In a water-based sprinkler system, which device signals water flow and is often used to initiate alarms in the fire alarm system?

• A. Water flow switch
• B. Pressure relief valve
• C. Alarm valve
• D. Drain valve

Answer: (A)

Detecting water flow to trigger alarms is the key idea. A water flow switch is placed in the sprinkler piping and senses when water starts moving—such as when a sprinkler head is opened by heat. When flow is detected, the switch completes a circuit or sends a signal to the fire alarm control panel, which then activates the building alarms. This direct sensing of actual water movement is what makes the switch the device used to initiate alarm signaling.

The other devices serve different roles: a pressure relief valve protects the system from overpressure, not from signaling alarms; an alarm valve is involved in controlling water entry in dry-pipe or deluge systems and is not the primary sensor that triggers the alarm; a drain valve is used to drain water for maintenance and has no role in signaling fire alarms.