flow switch sprinkler

A water flow detector, also known as a flow switch, is an electro-mechanical device designed to send a signal to a local alarm or monitored panel and/or fire department when a continuous flow of water occurs through a fire sprinkler system’s piping. This flow signifies an activated sprinkler head or a leak in the system.

A vane-type 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. Some water flow detectors can also install in 1 in., 1-1/4 in., 1-1/2 in. and 2 in ferrous and brass threaded tees; 1 in., 1-1/4 in., and 2 in. copper sweat tees; or 1 in. CPVC tees. 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.

What about false alarms? As you’ve learned thus far, the 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?

That’s why Safe Signal’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 a horizontal pipe, it should be mounted on the top to avoid rust or particle accumulation from interfering with its operation.
On a 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 device is showing signs of wear and tear, is leaking, or is otherwise non-functional, it should be replaced by a qualified fire protection contractor immediately.

At QRFS, we offer Safe Signal vane-type water flow detectors in sizes ranging from 1″ 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 manufacturer’s warranty.

What is a flow switch in a sprinkler system?

Paddle-type, also known as vane-type, flow switches are used in wet sprinkler systems to detect the flow of water and to send an alarm signal. 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.

Browse All QRFS Safe Signal Waterflow Detectors

This blog was originally posted by Jason Hugo at blog.qrfs.com on February 26, 2013, and updated on April 22, 2022. If you like what you’ve read, check us out on Facebook or Twitter.CategoriesFire Sprinkler System Components, Fire Sprinkler Systems

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What is a flow switch in a sprinkler system?

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What's a Flow Switch or Water Flow Detector in Fire Sprinklers?