A water flow detector, commonly produced by System Sensor, is an electro-mechanical device designed to send an alarm to a fire alarm panel and/or fire department when a continuous flow of water occurs through the fire sprinkler system’s piping from an activated sprinkler head or leak in the system.

The water flow detector includes a plastic vane or paddle that is installed through an opening (or hole) in sizes two-inch through eight-inch schedule 10 or schedule 40 fire sprinkler pipe (see diagram below), either vertically or horizontally. If water flow greater than 10 gallons per minute is detected, the vane or paddle triggers a switch sending a signal to an alarm panel and bell.

Flow Switch Diagram

Picture courtesy of System Sensor

What about false alarms? As you’ve learned thus far, this device relies on accurately reading the flow of water through a pipe and water flow is not a constant. Surges in water pressure happen regularly – as an example, ever been in the shower when someone flushes a toilet?

System Sensor’s water flow detector has a mechanical delay mechanism. Essentially, this timer, which can be set from 0 to 90 seconds, delays the alarm-triggering mechanism long enough to ensure that the change in water flow is not a one-off incident but rather a constant flow resulting from an activated sprinkler or serious leak. If water flow decreases to four gallons per minute or less, the water flow detector resets.

For optimal performance, water flow detectors should be mounted in an area where there is adequate room to service the device and it will not be damaged by normal nearby activity. Other general installation rules include:

  • The flow switch should be mounted six to seven feet above the ground.
  • On horizontal pipe, it should be mounted on the top to avoid rust or particle accumulation from interfering with its operation.
  • On vertical pipe, it should be mounted where there is an upward flow of water.
  • Other general rules include mounting the device at least 6 inches from fittings that change the direction of water flow and at least two feet from a drain or valve.

The primary electrical components of a flow switch can be replaced without draining the fire sprinkler system. If a flow switch is showing signs of wear and tear, is leaking, or otherwise non-functional, it should be replaced by a qualified fire sprinkler contractor immediately.

System Sensor Waterflow Detector

At QRFS, we offer System Sensor flow switches in sizes ranging from 2 1/2″ to 8″. Combined with our superior customer service and extremely fast shipping, you won’t need to look anywhere else when you’re in the market for a fire protection flow switch. And as always, they are UL/FM approved and come standard with a 3-year warranty.

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This blog originally posted by Jason Hugo at QRFS.com/blog on February 26, 2013, and updated on January 1, 2019. If you like what you’ve read, check us out on Facebook or Twitter.