Sprinkler flow switch

What a flow switch actually is

Two mechanisms cover nearly everything in a Canadian building.

A vane type, or paddle type, switch has a flexible blade projecting into the pipe. Water moving past it deflects the blade, which drives a mechanical linkage into a set of contacts. These go on wet pipe systems, where the pipe is always full and movement means flow.

A pressure type switch senses a pressure change instead. It is used on dry, preaction and deluge systems, where the pipe holds air until the valve trips, and on wet systems where the alarm is taken off an alarm check valve rather than off the pipe.

Either way the device does one thing: it closes a contact. Everything else, the signal type, the zone, the annunciation, the transmission to the monitoring station, is decided at the fire alarm control unit.

What the Ontario Building Code requires

Article 3.2.4.15, System Monitoring, is the provision. It requires an automatic sprinkler system to be equipped with waterflow detecting devices and, where an annunciator is required, installed so that each device serves not more than one storey and, on each storey, an area no larger than the system area limits specified in NFPA 13. It requires those devices to be connected to the fire alarm system so that activation produces an alert signal or an alarm signal. And it requires each device's activation to be indicated separately on the annunciator.

Note the reference. NFPA 13 is named in the Canadian code text itself, so unlike NFPA 72 it is a legitimate part of a Canadian requirement here. That is the exception, not the rule: an American number is only a requirement in Canada when a Canadian code adopts it by name.

Installation of the fire alarm side, the wiring, supervision and connection, is CAN/ULC-S524, with the one time verification under CAN/ULC-S537 and annual inspection and testing of the fire alarm system under CAN/ULC-S536. The sprinkler side has its own inspection regime under the Ontario Fire Code, on a different schedule and usually a different trade.

Alarm, not supervisory

A flow switch tells you water is moving, which in a wet system means a head has operated and there is a fire. That is an alarm condition. The valve tamper switch on the control valve next to it tells you somebody has closed the valve, which is an impairment rather than a fire, and that is a supervisory condition. Wire or program them the same way and you have either a building that does not evacuate on a sprinkler operation, or a nuisance evacuation every time a valve is exercised. The distinction is set out in alarm, supervisory and trouble signals.

The retard, and what goes wrong

A vane type switch on a wet system needs a retard: a delay, usually pneumatic and adjustable, that lets a brief pressure surge pass without operating the contact. Municipal supply pressure moves, and a switch with no retard will report a fire every time it does.

• Retard cranked to maximum to stop nuisance signals, which delays a real alarm. If the surges are that bad, the fix is on the water side.
• Paddle wrong for the pipe. The vane is trimmed to the pipe size, and a paddle sized for the wrong diameter either drags on the pipe wall or barely reaches the flow.
• Installed backwards. The body carries a flow arrow, and reversed it may still operate, unreliably.
• Tested at the main drain instead of the inspector's test connection. A main drain test proves the supply, not the switch at the far end of the system.
• Programmed as supervisory, or grouped so several devices share one point, which defeats the separate annunciation Article 3.2.4.15 requires.
• Nobody owns it. The sprinkler contractor assumes the fire alarm technician tested it and the fire alarm technician assumes the reverse. Put it on both scopes in writing.

Where it sits next to the other devices

A flow switch is not a detector. It does not see a fire, it sees the consequence of one, and it reports after the sprinkler has already acted. That is why it sits alongside detection rather than replacing it, and why a sprinklered building still has smoke detectors in the spaces the Building Code names.

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