Douglas Krantz - Technical Writer - Describing How It Works

Why did the Waterflow Switch Shorten Its Delay?

By Douglas Krantz | Suppression

Why did the Waterflow Switch Shorten Its Delay?

Why did the Waterflow Switch Shorten Its Delay?

Greetings Douglas,

We are questioning a billing for a repair of our Fire Alarm Flow Switch here at our facility. We have a platinum service contract for the fire alarm and sprinkler system.

The vendor is stating that "Replacing the defective flow switch is chargeable. The delay timers are mechanical and are typically testing during our semi-annual sprinkler inspections. They do come out of adjustment over time, but we do check them semi-annually."

Is this possible for them to come out of adjustment over time? Our system was inspected six months ago. At that time, the 2nd floor flow switch was set at 43 seconds. Now, on the inspection, the 2nd floor flow switch had "zero delay". Just wondering, please let me know and thank you for your time.

Thank you, P

A waterflow switch is attached to the fire suppression sprinkler pipe

A waterflow switch detects when water is actually moving in the sprinkler system.

A waterflow switch consists of a paddle, to be pushed aside when water is flowing, a lever, an air damper, and a switch

When water flows, a paddle is pushed by the water, and that releases the adjustable air-damper. Because of changing water-pressure from the city, water will often push this paddle for a few seconds. Without the air-damper, this momentary movement would sound the alarms.

The air damper slowly releases air from inside the dashpot, and when enough air is released, them the switches themselves are activated.

Inside the waterflow switch assembly is a retarder, with an adjustment dial

In order to increase or decrease the delay caused by the air-damper (retarder), at the bottom of the dashpot is an air releasing adjustment.

Rubber Diaphragm

The issue with the shortening delay is that part of the air-damper assembly is a diaphragm made out of rubber. Slowly, after years of service, this diaphragm will dry out and start cracking. The cracks will let the air out quicker, speeding up the damper movement, decreasing the delay time.

It doesn't help that the diaphragm is protected by the plastic enclosure of the air-damper, so the cracks won't be visible. Once the cracks start forming, however, the delay time starts to shorten. Adjustments to the air-damper are only a short-term fix. The only proper solution is to replace the whole waterflow switch assembly.

There is a good possibility that, once the cracks started forming, the rubber degraded rapidly, so, in 3 months-time, the delay can drop from :43 seconds to :05 seconds.

To prevent false alarms, the waterflow switch should be replaced.

Douglas Krantz
Life Safety
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