NFPA 72 code sections · Devices & Signal Flow: How the Panel Hears and Speaks
Waterflow switch: the sprinkler system reporting that it is fighting a fire
When a sprinkler head opens, water moves in the pipe. A vane-type or pressure-type waterflow switch senses that movement and, after a short retard to ride through surges, sends an alarm signal to the panel — the code requires the alarm to be initiated within 90 seconds of a flow equal to one sprinkler. The panel treats it exactly like any other alarm: notification appliances within 10 seconds, emergency control functions per the matrix, transmission to the supervising station. Many buildings also ring an outside water-motor gong or bell at the riser so the fire department can find the connection.
NFPA 72 reference
Chapter 17 — Initiating Devices
17.12 Sprinkler Waterflow Alarm-Initiating Devices (17.13 in some editions): 17.12.2 alarm initiated within 90 seconds of waterflow; 10.11.1 10-second panel response; Chapter 26 transmission to the supervising station
References use NFPA 72 2019/2022 numbering — section numbers can shift between editions, so confirm in the edition your AHJ has adopted.
On the job, step by step
- A sprinkler head opens over a storage rack on the ground floor at 2 a.m.
- Water flows past the riser's vane switch; the retard times out at about 30 seconds and the switch sends an alarm to the panel.
- The panel declares a waterflow alarm, activates building notification within 10 seconds and recalls the elevators per the matrix.
- The communicator sends 'WATERFLOW — RISER 1' to the supervising station, which dispatches the fire department.
- The alarm cannot be cleared at the panel until the sprinkler control valve is closed and the flow stops — then the switch restores and the panel can be reset.
Quick check
1. A waterflow switch must initiate an alarm within:
2. The panel treats a waterflow signal as a(n):
3. The waterflow switch's retard exists to:
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