve.