Waterflow and supervisory signals from the sprinkler system
The 90 seconds is the device, not the horns. What the waterflow and supervisory devices have to do, and how many go on one circuit.
The fire alarm system watches the sprinkler system through waterflow devices, which report water moving, and supervisory devices, which report a valve, pressure, level or temperature off normal. NFPA 72 Chapter 17 sets what each has to do.
The 90 second waterflow requirement
The waterflow initiating device has to operate within 90 seconds of a flow equal to or greater than the flow from a single sprinkler of the smallest orifice size installed in the system. That 90 seconds is the device operating, not the building being notified. The control unit is then allowed its own short interval under Chapter 10 to process the signal and drive notification, so the permitted time from flow to horns is longer than the 90 seconds people quote.
From the field
Find the smallest orifice head actually installed, not the one on the drawing. A single small head on a remote branch sets the bar. And failing a system for taking slightly over 90 seconds to sound is a common and wrong call.
What the retard is for
Movement of water due to waste, surges or variable pressure must not start an alarm. That is the job of the retard. It is not there to mask a real flow, and it cannot push the device past 90 seconds.
From the field
Retard settings get turned up to stop nuisance alarms and quietly break the 90 second requirement. Time it.
Supervisory devices
Every supervisory device produces two separate signals: one when the condition goes off normal and another when it is restored. That applies to control valves, pressure, water level and water temperature alike.
| Device | Signals off normal |
|---|---|
| Control valve | Within the first two revolutions of the handwheel, or one fifth of the travel of the valve control apparatus. Does not restore at any position except fully normal. |
| Pressure, pressure tank or dry pipe valve | High and low, on a change of 10 psi either way |
| Pressure, low air pressure dry pipe valve | As the manufacturer's installation instructions say |
| Steam pressure | Before pressure falls below 110 percent of the minimum operating pressure |
| Water level, pressure tank | High and low, on a rise or fall of 3 in. |
| Water level, any other tank | Low, when the level falls 12 in. |
| Water or room temperature | On a drop to 40 degrees F, and again on restoration above 40 degrees F |
From the field
A valve that has to be most of the way closed before it signals is worse than no switch at all. Test the restore as well: a switch that clears early is the same defect in reverse. A device that only reports the fault and never the restoration is half installed.
How many devices on one circuit
NFPA 72 Chapter 23 allows no more than five waterflow alarm initiating devices on a single initiating device circuit, so an alarm still tells you roughly where the water is. Supervisory devices are capped at 20 per circuit. Both caps are per circuit, which is not always the same thing as a zone.
A valve in the connection between a sprinkler system and an initiating device is itself supervised, unless it is arranged to operate the supervisory device when closed. Where waterflow devices have to be electronically monitored and there is no building fire alarm system, they go on a dedicated function control unit designated as a sprinkler waterflow and supervisory system, identified on the unit and on the record drawings.
The manual box that monitoring jobs forget
Under NFPA 72 Chapter 23, a fire alarm system connected to a supervising station that initiates from automatic detectors or waterflow devices has to include a manual fire alarm box to send a signal to the supervising station. Systems dedicated to elevator recall control and supervisory service are exempt.
From the field
Sprinkler only monitoring jobs miss this constantly. One station, usually at the panel or the main entrance.
Keep reading
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