Check valve

A check valve (or non-return valve) is a simple automatic valve that allows water to flow one way and closes to stop it flowing back. Unlike a gate valve, which you open and shut by hand to isolate a supply, a check valve has no handle — it reacts to the flow itself, opening under forward pressure and snapping shut the instant flow tries to reverse. In UAE homes you'll typically find them on booster-pump discharge lines, tank feeds and the cold inlet of some water heaters, where they stop a pump losing its prime or hot and cold water crossing over. A check valve is not the same as a backflow preventer — that's a tested assembly (often containing check valves) that protects the city mains from contamination; a plain check valve just stops reverse flow inside your own system. When one fails the signs are fairly clear: a booster pump that short-cycles or hammers (see water hammer), water draining back and the pump losing prime, or hot water pushing into the cold line. A seized or leaking check valve is a straightforward swap for a plumber in Dubai, who will size the replacement to the pipe and set it the right way round for the flow.