What is a waterflow switch in a fire suppression system?

Waterflow switches detect the movement of water in wet sprinkler system pipes. An alarm signal will be activated no more than 90 seconds after waterflow is detected. Under normal conditions there is no reason for water to flow through the fire suppression system, so the activation of a waterflow switch will either indicate that a sprinkler head has been activated by heat, or there is a rupture in the lines. There are several types of waterflow switches, including vane (paddle) type, piston (shuttle) type, and thermal dispersion flow switches.