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What is Causing The False Waterflow Alarms?

City water pressure is constantly changing. When pressure goes up, water flows past the waterflow switch. To flow into the system, water has to first leak out. Trapped air in the sprinkler pipes pushes the water out, and when water comes in again past the switch, the air compresses.

What is Causing The False Waterflow Alarms?


What is Causing The False Waterflow Alarms?


Greetings Douglas,

Twice the fire pump in a condo building with automatic fire sprinkler system triggered a false alarm. The power supply in our country is 240V. As per our building engineer, if there is 10% increase and/or decrease in utility power supply, it triggers an alarm.

I am not convinced, that is why I am asking this question. Would appreciate very much your response on the matter. Thank you and more power.

Thank you, T O

Alarm Sensing

Alarms for a sprinkler system usually are sent to the fire alarm system when water actually pushed past a paddle across the inside of the sprinkler pipe. This paddle pushes on a switch (waterflow switch) which sends in the alarm.

To reduce false alarms, there is an air damper between the paddle and the switch requiring the paddle to sense water-is-flowing for :45 seconds.

Fire Pump Controller

The fire pump is a big pump to give the sprinkler more water pressure than usually comes from the city water system. The fire pump controller is what turns on and off the fire pump. Basically, the controller is a pressure switch. When the pressure in the sprinkler system gets below a certain point, the controller turns on the pump to push more water into the system.

Once in a great while, signals from the fire pump controller can send "Red-Light Full Alarms", but usually the fire pump controller will only send lower level "Yellow-Light Supervisory Alarms". A Red-Light Full Alarm sets off the horns and strobes in the building, and often calls the fire department; a Yellow-Light Supervisory Alarm doesn't set off the horns and strobes, only turns on a buzzer in the fire alarm panel, and doesn't call the fire department.

The signals from the controller include "Pump Running", and other signals are determined by whether the pump is an electric pump or a diesel pump. If the fire pump is an electric pump, the signals include "Phase Loss", "Phase Reversal", and "Trouble". The fire pump itself does not send any signals.

It could be that there is an "Over-Voltage" and "Under-Voltage" sensor. If so, signals from these are usually Yellow-Light Supervisory Signals, and almost never will turn on the horns and strobes.

Jockey Pump Controller

The jockey pump is a small pump meant only to keep the water pressure in the sprinkler system higher than the pressure that would turn on the fire pump. The controller is another pressure switch that turns on the jockey pump when the pressure in the sprinkler system has dropped only a little bit.

The jockey pump controller does not usually send any signals.

By Douglas Krantz Douglas Krantz Check It Out

Air Bubbles

Whenever the sprinkler company comes in to perform maintenance on the sprinkler system, they let the water out. In order to let the water out, air has to be let in. Once they finish their maintenance and recharge the sprinkler system with water, the water pushes the air further into the sprinkler system.

Most sprinkler systems don't have a means of bleeding out this air. The now compressed air makes the pipes in the sprinkler system into a long, thin pressure tank.

False Waterflow Alarms

Almost every time there is a Red-Light Alarm from the sprinkler system, water is flowing past the paddle in the pipe. This is true for real alarms and this is true for false alarms.

Repeated false alarms are caused by a sequence of events. Water leaks out of the sprinkler system, the air expands to fill in where the water has left, the air loses pressure because it is expanding, the jockey pump starts because the pressure is lower, the jockey pump runs longer than the :45 seconds, water pushes the paddle longer than :45 seconds, the waterflow switch sends a Red-Light Alarm to the fire alarm system.

Shortly after that, the pressure is restored and the jockey pump stops.

It's the Water Leaking Out

The sequence will only repeat if water continually leaks out of the system. If water leaks out of the sprinkler system back through the one-way valve (check valve) at the beginning of the sprinkler system, this water leaking could be the cause of false alarms. If water leaks out of the sprinkler system through a leaky drain valve, the water leaking can be the cause of false alarms.

Most of the time, with repeated false alarms from the sprinkler system, the cause is water leaking out of the system. Almost never are false alarms caused by Over-Voltage or Under-Voltage.

Over-Voltage and Under-Voltage Alarms

If the false alarms are being caused by Over-Voltage or Under-Voltage, you may wish to talk to the local fire marshal or fire inspector. Get permission to change this from a Red-Light Alarm Signal to a Yellow-Light Supervisory Signal on the fire alarm system.

Before talking to the fire marshal, though, check out the leakage problems first. Water leakage is usually the cause of the false alarms.

Douglas Krantz Douglas Krantz
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer
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