An electrically operated valve, known as the pre-action valve, keeps water from entering pipes. This valve is controlled by flames, heat or smoke detection.
To initiate sprinkler discharge two separate events must take place.
- First, the detection system must detect a developing fire and then open the pre-action valve allowing water to flow into the pipes before sprinklers are set off.
- Second, once the heat activates sprinklers, water flows through immediately, like a wet pipe system.
Pre-action systems are most commonly used in freezer warehouses. Pre-action systems act faster than Dry systems , but are usually more expensive and require regular maintenance to ensure reliability.