What is a non-return valve and how does it protect a cold water system?

• A. A valve that vents air from the system.
• B. A one-way valve that allows flow in only one direction, preventing reverse flow and backflow into the supply.
• C. A device that senses temperature.
• D. A valve that diverts water to waste.

Answer: (B)

A non-return valve is a one-way valve that allows water to flow in only one direction and blocks it from flowing backward into the supply. In a cold water system, this means water can move from the mains to fixtures and appliances, but if pressure drops or a backflow situation occurs, the valve automatically closes so water and any potential contaminants cannot be drawn back into the potable supply. This prevents cross-connections and back-siphonage, protecting the integrity of the cold water system. The valve opens when there is forward pressure and seals when reverse pressure appears (often with a spring bias). Proper orientation is important for it to function correctly. It isn’t meant to vent air, sense temperature, or divert water to waste.