This is the second installation of a three-part series introducing the new publication, Fire Sprinkler Systems Monitoring Application Guide. Waterflow detectors are the focus of this article. A subsequent article will feature pressure switches. The previous article discussed supervisory switches.
The main goal of a sprinkler system is to provide a steady supply of fire extinguishing material that’s ready to burst into action should a fire break out. A properly installed and maintained automatic fire sprinkler system can help save lives by dramatically reducing the heat, flames and smoke produced in a fire, allowing people time to evacuate.
Waterflow detectors, which are installed in fire alarm sprinkler systems, monitor the flow of water to sprinkler heads with a specially designed paddle. Waterflow detectors are extremely useful as security and safety tools because they eliminate the possibility of sprinkler malfunction.
Vane or paddle type water flow detectors are used to detect the flow of water in a wet pipe sprinkler system and to send an alarm signal. Water flow detectors can be mounted to vertical up flow or horizontal run distribution pipes in wet pipe sprinkler systems.
The detectors include a plastic vane or paddle, which installs through an opening in the wall of the distribution pipe. When the flow of water is greater than 10 gallons per minute, the vane or paddle deflects, which produces a switched output, usually after a preset time delay.
To minimize false alarms due to pressure surges or air trapped in the sprinkler system, a mechanical delay is often used to postpone switch activation. Often referred to as a retard, this delay takes the place of the previously mentioned retard chamber in wet pipe systems. If water flow decreases to four gallons per minute or below, the timing mechanism will reset to zero; delays do not accumulate. Time delays are adjustable from 0 to 90 seconds.
Typically, water flow detectors are equipped with dual SPDT (Form C) switches for activation of an alarm panel and alarm bell, or an A/V device. When a water flow detector is connected to a listed sprinkler/fire alarm control panel, the initiating circuit must be non-silenceable. Water flow detectors are designed to be installed in a variety of environments and are approved for both indoor and outdoor applications. U-bolt type water flow detectors are designed primarily for use in commercial applications.
T-tap type water flow detectors are also available and are primarily used in residential applications and branch line signaling in larger systems. The only differences between U-bolt and T-tap style water flow detectors are the methods in which they attach to the pipe. T-tap style water flow detectors also are available without a time delay mechanism.
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Tags: Fire sprinklers, Web exclusive
Posted in Commercial, Design and Installation, Fall 2008, Sprinkler Systems Monitoring
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